# Patent

## Title
Opsin polypeptides and methods of use thereof

## Abstract

The present disclosure provides opsins, including variant opsins with increased activity and/or increased trafficking to the plasma membrane. The opsins are useful in therapeutic and screening applications, which are also provided.

## Background
CROSS-REFERENCE
This application is a divisional application of U.S. patent application Ser. No. 15/097,925, filed Apr. 13, 2016, now U.S. Pat. No. 9,505,817, which is a divisional application of U.S. patent application Ser. No. 14/365,477, filed Jun. 13, 2014, now U.S. Pat. No. 9,365,628, which is a national stage filing under 35 U.S.C. §371 of PCT/US2012/069133, filed Dec. 12, 2012, which claims the benefit of U.S. Provisional Patent Application No. 61/576,858, filed Dec. 16, 2011, each of which applications is incorporated herein by reference in its entirety.


BACKGROUND
Diverse and elegant mechanisms have evolved to enable organisms to harvest light for a variety of survival functions, including energy generation and the identification of suitable survival environments. A major class of light-sensitive protein consists of 7-transmembrane rhodopsins that can be found across all kingdoms of life and serve a diverse range of functions. Many prokaryotes employ these proteins to control proton gradients and to maintain membrane potential and ionic homeostasis, and many motile microorganisms have evolved opsin-based photoreceptors to modulate flagellar beating and thereby direct phototaxis toward environments with optimal light intensities for photosynthesis.
Owing to their structural simplicity (both light sensation and effector domains are encoded within a single gene) and fast kinetics, microbial opsins can be treated as precise and modular photosensitization components for introduction into non-light sensitive cells to enable rapid optical control of specific cellular processes. In recent years, the development of cellular perturbation tools based on these and other light sensitive proteins has resulted in a technology called optogenetics, referring to the integration of genetic and optical control to achieve gain- or loss-of-function of precisely defined events within specified cells of living tissue.
There is a need in the art for depolarizing and hyperpolarizing optogenetic tools, e.g., for use in controlling neural activity.
SUMMARY
The present disclosure provides opsins, including variant opsins with increased activity and/or increased trafficking to the plasma membrane. The opsins are useful in therapeutic and screening applications, which are also provided.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1F depict properties of hyperpolarizing tools.
FIGS. 2A-2F depict performance of hyperpolarizing tools.
FIGS. 3A-3F depict characterization of a ChR from Dunaliella salina. For FIG. 3B: DChR1 (SEQ ID NO: 15), CChR1 (SEQ ID NO: 16), CChR2 (SEQ ID NO: 17), VChR1 (SEQ ID NO: 18), and VChR2 (SEQ ID NO: 19).
FIG. 4 depicts a nucleotide sequence encoding a ChR from Dunaliella salina (SEQ ID NO: 20).
FIG. 5 depicts a nucleotide sequence encoding a ChR from Dunaliella salina, codon optimized for expression in mammalian cells (SEQ ID NO: 21).
FIG. 6 depicts an amino acid sequence of Dunaliella salina ChR (SEQ ID NO: 22).
FIGS. 7A-7E depict the amino acid sequences of exemplary variant opsins:
FIG. 7A (SEQ ID NO: 23); FIG. 7B (SEQ ID NO: 24); FIG. 7C (SEQ ID NO: 25); FIG. 7D (SEQ ID NO: 26); and FIG. 7E (SEQ ID NO: 27).
FIGS. 8A-8C depict an amino acid sequence of Halorubrum sodomense archaerhodopsin-3; and nucleotide sequences encoding same: FIG. 8A (SEQ ID NO: 28); FIG. 8B (SEQ ID NO: 29); and FIG. 8C (SEQ ID NO: 30).
FIGS. 9A and 9B depict an amino acid sequence of Halorubrum sodomense strain TP009 opsin; and a nucleotide sequence encoding same: FIG. 9A (SEQ ID NO: 31) and FIG. 9B (SEQ ID NO: 32).
FIGS. 10A-10C depict an amino acid sequence of Leptosphaeria maculans opsin and nucleotides sequences encoding same: FIG. 10A (SEQ ID NO: 33); FIG. 10B (SEQ ID NO: 34); and FIG. 10C (SEQ ID NO: 35).



