DEVICES, SYSTEMS AND METHODS FOR OPTOGENETIC MODULATION OF ACTION POTENTIALS IN TARGET CELLS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 61/817,221, filed Apr. 29, 2013, which application is incorporated herein by reference in its entirety.

[0002] A Sequence Listing is provided herewith as a text file, “STAN-1030WO SeqList_ST25.txt” created on Apr. 29, 2014 and having a size of 208 KB. The contents of the text file are incorporated by reference herein in their entirety.

[0003] Optogenetics refers to the combination of genetic and optical methods used to control specific events in target cells with the temporal precision (millisecond-timescale) needed to keep pace with functioning intact biological systems. Optogenetics involves the introduction of fast light-responsive ion channel or pump proteins into the plasma membranes of target cells to allow temporally precise manipulation of membrane potentials while maintaining cell-type resolution through the use of specific targeting mechanisms, such as tissue-specific promoters.

[0004] A major limiting step in optogenetic electrical inhibition is that the existing tools do not cause input resistance changes, and only generate relatively weak photocurrents because the existing ion pump proteins only move one ion per photon. Conversely, a major limiting step in optogenetic excitation is that when exciting a projection of a target cell, such as an axon, retrograde propagating action potentials can return to the cell body and proceed down collateral cell projections, thereby reducing specificity. As such, there is a need for devices, systems and methods that can be used to inhibit and/or intercept action potentials in target cells, thereby expanding the potential uses of optogenetic technology.

[0005] Aspects of the disclosure include devices, systems and methods for optogenetic modulation of action potentials in target cells. The subject devices include light-generating devices, control devices, and delivery devices for delivering vectors to target cells. The subject systems include light-activated proteins, response proteins, nucleic acids comprising nucleotide sequences encoding these proteins, as well as expression systems that facilitate expression of these proteins in target cells. Also provided are methods of using the subject devices and systems to optogenetically inhibit and intercept action potentials in target cells, e.g., to treat a neurological or psychiatric condition in a human or non-human animal subject.

[0039] As used herein, an “individual,” “subject,” or “patient” can be a mammal, including a human. Mammals include, but are not limited to, ungulates, canines, felines, bovines, ovines, non-human primates, lagomorphs (e.g., rabbits), and rodents (e.g., mice and rats). In one aspect, an individual is a human. In another aspect, an individual is a non-human mammal.

[0040] Amino acid substitutions in a native protein sequence may be “conservative” or “non-conservative” and such substituted amino acid residues may or may not be one encoded by the genetic code. A “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a chemically similar side chain (i.e., replacing an amino acid possessing a basic side chain with another amino acid with a basic side chain). A “non-conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a chemically different side chain (i.e., replacing an amino acid having a basic side chain with an amino acid having an aromatic side chain). The standard twenty amino acid “alphabet” is divided into chemical families based on chemical properties of their side chains. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and side chains having aromatic groups (e.g., tyrosine, phenylalanine, tryptophan, histidine).

[0041] As used herein, an “effective dosage” or “effective amount” of drug, compound, or pharmaceutical composition is an amount sufficient to effect beneficial or desired results. For prophylactic use, beneficial or desired results include results such as eliminating or reducing the risk, lessening the severity, or delaying the onset of the disease, including biochemical, histological and/or behavioral symptoms of the disease, its complications and intermediate pathological phenotypes presenting during development of the disease. For therapeutic use, beneficial or desired results include clinical results such as decreasing one or more symptoms resulting from the disease, increasing the quality of life of those suffering from the disease, decreasing the dose of other medications required to treat the disease, enhancing effect of another medication such as via targeting, delaying the progression of the disease, and/or prolonging survival. An effective dosage can be administered in one or more administrations. For purposes of this disclosure, an effective dosage of drug, compound, or pharmaceutical composition is an amount sufficient to accomplish prophylactic or therapeutic treatment either directly or indirectly. As is understood in the clinical context, an effective dosage of a drug, compound, or pharmaceutical composition may or may not be achieved in conjunction with another drug, compound, or pharmaceutical composition. Thus, an “effective dosage” may be considered in the context of administering one or more therapeutic agents, and a single agent may be considered to be given in an effective amount if, in conjunction with one or more other agents, a desirable result may be or is achieved.

[0042] As used herein, “treatment” or “treating” is an approach for obtaining beneficial or desired results including clinical results. For purposes of this disclosure, beneficial or desired clinical results include, but are not limited to, one or more of the following: decreasing symptoms resulting from the disease, increasing the quality of life of those suffering from the disease, decreasing the dose of other medications required to treat the disease, delaying the progression of the disease, and/or prolonging survival of individuals.

[0043] Before the present invention is described in greater detail, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0044] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0045] Certain ranges are presented herein with numerical values being preceded by the term “about” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number.

[0046] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are now described.

[0047] All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

[0048] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0049] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

[0050] In further describing various aspects of embodiments of the invention in greater detail, aspects of the systems and devices of various embodiments are reviewed first in greater detail, followed by a discussion of methods and kits according to certain embodiments of the invention.

[0051] Aspects of the disclosure include devices, systems and methods for optogenetic modulation of action potentials in target cells. The subject devices include light-generating devices, control devices, and delivery devices for delivering vectors to target cells. The subject systems include light-activated proteins, response proteins, nucleic acids comprising nucleotide sequences encoding these proteins, as well as expression systems that facilitate expression of these proteins in target cells. Also provided are methods of using the subject devices and systems to optogenetically inhibit and intercept action potentials in target cells, e.g., to treat a neurological or psychiatric condition in a human or animal subject.

[0052] Aspects of the present disclosure include systems and devices configured for optogenetically modulating action potentials in target cells. The subject systems generally include a light-activated protein, a response protein, and one or more devices for delivering light of an activating wavelength to a target cell. The subject systems further include nucleic acids comprising nucleotide sequences encoding the subject proteins, as well as additional components, such as transcriptional control elements (e.g., promoter sequences, such as tissue-specific or cell type-specific promoter sequences), trafficking sequences, signal sequences, endoplasmic reticulum export sequences, and the like. Also provided are devices for delivering the subject nucleic acids to target cells, and devices for controlling the delivery of light to the target cells. Each of these components is now further described in greater detail.

[0053] As summarized above, aspects of the present disclosure include light-activated proteins that allow one or more ions to pass through the plasma membrane of a target cell when the protein is illuminated with light of an activating wavelength. Light-activated proteins may be characterized as ion pump proteins, which facilitate the passage of a small number of ions through the plasma membrane per photon of light, or as ion channel proteins, which allow a stream of ions to freely flow through the plasma membrane when the channel is open. The subject light-activated proteins are in some embodiments specific to a particular species of ion, meaning that the subject light-activated proteins only allow ions of a particular species to pass through the membrane.

[0054] Examples of suitable light-responsive polypeptides include, e.g., the Halorhodopsin family of light-responsive chloride pumps (e.g., NpHR, NpHR2.0, NpHR3.0, NpHR3.1). As another example, the GtR3 proton pump can be used to promote neural cell membrane hyperpolarization in response to light. As another example, eArch (a proton pump) can be used to promote neural cell membrane hyperpolarization in response to light. As another example, an ArchT opsin protein or a Mac opsin protein can be used to promote neural cell membrane hyperpolarization in response to light.

[0055] Examples of suitable light-responsive polypeptides include, e.g., members of the

[0056] Channelrhodopsin family of light-responsive cation channel proteins (e.g., ChR2, SFOs, SSFOs, C1V1s), which can be used to promote neural cell membrane depolarization or depolarization-induced synaptic depletion in response to a light stimulus.

[0057] The present disclosure provides for the modification of light-responsive opsin proteins expressed in a cell by the addition of one or more amino acid sequence motifs which enhance transport to the plasma membranes of mammalian cells. Light-responsive opsin proteins having components derived from evolutionarily simpler organisms may not be expressed or tolerated by mammalian cells or may exhibit impaired subcellular localization when expressed at high levels in mammalian cells. Consequently, in some embodiments, the light-responsive opsin proteins expressed in a cell can be fused to one or more amino acid sequence motifs selected from the group consisting of a signal peptide, an endoplasmic reticulum (ER) export signal, a membrane trafficking signal, and/or an N-terminal golgi export signal. The one or more amino acid sequence motifs which enhance light-responsive protein transport to the plasma membranes of mammalian cells can be fused to the N-terminus, the C-terminus, or to both the N- and C-terminal ends of the light-responsive protein. Optionally, the light-responsive protein and the one or more amino acid sequence motifs may be separated by a linker. In some embodiments, the light-responsive protein can be modified by the addition of a trafficking signal (ts) which enhances transport of the protein to the cell plasma membrane. In some embodiments, the trafficking signal can be derived from the amino acid sequence of the human inward rectifier potassium channel Kir2.1. In other embodiments, the trafficking signal can comprise the amino acid sequence KSRITSEGEYIPLDQIDINV (SEQ ID NO:37).

[0058] Trafficking sequences that are suitable for use can comprise an amino acid sequence having 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to an amino acid sequence such a trafficking sequence of human inward rectifier potassium channel Kir2.1 (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)).

[0059] A trafficking sequence can have a length of from about 10 amino acids to about 50 amino acids, e.g., from about 10 amino acids to about 20 amino acids, from about 20 amino acids to about 30 amino acids, from about 30 amino acids to about 40 amino acids, or from about 40 amino acids to about 50 amino acids.

[0060] Signal sequences that are suitable for use can comprise an amino acid sequence having 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to an amino acid sequence such as one of the following:

• [0061] 1) the signal peptide of hChR2 (e.g., MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO:38))
• [0062] 2) the β2 subunit signal peptide of the neuronal nicotinic acetylcholine receptor (e.g., MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO:39));
• [0063] 3) a nicotinic acetylcholine receptor signal sequence (e.g., MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO:40)); and
• [0064] 4) a nicotinic acetylcholine receptor signal sequence (e.g., MRGTPLLLVVSLFSLLQD (SEQ ID NO:41)).

[0065] A signal sequence can have a length of from about 10 amino acids to about 50 amino acids, e.g., from about 10 amino acids to about 20 amino acids, from about 20 amino acids to about 30 amino acids, from about 30 amino acids to about 40 amino acids, or from about 40 amino acids to about 50 amino acids.

[0066] Endoplasmic reticulum (ER) export sequences that are suitable for use in a modified opsin of the present disclosure include, e.g., VXXSL (where X is any amino acid) (SEQ ID NO:42) (e.g., VKESL (SEQ ID NO:43); VLGSL (SEQ ID NO:44); etc.); NANSFCYENEVALTSK (SEQ ID NO:45); FXYENE (SEQ ID NO:46) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO:47); and the like. An ER export sequence can have a length of from about 5 amino acids to about 25 amino acids, e.g., from about 5 amino acids to about 10 amino acids, from about 10 amino acids to about 15 amino acids, from about 15 amino acids to about 20 amino acids, or from about 20 amino acids to about 25 amino acids.

[0067] In some embodiments, the signal peptide sequence in the protein can be deleted or substituted with a signal peptide sequence from a different protein.

[0068] In some embodiments, a light-activated protein is an Archaerhodopsin (Arch) proton pump that can transport one or more protons across the plasma membrane of a cell when the cell is illuminated with light. The light can have a wavelength between about 530 and about 595 nm or can have a wavelength of about 560 nm. In some embodiments, the Arch protein can comprise an amino acid sequence that is at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:1 (Arch). The Arch protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the Arch protein to transport ions across the plasma membrane of a target cell. Additionally, the Arch protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The Arch protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to transport ions across the plasma membrane of a target cell in response to light.

[0069] In some embodiments, an Arch protein comprises at least one (such as one, two, three, or more) amino acid sequence motifs that enhance transport to the plasma membranes of target cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the Arch protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the Arch protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the Arch protein comprises an N-terminal signal peptide, a C-terminal ER export signal, and a C-terminal trafficking signal. In some embodiments, the Arch protein comprises a C-terminal ER export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0070] In some embodiments, the light-responsive proton pump protein can be responsive to blue light and can be derived from Guillardia theta, wherein the proton pump protein can be capable of mediating a hyperpolarizing current in the cell when the cell is illuminated with blue light. The light can have a wavelength between about 450 and about 495 nm or can have a wavelength of about 490 nm. In another embodiment, the light-responsive proton pump protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:4 (GtR3). The light-responsive proton pump protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the light-responsive proton pump protein to regulate the polarization state of the plasma membrane of the cell. Additionally, the light-responsive proton pump protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The light-responsive proton pump protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to hyperpolarize the plasma membrane of a neuronal cell in response to light.

[0071] In other aspects of the methods disclosed herein, the light-responsive proton pump protein can comprise a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:4 and at least one (such as one, two, three, or more) amino acid sequence motifs which enhance transport to the plasma membranes of mammalian cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the light-responsive proton pump protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the light-responsive proton pump protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the light-responsive proton pump protein comprises an N-terminal signal peptide, a C-terminal ER Export signal, and a C-terminal trafficking signal. In some embodiments, the light-responsive proton pump protein comprises a C-terminal ER Export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER Export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER Export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0072] Also provided herein are isolated polynucleotides encoding any of the light-responsive proton pump proteins described herein, such as a light-responsive proton pump protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:4. Also provided herein are expression vectors (such as a viral vector described herein) comprising a polynucleotide encoding the proteins described herein, such as a light-responsive proton pump protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:4.

[0073] In some embodiments, a light-activated protein is an Oxyrrhis marina (Oxy) proton pump that can transport one or more protons across the plasma membrane of a cell when the cell is illuminated with light. The light can have a wavelength between about 500 and about 560 nm or can have a wavelength of about 530 nm. In some embodiments, the Oxy protein can comprise an amino acid sequence that is at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:5. The Oxy protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the Oxy protein to transport ions across the plasma membrane of a target cell. Additionally, the Oxy protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The Oxy protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to transport ions across the plasma membrane of a target cell in response to light.

[0074] In some embodiments, an Oxy protein comprises at least one (such as one, two, three, or more) amino acid sequence motifs that enhance transport to the plasma membranes of target cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the Oxy protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the Oxy protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the Oxy protein comprises an N-terminal signal peptide, a C-terminal ER export signal, and a C-terminal trafficking signal. In some embodiments, the Oxy protein comprises a C-terminal ER export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0075] In some embodiments, the light-responsive proton pump protein can be responsive to light and can be derived from Leptosphaeria maculans, wherein the proton pump protein can be capable of pumping protons across the membrane of a cell when the cell is illuminated with 520 nm to 560 nm light. The light can have a wavelength between about 520 nm to about 560 nm. In another embodiment, the light-responsive proton pump protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:6 or SEQ ID NO:7 (Mac; Mac 3.0). The light-responsive proton pump protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the light-responsive proton pump protein to regulate the polarization state of the plasma membrane of the cell. Additionally, the light-responsive proton pump protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The light-responsive proton pump protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to pump protons across the plasma membrane of a neuronal cell in response to light.

[0076] In other aspects of the methods disclosed herein, the light-responsive proton pump protein can comprise a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:6 and at least one (such as one, two, three, or more) amino acid sequence motifs which enhance transport to the plasma membranes of mammalian cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the light-responsive proton pump protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the light-responsive proton pump protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the light-responsive proton pump protein comprises an N-terminal signal peptide, a C-terminal ER Export signal, and a C-terminal trafficking signal. In some embodiments, the light-responsive proton pump protein comprises a C-terminal ER Export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER Export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER Export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0077] Also provided herein are isolated polynucleotides encoding any of the light-responsive proton pump proteins described herein, such as a light-responsive proton pump protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:6. Also provided herein are expression vectors (such as a viral vector described herein) comprising a polynucleotide encoding the proteins described herein, such as a light-responsive proton pump protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:6.

[0078] Further disclosure related to light-activated proton pump proteins can be found in International Patent Application No. PCT/US2011/028893, the disclosure of which is hereby incorporated by reference in its entirety.

[0079] In some aspects, the light-responsive cation channel protein can be derived from Chlamydomonas reinhardtii, wherein the cation channel protein can be capable of transporting cations across a cell membrane when the cell is illuminated with light. In another embodiment, the light-responsive cation channel protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:8. The light used to activate the light-responsive cation channel protein derived from Chlamydomonas reinhardtii can have a wavelength between about 460 and about 495 nm or can have a wavelength of about 480 nm. Additionally, light pulses having a temporal frequency of about 100 Hz can be used to activate the light-responsive protein. In some embodiments, activation of the light-responsive cation channel derived from Chlamydomonas reinhardtii with light pulses having a temporal frequency of about 100 Hz can cause depolarization-induced synaptic depletion of the neurons expressing the light-responsive cation channel. The light-responsive cation channel protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the light-responsive cation channel protein to regulate the polarization state of the plasma membrane of the cell. Additionally, the light-responsive cation channel protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The light-responsive proton pump protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to transport cations across a cell membrane. In another embodiment, the light-responsive cation channel protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the C1C2 amino sequence shown in FIG. 13E, and set forth in SEQ ID NO:29. A crystal structure of C1C2 is presented in Kato et al. (2012) Nature 482:369. In another embodiment, the light-responsive cation channel protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the ReaChR amino sequence shown in FIG. 13F, and set forth in SEQ ID NO:30.

[0080] In some embodiments, the light-responsive cation channel comprises a T159C substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises a L132C substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises an E123T substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises an E123A substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises a T159C substitution and an E123T substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises a T159C substitution and an E123A substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises a T159C substitution, an L132C substitution, and an E123T substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises a T159C substitution, an L132C substitution, and an E123A substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises an L132C substitution and an E123T substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises an L132C substitution and an E123A substitution of the amino acid sequence set forth in SEQ ID NO:8. In some embodiments, the light-responsive cation channel comprises an H143R amino acid substitution of the amino acid sequence set forth in SEQ ID NO:8.

[0081] In some embodiments, a ChR2 protein comprises at least one (such as one, two, three, or more) amino acid sequence motifs that enhance transport to the plasma membranes of target cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the ChR2 protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the ChR2 protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the ChR2 protein comprises an N-terminal signal peptide, a C-terminal ER export signal, and a C-terminal trafficking signal. In some embodiments, the ChR2 protein comprises a C-terminal ER export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0082] In other embodiments, the light-responsive cation channel protein can be a step function opsin (SFO) protein or a stabilized step function opsin (SSFO) protein that can have specific amino acid substitutions at key positions throughout the retinal binding pocket of the protein. In some embodiments, the SFO protein can have a mutation at amino acid residue C128 of SEQ ID NO:8. In other embodiments, the SFO protein has a C128A mutation in SEQ ID NO:5. In other embodiments, the SFO protein has a C128S mutation in SEQ ID NO:8. In another embodiment, the SFO protein has a C128T mutation in SEQ ID NO:8. In some embodiments, the SFO protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:9.

[0083] In some embodiments, the SSFO protein can have a mutation at amino acid residue D156 of SEQ ID NO:8. In other embodiments, the SSFO protein can have a mutation at both amino acid residues C128 and D156 of SEQ ID NO:8. In one embodiment, the SSFO protein has an C128S and a D156A mutation in SEQ ID NO:8. In another embodiment, the SSFO protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:10. In another embodiment, the SSFO protein can comprise a C128T mutation in SEQ ID NO:8. In some embodiments, the SSFO protein comprises C128T and D156A mutations in SEQ ID NO:8.

[0084] In some embodiments the SFO or SSFO proteins provided herein can be capable of mediating a depolarizing current in the cell when the cell is illuminated with blue light. In other embodiments, the light can have a wavelength of about 445 nm. Additionally, in some embodiments the light can be delivered as a single pulse of light or as spaced pulses of light due to the prolonged stability of SFO and SSFO photocurrents. In some embodiments, activation of the SFO or SSFO protein with single pulses or spaced pulses of light can cause depolarization-induced synaptic depletion of the neurons expressing the SFO or SSFO protein. In some embodiments, each of the disclosed step function opsin and stabilized step function opsin proteins can have specific properties and characteristics for use in depolarizing the membrane of a neuronal cell in response to light.

[0085] Further disclosure related to SFO or SSFO proteins can be found in International Patent Application Publication No. WO 2010/056970, the disclosure of which is hereby incorporated by reference in its entirety.

[0086] In other embodiments, the light-responsive cation channel protein can be a C1V1 chimeric protein derived from the VChR1 protein of Volvox carteri and the ChR1 protein from Chlamydomonas reinhardti, wherein the protein comprises the amino acid sequence of VChR1 having at least the first and second transmembrane helices replaced by the first and second transmembrane helices of ChR1; is responsive to light; and is capable of mediating a depolarizing current in the cell when the cell is illuminated with light. In some embodiments, the C1V1 protein can further comprise a replacement within the intracellular loop domain located between the second and third transmembrane helices of the chimeric light responsive protein, wherein at least a portion of the intracellular loop domain is replaced by the corresponding portion from ChR1. In another embodiment, the portion of the intracellular loop domain of the C1V1 chimeric protein can be replaced with the corresponding portion from ChR1 extending to amino acid residue A145 of the ChR1. In other embodiments, the C1V1 chimeric protein can further comprise a replacement within the third transmembrane helix of the chimeric light responsive protein, wherein at least a portion of the third transmembrane helix is replaced by the corresponding sequence of ChR1. In yet another embodiment, the portion of the intracellular loop domain of the C1V1 chimeric protein can be replaced with the corresponding portion from ChR1 extending to amino acid residue W163 of the ChR1. In other embodiments, the C1V1 chimeric protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:11.

[0087] In some embodiments, the C1V1 protein can mediate a depolarizing current in the cell when the cell is illuminated with green light. In other embodiments, the light can have a wavelength of between about 540 nm to about 560 nm. In some embodiments, the light can have a wavelength of about 542 nm. In some embodiments, the C1V1 chimeric protein is not capable of mediating a depolarizing current in the cell when the cell is illuminated with violet light. In some embodiments, the chimeric protein is not capable of mediating a depolarizing current in the cell when the cell is illuminated with light having a wavelength of about 405 nm. Additionally, in some embodiments, light pulses having a temporal frequency of about 100 Hz can be used to activate the C1V1 protein. C1V1 chimeric mutant variants

[0088] In some aspects, the present disclosure provides polypeptides comprising substituted or mutated amino acid sequences, wherein the mutant polypeptide retains the characteristic light-activatable nature of the precursor C1V1 chimeric polypeptide but may also possess altered properties in some specific aspects. For example, the mutant light-responsive C1V1 chimeric proteins described herein can exhibit an increased level of expression both within an animal cell or on the animal cell plasma membrane; an altered responsiveness when exposed to different wavelengths of light, particularly red light; and/or a combination of traits whereby the chimeric C1V1 polypeptide possess the properties of low desensitization, fast deactivation, low violet-light activation for minimal cross-activation with other light-responsive cation channels, and/or strong expression in animal cells.

[0089] Accordingly, provided herein are C1V1 chimeric light-responsive opsin proteins that can have specific amino acid substitutions at key positions throughout the retinal binding pocket of the VChR1 portion of the chimeric polypeptide. In some embodiments, the C1V1 protein can have a mutation at amino acid residue E122 of SEQ ID NO:11. In some embodiments, the C1V1 protein can have a mutation at amino acid residue E162 of SEQ ID NO:11. In other embodiments, the C1V1 protein can have a mutation at both amino acid residues E162 and E122 of SEQ ID NO:11. In other embodiments, the C1V1 protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:12, SEQ ID NO:13, or SEQ ID NO:14.

[0090] In some aspects, the C1V1-E122 mutant chimeric protein is capable of mediating a depolarizing current in the cell when the cell is illuminated with light. In some embodiments the light can be green light. In other embodiments, the light can have a wavelength of between about 540 nm to about 560 nm. In some embodiments, the light can have a wavelength of about 546 nm. In other embodiments, the C1V1-E122 mutant chimeric protein can mediate a depolarizing current in the cell when the cell is illuminated with red light. In some embodiments, the red light can have a wavelength of about 630 nm. In some embodiments, the C1V1-E122 mutant chimeric protein does not mediate a depolarizing current in the cell when the cell is illuminated with violet light. In some embodiments, the chimeric protein does not mediate a depolarizing current in the cell when the cell is illuminated with light having a wavelength of about 405 nm. Additionally, in some embodiments, light pulses having a temporal frequency of about 100 Hz can be used to activate the C1V1-E122 mutant chimeric protein. In some embodiments, activation of the C1V1-E122 mutant chimeric protein with light pulses having a frequency of 100 Hz can cause depolarization-induced synaptic depletion of the neurons expressing the C1V1-E122 mutant chimeric protein.

[0091] In other aspects, the C1V1-E162 mutant chimeric protein is capable of mediating a depolarizing current in the cell when the cell is illuminated with light. In some embodiments the light can be green light. In other embodiments, the light can have a wavelength of between about 535 nm to about 540 nm. In some embodiments, the light can have a wavelength of about 542 nm. In other embodiments, the light can have a wavelength of about 530 nm. In some embodiments, the C1V1-E162 mutant chimeric protein does not mediate a depolarizing current in the cell when the cell is illuminated with violet light. In some embodiments, the chimeric protein does not mediate a depolarizing current in the cell when the cell is illuminated with light having a wavelength of about 405 nm. Additionally, in some embodiments, light pulses having a temporal frequency of about 100 Hz can be used to activate the C1V1-E162 mutant chimeric protein. In some embodiments, activation of the C1V1-E162 mutant chimeric protein with light pulses having a frequency of 100 Hz can cause depolarization-induced synaptic depletion of the neurons expressing the C1V1-E162 mutant chimeric protein.

[0092] In yet other aspects, the C1V1-E122/E162 mutant chimeric protein is capable of mediating a depolarizing current in the cell when the cell is illuminated with light. In some embodiments the light can be green light. In other embodiments, the light can have a wavelength of between about 540 nm to about 560 nm. In some embodiments, the light can have a wavelength of about 546 nm. In some embodiments, the C1V1-E122/E162 mutant chimeric protein does not mediate a depolarizing current in the cell when the cell is illuminated with violet light. In some embodiments, the chimeric protein does not mediate a depolarizing current in the cell when the cell is illuminated with light having a wavelength of about 405 nm. In some embodiments, the C1V1-E122/E162 mutant chimeric protein can exhibit less activation when exposed to violet light relative to C1V1 chimeric proteins lacking mutations at E122/E162 or relative to other light-responsive cation channel proteins. Additionally, in some embodiments, light pulses having a temporal frequency of about 100 Hz can be used to activate the C1V1-E122/E162 mutant chimeric protein. In some embodiments, activation of the C1V1-E122/E162 mutant chimeric protein with light pulses having a frequency of 100 Hz can cause depolarization-induced synaptic depletion of the neurons expressing the C1V1-E122/E162 mutant chimeric protein.

[0093] In some embodiments, the light-responsive ion channel protein can be responsive to 470 nm-510 nm light and can be derived from Dunaliella salina, wherein the ion channel protein can be capable of mediating a hyperpolarizing current in the cell when the cell is illuminated with light. The light can have a wavelength between about 470 nm and about 510 nm or can have a wavelength of about 490 nm. In another embodiment, the light-responsive ion channel protein can comprise an amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:15. The light-responsive ion channel protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the light-responsive ion channel protein to regulate the polarization state of the plasma membrane of the cell. Additionally, the light-responsive ion channel protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The light-responsive ion channel protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to transport ions across the plasma membrane of a neuronal cell in response to light.

[0094] In other aspects of the methods disclosed herein, the light-responsive ion channel protein can comprise a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:15 and at least one (such as one, two, three, or more) amino acid sequence motifs which enhance transport to the plasma membranes of mammalian cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the light-responsive proton ion channel comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the light-responsive ion channel protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the light-responsive ion channel protein comprises an N-terminal signal peptide, a C-terminal ER Export signal, and a C-terminal trafficking signal. In some embodiments, the light-responsive ion channel protein comprises a C-terminal ER Export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER Export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER Export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0095] Also provided herein are isolated polynucleotides encoding any of the light-responsive channel proteins described herein, such as a light-responsive ion channel protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:15. Also provided herein are expression vectors (such as a viral vector described herein) comprising a polynucleotide encoding the proteins described herein, such as a light-responsive channel protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:15.

[0096] In some aspects, said one or more light-responsive chloride pump proteins expressed on the plasma membranes of the neurons described above can be derived from Natronomonas pharaonis. In some embodiments, the light-responsive chloride pump proteins can be responsive to amber light as well as red light and can mediate a hyperpolarizing current in the neuron when the light-responsive chloride pump proteins are illuminated with amber or red light. The wavelength of light which can activate the light-responsive chloride pumps can be between about 580 and 630 nm. In some embodiments, the light can be at a wavelength of about 589 nm or the light can have a wavelength greater than about 630 nm (e.g. less than about 740 nm). In another embodiment, the light has a wavelength of around 630 nm. In some embodiments, the light-responsive chloride pump protein can hyperpolarize a neural membrane for at least about 90 minutes when exposed to a continuous pulse of light. In some embodiments, the light-responsive chloride pump protein can comprise an amino acid sequence at least about 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:16. Additionally, the light-responsive chloride pump protein can comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the light-responsive protein to regulate the polarization state of the plasma membrane of the cell. In some embodiments, the light-responsive chloride pump protein contains one or more conservative amino acid substitutions. In some embodiments, the light-responsive protein contains one or more non-conservative amino acid substitutions. The light-responsive protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to hyperpolarize the plasma membrane of a neuronal cell in response to light.

[0097] Additionally, in other aspects, the light-responsive chloride pump protein can comprise a core amino acid sequence at least about 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:16 and an endoplasmic reticulum (ER) export signal. This ER export signal can be fused to the C-terminus of the core amino acid sequence or can be fused to the N-terminus of the core amino acid sequence. In some embodiments, the ER export signal is linked to the core amino acid sequence by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments, the ER export signal can comprise the amino acid sequence FXYENE (SEQ ID NO:46), where X can be any amino acid. In another embodiment, the ER export signal can comprise the amino acid sequence VXXSL (SEQ ID NO:42), where X can be any amino acid. In some embodiments, the ER export signal can comprise the amino acid sequence FCYENEV (SEQ ID NO:47).

[0098] Endoplasmic reticulum (ER) export sequences that are suitable for use in a modified opsin of the present disclosure include, e.g., VXXSL (where X is any amino acid) (SEQ ID NO:42) (e.g., VKESL (SEQ ID NO:43); VLGSL (SEQ ID NO:44); etc.); NANSFCYENEVALTSK (SEQ ID NO:45); FXYENE (where X is any amino acid) (SEQ ID NO:46), e.g., FCYENEV (SEQ ID NO:47); and the like. An ER export sequence can have a length of from about 5 amino acids to about 25 amino acids, e.g., from about 5 amino acids to about 10 amino acids, from about 10 amino acids to about 15 amino acids, from about 15 amino acids to about 20 amino acids, or from about 20 amino acids to about 25 amino acids.

[0099] In other aspects, the light-responsive chloride pump proteins described herein can comprise a light-responsive protein expressed on the cell membrane, wherein the protein comprises a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:16 and a trafficking signal (e.g., which can enhance transport of the light-responsive chloride pump protein to the plasma membrane). The trafficking signal may be fused to the C-terminus of the core amino acid sequence or may be fused to the N-terminus of the core amino acid sequence. In some embodiments, the trafficking signal can be linked to the core amino acid sequence by a linker which can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments, the trafficking signal can be derived from the amino acid sequence of the human inward rectifier potassium channel Kir2.1. In other embodiments, the trafficking signal can comprise the amino acid sequence KSRITSEGEYIPLDQIDINV (SEQ ID NO:37).

[0100] In some aspects, the light-responsive chloride pump protein can comprise a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:16 and at least one (such as one, two, three, or more) amino acid sequence motifs which enhance transport to the plasma membranes of mammalian cells selected from the group consisting of an ER export signal, a signal peptide, and a membrane trafficking signal. In some embodiments, the light-responsive chloride pump protein comprises an N-terminal signal peptide, a C-terminal ER Export signal, and a C-terminal trafficking signal. In some embodiments, the C-terminal ER Export signal and the C-terminal trafficking signal can be linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker can also further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER Export signal can be more C-terminally located than the trafficking signal. In other embodiments the trafficking signal is more C-terminally located than the ER Export signal. In some embodiments, the signal peptide comprises the amino acid sequence MTETLPPVTESAVALQAE (SEQ ID NO:48). In another embodiment, the light-responsive chloride pump protein comprises an amino acid sequence at least 95% identical to SEQ ID NO:17.

[0101] Moreover, in other aspects, the light-responsive chloride pump proteins can comprise a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:16, wherein the N-terminal signal peptide of SEQ ID NO:16 is deleted or substituted. In some embodiments, other signal peptides (such as signal peptides from other opsins) can be used. The light-responsive protein can further comprise an ER transport signal and/or a membrane trafficking signal described herein. In some embodiments, the light-responsive chloride pump protein comprises an amino acid sequence at least 95% identical to SEQ ID NO:18.

[0102] In some embodiments, the light-responsive opsin protein is a NpHR opsin protein comprising an amino acid sequence at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% identical to the sequence shown in SEQ ID NO:16. In some embodiments, the NpHR opsin protein further comprises an endoplasmic reticulum (ER) export signal and/or a membrane trafficking signal. For example, the NpHR opsin protein comprises an amino acid sequence at least 95% identical to the sequence shown in SEQ ID NO:16 and an endoplasmic reticulum (ER) export signal. In some embodiments, the amino acid sequence at least 95% identical to the sequence shown in SEQ ID NO:16 is linked to the ER export signal through a linker. In some embodiments, the ER export signal comprises the amino acid sequence FXYENE (SEQ ID NO:46), where X can be any amino acid. In another embodiment, the ER export signal comprises the amino acid sequence VXXSL (SEQ ID NO:42), where X can be any amino acid. In some embodiments, the ER export signal comprises the amino acid sequence FCYENEV (SEQ ID NO:47). In some embodiments, the NpHR opsin protein comprises an amino acid sequence at least 95% identical to the sequence shown in SEQ ID NO:16, an ER export signal, and a membrane trafficking signal. In other embodiments, the NpHR opsin protein comprises, from the N-terminus to the C-terminus, the amino acid sequence at least 95% identical to the sequence shown in SEQ ID NO:16, the ER export signal, and the membrane trafficking signal. In other embodiments, the NpHR opsin protein comprises, from the N-terminus to the C-terminus, the amino acid sequence at least 95% identical to the sequence shown in SEQ ID NO:16, the membrane trafficking signal, and the ER export signal. In some embodiments, the membrane trafficking signal is derived from the amino acid sequence of the human inward rectifier potassium channel Kir2.1. In some embodiments, the membrane trafficking signal comprises the amino acid sequence KSRITSEGEYIPLDQIDINV (SEQ ID NO:37). In some embodiments, the membrane trafficking signal is linked to the amino acid sequence at least 95% identical to the sequence shown in SEQ ID NO:16 by a linker. In some embodiments, the membrane trafficking signal is linked to the ER export signal through a linker. The linker may comprise any of 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments, the light-responsive opsin protein further comprises an N-terminal signal peptide. In some embodiments, the light-responsive opsin protein comprises the amino acid sequence of SEQ ID NO:17. In some embodiments, the light-responsive opsin protein comprises the amino acid sequence of SEQ ID NO:18.

[0103] Also provided herein are polynucleotides encoding any of the light-responsive chloride ion pump proteins described herein, such as a light-responsive protein comprising a core amino acid sequence at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:16, an ER export signal, and a membrane trafficking signal. In another embodiment, the polynucleotides comprise a sequence which encodes an amino acid at least 95% identical to SEQ ID NO:17 and SEQ ID NO:18. The polynucleotides may be in an expression vector (such as, but not limited to, a viral vector described herein). The polynucleotides may be used for expression of the light-responsive chloride ion pump proteins.

[0104] Further disclosure related to light-responsive chloride pump proteins can be found in U.S. Patent Application Publication Nos: 2009/0093403 and 2010/0145418 as well as in International Patent Application No: PCT/US2011/028893, the disclosures of each of which are hereby incorporated by reference in their entireties.

[0105] In some embodiments, a suitable light-responsive polypeptide is a rhodopsin from Coccomyxa subellipsoidea (Chlorella vulgaris). In some embodiments, a suitable light-responsive polypeptide comprises an amino acid sequence that is at least about 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:62. Additionally, the light-responsive polypeptide can comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to light, increase or decrease sensitivity to particular wavelengths of light, and/or increase or decrease the ability of the light-responsive protein to regulate the polarization state of the plasma membrane of the cell. In some embodiments, the light-responsive polypeptide contains one or more conservative amino acid substitutions. In some embodiments, the light-responsive polypeptide contains one or more non-conservative amino acid substitutions. The light-responsive polypeptide comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the ability to hyperpolarize the plasma membrane of a neuronal cell in response to light.

[0106] In some cases, a suitable light-responsive polypeptide comprises an amino acid sequence that is at least about 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:62; and comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47)). In some cases, a suitable light-responsive polypeptide comprises an amino acid sequence that is at least about 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:62; and comprises a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)). In some cases, a suitable light-responsive polypeptide comprises an amino acid sequence that is at least about 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:62; and comprises a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)) and an ER export signal (e.g., FCYENEV (SEQ ID NO:47)).

(SEQ ID NO: 62)

MAVHQIGEGGLVMYWVTFGLMAFSALAFAVMTFTRPLNKRSHGYITLAIV

TIAAIAYYAMAASGGKALVSNPDGNLRDIYYARYIDWFFTTPLLLLDIIL

LTGIPIGVTLWIVLADVAMIMLGLFGALSTNSYRWGYYGVSCAFFFVVLW

GLFFPGAKGARARGGQVPGLYFGLAGYLALLWFGYPIVWGLAEGSDYISV

TAEAASYAGLDIAAKVVFGWAVMLSHPLIARNQTDGSLLINSTNDPFVAS

TTHIPERQGGIFGGLMGKKRGAGTPLATNEGVPRKAAPTAATTTAGNPAT

AAEVRTPRELMARL.

[0107] As summarized above, aspects of the present disclosure include response proteins that allow one or more ions to pass through a membrane when the response protein detects the presence of one or more ions that have passed through a subject light-activated protein. Response proteins may be characterized as ion pump proteins, which facilitate the passage of a small number of ions through the membrane per action cycle, or as ion channel proteins, which allow a stream of ions to freely flow through the membrane. The subject response proteins are specific to a particular species of ion or to a particular group of ions (e.g., cations) meaning that the subject response proteins only allow ions of a particular species or group to pass through the membrane. In some cases, the response protein is a heterologous protein for a given cell, e.g., the response protein is one that is not normally expressed in the cell. In other cases, the response protein is native to a given cell, e.g., the response protein is one that is normally expressed in the cell. A response protein can be a mammalian protein (e.g., a human protein, a non-human protein), a bacterial protein, an archael protein, etc.

[0108] In some embodiments, the response protein is an ion channel. In some cases, the response protein is a cation channel, e.g., a potassium channel or a calcium channel. In some cases, the response protein is an anion channel, e.g., a chloride ion channel or a sodium channel. In other instances, the response protein is a proton pump. Response proteins can be voltage-gated or ligand-gated.

[0109] Non-limiting examples of suitable response proteins include, e.g., a voltage-gated potassium channel (e.g., KVLQT1); a potassium channel (e.g., HERG); an inward rectifier K⁺ channel (e.g., Kir2.1); an acid sensing sodium ion channel; and the like. In some cases, the response protein is an ion exchanger (antiporter), e.g. the sodium-calcium exchanger (NCX), the potassium-dependent sodium-calcium exchanger (SLC24) or the sodium-hydrogen exchanger (NhaA). In some cases, the response protein is an ion co-transporter of the symport variety, e.g. the sodium-potassium-chloride co-transporter (NKCC1 and NKCC2) or the sodium-phosphate co-transporter (SLC34A1).

[0110] For example, a suitable response protein can comprise an amino acid sequence having at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% amino acid sequence identity to a contiguous stretch of from about 100 amino acid (aa) to about 200 aa, from about 200 aa to about 300 aa, from about 300 aa to about 400 aa, from about 400 aa to about 500 aa, from about 500 aa to about 600 aa, from about 600 aa to about 700 aa, from about 700 aa to about 800 aa, from about 800 aa to about 900 aa, from 900 aa to about 1000 aa, from about 1000 aa to about 1100 aa, up to the full length, of the amino acid sequence shown in one of FIGS. 14A-H (SEQ ID NOs:19-28).