DEFINITIONS
The terms “polypeptide,” “peptide,” and “protein,” used interchangeably herein, refer to a polymeric form of amino acids of any length, which can include coded and non-coded amino acids, chemically or biochemically modified or derivatized amino acids, and polypeptides having modified peptide backbones. The term includes fusion proteins, including, but not limited to, fusion proteins with a heterologous amino acid sequence, fusions with heterologous and homologous leader sequences, with or without N-terminal methionine residues; immunologically tagged proteins; and the like. NH2 refers to the free amino group present at the amino terminus of a polypeptide. COOH refers to the free carboxyl group present at the carboxyl terminus of a polypeptide. In keeping with standard polypeptide nomenclature, J. Biol. Chem., 243 (1969), 3552-59 is used.
The terms “polynucleotide” and “nucleic acid,” used interchangeably herein, refer to a polymeric form of nucleotides of any length, either ribonucleotides or deoxynucleotides. Thus, this term includes, but is not limited to, single-, double-, or multi-stranded DNA or RNA, genomic DNA, cDNA, DNA-RNA hybrids, or a polymer comprising purine and pyrimidine bases or other natural, chemically or biochemically modified, non-natural, or derivatized nucleotide bases.
The nucleic acid may be double stranded, single stranded, or contain portions of both double stranded or single stranded sequence. As will be appreciated by those in the art, the depiction of a single strand (“Watson”) also defines the sequence of the other strand (“Crick”). By the term “recombinant nucleic acid” herein is meant nucleic acid, originally formed in vitro, in general, by the manipulation of nucleic acid by endonucleases, in a form not normally found in nature. Thus an isolated nucleic acid, in a linear form, or an expression vector formed in vitro by ligating DNA molecules that are not normally joined, are both considered recombinant for the purposes of this invention. It is understood that once a recombinant nucleic acid is made and reintroduced into a host cell or organism, it will replicate non-recombinantly, i.e. using the in vivo cellular machinery of the host cell rather than in vitro manipulations; however, such nucleic acids, once produced recombinantly, although subsequently replicated non-recombinantly, are still considered recombinant for the purposes of the invention.
Nucleic acid sequence identity (as well as amino acid sequence identity) is calculated based on a reference sequence, which may be a subset of a larger sequence, such as a conserved motif, coding region, flanking region, etc. A reference sequence will usually be at least about 18 residues long, more usually at least about 30 residues long, and may extend to the complete sequence that is being compared. Algorithms for sequence analysis are known in the art, such as BLAST, described in Altschul et al. (1990), J. Mol. Biol. 215:403-10 (using default settings, i.e. parameters w=4 and T=17).
The term “genetic modification” and refers to a permanent or transient genetic change induced in a cell following introduction into the cell of new nucleic acid (i.e., nucleic acid exogenous to the cell). Genetic change (“modification”) can be accomplished by incorporation of the new nucleic acid into the genome of the host cell, or by transient or stable maintenance of the new nucleic acid as an extrachromosomal element. Where the cell is a eukaryotic cell, a permanent genetic change can be achieved by introduction of the nucleic acid into the genome of the cell. Suitable methods of genetic modification include viral infection, transfection, conjugation, protoplast fusion, electroporation, particle gun technology, calcium phosphate precipitation, direct microinjection, and the like.
As used herein the term “isolated” is meant to describe a polynucleotide, a polypeptide, or a cell that is in an environment different from that in which the polynucleotide, the polypeptide, or the cell naturally occurs. An isolated genetically modified host cell may be present in a mixed population of genetically modified host cells. An isolated polypeptide will in some embodiments be synthetic. “Synthetic polypeptides” are assembled from amino acids, and are chemically synthesized in vitro, e.g., cell-free chemical synthesis, using procedures known to those skilled in the art.
By “purified” is meant a compound of interest (e.g., a polypeptide) has been separated from components that accompany it in nature. “Purified” can also be used to refer to a compound of interest separated from components that can accompany it during manufacture (e.g., in chemical synthesis). In some embodiments, a compound is substantially pure when it is at least 50% to 60%, by weight, free from organic molecules with which it is naturally associated or with which it is associated during manufacture. In some embodiments, the preparation is at least 75%, at least 90%, at least 95%, or at least 99%, by weight, of the compound of interest. A substantially pure polypeptide can be obtained, for example, by chemically synthesizing the polypeptide, or by a combination of purification and chemical modification. A substantially pure polypeptide can also be obtained by, for example, affinity chromatography. Purity can be measured by any appropriate method, e.g., chromatography, mass spectroscopy, high performance liquid chromatography analysis, etc.