[0111] In some embodiments, a response protein is an Acid Sensing Ion Channel variant 2a (ASIC2a) sodium ion channel protein that allows a plurality of sodium ions to flow across the plasma membrane of a target cell when the ASIC2a protein detects acidic conditions, such as the presence of a plurality of hydrogen ions on or near the external surface of the plasma membrane. In some embodiments, the ASIC2a protein can comprise an amino acid sequence that is at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:19. The ASIC2a protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to acidic conditions, and/or increase or decrease the ability of the ASIC2a protein to regulate the flow of sodium ions across the plasma membrane of a target cell. Additionally, the ASIC2a protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The ASIC2a protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the functionality of the ASIC2a protein.

[0112] In some embodiments, an ASIC2a protein comprises at least one (such as one, two, three, or more) amino acid sequence motifs that enhance transport to the plasma membranes of target cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the ASIC2a protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the ASIC2a protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the ASIC2a protein comprises an N-terminal signal peptide, a C-terminal ER export signal, and a C-terminal trafficking signal. In some embodiments, the ASIC2a protein comprises a C-terminal ER export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0113] In some embodiments, a response protein is a Helicobacter pylori potassium ion channel protein (HpKchA) that allows a plurality of potassium ions to flow across the plasma membrane of a target cell when the HpKchA protein detects acidic conditions, such as the presence of a plurality of hydrogen ions on or near the external surface of the plasma membrane. In some embodiments, the HpKchA protein can comprise an amino acid sequence that is at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to the sequence shown in SEQ ID NO:20. The HpKchA protein can additionally comprise substitutions, deletions, and/or insertions introduced into a native amino acid sequence to increase or decrease sensitivity to acidic conditions, and/or increase or decrease the ability of the HpKchA protein to regulate the flow of potassium ions across the plasma membrane of a target cell. Additionally, the HpKchA protein can contain one or more conservative amino acid substitutions and/or one or more non-conservative amino acid substitutions. The HpKchA protein comprising substitutions, deletions, and/or insertions introduced into the native amino acid sequence suitably retains the functionality of the HpKchA protein.

[0114] In some embodiments, an HpKchA protein comprises at least one (such as one, two, three, or more) amino acid sequence motifs that enhance transport to the plasma membranes of target cells selected from the group consisting of a signal peptide, an ER export signal, and a membrane trafficking signal. In some embodiments, the HpKchA protein comprises an N-terminal signal peptide and a C-terminal ER export signal. In some embodiments, the HpKchA protein comprises an N-terminal signal peptide and a C-terminal trafficking signal. In some embodiments, the HpKchA protein comprises an N-terminal signal peptide, a C-terminal ER export signal, and a C-terminal trafficking signal. In some embodiments, the HpKchA protein comprises a C-terminal ER export signal and a C-terminal trafficking signal. In some embodiments, the C-terminal ER export signal and the C-terminal trafficking signal are linked by a linker. The linker can comprise any of about 5, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 400, or 500 amino acids in length. The linker may further comprise a fluorescent protein, for example, but not limited to, a yellow fluorescent protein, a red fluorescent protein, a green fluorescent protein, or a cyan fluorescent protein. In some embodiments the ER export signal is more C-terminally located than the trafficking signal. In some embodiments the trafficking signal is more C-terminally located than the ER Export signal.

[0115] In some cases, the light-responsive protein and the response protein are present together in a single polypeptide chain, e.g., the light-responsive protein and the response protein are a fusion protein. The present disclosure provides a two-component optogenetic fusion polypeptide comprising a light-responsive polypeptide and a response polypeptide.

[0116] In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide (as described above); and b) a response protein (as described above). In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a response protein; and b) a light-responsive polypeptide. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a linker peptide; and c) a response protein. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; and c) a response protein. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; c) a response protein; and d) a membrane trafficking signal. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; c) a self-cleaving polypeptide; d) a response protein; and e) a membrane trafficking signal.

[0117] In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; c) a spacer polypeptide; d) a response protein; and d) an ER export signal. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; c) a spacer polypeptide; d) a response protein; e) a membrane trafficking signal; and f) an ER export signal. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; c) a response protein; d) a membrane trafficking signal; and e) an ER export signal. In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) a light-responsive polypeptide; b) a membrane trafficking signal; c) a self-cleaving polypeptide; d) a response protein; e) a membrane trafficking signal; and f) an ER export signal.

[0118] Suitable self-cleaving polypeptides include, e.g., a 2A peptide such as a P2A peptide: ATNFSLLKQAGDVEENPGP (SEQ ID NO:49); a T2A peptide: EGRGSLLTCGDVEENPGP (SEQ ID NO:50); an E2A peptide: QCTNYALLKLAGDVESNPGP (SEQ ID NO:51); an F2A peptide: VKQTLNFDLLKLAGDVESNPGP (SEQ ID NO:52); and the like. In some cases, the self-cleaving peptide is a P2A peptide: ATNFSLLKQAGDVEENPGP (SEQ ID NO:49). In some cases, a P2A peptide comprises the amino acid sequence GSGATNFSLLKQAGDVEENPGP (SEQ ID NO:61).

[0119] In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; b) a membrane trafficking signal; c) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and d) a membrane trafficking signal. In some cases, the membrane trafficking signal is: KSRITSEGEYIPLDQIDINV (SEQ ID NO:37). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0120] In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; b) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)); c) a polypeptide linker of from about 5 amino acids to about 100 amino acids, e.g., a polypeptide linker of from about 20 amino acids to about 25 amino acids in length; d) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and e) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0121] In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; b) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)); c) a polypeptide linker of from about 5 amino acids to about 100 amino acids, e.g., a polypeptide linker of from about 40 amino acids to about 45 amino acids in length; d) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and e) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0122] In some embodiments, a subject two-component optogenetic fusion polypeptide comprises, in order from amino terminus to carboxyl terminus: a) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; b) a membrane trafficking signal; c) a self-cleaving peptide (e.g., ATNFSLLKQAGDVEENPGP (SEQ ID NO:49)); d) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and e) a membrane trafficking signal. In some cases, the membrane trafficking signal is: KSRITSEGEYIPLDQIDINV (SEQ ID NO:37). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0123] Suitable linkers include “flexible linkers”. If present, the linker polypeptide is generally of sufficient length to allow some flexible movement between the polypeptides connected by the linker. Suitable linkers can be readily selected and can be of any of a suitable of different lengths, such as from 5 amino acids to 100 amino acids, e.g., from 5 amino acids (aa) to 10 aa, from 10 aa to 15 aa, from 15 aa to 25 aa, from 25 aa to 40 aa, from 40 aa to 60 aa, from 60 aa to 80 aa, or from 80 aa to 100 aa. In some cases, the polypeptide linker, if present, is from 20 aa to 25 aa in length. In some cases, the polypeptide linker, if present, is from 40 aa to 45 aa in length.

[0124] Exemplary polypeptide linkers include glycine polymers (G)_n, glycine-serine polymers (including, for example, (GS)_n, (GSGGS)_n (SEQ ID NO:53) and (GGGS)_n(SEQ ID NO:54), where n is an integer of at least one, e.g., 1, 2, 3, 4, 5, or from 5 to 10), glycine-alanine polymers, alanine-serine polymers, and other polypeptide linkers known in the art. Exemplary flexible linkers include, but are not limited GGSG (SEQ ID NO:55), GGSGG (SEQ ID NO:56), GSGSG (SEQ ID NO:57), GSGGG (SEQ ID NO:58), GGGSG (SEQ ID NO:59), GSSSG (SEQ ID NO:60), and the like. The ordinarily skilled artisan will recognize that design of a linker polypeptide can include linkers that are all or partially flexible, such that the linker can include a flexible linker as well as one or more portions that confer less flexible structure.

[0125] In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:31 (Champ 1.0). In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:32 (Champ 2.0). In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:33 (Champ 3.0). In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:34 (Champ 4.0).

[0126] In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:31 (Champ 1.0) without the yellow fluorescent protein (eYFP) sequence. In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:32 (Champ 2.0) without the yellow fluorescent protein (eYFP) sequence. In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:33 (Champ 3.0) without the yellow fluorescent protein (eYFP) sequence. In some cases, a subject two-component optogenetic fusion polypeptide comprises an amino acid sequence having at least 85%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:34 (Champ 4.0) without the yellow fluorescent protein (eYFP) sequence.

[0127] The present disclosure provides a nucleic acid comprising a nucleotide sequence encoding a fusion polypeptide as described above. The present disclosure provides a recombinant expression vector comprising a nucleic acid comprising a nucleotide sequence encoding a fusion polypeptide as described above. In some cases, the nucleotide sequence encoding the fusion polypeptide is operably linked to a neuron-specific transcriptional control element. Suitable expression vectors and neuron-specific transcriptional control elements are described herein. The present disclosure provides a cell genetically modified with a recombinant expression vector comprising a nucleic acid comprising a nucleotide sequence encoding a fusion polypeptide as described above. In some embodiments, the cell is a neuron.

[0128] The present disclosure provides various compositions, which include, but are not limited to, the following:

[0129] a) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an ion channel, e.g., an anion channel;

[0130] b) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a chloride ion channel;

[0131] c) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an ion channel, e.g., a cation channel;

[0132] d) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a potassium ion channel;

[0133] e) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium ion channel;

[0134] f) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an ion channel, e.g., an anion channel;

[0135] g) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a chloride ion channel;

[0136] h) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an ion channel, e.g., a cation channel;

[0137] i) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a potassium channel;

[0138] j) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium channel;

[0139] k) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a proton pump;

[0140] l) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a proton pump;

[0141] m) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a chloride ion pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an anion channel;

[0142] n) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a chloride ion pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a cation channel;

[0143] o) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a chloride ion pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a potassium channel;

[0144] p) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a chloride ion pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium channel; and

[0145] q) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a chloride ion pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a proton pump.

[0146] The present disclosure provides various compositions, which include, but are not limited to, the following:

[0147] a) a composition comprising i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light responsive polypeptide is a ion pump or channel, and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein wherein the response protein an ion exchanger, transporter, antiporter, or symport co-transporter;

[0148] b) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium-phosphate co-transporter;

[0149] c) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium-potassium-chloride co-transporter;

[0150] d) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a proton pump; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an ion exchanger (antiporter), e.g. a sodium-calcium exchanger, a potassium-dependent sodium-calcium exchanger, or a sodium-hydrogen exchanger;

[0151] e) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium-phosphate co-transporter;

[0152] f) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is a sodium-potassium-chloride co-transporter;

[0153] g) a composition comprising: i) a nucleic acid comprising a nucleotide sequence encoding a light-responsive polypeptide, where the light-responsive polypeptide is a channelrhodopsin; and ii) a nucleic acid comprising a nucleotide sequence encoding a response protein, wherein the response protein is an ion exchanger (antiporter), e.g. a sodium-calcium exchanger, a potassium-dependent sodium-calcium exchanger, or a sodium-hydrogen exchanger.

[0154] The present disclosure provides various compositions, which include, but are not limited to, the following:

[0155] a) a composition comprising a nucleic acid comprising a nucleotide sequence encoding a two-component optogenetic fusion polypeptide, as described above;

[0156] b) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) a light-responsive polypeptide (as described above); and ii) a response protein (as described above).

[0157] c) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) a response protein; and ii) a light-responsive polypeptide.

[0158] d) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) a light-responsive polypeptide; ii) a linker peptide; and ii) a response protein.

[0159] e) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) a light-responsive polypeptide; ii) a membrane trafficking signal; and iii) a response protein.

[0160] f) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) a light-responsive polypeptide; ii) a membrane trafficking signal; iii) a response protein; and iv) a membrane trafficking signal.

[0161] g) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) a light-responsive polypeptide; ii) a membrane trafficking signal; iii) a self-cleaving polypeptide; iv) a response protein; and v) a membrane trafficking signal.

[0162] h) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; ii) a membrane trafficking signal; iii) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and iv) a membrane trafficking signal. In some cases, the membrane trafficking signal is: KSRITSEGEYIPLDQIDINV (SEQ ID NO:37). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0163] i) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; ii) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)); iii) a polypeptide linker of from about 5 amino acids to about 100 amino acids, e.g., a polypeptide linker of from about 20 amino acids to about 25 amino acids in length; iv) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and v) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0164] j) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; ii) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)); iii) a polypeptide linker of from about 5 amino acids to about 100 amino acids, e.g., a polypeptide linker of from about 40 amino acids to about 45 amino acids in length; iv) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and v) a membrane trafficking signal (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO:37)). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0165] k) a composition comprising a nucleic acid comprising a two-component optogenetic fusion polypeptide that comprises, in order from amino terminus to carboxyl terminus: i) an eArch polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the eArch polypeptide amino acid sequence set forth in SEQ ID NO:1; ii) a membrane trafficking signal; iii) a self-cleaving peptide (e.g., ATNFSLLKQAGDVEENPGP (SEQ ID NO:49)); iv) an ASIC2a polypeptide comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%, amino acid sequence identity to the ASIC2a polypeptide amino acid sequence set forth in SEQ ID NO:19; and v) a membrane trafficking signal. In some cases, the membrane trafficking signal is: KSRITSEGEYIPLDQIDINV (SEQ ID NO:37). In some of these embodiments, the two-component optogenetic fusion polypeptide further comprises an ER export signal (e.g., FCYENEV (SEQ ID NO:47).

[0166] In some cases, the above-noted nucleic acids are expression vectors comprising a nucleotide sequence encoding a light-responsive protein and/or a response protein. In some cases, a subject composition comprises a first expression vector that comprises a nucleotide sequence encoding a light-responsive protein; and a second expression vector that comprises a nucleotide sequence encoding a response protein. In some cases, a subject composition comprises a single expression vector that includes a nucleotide sequence encoding a light-responsive protein and a nucleotide sequence encoding a response protein. Where the composition comprises a single expression vector, in some cases, the nucleotide sequence encoding the light-responsive protein and the nucleotide sequence encoding the response protein are under transcriptional control (operably linked) to the same transcriptional control element (e.g., promoter). Where the composition comprises a single expression vector, in some cases, the nucleotide sequence encoding the light-responsive protein and the nucleotide sequence encoding the response protein are under transcriptional control (operably linked) to two different promoters.

[0167] The present disclosure provides a system for modulating the membrane potential of a cell, the system comprising: i) a first nucleic acid comprising a nucleotide sequence encoding a light-activated protein that is adapted to allow a first ion to pass through a cell membrane in response to light; ii) a second nucleic acid comprising a nucleotide sequence encoding a response protein that responds to the passage of the first ion through the cell membrane by allowing a second ion to pass through the cell membrane; and iii) a device configured to illuminate a target location with a light. Any of the above-noted combinations of nucleic acids can be included in a subject system.

[0168] Aspects of the present disclosure include nucleic acids, such as polynucleotides, that comprise a nucleotide sequence that encodes one or more of the subject proteins described herein (e.g., one or more light-activated proteins or response proteins as described above). In some embodiments, a subject polynucleotide comprises an expression cassette, wherein the expression cassette contains a plurality of components (e.g., a plurality of coding sequences) that are utilized to express one or more proteins encoded by the polynucleotide in a target cell.

[0169] In some embodiments, a portion of a polynucleotide encoding a subject protein is operably linked to a promoter sequence. Any suitable promoter that functions in a target cell can be used for expression of the subject polynucleotides. In certain embodiments, a promoter sequence can be a promoter that is specific to a particular target cell type or to a particular tissue type, such as a particular neuron or a pan-neuronal promoter. Initiation control regions of promoters, which are useful to drive expression of polynucleotides in a specific animal cell, are numerous and familiar to those skilled in the art. Virtually any promoter capable of driving expression of the subject polynucleotides can be used. In some embodiments, the promoter used to drive expression of a subject protein can be the Thy1 promoter (See, e.g., Llewellyn, et al., 2010, Nat. Med., 16(10):1161-1166). In some embodiments, the promoter used to drive expression of a subject protein can be a human synapsin (hSyn) promoter, a human elongation factor 1-α (EF1α) promoter, a cytomegalovirus (CMV) promoter, a CMV early enhancer/chicken β actin (CAG) promoter, a synapsin-I promoter (e.g., a human synapsin-I promoter), a human synuclein 1 promoter, a human Thy1 promoter, a calcium/calmodulin-dependent kinase II alpha (CAMKIIα) promoter, or any other promoter capable of driving expression of the a subject nucleic acid sequence in a target cell.

[0170] In some embodiments, a promoter may be an inducible promoter. For example, the promoter may be induced by a trans-acting factor that responds to an exogenously administered drug. Examples of inducible promoters include, but are not limited to, tetracycline-on or tetracycline-off promoters, or tamoxifen-inducible CreER.

[0171] In some embodiments, a subject polynucleotide may comprise a ribosomal skip sequence that can be used to generate two separate proteins from the same transcript. In such embodiments, a subject polynucleotide will typically include a coding sequence that encodes a light-activated protein as well as a response protein. In these embodiments, a ribosomal skip sequence may be placed between the two coding sequences to produce two distinct proteins (namely, the light-activated protein and the response protein) from the same transcript.

[0172] Also provided herein are vectors comprising the subject polynucleotides or any variant thereof as described herein. Vectors according to the present disclosure also include vectors comprising a nucleotide sequence that encodes an RNA (e.g., an mRNA) that when transcribed from the polynucleotides of the vector will result in the accumulation of a subject protein on the plasma membranes of target cells. Vectors which may be used include, without limitation, lentiviral, HSV, adenoviral, and adeno-associated viral (AAV) vectors. Lentiviruses include, but are not limited to HIV-1, HIV-2, SIV, FIV and EIAV. Lentiviruses may be pseudotyped with the envelope proteins of other viruses, including, but not limited to VSV, rabies, Mo-MLV, baculovirus and Ebola. Such vectors may be prepared using standard methods in the art.

[0173] In some embodiments, a vector may be a recombinant AAV vector. AAV vectors are DNA viruses of relatively small size that can integrate, in a stable and site-specific manner, into the genome of the cells that they infect. They are able to infect a wide spectrum of cells without inducing any effects on cellular growth, morphology or differentiation, and they do not appear to be involved in human pathologies. The AAV genome has been cloned, sequenced and characterized. It encompasses approximately 4700 bases and contains an inverted terminal repeat (ITR) region of approximately 145 bases at each end, which serves as an origin of replication for the virus. The remainder of the genome is divided into two essential regions that carry the encapsidation functions: the left-hand part of the genome that contains the rep gene involved in viral replication and expression of the viral genes; and the right-hand part of the genome that contains the cap gene encoding the capsid proteins of the virus. AAV vectors may be prepared using standard methods in the art. Adeno-associated viruses of any serotype are suitable (see, e.g., Blacklow, pp. 165-174 of “Parvoviruses and Human Disease” J. R. Pattison, ed. (1988); Rose, Comprehensive Virology 3:1, 1974; P. Tattersall “The Evolution of Parvovirus Taxonomy” In Parvoviruses (J R Kerr, S F Cotmore. M E Bloom, R M Linden, C R Parrish, Eds.) p5-14, Hudder Arnold, London, UK (2006); and D E Bowles, J E Rabinowitz, R J Samulski “The Genus Dependovirus” (J R Kerr, S F Cotmore. M E Bloom, R M Linden, C R Parrish, Eds.) p15-23, Hudder Arnold, London, UK (2006), the disclosures of each of which are hereby incorporated by reference herein in their entireties). Methods for purifying for vectors may be found in, for example, U.S. Pat. Nos. 6,566,118, 6,989,264, and 6,995,006 and WO/1999/011764 titled “Methods for Generating High Titer Helper-free Preparation of Recombinant AAV Vectors”, the disclosures of which are herein incorporated by reference in their entirety. Methods of preparing AAV vectors in a baculovirus system are described in, e.g., WO 2008/024998. AAV vectors can be self-complementary or single-stranded. Preparation of hybrid vectors is described in, for example, PCT Application No. PCT/US2005/027091, the disclosure of which is herein incorporated by reference in its entirety. The use of vectors derived from the AAVs for transferring genes in vitro and in vivo has been described (See e.g., International Patent Application Publication Nos.: 91/18088 and WO 93/09239; U.S. Pat. Nos. 4,797,368, 6,596,535, and 5,139,941; and European Patent No.: 0488528, all of which are hereby incorporated by reference herein in their entireties). These publications describe various AAV-derived constructs in which the rep and/or cap genes are deleted and replaced by a gene of interest, and the use of these constructs for transferring the gene of interest in vitro (into cultured cells) or in vivo (directly into an organism). The replication-defective recombinant AAVs according to the present disclosure can be prepared by co-transfecting a plasmid containing the nucleic acid sequence of interest flanked by two AAV inverted terminal repeat (ITR) regions, and a plasmid carrying the AAV encapsidation genes (rep and cap genes), into a cell line that is infected with a human helper virus (for example an adenovirus). The AAV recombinants that are produced are then purified by standard techniques.

[0174] In some embodiments, the vector(s) for use in the methods of the present disclosure are encapsidated into a virus particle (e.g. AAV virus particle including, but not limited to, AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAV11, AAV12, AAV13, AAV14, AAV15, and AAV16). Accordingly, the present disclosure includes a recombinant virus particle (recombinant because it contains a recombinant polynucleotide) comprising any of the vectors described herein. Methods of producing such particles are known in the art and are described in U.S. Pat. No. 6,596,535, the disclosure of which is hereby incorporated by reference in its entirety.

[0175] FIG. 5 provides an example of a subject polynucleotide. The depicted polynucleotide, from 5′ to 3′, comprises a light-activated protein sequence (Arch), a trafficking sequence (ts), a ribosomal skip sequence (p2A), a response protein sequence (ASIC2a), and a yellow fluorescent protein sequence (EYFP). FIG. 6 provides an different example of a subject polynucleotide. The depicted polynucleotide, from 5′ to 3′, comprises a light-activated protein sequence (Arch), a trafficking sequence (ts), a ribosomal skip sequence (p2A), a response protein sequence (ASIC2a), a trafficking sequence (ts), a yellow fluorescent protein sequence (EYFP), and an endoplasmic reticulum export sequence (ER).

[0176] FIG. 7 provides an example of a subject vector. The depicted vector includes, from 5′ to 3′, a CamKII promoter sequence, an Arch coding sequence, a trafficking sequence (ts), a ribosomal skip sequence (p2A), an ASIC2a coding sequence, a trafficking sequence (ts), a yellow fluorescent protein sequence (EYFP), and an endoplasmic reticulum export sequence (ER). FIG. 8 provides another example of a subject vector. The depicted vector includes, from 5′ to 3′, an hSyn promoter sequence, an Arch coding sequence, a trafficking sequence (ts), a ribosomal skip sequence (p2A), an ASIC2a coding sequence, and a yellow fluorescent protein sequence (EYFP).

[0177] Aspects of the present disclosure include pharmaceutical compositions that comprise the subject polynucleotides, vectors, or components thereof. The subject pharmaceutical compositions may be administered to a subject for purposes genetically modifying a target cell so that the target cell expresses one or more subject proteins. A subject pharmaceutical composition may, in some embodiments, comprise a pharmaceutically acceptable excipient. In some embodiments, a pharmaceutical composition may comprise components to facilitate delivery of the subject polynucleotides or vectors to a target cell, including but not limited to transfection reagents or components thereof, such as lipids, polymers, and the like.

[0178] In some embodiments, a subject pharmaceutical composition will be suitable for injection into a subject, e.g., will be sterile. For example, in some embodiments, a subject pharmaceutical composition will be suitable for injection into a subject, e.g., where the composition is sterile and is free of detectable pyrogens and/or other toxins.

[0179] Pharmaceutically acceptable excipients, such as vehicles, adjuvants, carriers or diluents, are readily available to the public. Moreover, pharmaceutically acceptable auxiliary substances, such as pH adjusting and buffering agents, tonicity adjusting agents, stabilizers, wetting agents and the like, are readily available to the public as well, and may be incorporated into the pharmaceutical compositions of the present disclosure without limitation.

[0180] As summarized above, aspects of the present disclosure include delivering the subject polynucleotides, or components thereof, to target cells. Target cells are generally cells that carry or transmit electrical impulses, such as nerve cells. In some embodiments, a target cell may be, e.g., a sensory neuron, a motor neuron, or an interneuron. Target cells of the disclosure may include cells of the central nervous system and/or cells of the peripheral nervous system. In some embodiments, a target tissue may include a plurality of nerve fibers, a nerve, a nerve cell ganglion, a neuromuscular junction, a tissue that is innervated by nerves, including but not limited to muscle, skin, or endocrine tissue, or an anatomical region, such as a portion or sub-portion of the brain or spinal cord. In some embodiments, a target tissue may be a portion of an individual cell, such as specific axon of a nerve cell.

[0181] Once the subject polynucleotides have been delivered to a target cell or tissue, the polynucleotides enter the target cells and are expressed. In some embodiments, the subject polynucleotides may contain tissue-specific promoters so that expression only occurs in target cells wherein the tissue-specific promoter is active. In this way, if a subject polynucleotide is delivered to cells other than a target cell, the polynucleotide will not be expressed in the non-target cells because the tissue-specific promoter will be inactive in those cells. In some embodiments, a subject polynucleotide may contain an inducible promoter, such that expression of the polynucleotide only takes place when an exogenously administered drug is present is a sufficient concentration within the cell to activate the promoter.

[0182] In some cases, the present disclosure provides methods for modulating activity of a target cell that expresses a light-responsive protein and a response protein, as described above, where the method involves activating the light-responsive protein with light. In some cases, the present disclosure provides methods for modulating activity of a target cell that is proximal to a cell that expresses a light-responsive protein and a response protein, as described above, where the method involves activating the light-responsive protein with light. Thus, the target cell may not express the light-responsive protein and the response protein, but the activity of the target cell is modulated upon activating with light the light-responsive protein in a cell proximal to the target cell. A target cell that is “proximal” to a cell that expresses a light-responsive protein and a response protein, as described above, includes a cell that is in direct physical contact with the cell that expresses a light-responsive protein and a response protein, as described above. A target cell that is “proximal” to a cell that expresses a light-responsive protein and a response protein, as described above, includes a cell that is not in direct physical contact with the cell that expresses a light-responsive protein and a response protein, as described above, but whose activity is modulated by the cell that expresses a light-responsive protein and a response protein, as described above, e.g., modulated by neurotransmitter produced by the cell that expresses a light-responsive protein and a response protein, as described above; etc.

[0183] As summarized above, aspects of the present disclosure include various devices that can be used to carry out aspects of the subject methods. Devices that find use in the subject methods include delivery devices that can be used to deliver the subject polynucleotides to target cells and tissues, light-generating devices that can be used to illuminate target cells that express the subject light-activated proteins, and control devices that can be used to control the delivery of light to specific target cells or tissues. Each of these devices is further described below.

[0184] Aspects of the present disclosure include delivery devices that can be used to deliver a subject pharmaceutical composition to a target cell. The subject delivery devices may provide regular, irregular, programmed, or clinician- or patient-activated doses of the subject pharmaceutical compositions to one or more target cells to ensure that the target cells continue to express the subject proteins.

[0185] The subject delivery devices may generally include various components, such as reservoirs, pumps, actuators, tubing components, needles, catheters, and any other suitable components for delivering the subject pharmaceutical compositions to a target cell or tissue of a patient. Delivery devices may also include components that facilitate computerized operation, such as a power source, a processor comprising a memory, a user input device, and/or a graphical user interface. In some embodiments, a delivery device may be completely or partially implantable within a patient. In some embodiments, a delivery device may be operated by a caregiver, wherein the device is introduced into a portion of the patient's body, e.g., into the patient's brain, and a subject pharmaceutical composition is delivered to a target tissue, e.g., a portion of the patient's brain. In some embodiments, following delivery of the pharmaceutical composition, the device may be removed. In other embodiments, the device may be kept in place for later delivery of additional pharmaceutical compositions.

[0186] Aspects of the present disclosure include light-generating devices that can be used to deliver light to target cells that express one or more of the subject proteins. Light-generating devices in accordance with embodiments of the present disclosure can generally produce light of a variety of different wavelengths from one or more light sources on the device. In some embodiments, a light-generating device may include a light cuff or sleeve that can be placed around or near target cells expressing one or more subject proteins. In some embodiments, a portion of the light source or the entire light source may be implantable. The subject light-generating devices may be of any useful configuration for stimulating the light-activated proteins disclosed herein. In some embodiments, for example, a light-generating device may comprise components that facilitate exclusive illumination of a target cell or tissue. For example, in some embodiments, a light-generating device may exclusively direct light to a target cell, a portion of a target cell, e.g., a particular axon of a nerve cell, or a specific anatomical structure, such as, e.g. a bundle of nerve fibers, a target tissue, or a portion of the spinal cord. By “exclusively direct light” is meant that the light-generating device only delivers light to the specific target structure, and does not illuminate other structures. For examples, in some embodiments, a light-generating device may be configured to illuminate an axon of a nerve cell, but not illuminate any other portion of the nerve cell. In this way, the light from the light-generating device only affects light-activated proteins in the specific target structure that is illuminated.

[0187] In some embodiments, a light-generating device may not completely surround the region containing a target cell expressing a light-activated protein, but, rather, can have a U-shape. In some embodiments, a light-generating device can have an attachment arm that can be used to guide the light-generating device to a specific region or target structure, e.g., a specific neuronal region. The attachment arm can be removed following implantation of the light-generating device or can be left in place to fix the position of the light-generating device in proximity to the target cells of interest.

[0188] In some embodiments, the subject light-generating devices may comprise an inner body, the inner body having at least one means for generating light which is connected to a power source. In some embodiments, the power source can be an internal battery for powering the light-generating device. In some embodiments, an implantable light-generating device may comprise an external antenna for receiving wirelessly transmitted electromagnetic energy from an external source for powering device. The wirelessly transmitted electromagnetic energy can be a radio wave, a microwave, or any other electromagnetic energy source that can be transmitted from an external source to power the light-generating device. In some embodiments, the light-generating device is controlled by, e.g., an integrated circuit produced using semiconductor or other processes known in the art.

[0189] In some embodiments, the light-generating device may comprise a light emitting diode (LED).

[0190] In some embodiments, the LED can generate blue and/or green light. In other embodiments, the LED can generate amber and/or yellow light. In some embodiments, several micro LEDs are embedded into the inner body of the light-generating device. In other embodiments, the light-generating device is a solid state laser diode or any other means capable of generating light. The light-generating device can generate light having a wavelength and intensity sufficient to activate a subject light-activated protein. In some embodiments, a light-generating device produces light having an intensity of any of about 0.05 mW/mm², 0.1 mW/mm², 0.2 mW/mm², 0.3 mW/mm², 0.4 mW/mm², 0.5 mW/mm², about 0.6 mW/mm², about 0.7 mW/mm², about 0.8 mW/mm², about 0.9 mW/mm², about 1.0 mW/mm², about 1.1 mW/mm², about 1.2 mW/mm², about 1.3 mW/mm², about 1.4 mW/mm², about 1.5 mW/mm², about 1.6 mW/mm², about 1.7 mW/mm², about 1.8 mW/mm², about 1.9 mW/mm², about 2.0 mW/mm², about 2.1 mW/mm², about 2.2 mW/mm², about 2.3 mW/mm², about 2.4 mW/mm², about 2.5 mW/mm², about 3 mW/mm², about 3.5 mW/mm², about 4 mW/mm², about 4.5 mW/mm², about 5 mW/mm², about 5.5 mW/mm², about 6 mW/mm², about 7 mW/mm², about 8 mW/mm², about 9 mW/mm², or about 10 mW/mm², inclusive, including values in between these numbers. In some embodiments, the light-generating device produces light having an intensity of at least about 10 Hz, such as up to about 25 Hz, such as up to about 50 Hz, such as up to about 75 Hz, such as up to about 100 Hz.

[0191] The subject light-generating devices are generally capable of generating light having a wavelength ranging from about 350 nm, up to about 360 nm, up to about 370 nm, up to about 380 nm, up to about 390 nm, up to about 400 nm, up to about 410 nm, up to about 420 nm, up to about 430 nm, up to about 440 nm, up to about 450 nm, up to about 460 nm, up to about 470 nm, up to about 480 nm, up to about 490 nm, up to about 500 nm, up to about 510 nm, up to about 520 nm, up to about 530 nm, up to about 540 nm, up to about 550 nm, up to about 560 nm, up to about 570 nm, up to about 580 nm, up to about 590 nm, up to about 600 nm, up to about 610 nm, up to about 620 nm, up to about 630 nm, up to about 640 nm, up to about 650 nm, up to about 660 nm, up to about 670 nm, up to about 680 nm, up to about 690 nm, up to about 700 nm, up to about 710 nm, up to about 720 nm, up to about 730 nm, up to about 740 nm, and/or up to about 750 nm.

[0192] In some embodiments, a subject light-generating device may include one or more optical fibers that can transmit light from a light source and deliver the light to a target structure. The optical fibers may comprise plastic or glass materials, and in some embodiments may be suitably flexible to facilitate placement of the light-generating device in locations that could not be accommodated by rigid structures. For example, in some embodiments, a light-generating device may comprise a light source that generates light, as well as one or more optical fibers that can be placed in various locations on or in the patient's body. Light from the light source can pass through the optical fiber, passing around corners and bends in the optical fiber, and emerge at the end of the optical fiber to deliver light to a target structure.

[0193] In some embodiments, the subject light-generating devices may comprise a plurality of light sources that can be used to illuminate a target tissue with different wavelengths of light. For example, in some embodiments, a light-generating device may comprise a first light source that generates light of a first wavelength, e.g., red light, and a second light source that generates light of a second wavelength, e.g., green light. Such light-generating devices may be used to simultaneously illuminate the same target tissue with light of both wavelengths, or may alternately illuminate the target tissue with light of the first wavelength and light of the second wavelength. In some embodiments, such light generating devices may be used to deliver light from the same light source different target tissues. For example, in some embodiments a light-generating device may deliver light of a first wavelength to a first target tissue, and may deliver light of a second wavelength to a different target tissue.

[0194] Aspects of the present disclosure include control devices that can control, or modulate, the amount of light that is emitted from the subject light-generating devices. In some embodiments, a control device may be configured to modulate the wavelength and/or the intensity of light that is delivered to a target tissue from a light-generating device. In some embodiments, a control device may be configured to modulate the frequency and/or duration of light that is delivered to a target tissue from a light-generating device. For example, in some embodiments, a control device may be configured to deliver pulses of light from the light-generating device to a target tissue. The control device can modulate the frequency and/or duration of the light pulses such that the target tissue is illuminated with light from the light-generating device, e.g., at a regular or irregular rate, according to a user input, etc. In some embodiments, a control device can produce pulses of light from the light-generating device that have a duration ranging from about 1 millisecond or less, up to about 1 second, up to about 10 seconds, up to about 20 seconds, up to about 30 seconds, up to about 40 seconds, up to about 50 seconds, up to about 60 seconds or more. In some embodiments, a control device can produce pulses of light from the light-generating device that have a frequency of 1 pulse per millisecond, up to about 1 pulse per second, up about 1 pulse per minute, up to about 1 pulse per 10 minutes, up to about 1 pulse per 20 minutes, up to about 1 pulse per 30 minutes.

[0195] In some embodiments, a subject control device may comprise a power source that can be mounted to a transmitting coil. In some embodiments, a battery can be connected to the power source for providing power thereto. A switch can be connected to the power source, allowing an operator (e.g., a patient or caregiver) to manually activate or deactivate the power source. In some embodiments, upon activation of the switch, the power source can provide power to the light-generating device through electromagnetic coupling between the transmitting coil on the control device and an external antenna of an implantable light-generating device (such as a light cuff or sleeve). The transmitting coil can establish an electromagnetic coupling with the external antenna of the implantable light-generating device when in proximity thereof, for supplying power to the light-generating device and for transmitting one or more control signals to the light-generating device. In some embodiments, the electromagnetic coupling between the transmitting coil of the control device and the external antenna of the implantable light-generating device can be radio-frequency magnetic inductance coupling. When radio-frequency magnetic inductance coupling is used, the operational frequency of the radio wave can be between about 1 and 20 MHz, inclusive, including any values in between these numbers (for example, about 1 MHz, about 2 MHz, about 3 MHz, about 4 MHz, about 5 MHz, about 6 MHz, about 7 MHz, about 8 MHz, about 9 MHz, about 10 MHz, about 11 MHz, about 12 MHz, about 13 MHz, about 14 MHz, about 15 MHz, about 16 MHz, about 17 MHz, about 18 MHz, about 19 MHz, or about 20 MHz). However, other coupling techniques may be used, such as an optical receiver, infrared, or a biomedical telemetry system (See, e.g., Kiourti, “Biomedical Telemetry: Communication between Implanted Devices and the External World, Opticon1826, (8): Spring, 2010).

[0196] Turning now to FIG. 9, a first example of an optical stimulation system 100 is depicted. The optical stimulation system 100 comprises a delivery device 101 for delivering a subject polynucleotide to a target tissue, e.g., brain tissue 107 of a patient. Also provided are a light-generating device 102, a control device 103, and optical fibers 104 for conveying light generated by the light-generating device 102 to a light array 105 positioned on a light cuff 106.

[0197] Turning now to FIG. 10, a second example of an optical stimulation system 110 is depicted. The optical stimulation system 110 comprises a catheter 112 for delivering a subject polynucleotide to a target tissue, e.g., brain tissue 107 of a patient. Also provided are a light-generating device 102, a control device 103, and optical fibers 104 for conveying light generated by the light-generating device 102 to the end of the optical fibers 104.

[0198] Turning now to FIG. 11, a third example of an optical stimulation system 120 is depicted. The optical stimulation system 120 comprises a light-generating device 102, a control device 103, and optical fibers 104 for conveying light generated by the light-generating device 102 to various positions along the spinal cord 121 of the patient.

[0199] Aspects of the present disclosure include methods for optogenetic modulation of action potentials in target cells. The subject methods generally involve introducing a light-activated protein and a response protein into a target cell and illuminating the target cell with light of an activating wavelength. Illumination of the target cell with light of an activating wavelength causes the light-activated protein to allow one or more of a first species of ions to pass through the plasma membrane of the target cell. The presence of the first species of ions that passed through the light-activated protein causes the response protein to allow a second species of ions to pass through the plasma membrane of the target cell. The passage of the second species of ions through the plasma membrane of the target cell has a desired effect, such as, e.g., modulating the membrane potential of the plasma membrane, activating or inactivating an ion channel, etc. In some embodiments, the passage of the second ion species through the plasma membrane may be used to modulate one or more neurological responses or processes in a patient, and may therefore by used to treat a disease or condition in the patient. As such, in some embodiments, the subject methods involve treating a patient for a condition, such as a neurological condition, using the systems and devices provided herein. The subject methods are now described in greater detail below.

[0200] As discussed above, in some cases, a target cell does not express the light-responsive protein and the response protein, but the activity of the target cell is modulated upon activating with light the light-responsive protein in a cell proximal to the target cell. A target cell that is “proximal” to a cell that expresses a light-responsive protein and a response protein, as described above, includes a cell that is in direct physical contact with the cell that expresses a light-responsive protein and a response protein, as described above. A target cell that is “proximal” to a cell that expresses a light-responsive protein and a response protein, as described above, includes a cell that is not in direct physical contact with the cell that expresses a light-responsive protein and a response protein, as described above, but whose activity is modulated by the cell that expresses a light-responsive protein and a response protein, as described above, e.g., modulated by neurotransmitter produced by the cell that expresses a light-responsive protein and a response protein, as described above; etc.

[0201] In some embodiments, the subject methods involve modulating membrane potentials in target cells using the subject systems and devices. In some embodiments, a nucleic acid encoding a subject light-activated protein and a subject response protein is introduced into a target cell such that the target cell expresses both the light-activated protein and the response protein. The target cell is then illuminated with light of an activating wavelength using a light-generating device. Illumination of the light-activated protein results in the movement of one or more ions of a first species through the plasma membrane of the cell in response to light. In some embodiments, for example, the light-activated protein is a proton pump, and in response to light moves proteins from the internal side of the plasma membrane to the external side of the plasma membrane.