The terms “individual,” “subject,” “host,” and “patient,” used interchangeably herein, refer to a mammal, including, but not limited to, murines (rats, mice), non-human primates, humans, canines, felines, ungulates (e.g., equines, bovines, ovines, porcines, caprines), etc. In some embodiments, the individual is a human. In some embodiments, the individual is a murine.
The terms “treatment,” “treating,” “treat,” and the like are used herein to generally refer to obtaining a desired pharmacologic and/or physiologic effect. The effect may be prophylactic in terms of completely or partially preventing a disease or symptom thereof and/or may be therapeutic in terms of a partial or complete stabilization or cure for a disease and/or adverse effect attributable to the disease. “Treatment” as used herein covers any treatment of a disease in a mammal, particularly a human, and includes: (a) preventing the disease or symptom from occurring in a subject which may be predisposed to the disease or symptom but has not yet been diagnosed as having it; (b) inhibiting the disease symptom, i.e., arresting its development; or (c) relieving the disease symptom, i.e., causing regression of the disease or symptom.
A “therapeutically effective amount” or “efficacious amount” means the amount of an agent that, when administered to a mammal or other subject for treating a disease, is sufficient to effect such treatment for the disease. The “therapeutically effective amount” will vary depending on agent, the disease or condition and its severity and the age, weight, etc., of the subject to be treated.
Before the present invention is further described, 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.
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.
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, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
It must be 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. Thus, for example, reference to “a variant opsin polypeptide” includes a plurality of such polypeptides and reference to “the trafficking signal” includes reference to one or more trafficking signals and equivalents thereof known to those skilled in the art, and so forth. 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.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. All combinations of the embodiments pertaining to the invention are specifically embraced by the present invention and are disclosed herein just as if each and every combination was individually and explicitly disclosed. In addition, all sub-combinations of the various embodiments and elements thereof are also specifically embraced by the present invention and are disclosed herein just as if each and every such sub-combination was individually and explicitly disclosed herein.
The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to 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.
DETAILED DESCRIPTION
The present disclosure provides opsins, including variant opsins with increased activity and/or increased trafficking to the plasma membrane. The opsins are useful in therapeutic and screening applications, which are also provided.
Opsins
The present disclosure provides opsin polypeptides, and nucleic acids (“opsin nucleic acids”) comprising nucleotide sequences encoding the opsin polypeptides. The present disclosure also provides genetically modified host cells comprising an opsin nucleic acid. An opsin polypeptide is also referred to herein as a “tool.”
A subject isolated opsin polypeptide comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to a contiguous stretch of from about 500 amino acids to about 550 amino acids, from about 550 amino acids to about 600 amino acids, from about 600 amino acids to about 650 amino acids, from about 650 amino acids to about 700 amino acids, or from about 700 amino acids to 720 amino acids, of the amino acid sequence depicted in FIG. 6. Such an opsin can be referred to as “DChR1.”
A subject isolated opsin polypeptide can have a length of from about 500 amino acids to about 550 amino acids, from about 550 amino acids to about 600 amino acids, from about 600 amino acids to about 650 amino acids, from about 650 amino acids to about 700 amino acids, or from about 700 amino acids to 720 amino acids.
An isolated opsin polypeptide of the present disclosure can be encoded by a nucleotide sequence having at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, or 100%, nucleotide sequence identity to a contiguous stretch of from about 1800 nucleotides to about 1900 nucleotides, from about 1900 nucleotides to about 2000 nucleotides, from about 2000 nucleotides to about 2100 nucleotides, or from about 2100 nucleotides to 2163 nucleotides, of the nucleotide sequence depicted in FIG. 