[0202] Once the first ion species has been moved across the plasma membrane of the target cell, the response protein responds to the presence of the first ion species by transporting a second ion species across the plasma membrane of the target cell. In some embodiments, for example, the response protein is an acid sensing ion channel, such as, e.g., ASIC2a, which detects the presence of acidic conditions, such as the presence of protons on the external side of the plasma membrane, and responds by opening an ion channel, such as a sodium ion channel, that allows ions of a second species to pass through the plasma membrane. The passage of the second species of ions through the plasma membrane modulates the membrane potential of the cell by changing the charge distribution across the plasma membrane. For example, in some embodiments, the passage of the second species of ions through the plasma membrane results in a build-up of positive charge inside the cell, which modulates the membrane potential of the cell. As such, using the subject light-activated proteins in combination with the subject response proteins, the methods of the present disclosure can be used to modulate the membrane potential of a target cell in response to light of an activating wavelength.

[0203] In some embodiments, the subject methods involve inhibiting the activity of voltage-gated sodium channels (VGSCs) that may be present in a nerve cell. VGSCs are a class of ion channels that are activated by changes in the membrane potential of nerve cells, and are generally involved with rapid, coordinated depolarization of nerve cell membranes in response to a given stimulus. For example, VGSCs are frequently found along the axons of nerve cells, and generally facilitate propagation of an action potential along the axon.

[0204] VGSCs function by allowing sodium ions to flow into the nerve cell from outside the plasma membrane. The flow of positively-charged sodium ions into the nerve cell changes the membrane potential and thereby propagates an action potential along the length of the nerve cell. Following activation, the VGSCs inactivate in a time-dependent manner. Once inactivated, the VGSC remains in a refractory inactivated state until the cell membrane potential repolarizes. As such, inactivation of VGSCs is a powerful technique for controlling nerve cell activity because, once inactivated, the VGSCs cannot regain activity until the nerve cell has repolarized.

[0205] In some embodiments, the subject methods involve inhibiting the activity of VGSCs by introducing into a nerve cell a light-activated protein, such as a light-activated proton pump (e.g., Arch), and a response protein, such as an acid sensing sodium ion channel (e.g., ASIC2a). Polynucleotides encoding these proteins are introduced into the nerve cell, and the proteins are expressed by the nerve cell and inserted into the plasma membrane of the nerve cell. Next, the nerve cell is illuminated with light of an activating wavelength from a light-generating device to cause the light-activated proton pump to transport protons through the plasma membrane from inside the cell to the outside of the cell. When the protons are present on or near the external surface of the plasma membrane, the response protein detects the presence of the protons and responds by opening a sodium ion channel. The sodium ion channel allows sodium ions to pass through the plasma membrane from outside the cell to the inside of the cell.

[0206] Once inside the nerve cell, the sodium ions depolarize the membrane sufficiently to inactivate one or more VGSCs in the plasma membrane. The inactivation of the VGSCs prevents the VGSCs from generating further action potentials in the nerve cell until the membrane repolarizes, which is facilitated by the cessation of light and decay of the response protein current, and the refractory period ends. As such, the propagation of action potentials along the nerve cell is blocked for the duration of the light pulse, the response protein current decay, and the refractory period. Accordingly, the subject methods may be used to block the propagation of an action potential along a nerve cell by introducing the subject proteins into the nerve cell plasma membrane and illuminating the cell with light of an activating wavelength from a light-generating device to inactivate one or more VGSCs in the nerve cell. Since the duration of action potential blockade outlasts the duration of the light pulse, inhibition of action potentials may be achieved using pulsed light delivery, rather than continuous light delivery.

[0207] In some embodiments, the subject methods involve inhibiting the activity of one or more voltage-gated calcium channels (VGCCs) that may be present in a target tissue. For example, in some cells and tissues, voltage-gated calcium channels (VGCCs) play analogous roles to those described above regarding voltage-gated sodium channels (VGSCs), and also exhibit voltage-dependent inactivation. Moreover, VGCCs also mediate neurotransmitter release, modulator and hormone release, and muscle contraction. Accordingly, in some embodiments, the subject methods involve inhibiting the activity of VGCCs by introducing into a target cell a light-activated protein, such as a light-activated proton pump (e.g., Arch), and a response protein, such as an acid sensing sodium ion channel (e.g., ASIC2a). Polynucleotides encoding these proteins are introduced into the target cell, and the proteins are expressed by the target cell and inserted into the plasma membrane of the target cell. Next, the target cell is illuminated with light of an activating wavelength from a light-generating device to cause the light-activated proton pump to transport protons through the plasma membrane from inside the cell to the outside of the cell. When the protons are present on or near the external surface of the plasma membrane, the response protein detects the presence of the protons and responds by opening a sodium ion channel. The sodium ion channel allows sodium ions to pass through the plasma membrane from outside the cell to the inside of the cell.

[0208] Once inside the target cell, the sodium ions depolarize the membrane sufficiently to inactivate one or more VGCCs in the plasma membrane. The inactivation of the VGCCs prevents the VGCCs from, e.g., generating further action potentials in the target cell; mediating the release of neurotransmitters, modulators, or hormones; mediating muscle contraction; and the like until the membrane repolarizes, which is facilitated by the cessation of light and decay of the response protein current, and the refractory period ends. As such, various functions of the VGCCs in the target cell are blocked for the duration of the light pulse, the response protein current decay, and the refractory period. Accordingly, the subject methods may be used to block various functions of VGCCs in a target cell by introducing the subject proteins into the target cell plasma membrane and illuminating the cell with light of an activating wavelength from a light-generating device to inactivate one or more VGCCs in the target cell. Since the duration of the VGCC blockade outlasts the duration of the light pulse, inhibition of VGCCs may be achieved using pulsed light delivery, rather than continuous light delivery.

Inhibiting and/or Blocking Retrograde Action Potentials in Nerve Cells

[0209] In some embodiments, the subject methods involve inhibiting and/or blocking the propagation of a retrograde action potential along a portion of a nerve cell (e.g., along an axon of a nerve cell) using the subject systems and devices. For example, in some embodiments, the subject methods involve introducing into a nerve cell a light-activated protein, such as a light-activated proton pump (e.g., Arch), and a response protein, such as an acid sensing sodium ion channel (e.g., ASIC2a). Polynucleotides encoding the proteins are introduced into the nerve cell, and the proteins are expressed by the nerve cell and inserted into the plasma membrane of the nerve cell.

[0210] Next, a light-generating device is positioned such that only a target portion of the nerve cell (e.g., only the axon, or only a portion of the axon, of the nerve cell) is illuminated with light of an activating wavelength when the light-generating device is activated. Next, the light-generating device is activated to deliver light to the desired portion of the nerve cell to cause the light-activated proton pump to transport protons through the plasma membrane from inside the cell to the outside of the cell. When the protons are present on or near the external surface of the plasma membrane, the response protein detects the presence of the protons and responds by opening a sodium ion channel. The sodium ion channel allows sodium ions to pass through the plasma membrane from outside the cell to the inside of the cell.

[0211] Once inside the cell, the sodium ions depolarize the membrane sufficiently to inactivate one or more VGSCs in the plasma membrane in the portion of the cell that is illuminated with light from the light-generating device. The inactivation of the VGSCs in the designated area of the nerve cell prevents the VGSCs from generating further action potentials in the nerve cell until the membrane repolarizes, which is facilitated by the cessation of light and decay of the response protein current, and the refractory period ends. As such, the propagation of action potentials along the nerve cell in the illuminated area is blocked for the duration of the light pulse, the response protein current decay and the refractory period. Accordingly, the subject methods may be used to block the propagation of an action potential along a particular portion of a nerve cell by introducing the subject proteins into the nerve cell plasma membrane and illuminating only a specific portion of the nerve cell with light of an activating wavelength from a light-generating device to inactivate one or more VGSCs in the illuminated portion of nerve cell or axon. Since the duration of action blockade outlasts the duration of the light pulse, inhibition of action potentials may be achieved using pulsed light delivery, rather than continuous light delivery. Accordingly, the subject methods may be used to block or inhibit the propagation of action potentials along a particular portion of a nerve cell or axon by delivering light of an activating wavelength to the specific portion of the nerve cell. Importantly, action potentials may still propagate through other portions of the nerve cell or axon that are not illuminated with light of a wavelength that activates the subject light-activated protein. In this way, specificity is achieved for restricting action potential propagation (anterograde and/or orthograde, and elicited naturally, optically, or electrically) to subdomains of the axonal arborization or cell.

[0212] In some embodiments, the subject methods may be used to treat a patient for a condition or disorder, such as a neurological condition or disorder, by optogenetically modulating the action potentials of target cells within the patient. In some embodiments, the subject methods involve introducing a light-activated protein, such as such as a light-activated proton pump (e.g., Arch), and a response protein, such as an acid sensing sodium ion channel (e.g., ASIC2a) in a target tissue within the patient. In some embodiments, introduction of the subject proteins into the target tissue is accomplished using a subject delivery device. The polynucleotides encoding the subject proteins are introduced into the target tissue, and the proteins are expressed by nerve cells in the target tissue and inserted into the plasma membrane of the nerve cells.

[0213] Next, a light-generating device is positioned to illuminate the target tissue with light of an activating wavelength when the light-generating device is activated. The light-generating device is activated (either by the patient or by a caregiver) to deliver light to the target tissue to cause the light-activated proton pump to transport protons through the plasma membrane from inside a cell in the target tissue to the outside of the cell. When the protons are present on or near the external surface of the plasma membrane, the response protein detects the presence of the protons and responds by opening a sodium ion channel. The sodium ion channel allows sodium ions to pass through the plasma membrane from outside the cell to the inside of the cell.

[0214] Once inside the cell, the sodium ions depolarize the membrane sufficiently to inactivate one or more VGSCs in the plasma membrane in the portion of the cell that is illuminated with light from the light-generating device. The inactivation of the VGSCs in the designated area of the nerve cell prevents the VGSCs from generating further action potentials in the nerve cell until the membrane repolarizes, which is facilitated by the cessation of light and decay of the response protein current, and the refractory period ends. As such, the propagation of action potentials along the nerve cell is blocked for the duration of the light pulse, the response protein current decay and the refractory period. Accordingly, the subject methods may be used to block the propagation of an action potential in a nerve cell by introducing the subject proteins into the nerve cell plasma membrane and illuminating the nerve cell with light of an activating wavelength from a light-generating device to inactivate one or more VGSCs in the illuminated portion of nerve cell. As the duration of action blockade outlasts the duration of the light pulse, inhibition of action potentials may be achieved using pulsed light delivery, rather than continuous light delivery.

[0215] In some embodiments, the subject methods involve treating a subject for a disorder by inhibiting the activity of one or more voltage-gated calcium channels (VGCCs) that may be present in a target tissue. For example, in some cells and tissues, voltage-gated calcium channels (VGCCs) play analogous roles to those described above regarding voltage-gated sodium channels (VGSCs), and also exhibit voltage-dependent inactivation. Moreover, VGCCs also mediate neurotransmitter release, modulator and hormone release, and muscle contraction. Accordingly, in some embodiments, the subject methods involve treating a subject by inhibiting the activity of VGCCs by introducing into a target cell a light-activated protein, such as a light-activated proton pump (e.g., Arch), and a response protein, such as an acid sensing sodium ion channel (e.g., ASIC2a). Polynucleotides encoding these proteins are introduced into the target cell, and the proteins are expressed by the target cell and inserted into the plasma membrane of the target cell. Next, the target cell is illuminated with light of an activating wavelength from a light-generating device to cause the light-activated proton pump to transport protons through the plasma membrane from inside the cell to the outside of the cell. When the protons are present on or near the external surface of the plasma membrane, the response protein detects the presence of the protons and responds by opening a sodium ion channel. The sodium ion channel allows sodium ions to pass through the plasma membrane from outside the cell to the inside of the cell.

[0216] Once inside the target cell, the sodium ions depolarize the membrane sufficiently to inactivate one or more VGCCs in the plasma membrane. The inactivation of the VGCCs prevents the VGCCs from, e.g., generating further action potentials in the target cell; mediating the release of neurotransmitters, modulators, or hormones; mediating muscle contraction; and the like until the membrane repolarizes, which is facilitated by the cessation of light and decay of the response protein current, and the refractory period ends. As such, various functions of the VGCCs in the target cell are blocked for the duration of the light pulse, the response protein current decay, and the refractory period. Accordingly, the subject methods may be used to treat a subject for a disorder by blocking various functions of VGCCs in a target cell by introducing the subject proteins into the target cell plasma membrane and illuminating the cell with light of an activating wavelength from a light-generating device to inactivate one or more VGCCs in the target cell. Since the duration of the VGCC blockade outlasts the duration of the light pulse, inhibition of VGCCs may be achieved using pulsed light delivery, rather than continuous light delivery.

[0217] Accordingly, the subject methods may be used to treat any disease or condition in which blocking or inhibiting the propagation of an action potential along an excitable or nerve cell, or along a particular portion of an excitable or nerve cell, would have a therapeutic effect for the patient, or wherein blocking the function of a VGCC would have a therapeutic effect for the patient. Examples of therapeutic applications of the subject methods include, without limitation, therapy for cardiac rhythm disorders, such as pacing, cardioversion, defibrillation, resynchronization, or other cardiac-related conditions; gastrointestinal therapy, such as therapy to address obesity, motility disorders (e.g., gastroparesis), dyspepsia, or other therapies, therapy for pelvic floor tissue (e.g., sacral or pudendal nerve tissue) to support pelvic floor therapy such as pain therapy, urinary or fecal incontinence therapy, sexual dysfunction, or other therapies; cranial nerve therapy, such as therapy to relieve occipital neuralgia, trigeminal neuralgia, facial pain, migraine headaches; therapy for the treatment of pain, such as nociceptive pain or neuropathic pain; therapy for neurological and/or psychiatric conditions; therapy for endocrine conditions; or the like.

[0218] Specificity can be achieved as above for restricting action potential propagation (anterograde and/or orthograde, and elicited naturally, optically, or electrically) to subdomains of the axonal arborization or cell.

[0219] In some embodiments, the subject methods involve combination treatments that involve activating or initiating an action potential in a first tissue, and also involve blocking or inhibiting the propagation of an action potential within a second tissue. For example, in some embodiments, the subject methods involve introducing a first light-activated protein into a first tissue, such as a nerve cell, by introducing into the cell a polynucleotide that encodes a first light-activated protein. The first light-activated protein is capable of transporting one or more ions across the plasma membrane of cells in the target tissue to trigger an action potential in the first tissue in response to light of an activating wavelength.

[0220] Simultaneously, a second light-activated protein, such as a light-activated proton pump (e.g., Arch), and a response protein, such as an acid sensing sodium ion channel (e.g., ASIC2a) are also introduced into the tissue. Next, a light-generating device is positioned near the target tissue to illuminate the target tissue. The light-generating device comprises a plurality of light sources, such that the target tissue, or portions thereof, can be illuminated with light of different wavelengths. A portion of the light-generating device is positioned to exclusively illuminate a portion of the target tissue in which it is desirable to block or inhibit action potentials. For example, a portion of the light-generating device, such as a particular light cuff or sleeve, may be positioned to exclusively illuminate, e.g., a particular portion of a nerve cell, such as an axon of the nerve cell, with a particular wavelength of light.

[0221] Next, the light-generating device is activated to deliver light of a wavelength that activates the first light-activated protein in the target tissue. This illumination generates an action potential in the target tissue that propagates through nerve cells in the target tissue. Simultaneously, the light-generating device is activated to deliver light of a wavelength that activates the second light-activated protein to the specific portion of the target tissue in which it is desirable to block or inhibit action potentials. This illumination causes the light-activated proton pump to transport protons through the plasma membrane from inside the cell to the outside of the cell. When the protons are present on or near the external surface of the plasma membrane, the response protein detects the presence of the protons and responds by opening a sodium ion channel. The sodium ion channel allows sodium ions to pass through the plasma membrane from outside the cell to the inside of the cell depolarizing the cell sufficiently to render native voltage-gated sodium channels inactive, a phenomenon known as depolarization block.

[0222] The voltage-dependent inactivation of the VGSCs in the designated portion of the target tissue prevents the VGSCs from generating further action potentials in the nerve cell until the membrane repolarizes, which is facilitated by the cessation of light and decay of the response protein current, and the refractory period ends. As such, the propagation of action potentials along the nerve cell in the specified area is profoundly blocked for the duration of the light pulse, the decay of the response protein current, and the refractory period. Accordingly, the subject methods may be used to control the flow of action potentials through a target tissue by initiating an action potential in a target tissue using light of a first activating wavelength, and simultaneously blocking or inhibiting the propagation of the action potential through a specific portion of the target tissue by inactivating VGSCs in the specific portion of the target tissue. Additionally, since the duration of action blockade outlasts the duration of the light pulse, inhibition of action potentials may be achieved using pulsed light delivery, rather than continuous light delivery. In this way, the subject methods provide for directing and controlling the flow of action potentials through a target tissue using the subject systems and devices. FIG. 12 provides a flow diagram that illustrates the steps of an example of the subject methods.

[0223] Also provided are kits that at least include the subject systems and devices or components thereof, e.g., as described above, and instructions for how to use the subject systems and/or devices to optogenetically modulate action potentials in a target tissue. In some embodiments, a kit may include one or more of the subject polynucleotides, vectors, or pharmaceutical compositions. Kits in accordance with embodiments of the present disclosure may also include one or more devices, such as one or more delivery devices, one or more light-generating device, and/or one or more control devices.

[0224] The instructions for using the systems and devices as discussed above are generally recorded on a suitable recording medium. For example, the instructions may be printed on a substrate, such as paper or plastic, etc. As such, the instructions may be present in the kits as a package insert, in the labeling of the container of the kit or components thereof (i.e. associated with the packaging or sub-packaging) etc. In other embodiments, the instructions are present as an electronic storage data file present on a suitable computer-readable storage medium, e.g., a digital storage medium, e.g., a CD-ROM, diskette, etc. The instructions may take any form, including complete instructions for how to use the systems and devices or as a website address with which instructions posted on the Internet may be accessed.

[0225] A nerve cell was transfected with a polynucleotide that encodes a light-activated proton pump protein (eArch3.0) and an acid sensing sodium ion channel response protein (ASIC2a). The proteins were expressed in the nerve cell and were present in the plasma membrane of the nerve cell. A pulse of 560 nm light activated eArch3.0, causing a fast outward proton current, resulting in early hyperpolarization of the plasma membrane. The extracellular protons then activated an inward cation current carried by ASIC2a resulting in sustained membrane depolarization and subsequent inactivation of native voltage-gated sodium channels, causing depolarization block and suppression of evoked spiking. Results are shown in FIG. 1.

[0226] A hippocampal cultured neuron was transfected with a polynucleotide that encodes an acid sensing sodium ion channel response protein (ASIC2a). The protein was expressed in the nerve cell and was present in the plasma membrane of the nerve cell. A 1000 pA current was injected into the cell at 10 Hz, and whole cell patch clamp recordings were collected. In response to the 1000 pA current pulse injections, the outward current component inhibited spiking. During 2000 pA current pulse injections, however, only the depolarization block caused by the ASIC component was sufficient to inhibit spiking. The results are shown in FIG. 2. Insets show the voltage-clamp trace of each cell in response to a 1 second green light pulse.

[0227] A nerve cell was transfected with a polynucleotide that encodes a light-activated proton pump protein (eArch3.0) and an acid sensing sodium ion channel response protein (ASIC2a). The proteins were expressed in the nerve cell and were present in the plasma membrane of the nerve cell. Spikes were evoked at baseline using suprathreshold (high reliability spiking) current pulse injections at 10 Hz. When light was applied, the eArch3.0-mediated hyperpolarization was insufficient to inhibit spiking, whereas the ASIC2a-mediated depolarization strongly suppressed spiking throughout the remainder of the light pulse, due to depolarization block. The insets to the right show the voltage-clamp response of the same neurons to a 1 second pulse of 560 nm light, with the amplitude of outward and inward currents provided. Results are shown in FIG. 3.

[0228] A nerve cell was transfected with a polynucleotide that encodes a light-activated proton pump protein (eArch3.0) and an acid sensing sodium ion channel response protein (ASIC2a). The proteins were expressed in the nerve cell and were present in the plasma membrane of the nerve cell. In this example, the inward:outward current ratio was small (≈1), therefore the depolarization caused by the ASIC component was insufficient to cause depolarization block and overcome the evoked spiking. Results are shown in FIG. 4.

[0229] In this example, it is described how extracellular ions, in particular protons, can influence local neural activity in non-cell-autonomous fashion through activation of acid-sensitive membrane proteins. An approach for manipulating cellular function, which couples light-sensitive proton pumps to acid-sensitive ion channels, permitting longer lasting, ion-specific regulation of transmembrane currents with many possible permutations for flexible neural control, is described.

[0230] All experiments were conducted under protocols approved by the Stanford Administrative Panel on Laboratory Animal Care.

[0231] Stereotactic injections: For expression of ChR2(H134R), eArch3.0 or eNpHR3.0 in CamKII-positive neurons, adeno-associated virus (AAV) serotype 2/5 was produced by the University of North Carolina Chapel Hill Vector Core at a genomic titer of ˜4-16×10¹² pfu mL⁻¹. 1 L of virus was stereotactically injected at two sites unilaterally into the CA1 region of the hippocampus of 3-4 week-old mice. Coordinates for all animals at injection site #1 were −2.2 anteroposterior, 1.5 mediolateral (left side) and −1.3 dorsoventral (in mm from bregma) and for injection site #2 were −1.7 anteroposterior, 1.25 mediolateral (left side) and −1.5 dorsoventral (in mm from bregma). For cortical bystander experiments, Thy1::ChR2 (line 18) mice (Arenkiel et al, 2007) were used (bred in-house).

[0232] Acute slice electrophysiology recordings: Acute brain slices were prepared from mice at 4-8 weeks post virus injection, or at 4 weeks of age for transgenic mice. After lethal anesthesia, transcardial perfusion was performed prior to decapitation, followed by rapid brain extraction and submersion of the brain in ice-cold sucrose-based slicing solution (234 mM sucrose, 11 mM glucose, 10 mM MgSO₄.7H₂0, 2.5 KCl, 1.25 mM NaH₂PO₄.H₂O, 0.5 mM CaCl₂.2H₂0). 300 μm thick slices of hippocampus were cut on a Leica vibratome (Leica VT1000S). After cutting, slices were submerged in a hypertonic recovery solution (artificial cerebrospinal fluid (ACSF) at an 8% increased concentration) at 33° C. for 15 mins before being transferred to standard ACSF (123 mM NaCl, 26 mM NaHCO₃, 11 mM glucose, 3 mM KCl, 2 mM CaCl₂.2H₂0, 1.25 mM NaH₂PO₄.H₂O, 1 mM MgCl₂.6H₂O) for a further 45 mins at 33° C., at which point they were transferred to room temperature.

[0233] Whole cell patch clamp recordings on cortical and hippocampus neurons were performed on an upright Leica DM-LFSA microscope. Slices were continually perfused in warmed (33° C.) ACSF at a rate of 7 ml min⁻¹ Patching was performed in the presence of synaptic transmission blockers 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50 μM) and D(−)-2-amino-5-phosphonovaleric acid (APV, 25 μM) and gabazine (25 μM) (Tocris Bioscience) except for during testing of electrically-evoked synaptic responses. For amiloride experiments, amiloride was added to the ACSF at a concentration of 500 μM (Tocris). Borosilicate glass (Sutter Instruments) pipette resistances were pulled to 3-6 MΩ and filled with potassium gluconate intracellular solution (130 mM K Gluconate, 10 mM KCl, 10 mM HEPES, 10 mM EGTA, 2 mM MgCl₂, pH adjusted with KOH to 7.3). Voltage and current clamp electrophysiological recordings and manipulations were performed using pClamp (Axon Instruments). Cells were held at −70 mV for all experiments. Cells with leak current greater than −300 pA or pipette resistance greater than 30 MΩ were excluded. Light (full-field illumination) was emitted from a 300 W DG-4 lamp (Sutter Instruments, Novato, Calif., USA) fitted with a Lambda 10-3 filter wheel (Sutter Instruments) with a 10-position wheel for filters of different wavelengths, or external filters (wavelength in nm/bandwidth in nm: 470/20; 560/25; 590/20). Light pulses were delivered through a 40×, 0.8 NA water-immersion objective at 4-7 mW/mm² light power density. Extracellular electrical stimulation was performed using a concentric bipolar electrode of platinum iridium (FHC, Bowdoin, Me., USA) or tungsten (World Precision Instruments, Sarasota, Fla. USA). Electrical pulses were delivered using a stimulus isolator (ISO-Flex, A.M.P.I) controlled by pClamp to deliver 200 μs square pulses at intensities ranging from 500 μA-2.5 mA and frequencies of 5-10 Hz.

[0234] Immunohistochemistry: For identification of bystanders in slice preparations, 0.3% biocytin was added to the intracellular pipette solution and following recording slices were fixed in 4% paraformaldehyde perfusion fix solution (Electron Microscopy Services, Hatfield, Pa., USA) for 24 hours then transferred to 1× phophate buffered saline (Gibco, Life Technologies). Biocytin was stained with fluorescent streptavidin (Alexa Fluor 546 conjugate, Invitrogen, over 3 hours. For YFP staining, slices were incubated in anti-GFP primary antibody (Invitrogen, 1:500 dilution) for 24 hours. Cy5 secondary antibody (Jackson Laboratories, West Grove, Pa., 1:500 dilution) was applied in 2% NDS for 1 hour at room temperature for 3 hours followed by DAPI (1:50,000) for 30 mins, then mounted, and coverslipped with PVA-DABCO (Sigma). Images were obtained on a Leica confocal microscope (DM600B) at 1024×1024 pixel resolution using 5× and 10× dry objectives and 20×, 40× and 63× oil objectives.

[0235] Data analysis: Analysis of all of physiological results was performed using Clampfit software (Axon Instruments). Pipette (access) resistance (R_a) and membrane resistance (R_m) were monitored at 5 minute intervals to ensure stability of the recording and data was only included when leak current was less than 300 pA and R_a less than 30 MΩ with less than 25% change in R_a for the duration of periods of drug application and between sequential membrane tests. Reversal potentials were corrected for an estimated liquid junction potential of 14 mV. Statistical analysis was performed using GraphPad Prism 6.0 for Mac OS X. For comparisons between YFP controls and opsin or electrical stimulation groups we performed non-parametric unpaired 2-tailed Mann Whitney tests to compare mean ranks between groups, without assuming a Gaussian distribution. For comparison of the functional impact of light on bystander neuron spiking, we compared successive light-on vs light-off epochs for each opsin, using a non-parametric, paired Wilcoxin signed rank test, again without assuming a Gaussian distribution. Significance thresholds were set at p<0.05 (*), p<0.01 (**), p<0.001 (***) and p<0.0001 (****).

[0236] Two-component optogenetics experiments. Construct design and expression in Xenopus laevis oocytes: The coding sequences for rat ASICs (in pRSSP6009) were provided by Stefan Grander (Aachen). The pRSSP6009 plasmid coding for ASICs and the pGEM plasmid coding for Coccomyxa subellipsoidea C-169 Rhodopsin CsR_T46N were linearized by MulI site in pRSSP 6009 and by NheI in pGEM. After transcription into RNA using T7 (pGEM) or SP6 (pRSSP6009) mMessage mMachine Kit (Ambion Inc, Texas, USA) 32 ng of capped RNA encoding CsR pump and one type of ASIC were co-injected into Xenopus leavis oocytes with a molar ratio of 1:1 pump:channel for ASIC1 and ASIC2a and a molar ratio of 1:2 for ASIC3. Oocytes were incubated for 3 days at 18° C. in ORI solution with 1 μM all-trans retinal (Tsunoda & Hegemann, 2009).

[0237] Two-electrode voltage clamp measurements: TEVC measurements on X. laevis oocytes were performed using a GeneClamp 500 amplifier (Axon Instruments, Union City). Data acquisition, buffer exchange and light triggering were controlled with pClamp software via a Digidata 1322A interface (Molecular Devices, Sunnyvale). The light supplied by a 75 W Xenon lamp (Jena-Instruments, Jena, Germany) was passed through a K55 filter (Balzers, Liechtenstein) and applied to the oocytes using a light guide (diameter of 2 mm) The light intensity was 8.5×10²⁰ photons s⁻¹ m⁻² at the surface of the oocyte. The bulk buffer (chamber volume 300 μl) was continuously perfused at a flow rate of 1.8±0.2 ml min⁻¹. Data was acquired at 1 kHz and filtered at 0.5 kHz. If not otherwise specified the extracellular buffer was composed of 100 mM NaCl, 1 mM KCl, 1 mM MgCl₂, 0.1 mM CaCl₂ and 0.1 to 5 mM MOPS at pH 7.5. For pH titration, buffer solutions were adjusted with 5 mM MOPS/MES/Citrate over the range of pH 8.0 to 4.0, and were subsequently compared with photocurrents measured at 0.1 mM MOPS at pH 7.5

[0238] Construct design for hippocampal neurons: The protein sequence of rat ASIC2a (Genbank accession number NM_—001034014.1) was human codon optimized and synthesized by Genscript. eArch3.0 and ASIC-YFP fusions were cloned into an AAV2 backbone either under a CaMKIIα or human synapsin promoter. The trafficking signal (TS) and endoplasmic reticulum export signal (ER) sequences were appropriately added to enhance membrane trafficking. All maps and sequence details are on the website: www(dot)optogenetics(dot)org.

[0239] Hippocampal neuron culture and calcium phosphate transfection (as per Mattis et al. (Nat Methods 2011; 9: 159-72)). Primary cultured hippocampal neurons were prepared from PO Sprague-Dawley rat pups (Charles River). CA1 and CA3 were isolated, digested with 0.4 mg ml⁻¹ papain (Worthington), and plated onto glass coverslips precoated with 1:30 Matrigel (Becton Dickinson Labware). Cultures were maintained in a 5% CO₂ humid incubator with Neurobasal-A medium (Invitrogen) containing 1.25% FBS (HyClone), 4% B-27 supplement (Gibco), 2 mM Glutamax (Gibco) and 2 mg ml⁻¹ fluorodeoxyuridine (FUDR) (Sigma), and grown on coverslips in a 24-well plate at a density of 65,000 cells per well. For each well, a DNA-CaCl₂ mix was prepared with 2 μg DNA (Qiagen endotoxin-free preparation) and 1.875 μl 2 M CaCl₂ (final Ca²⁺ concentration 250 mM) in 15 μl H₂O. To DNA-CaCl₂ was added 15 μl of 2× HEPES-buffered saline (pH 7.05). After 20 min at room temperature (20-22° C.), the mix was added dropwise into each well (from which the growth medium had been removed and replaced with pre-warmed minimal essential medium (MEM)) and transfection proceeded for 45-60 min at 37° C., after which each well was washed with 3×1 ml warm MEM before the original growth medium was returned.

[0240] Electrophysiological recordings in cultured hippocampal neurons: Whole cell patch clamp recordings were performed on cultured hippocampal neurons 4-8 days post-transfection on an upright Leica DM-LFSA microscope (Mattis et al, 2011). Cells were continuously perfused in standard extracellular Tyrode's solution (NaCl: 125 mM, KCl 2 mM, CaCl₂ 2 mM, MgCl₂ 2 mM, glucose 30 mM, HEPES 25 mM, titrated to pH 7.3-7.4 with NaOH, 320 mOsm) or in low HEPES Tyrode's solution (NaCl: 125 mM, KCl 2 mM, CaCl₂ 2 mM, MgCl₂ 2 mM, glucose 55 mM, HEPES 0.1 mM, titrated to pH 7.3-7.4, 320 mOsm) at a rate of 1-2 ml min⁻¹, in the presence of synaptic transmission blockers 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), D(−)-2-amino-5-phosphonovaleric acid (APV) and gabazine (25 μM; Tocris Bioscience). Patch pipette borosilicate glass electrodes (Sutter Instruments) with tip resistance of 3-6 MΩ were filled with a potassium gluconate intracellular solution (K-gluconate 130 mM, KCl 10 mM, HEPES 10 mM, EGTA 10 mM, MgCl₂ 2 mM, titrated to pH 7.3 with KOH, 300 mOsm). Data acquisition, current and light manipulations were controlled using pClamp (Axon Instruments) via a Digidata 1440A interface and analyzed using ClampFit software (Axon Instruments). Cells were held at −70 mV for all voltage-clamp experiments. Resting membrane potentials were corrected for an estimated liquid junction potential of 16 mV. Full-field illumination for activation of optogenetic tools was delivered by a 300 W DG-4 lamp (Sutter instruments) via a 40×, 0.8 numerical aperture (NA) water-immersion objective. The light was first passed through a 560/25 nm filter within a Lambda 10-3 filter wheel (Sutter Instruments). Light power density was ˜5 mWmm⁻² for all experiments. All experiments were performed at room temperature (24-25° C.).

[0241] Confocal images of cultured neurons: Confocal images were obtained by staining glass coverslips of transfected neurons with DAPI (1:50,000) which were then imaged using a Leica confocal microscope (DM600B) as 1,025×1,024 pixel resolution, at 40× magnification, 1.25 NA (oil). Excitation/emission wavelengths for eYFP were 488 nm/500-545 nm.

[0242] The existence of “bystander neurons”, defined here as neurons indirectly exposed to, but not direct expressors of, optogenetically-mediated changes in neural activity was tested. Two optogenetic targeting strategies were employed: first, an optogenetic construct containing one of CHR2(H134R), eArch3.0, eNpHR3.0 or a YFP control, driven by the calmodulin kinase IIα promoter (AAV5-CamKII-(opsin)-eYFP), was injected unilaterally in the CA1 region of hippocampus. Due to the contralateral axonal projections of these neurons, one could then record from non-expressing neurons (bystander neurons) surrounded by opsin-expressing axons in the contralateral CA1 . (FIGS. 15A and 15C). Bystander responses to the depolarizing opsin CHR2(H134R) (from now on referred to as ChR2), two hyperpolarizing opsins (enhanced for membrane targeted expression)—the proton pump archeorhodopsin (eArch3.0) and the chloride pump halorhodopsin (eNpHR3.0), and a YFP-control were compared in the hippocampal preparation, under matched experimental conditions. A second category of bystander neuron was identified using the transgenic mouse strain Thy1-ChR2 (line 18), where ChR2 is expressed in layer V cortical neurons and bystander neurons are located in superficial cortical layers, where they are surrounded by ChR2-expressing membrane processes but not expressing ChR2 themselves (FIGS. 15B and 15D).

[0243] Whole cell recordings from bystander neurons in the presence of ionotropic synaptic transmission blockers were performed in acute brain slices. In response to a 15 s blue light pulse, hippocampal ChR2 bystander neurons exhibited a depolarizing membrane current (mean=−155 pA) (FIG. 15E) with onset-kinetics several orders of magnitude slower (˜2 s) than a direct ChR2 photocurrent (FIG. 15J and FIG. 16). Cortical Thy1-ChR2 bystander neurons displayed a smaller inward current (mean=−27 pA) consistent with the smaller direct ChR2 photocurrent magnitude in Thy1-ChR2-expressing neurons (FIG. 17). These inward currents corresponded to a mean membrane depolarization of 6.1 mV for hippocampal ChR2 bystanders and 2.7 mV for cortical Thy1-ChR2 bystanders (FIG. 15F). AAV5-YFP control bystanders did not exhibit a change in membrane current or voltage. Given that pulsed-light paradigms are commonly used for depolarizing optogenetic applications, we examined bystander responses to 20 and 10 Hz light pulse trains, and again observed similar slow inward currents (mean=−73 pA for 20 Hz and −29 pA for 10 Hz) (FIG. 15G).

[0244] We next examined the impact of hyperpolarizing optogenetic tools on hippocampal bystander neurons. During a 30 s light pulse, AAV5-eArch3.0 bystanders exhibited a slow (˜5 s) hyperpolarizing current (mean=21 pA), several orders of magnitude slower than a direct eArch3.0 photocurrent and AAV5-eNpHR3.0 bystanders exhibited a smaller (mean=10 pA) and even slower (˜8 s) hyperpolarizing current (FIGS. 15H and 15J). These outward currents corresponded to a small mean membrane hyperpolarization of −3.3 mV for eArch3.0 and −1.1 mV for eNpHR3.0 whereas no change in membrane current or voltage was observed for AAV5-YFP control bystanders under matched experimental conditions (FIG. 15I).

[0245] During the application of light, ChR2 bystander neurons experienced a 24% mean decrease in membrane resistance, whereas eArch3.0-bystander neurons experienced a 9% increase in membrane resistance and eNpHR3.0 a 2% increase. YFP controls showed a 3% decrease in membrane resistance (FIG. 15L). Current-voltage relationships demonstrated a significantly positive slope for depolarizing bystanders and significantly negative slope for hyperpolarizing bystanders converging at a reversal potential between −10 to −40 mV (FIG. 15K). Functional and mechanistic investigation of the bystander effect.

[0246] FIGS. 15A-L. Identification and delineation of the bystander effect. A Unilateral injection of AAV5-CamKII-(opsin)-eYFP into CA1 of hippocampus yielded non-expressing bystander neurons in the contralateral hippocampus. Confocal image showing YFP expression and location of bystander neurons (star) (5×, scale bar 1 mm). B Cortical bystander neurons in superficial layers of cortex of Thy1-ChR2 (line 18) transgenic mice. Confocal image showing YFP expression and location of bystander neurons (star) (10×, scale bar 100 μm). C Biocytin-filled hippocampal bystander neurons labeled with streptavidin in CA1 (scale bars 100 μm and 20 μm). D Biocytin-filled cortical bystander neuron labeled with streptavidin, surrounded by but not overlapping with YFP fluorescence confirmed by anti-YFP antibody staining (scale bars 50 μm and 20 μm). E Depolarizing bystander currents in response to 15 s 470 nm light pulses for AAV5-ChR2 hippocampal bystanders (mean+/−SEM=−155+/−32 pA, n=11, p<0.0001 compared to YFP), Thy1-ChR2 cortical bystanders (−27+/−6 pA, n=6, p<0.001 compared to AAV5-YFP) and AAV5-YFP controls (0.7+/−0.7 pA, n=10), Example voltage clamp traces shown below summary plot. F Depolarizing bystander potentials for AAV5-ChR2 hippocampal bystanders (6.1+/−1.4 mV, n=11, p<0.0001), Thy1-ChR2 bystanders (2.7+/−0.6 mV, n=3, p<0.01) and AAV5-YFP controls (0.02+/−0.07 mV, n=9). Example current clamp traces shown below summary plot. G Bystander currents in response to 470 nm light pulse trains at 20 Hz (−73+/−18 pA, n=12) and 10 Hz (−29+/−6 pA, n=11). Example voltage clamp traces shown below summary plot. H Hyperpolarizing bystander currents in response to 30 s 560 nm light for AAV5-eArch3.0 (21+/−4 pA, n=12, p<0.0001), 590 nm for AAVS-eNpHR3.0 (10+/−2 pA, n=14, p<0.0001) and AAVS-YFP controls (1.3+/−0.8 pA, n=10, 560 nm light). Example voltage clamp traces shown below summary plot. I Hyperpolarizing bystander potentials for AAVS-eArch3.0 (−3.3+/−1.1 mV, n=12, p<0.0001), AAVS-eNpHR3.0 (−1.1+/−0.2 mV, n=12, p<0.001) and AAV5-YFP controls (−0.1+/−0.2 mV, n=9). Example current clamp traces shown below the summary plot. J Onset kinetics (τ_on) for depolarizing (ChR2: 1800+/−200 ms, n=8) and hyperpolarizing (eArch3.0: 4800+/−710 ms n=10, eNpHR3.0: 8300+/−850 ms, n=7) bystanders. K Current-voltage relationships for depolarizing ChR2 bystander currents (R² for slope (difference from 0)=0.71, p<0.0001)) and hyperpolarizing bystander currents (eArch3.0: R² for slope=0.43, p<0.0001, eNpHR3.0: R² for slope=0.26, p=0.0001) (n=5-12). L Change in membrane resistance from baseline in response to 30 s pulse of light for ChR2 (470 nm, 24% decrease in membrane resistance, n=8, p<0.001), eArch3.0 (560 nm, 9% increase in membrane resistance, n=12, p<0.0001) eNpHR3.0 (590 nm, 2% increase in membrane resistance, n=11, p<0.01) and YFP control bystanders (560 nm, 3% decrease in membrane resistance, n=11). All bar charts indicate mean values and error bars represent standard error of the mean (SEM). Individual data points indicate results from single cells. All statistical comparisons are between test (opsin) groups and YFP controls using the Mann Whitney (non-parametric) paired t-test.

[0247] FIG. 16: Kinetics of photocurrents and bystanders. Example traces illustrating the difference in on-kinetics between a ChR2 expressing-cell photocurrent and a ChR2 bystander current in response to a 470 nm light pulse (0.5 s and 15 s respectively). Dashed box shows a zoom-in of the first 0.5 s of both traces.

[0248] FIGS. 17A and 17B: Photocurrent magnitudes. A Steady state photocurrent magnitudes (in response to 1 s light) for opsin-expressing neurons present in same preparations as bystander neurons: AAV-ChR2 (n=20, 470 nm), Thy1-ChR2 (n=6, 470 nm), AAV-eArch3.0 (n=14, 560 nm), AAV-eNpHR3.0 (n=16, 590 nm). Bars indicate mean and SEM, filled circles indicate individual cell photocurrents. B Example photocurrent traces for AAV5-ChR2 (blue), AAV-eArch3.0 (green) and AAV-eNpHR3.0 (amber) expressing neurons.

[0249] The influence of the bystander effect on evoked action potential firing was investigated (FIG. 18). During epochs of illumination (470 nm, 560 nm or 590 nm), the proportion of action potentials evoked in bystander neurons was modulated in a bidirectional manner, approximately doubling in the case of AAV5-ChR2 bystanders and halving in the case of AAV5-eArch3.0 bystanders (FIGS. 18A and 18B). AAV5-eNpHR3.0 bystanders also experienced a modest but significant reduction in spiking success during illumination whereas no modulation by light epochs was observed in AAV5-YFP controls (FIGS. 18C and 18D).

[0250] FIGS. 18A-D. Functional impact of bystander currents on action potential firing. Spikes were evoked in the bystander neuron by intracellular injection of electrical current pulses at 10 Hz titrated to achieve a ˜50% success rate at baseline. Light pulses were applied and the change in evoked spiking was recorded. Plots show percentage of successfully evoked spikes during repeated light-off and light-on epochs for A AAV-ChR2 (n=4-10), B AAV-eArch3.0 (n=13-14), C AAV-eNpHR3.0 (n=9-14) and D AAV-YFP control bystander neurons Summary plots and individual cell data are shown with example traces. Dashed box shows zoom-in of the center light-off/light-on epochs. Bar charts indicate mean values and error bars represent SEM. All statistical comparisons (Wilcoxon matched pairs signed rank test) are between the light-on epoch and the preceding light-off epoch.

[0251] Having observed that the bystander effect tracked the direction of change in local neural activity we questioned whether the effect could be observed during manipulation of neural activity using electrical stimulation. Although electrical stimulation is not constrained to a genetically specified cell type or projection, we endeavored to create “electrical bystanders” by stimulating axonal inputs (Schaffer collaterals) to the CA1 region of hippocampus (FIG. 19A). The ability of the stimulation paradigm to induce synaptic release (FIG. 19B) was confirmed, then ionotropic synaptic transmission blockers were applied to isolate the impact of electrical axonal stimulation on the extracellular milieu. To mimic the intensity of the optogenetic manipulations, high amplitude (0.5-2.5 mA) extracellular current pulses at a frequency of 10 Hz for a period of 20 s were used (FIG. 19C). Electrical artifacts challenged the assessment of whole-cell current responses during stimulation, however the mean change in holding current immediately post-stimulation compared to baseline was significantly more negative than the YFP control group (−11 pA) (FIG. 19D), displaying a slow recovery comparable to the ChR2 optogenetic bystander currents. The possibility of a unique electrochemical reaction between the electrode metal and the extracellular fluid was controlled for by performing the experiments using both tungsten and platinum-iridium electrodes; similar effects were found with both electrode-types (FIG. 20).

[0252] It was hypothesized that the bystander effect could be driven by changes in local extracellular pH. Neural activity and synaptic release can modulate extracellular pH and many membrane proteins are modulated by extracellular protons such as acid-sensing ion channels (ASICs), which may be partially open at rest and are plentiful in the brain. The contribution of ASICs to the ChR2 bystander current was tested by using pharmacological blockade by the ASIC inhibitor, amiloride. A bystander current (15 s light pulse) was evoked in hippocampal ChR2 bystander neurons every 5 minutes for up to 75 minutes. Following two baseline measurements, 500 μM amiloride was applied for 20 minutes, then returned to ACSF alone for a “washout” period. During amiloride application, an increase in membrane resistance (in the absence of any illumination) (FIG. 15E) was observed, with a concurrent reduction in the magnitude of the light-evoked bystander current to ˜50% of the baseline value, which slowly recovered during the washout period (FIGS. 15F and 15G). To control for the effect of holding cells in whole-cell patch clamp configuration for long periods, the experiment was repeated in the absence of amiloride application and no consistent reduction in bystander current magnitude over time was seen (FIG. 21C). Measures of cell health confirmed the integrity of the pipette access and cell membrane for the duration of the recordings (FIGS. 22A and 22B).

[0253] The response of acid-sensing ion channels to extracellular protons was exploited through a concept that we term “two-component optogenetics” (TCO). A modular system was devised, in which a light-sensitive protein such as a proton pump (e.g. Coccomyxa subellipsoidea C-169 (CsR) or Archaerhodopsin (Arch)) is co-expressed with a secondary-coupled ion channel, such as an acid-sensing ion channel (ASIC), to evoke a light-triggered secondary current carried by a specific ionic species, as illustrated in FIG. 23A.

[0254] Oocytes: To test this approach in Xenopus laevis oocytes, we chose a light-driven proton pump of the arctic green alga Coccomyxa subellipsoidea C-169 (CsR) (Blanc et al, 2012), which has improved expression in oocytes compared to the well-characterized bacteriorhodopsin or archaerhodopsin, used for hyperpolarization of neurons. The CsR mutant T46N was used, which exhibits less voltage dependence than the wild type, with large photocurrents at negative voltages (FIG. 24).

[0255] In Xenopus laevis oocytes we co-expressed CsR with each of three different rat acid-sensing ion channels ASIC1a, ASIC2a or ASIC3. These channels are characterized by a steep pH-dependence of the proton-activated currents, more or less below the physiological pH. Immediately after light onset a small outward current carried by proton pumping of CsR was observed, followed by a large inward current carried by the co-expressed acid-sensing ion channel (FIGS. 23B-D). For both ASIC1a and ASIC3, the secondary activated inward current peaked within 1-2 s after light onset then rapidly decayed to the initial pump current, due to the high proton sensitivity and fast desensitization of ASIC1a and ASIC3 as described previously (Zhang & Canessa, 2002) (FIGS. 23B and 23D). In contrast ASIC2a mediated a long-lasting light activated inward current (FIG. 23C). The rise of the ASIC2a current was multiphasic at all voltages, a property not observed in previous studies in which the channel was directly activated by acidification of the bulk solution. This is possibly due to the indirect activation of the channel by the proton pump. In accordance with a low pH₅₀ of 5 and the reported slow and incomplete desensitization of ASIC2a (Zhang & Canessa 2002), the light-induced currents decayed only very slowly during illumination. Following light offset the current decayed to zero within ˜20 seconds and could be reactivated by illumination any time (FIG. 25A).

[0256] FIGS. 23A-D. Optical activation of three acid-sensitive ion channels. A Principle of the Two Component Optogenetic (TCO) approach. Upon illumination the light-activated proton pump may moderately acidify the local extracellular medium and activate acid-sensitive ion channels, ASICs, via their proton-sensing domain. This results in a remote but large sodium influx that can be used for sustained cell depolarization at moderate light intensities. In Xenopus oocytes, a light-driven proton pump of Coccomyxa subellipsoidea (CsR) was used. B-D Macroscopic currents of CsR_T46N coexpressed with rat ASIC1a, rat ASIC2a or rat ASIC3 in oocytes at a molar RNA ratio of 1:1 (for ASIC3 of 2:1). Cells were illuminated with 560 nm light at different holding voltages at 0.1 mM MOPS and pH 7.5 under constant perfusion. The small outward directed pump currents (CsR) triggers large inward sodium currents (ASIC). Inset zooming to the initial pump activity directly after starting to illuminate CsR_T46N-ASIC1a with green light. Note that ASIC1a and ASIC3 show strong inactivation in sustained light, whereas ASIC2a shows moderate to no inactivation at all.

[0257] FIGS. 24A-E. Photocurrents of Chlorellarhodopsin (CsR). A, B Light induced pump currents of CsR WT (A) and T46N (B) in Xenopus oocytes. The T46N mutant exhibits greater currents at negative membrane voltage compared to WT. C Current—voltage relationships, I(E), and D action spectra with maxima at 545 nm. E Comparison of CsR photocurrents (545 nm excitation) with those of bacteriorhodopsin (BR, 570 nm excitation) expressed under identical conditions. Current amplitudes of CsR are on average 10 fold greater than those of BR.

[0258] FIGS. 25A-D. Characterization of CsR-ASIC1a with and without permanent perfusion in Xenopus laevis oocytes. In “perfusion” conditions a measuring chamber of 300 μl was continuously perfused with 1.8±0.2 ml/min of standard measuring buffer containing 100 mM NaCl, 1 mM KCl, 1 mM MgCl₂, 0.1 mM CaCl₂, 0.1 mM MOPS (pH 7.5). In measurements “without perfusion” the buffer supply was disconnected and the peristaltic pump switched off. A Representative CsR_T46N-ASIC2a photocurrents at 40 s light pulses of 560 nm in a succession of conditions “without perfusion”, with continuous “perfusion” and “without perfusion” at different voltages. Insets: Repetitive photocurrent “without perfusion” and with “continuous perfusion” at −40 mV. B Comparison of normalized peak photocurrent with “perfusion” (open circles) and “without perfusion” (squares). Empty squares describe the response to the first light pulse and filled squares to the third light pulse (see A). C Normalized peak photocurrent at −40 mV in dependence on the initial CsR_T46N pump current in “perfusion” condition and “without perfusion” for 1^st light pulse empty for 3^rd light pulse (see A and B)). All currents were normalized to ASIC2a current at pH4 and −40 mV (see FIG. 5). D CsR_T46N-ASIC2a on-kinetics quantified by the time to reach the half maximal photocurrent t_1/2,on with perfusion (circles) and without perfusion (filled and empty squares, see B and C) E CsR_T46N-ASIC2a off-kinetics quantified by the time to reduce the photocurrent by half after light switched off t_1/2,off with perfusion (circles) and without perfusion (filled and empty squares, see B and C). Inset: Description of t_1/2,on and t_1/2,off (red) on a representative photocurrent at −40 mV.

[0259] The observed light activated inward currents were inversely proportional to the membrane voltage due to the increased driving force for Na⁺ at negative voltages and voltage independent gating and permeability of ASIC2a (Zhang & Canessa, 2002) (FIG. 23A; FIG. 26A). Changing the concentration of the major extracellular cation from Na⁺ to K⁻ or choline shifted the reversal potential and greatly decreased the magnitude of the inward current component, confirming the Na⁺ selectivity of the ASIC2a response as a major feature of the TCO pair (FIG. 26A).

[0260] To determine the fraction of ASIC2a channels that are activated by light, we titrated the ASIC2a currents by rapid buffer exchange. It was found that the maximal current (when holding the membrane potential at −60 mV) was only reached at pH 4 (FIG. 26B). Normalization of light-activated currents to this value revealed that approximately 25% of ASICs are activated by CsR-mediated acidification (FIGS. 26B-D) and allowed an approximation of the acidification sensed by ASICs at the cell surface (FIG. 26B green bar). It was also noticed that at pH values of 5.5 or below, ASIC2a inactivates more severely than at pH 6. Thus for neuronal applications, the degree of inactivation may serve as a useful indicator for the external pH value that may have been reached.

[0261] ASIC activation strongly depended on the number of active proton pumps as probed by application of light at different intensities (FIG. 26E). Furthermore efficient activation was expected to depend on the external buffering capacity for protons, namely buffer strength and extracellular volume. Indeed increasing the buffer strength from 0.1 mM to 5 mM strongly decreased the ASIC2a mediated inward current (FIG. 26C) and correspondingly the fraction of light activated ASIC2a channels from ˜25% at 0.1 mM MOPS to ˜2% at 5 mM MOPS (FIG. 26D). In contrast the extracellular bulk volume seemed of low importance. Consecutive exchange of the bulk medium during illumination by continuous perfusion only slightly decreased the light activated ASIC2a current compared to conditions with a constant bulk phase (FIG. 25).

[0262] FIG. 26A-E. Characterization of CsR-ASIC2a by two-electrode voltage clamp (TEVC) in oocytes. A Current-voltage dependency of normalized photocurrents in 100 mM NaCl, 100 mM KCl or 100 mM CholineCl extracellular medium (all media contained additionally 1 mM NaCl/KCl, 1 mM MgCl₂, 0.1 mM CaCl₂ and 0.1 mM MOPS, pH 7.5, n=5, normalized to ASIC2a current activated by pH 4). B ASIC2a currents measured during pH titration in darkness and comparison with photocurrents measured at pH 7.5. The boxed region highlights the percent activation of ASIC2a by illumination with green light at 0.1 mM MOPS (data shown in FIG. 5B). Inset: representative pH activated current trace of ASIC2a at −40 mV. C Macroscopic currents of CsR_T46N-ASIC2a activated by pH 4 or green light at different buffer concentrations (5 mM MOPS, 1 mM MOPS and 0.1 mM MOPS, −40 mV, constant perfusion) D Percent activation of ASIC2a by the light driven proton pump CsR_T46N in different buffer concentrations (5 mM MOPS, 1 mM MOPS and 0.1 mM MOPS, −40 mV, n=9, 100% activation taken as the peak ASIC current produced by pH 4). E Normalized ASIC2a and CsR_T46N photocurrents measured at different light intensities (0.1 mM MOPS, −40 mV, n=5, normalized to ASIC2a current activated by pH 4). Inset: representative current traces at −40 mV.

[0263] Neurons: For application to neuroscience, ASIC2a was tested in cultured hippocampal neurons. The channels were co-expressed with the light-driven proton pump eArch3.0, one of the highest-expressing pumps in neurons (Chow et al, 2010, Mattis et al, 2011). A single eArch3.0-ASIC2a construct was developed, termed Champ (Channel/pump), fusing the proton pump and ASIC2a channel at the DNA level, separating the two genes only by a linker sequence (FIG. 27A). The combination of eArch3.0-ASIC2a (Champ1.0) was enhanced for better membrane localization (Champ2.0) via trafficking signal (TS) and endoplasmic reticulum (ER) export motifs (Gradinaru et al, 2010) (FIGS. 27A and 27B). We performed whole-cell patch clamp recordings from cultured hippocampal pyramidal neurons, expressing the constructs under the human synapsin (hSyn) or calmodulin kinase IIα (CamKIIα) promoters and saw a characteristic biphasic membrane current in response to 560 nm light in voltage-clamp recordings (FIG. 27C). The mean current magnitudes were 246 pA for the outward proton pump-mediated component and −950 pA for the inward ASIC-mediated component (FIG. 27D). The biphasic current was observed in 48% of YFP-positive neurons (FIGS. 28A and 28B) and there was no evidence of adverse effects on cell health in neurons expressing the dual component construct (FIGS. 28C-F). The inward current magnitude was linearly related to the magnitude of the outward proton pump current (FIG. 27E). Peak inward and outward current magnitude did not vary significantly with the duration of light pulses (1 s to 15 s) in a HEPES buffered solution (FIGS. 29A and 29B), suggesting that maximal currents were achievable within 1 s, however off-kinetics, as fitted by a two-term exponential, increased with increasing light pulse duration (FIGS. 29C and 29D). For longer light pulses (15 s), a clear decay in the inward current magnitude over the course of the light pulse to approximately 80% of the initial value was observed (FIG. 27C and FIG. 30B), which may be explained by increases in extracellular acidity under sustained light conditions.

[0264] In a separate experiment we tested the effect of decreasing the concentration of HEPES buffer in the extracellular Tyrode's solution (from 25 mM to 0.1 mM) on the magnitude of the currents (FIG. 30). In a low (0.1 mM) HEPES solution, 7/11 (˜60%) neurons exhibited the characteristic biphasic membrane response (compared to 5/10 (50%) neurons in standard (25 mM) Tyrode's under otherwise matched conditions). There was a trend towards an increase in current magnitude in low HEPES solution, particularly during longer light pulses (15 s) (FIG. 30D-F) however this was accompanied by a decrease in the stability of the response with greater decay of the peak inward current over the duration of the light pulse (FIGS. 30A and 30B), likely due to the larger drop in extracellular pH in the weakly buffered solution.

[0265] Current clamp recordings of membrane potential responses of TCO-expressing neurons revealed that 560 nm light evoked an initial hyperpolarization (−33 mV) of the membrane potential, followed by a subsequent depolarization (87 mV) (FIGS. 27F and 27G) which was sufficient to generate action potentials (˜9 spikes) and persisted beyond the termination of the light pulse (FIGS. 27F and 27H). The extent of ASIC-mediated depolarization was proportional to the initial pump-mediated hyperpolarization (FIG. 31B), echoing the linear relationship between the inward and outward current components seen in voltage-clamp recordings. The light pulse duration did not significantly alter the magnitude of membrane potential change beyond 1 s light (FIG. 31).

[0266] FIGS. 27A-H. eArch3.0-ASIC2a (Champ) expression in hippocampal neurons. A Confocal images of yellow fluorescent protein (YFP) fluorescence from cultured hippocampal neurons expressing ASIC2a labeled with YFP in combination with the enhanced light-driven proton pump Arch3.0 at 40× magnification. Scale bars represent 30 μm. The construct expressed well under both the CamKIIα and human synapsin (hSyn) promoter. B Cartoon illustration of the two-component construct containing eArch (enhanced by trafficking sequence, TS) and ASIC2a, separated by a linker sequence and labeled with YFP. C Representative voltage clamp traces of the Champ current (eArch3.0-ASIC2a current in response to 1 s, 5 s and 15 s pulses of 560 nm light (timing of light pulse is indicated by horizontal line). Regions of the trace used to measure outward and inward current components and off-kinetics are indicated by dashed lines and arrows. D Magnitude of outward (mean+/−SEM=246+/−27 pA) and inward (−950+/−172 pA) components of the Champ current in response to a 1 s pulse of 560 nm light (n=21). E Relationship between the inward and outward components of the current response to 1 s pulse of 560 nm light (n=21). Linear regression analysis yields R²=0.33, p<0.01 for difference of slope from zero. F Examples of a variety of membrane potential responses to 1 s pulses of 560 nm light (light pulse timing indicated by horizontal lines) from 4 different eArch-ASIC2a (Champ) expressing cells recorded in current clamp. Regions of the trace used to measure hyperpolarizing and depolarizing components of the response are indicated. G Magnitude of hyperpolarizing (eArch3.0-mediated, −33+/−3 mV) and depolarizing (ASIC2a-mediated, 87+/−6 mV) components of the light response (n=13) H Number of spikes evoked in response to 1 s (n=17), 5 s (n=15) and 15 s (n=4) light pulses.

[0267] FIGS. 28A-F. Variable presence of the ASIC2a component in cultured hippocampal neurons. A Example of an eArch3.0-ASIC2a current when the ASIC2a component is small (upper trace) and example of an ASIC negative current, in which only the eArch3.0 (outward) component is present, with no inward ASIC2a component (lower trace). B Magnitude of outward current components for ASIC negative cells (eArch3.0 component present only, n=23) and ASIC positive cells (both outward (eArch3.0) and inward (ASIC2a) components present, n=21). C Leak current for all ASIC negative (n=23) and ASIC positive (n=21) cells. D Resting membrane potential for all ASIC negative (n=11) and ASIC positive (n=13) cells. E Pipette (access) resistance for all ASIC negative (n=23) and ASIC positive (n=21) cells. F Membrane resistance for all ASIC negative (n=23) and ASIC positive (n=21) cells.

[0268] FIGS. 29A and 29B. Champ currents and kinetics in response to light pulses of increasing duration. A Magnitude of outward and inward current components in response to 1 s (n=21), 5 s (n=14) and 15 s (n=10) light pulses. B Off-kinetics of Champ current in response to 1 s (n=18), 5 s (n=9) and 15 s (n=7) light pulses. The off-response is fitted by an exponential with a fast and slow term.

[0269] FIGS. 30A-F. Champ currents in low HEPES Tyrode's solution. A Example of an eArch3.0-ASIC2a (Champ) photocurrent in 0.1 mM HEPES, illustrating the rapid decay of the peak current over the duration of the 15 s light pulse. Regions of the trace used for measurement of peak and final currents are indicated. B Ratio of the peak : final current for cells patched in 25 mM HEPES (n=5) and 0.1 mM HEPES (n=6) in response to 15 s light pulses. C Magnitude of inward and outward current components in response to 15 s light pulses in 0.1 mM HEPES (n=6).

[0270] D Inward current magnitude in 25 mM and 0.1 mM HEPES during 1 s and 15 s light pulses (n=5-7) under otherwise matched conditions. E & F Outward and inward membrane currents during 1 s and 15 s light pulses in 0.1 mM HEPES.

[0271] FIGS. 31A and 31B. Champ potentials in response to light pulses of increasing duration and relationship between Champ-mediated hyperpolarization and depolarization. A Magnitude of membrane hyperpolarization and depolarization in response to 1 s (n=13), 5 s, (n=10) and 15 s (n=4) light pulses. B Linear regression analysis for the relationship between Champ-mediated membrane hyperpolarization and depolarization yields R²=0.47, p<0.01 for difference of slope from zero.

[0272] The impact of the proximity of the proton pump and ASIC components in generating the characteristic biphasic TCO response was explored. The molecular separation of the two components was systematically increased by interspersing a linker sequence of DNA of increasing length between the two genes: first, a short linker consisting of a 69 base pair trafficking sequence which closely fuses the two proteins (Champ3.0), second, a long (123 base pair) linker sequence that still tethers the two proteins but with a longer intervening peptide chain (Champ2.0), third, a ribosomal p2a skip sequence which cleaves the two proteins during translation (Szymczak-Workman et al. (Cold Spring Harbor Protocols 2012; 2012: 199-204); Prakash et al. (Nat Methods 2012; 9: 1171-1179)). Finally, the neurons were transfected simultaneously using two separate constructs (CamKII-Arch3.0-mCherry and CamKII-ASIC2a-YFP) co-expressing them but without generating a fusion construct. The 4 constructs and a CamKII-eArch3.0-YFP control were tested in a head-to-head comparison under matched experimental conditions (FIG. 32).

[0273] It was found that all four approaches resulted in good YFP expression, indicating successful expression of the ASIC construct. In the co-expression experiment good co-localization of mCherry fluorescence was observed, confirming expression of both constructs within single cells (FIGS. 32A-D). It was found that increasing the molecular separation between the constructs resulted in a lower probability of observing the inward current component of the TCO response, with the short linker sequence (TS) construct (Champ3.0) exhibiting the most reliable and largest inward ASIC-mediated currents at 0.1 mM buffer (mean inward current=−599 pA, mean outward current=150 pA) (FIG. 32A). We occasionally saw large ASIC currents with the separated (p2a split) construct; however these occurred less reliably (FIG. 32D). The co-expressed constructs generated eArch3.0 photocurrents (outward component) only, which were closer in magnitude (mean=377 pA) to the Arch3.0 control (mean=575 pA) than the fusion or p2a split constructs. The observed dependence of TCO function on the physical proximity of the proton pump and ASIC channel highlights the importance of nano-environment ion sensing in the interaction between the two components on the membrane.

[0274] FIGS. 32A-D. Head-to-head comparison of four Champ constructs: effect of increasing molecular distance. All electrophysiological recordings were performed in low HEPES (0.1 mM) Tyrode's solution. For each construct: a cartoon illustrates the structure of the two-component construct, confocal images demonstrate fluorescence expression in culture and graphs show the relative magnitude of the peak outward current and the current at the end of the light pulse. A more negative current at the end of the light pulse indicates a larger ASIC component. Insets: representative traces of the current responses to a 1 s pulse of 560 nm light for each two-component construct (timing of light pulse indicated by horizontal line). A Champ3.0: eArch3.0 and ASIC2a are fused by a short linker sequence consisting of a 69 base pair membrane trafficking signal (TS) (n=16). B Champ2.0: eArch3.0 and ASIC2a are fused by a longer (123 base pair) sequence (n=17). C Champ4.0: eArch3.0 and ASIC2a are separated during protein translation by the ribosomal skip sequence, p2A (n=14). D Co-transfection of eArch3.0 and ASIC2a: eArch3.0 is labeled with mCherry and ASIC2a is labeled with YFP to allow identification of both components in a single cell. Electrophysiological characterization of outward and end-of-light pulse currents for the co-transfected construct and an eArch3.0-only control (n=9 and n=9 respectively).

[0275] FIGS. 33A-D. Measures of cell health across 4 different Champ constructs with increasing molecular separation between proton pump and ASIC. There were no significant differences in any cell health measures across the 5 groups: Champ3.0, Champ2.0, Champ4.0, co-transfection of eArch3.0 and ASIC2a and eArch3.0 only (one-way ANOVA, F=1.56-2.27, p>0.05, n=9-17) A Leak current B Membrane resistance C Pipette resistance D Resting membrane potential.

• [0276] Anastassiou C A, Perin R, Markram H, Koch C. Nat Neurosci 2011; 14: 217-223. Ephaptic coupling of cortical neurons.
• [0277] Arenkiel B R, Peca J, Davison I G, Feliciano C, Deisseroth K, Augustine G J, Ehlers M D, Feng G. Neuron 2007; 205-218. In vivo light-induced activation of neural circuitry in transgenic mice expressing channelrhodopsin-2.
• [0278] Askwith C C, Wemmie J A, Price M P, Rokhlina T, Welsh M J. J Biol Chem 2004; 279: 18296-18305. Acid-sensing ion channel 2 (ASIC2) modulates ASIC H⁺-activated currents in hippocampal neurons.
• [0279] Babini E, Paukert M, Geisler H S, Grunder S. J Biol Chem 2002; 277: 41597-603. Alternative splicing and interaction with di- and polyvalent cations control the dynamic range of acid-sensing ion channell (ASIC1).
• [0280] Babinski K, Catarsi S, Biagini G, Seguela P. J Biol Chem 2000; 275: 28519-28525. Mammalian ASIC2a and ASIC3 subunits co-assemble into heteromeric proton-gated channels sensitive to Gd³⁺.
• [0281] Baburin I, Beyl S, Hering S. Pflügers Archiv 2006; 453.1: 117-123. Automated fast perfusion of Xenopus oocytes for drug screening.
• [0282] Bamann C, Gueta R, Kleinlogel S, Nagel G, Bamberg E. Biochemistry 2010; 49: 267-278. Structural guidance of the photocycle of channelrhodopsin-2 by an interhelical hydrogen bond.
• [0283] Baron A, Waldmann R, Lazdunski M. J Physiol 2002; 539: 485-494. ASIC-like, proton-activated currents in rat hippocampal neurons.
• [0284] Bassilana F, Champigny G, Waldmann R, de Weille J R, Heurteaux C, Lazdunski M. J Biol Chem 1997; 272: 28819-28822. The acid-sensitive ionic channel subunit ASIC and the mammalian degenerin MDEG form a heteromultumeric H⁺-gated Na⁺ channel with novel properties.
• [0285] Baylor D A & Nicholls J G. J Physiol 1969; 203: 555-569. Changes in extracellular potassium concentration produced by neuronal activity in the central nervous system of the leech.
• [0286] Berndt A, Yizhar O, Gunaydin L A, Hegemann P, Deisseroth K. Nat Neurosci 2009; 12: 229-234. Bi-stable neural state switches.
• [0287] Bevan S, Yeats J. J Physiol 1991; 433: 145-161. Protons activate a cation conductance in a sub-population of rat dorsal root ganglion neurones.
• [0288] Blanc G, Agarkova I, Grimwood J, Kuo A, Brueggeman A, Dunigan D D, Gurnon J, Ladunga I, Linguist E, Lucas S, Pangilinan J, Proschold T, Salamov A, Schmutz J, Weeks D, Yamada T, Lomsadze A, Borodovsky M, Claverie J M, Grigoriev I V, Van Etten J L. Genome Biology 2012; 13: R39. http://genomebiology.com/2012/15/5/R39
• [0289] Bolshakov K V, Essin K V, Buldakova S L, Dorofeeva N A, Skatchkov S N, Eaton M J, Tikhonov D B, Magazanik L G. Neuroscience 2002; 110: 723-730. Characterization of acid-sensitive ion channels in freshly isolated rat brain neurons.
• [0290] Bruun S, Naumann H, Kuhlmann U, Schulz C, Stehfest K, Hegemann P, Hildebrandt P. FEBS Lett 2011; 585: 3998-4001. The chromophore structure of the long-lived intermediate of the C128T channelrhodopsin-2 variant.
• [0291] Chen C C, England S, Akopian A, Wood J N. Proc Natl Acad Sci USA 1998; 95: 10240-10245. A sensory neuron-specific, proton-gated ion channel.
• [0292] Chesler M & Kalia K. TINS 1992; 15: 396-402. Modulation of pH by neuronal activity. Chow B Y, Han X, Dobry A S, Qian X, Chuong A S, Li M, Henninger M A, Belfort G M, Lin Y,
• [0293] Monahan P E, Boyden E S. Nature 2010; 463: 98-102. High-performance genetically targetable optical neural silencing by light-driven proton pumps.
• [0294] Deval E, Gasull X, Noel J, Salinas M, Baron A, Diochot S, Lingueglia E. Pharmacol Ther 2010; 128: 549-558. Acid-sensing ion channels (ASICs): pharmacology and implication in pain.
• [0295] Ferenczi E, Deisseroth K. Nat Neurosci 2012; 15: 1058-1060. When the electricity (and the lights) go out: transient changes in excitability.
• [0296] Goldin, A L. 2006. Expression of Ion Channels in Xenopus Oocytes. Expression and Analysis of Recombinant Ion Channels: From Structural Studies to Pharmacological Screening.
• [0297] Gutman M, Nachliel E, Friedman R. Biochim Biophys Acta 2006 1757: 931-41. The mechanism of proton transfer between adjacent sites on the molecular surface.
• [0298] Gradinaru V, Thompson K R, Deisseroth K. Brain Cell Biol 2008; 36:129-39. eNpHR: a Natronomonas halorhodopsin enhanced for optogenetic applications.
• [0299] Gradinaru V, Zhang F, Ramakrishnan C, Mattis J, Prakash R, Diester I, Goshen I, Thompson K R, Deisseroth K. Cell 2010; 141: 154-165. Molecular and cellular approaches for diversifying and extending optogenetics.
• [0300] Gruender S, Chen X. Int J Physiol Pathophysiol Pharmacol 2010; 2: 73-94. Structure, function and pharmacology of acid-sensing ion channels (ASICs): focus on ASIC1a.
• [0301] Heberle J, Riesle J, Thiedemann G, Oesterhelt D, Dencher N A. Nature 1994; 370: 379-382. Proton migration along the membrane surface and retarded surface to bulk transfer.
• [0302] Hodgkin A L & Huxley A F. J Physiol 1952; 117, 500-544. A quantitative description of membrane current and its application to conduction and excitation in nerve.
• [0303] Hodgkin A L & Katz B. J Physiol 1949; 108: 37-77. The effect of sodium ions on the electrical activity of the giant axon of the squid.
• [0304] Jasti J, Furukawa H, Gonzales E B, Gouaux E. Nature 2007; 449: 316-323. Structure of acid-sensing ion channel 1 at 1.9 A resolution and low pH.
• [0305] Jordt S E, Tominaga M, Julius D. Proc Natl Acad Sci USA 2000; 97: 8134-8139. Acid potentiation of the capsaicin receptor determined by a key extracellular site.
• [0306] Katz B, Schmitt O H. J Physiol 1940; 97: 471-488. Electric interaction between two adjacent nerve fibers.
• [0307] Krishtal O. TINS 2003; 26: 477-483. The ASICs: signaling molecules? modulators?
• [0308] Krishtal O A, Osipchuk Yu V, Shelest T N, Smirnoff S V. Brain Res 1987; 436: 352-356. Rapid extracellular pH transients related to synaptic transmission in rat hippocampal slices.
• [0309] Krishtal O A, Pidoplichko V I. Neuroscience 1980; 5: 2325-2327. A receptor for protons in the nerve cell membrane.
• [0310] Krishtal O A, Pidoplichko V I. Neurosci Lett 1981; 6: 2599-2601. A ‘receptor’ for protons in small neurons of trigeminal ganglia: possible role in nociception.
• [0311] Lindemann B. Nature 2001; 413: 219-225. Receptors and transduction in taste.
• [0312] Liske H, Xiang Q, Anikeeva P, Deisseroth K, Delp S. Optical control of neuronal excitation and inhibition using a single opsin protein. Scientific Reports 2013; 3: 3110.
• [0313] Mattis J, Tye K M, Ferenczi E A, Ramakrishnan C, O'Shea D J, Prakash R, Gunaydin L A, Hyun M, Fenno L E, Gradinaru V, Yizhar O, Deisseroth K. Nat Methods 2011; 9: 159-72. Principles for applying optogenetic tools derived from direct comparative analysis of microbial opsins.
• [0314] Nagel G, Szellas T, Huhn W, Kateriya S, Adeishvili N, Berthold P, Ollig D, Hegemann P, Bamberg E. Proc Natl Acad Sci USA 2003; 100: 13940-13945.
• [0315] Paukert M, Chen X, Polleichtner G, Schindelin H, Grunder S. J Biol Chem 2008; 283: 572-581. Candidate amino acids involved in H⁺ gating of acid-sensing ion channel 1a.
• [0316] Poolos N P, Mauk M D, Kocsis J D. J Neurophysiol 1987; 58: 404-416. Activity-evoked increases in extracellular potassium modulate presynaptic excitability in the CA1 region of the hippocampus.
• [0317] Prakash R, Yizhar O, Grewe B, Ramakrishnan C, Wang N, Goshen I, Packer A M, Peterka D S, Yuste R, Schnitzer M J, Deisseroth K. Nat Methods 2012; 9: 1171-1179. Two-photon optogenetic toolbox for fast inhibition, excitation and bistable modulation.
• [0318] Raimondo J V, Kay L, Ellender T J, Akerman C J. Nat Neurosci 2012; 15: 1102-4. Optogenetic silencing strategies differ in their effects on inhibitory synaptic transmission.
• [0319] Ritter E, Piwowarski P, Hegemann P, Barti F J. J Biol Chem 2013; 288: 10451-10458. Light-dark adaptation of channelrhodopsin C128T mutant.
• [0320] Schoenenberger P, Gerosa D, Oertner T G. PLos One 2009; 4: e8185. Temporal control of immediate early gene induction by light.
• [0321] Sherwood T W, Lee K G, Gormley M G, Askwith C C. J Neurosci 2011; 31: 9723-9734. Heteromeric acid-sensing ion channels (ASICs) composed of ASIC2b and ASIC1a display novel channel properties and contribute to acidosis-induced neuronal death.
• [0322] Stehfest K, Hegemann P. Chemphyschem 2010; 11: 1120-1126. Evolution of the channelrhodopsin photocycle model.
• [0323] Shuba Y M, Dietrich C J, Oermann E, Cleemann L, Morad M. Cell Calcium 2008; 44: 220-229. Local extracellular acidification caused by Ca²⁺-dependent exocytosis in PC12 cells.
• [0324] Szymczak-Workman A L, Vignali K M, Vignali D A. Cold Spring Harb Protoc 2012; 2012: 199-204. Design and construction of 2A peptide-linked multicistronic vectors.
• [0325] Torborg C L, Berg A P, Jeffries B W, Bayliss D A, McBain C J. J Neurosci 2006; 26: 7362-7367. TASK-like conductances are present within hippocampal CA1 stratum oriens interneuron subpopulations.
• [0326] Towne C, Montgomery K L, Iyer S M, Deisseroth K, Delp S L. Optogenetic Control of Targeted Peripheral Axons in Freely Moving Animals. PLoS ONE 2013; 8: e72691
• [0327] Waldmann R, Champigny G, Bassilana F, Heurteaux C, Lazdunski M. A proton-gated cation channel involved in acid-sensing. Nature 1997; 386: 173-177.
• [0328] Wang H, Sugiyama Y, Hikima T, Sugano E, Tomita H, Takahashi T, Ishizuka T, Yawo H. Molecular determinants differentiating photocurrent properties of two channelrhodopsins from chlamydomonas. J Biol Chem 2009; 284: 5685-96.
• [0329] Wang T-M, Holzhausen L C, Kramer R H. Imaging an optogenetic pH sensor reveals that protons mediate lateral inhibition in the retina. Nature Neuroscience 2014; 17: 262-268.
• [0330] Welch J M, Simon S A, Reinhart P H. Proc Natl Acad Sci USA 2000; 97: 13889-13894. The activation mechanism of rat vanilloid receptor 1 by capsaicin involves the pore domain and differs from the activation by either acid or heat.
• [0331] Wemmie J A, Taugher R J, Kreple C J. Nat Rev Neurosci 2013; 14: 461-471. Acid sensing ion channels in pain and disease.
• [0332] Weng J Y, Lin Y C, Lien C C. J Neurosci 2010; 30: 6548-58. Cell type-specific expression of acid-sensing ion channels in hippocampal interneurons.
• [0333] Xiong Z Q, Stringer J L. J Neurophysiol 2000; 83: 3519-3524. Extracellular pH responses in CA1 and the dentate gyrus during electrical stimulation, seizure discharges, and spreading depression.
• [0334] Yizhar O, Fenno L E, Davidson T J, Mogri M, Deisseroth K. Neuron 2011; 72: 9-34. Optogenetics in Neural Systems.
• [0335] Yermolaieva O, Leonard A S, Schnizler M K, Abboud F M, Welsh M J. Proc Natl Acad Sci USA 2004; 101: 6752-6757. Extracellular acidosis increases neuronal cell calcium by activating acid-sensing ion channel 1a.
• [0336] Yizhar O, Fenno L E, Prigge M, Schneider F, Davidson T J, O'Shea D J, Sohal V S, Goshen I, Finkelstein J, Paz J T, Stehfest K, Fudim R, Ramakrishnan C, Huguenard J R, Hegemann P, Deisseroth K. Nature 2011; 477: 171-178. Neocortical excitation/inhibition balance in information processing and social dysfunction.
• [0337] Zha X M, Wemmie J A, Green S H, Welsh M J. Proc Natl Acad Sci USA 2006; 103: 16556-16561. Acid-sensing ion channel 1a is a postsynaptic proton receptor that affects the density of dendritic spines.
• [0338] Zhang F, Vierock J, Yizhar O, Fenno L E, Tsunoda S, Kianianmomeni A, Prigge M, Berndt A, Cushman J, Polle J, Magnuson J, Hegemann P, Deisseroth K. Cell 2011; 147: 1446-1457. The microbial opsin family of optogenetic tools.
• [0339] Zhang F, Wang L P, Brauner M, Liewald J F, Kay K, Watzke N, Wood P G, Bamberg E, Nagel G, Gottschalk A, Deisseroth K. Nature 2007; 446: 633-639. Multimodal fast optical interrogation of neural circuitry.
• [0340] Zhang P, Canessa C M. J Gen Physiol 2002; 120: 553-566. Single channel properties of rat acid-sensitive ion channel-1alpha, -2a, and -3 expressed in Xenopus oocytes.
• [0341] Ziemann A E, Schnizler M K, Albert G W, Severson M A, Howard III M A, Welsh M J, Wemmie J A. Nat Neurosci 2008; 11: 816-822. Seizure termination by acidosis depends on ASIC1a.

[0342] Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.

[0343] Accordingly, the preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims.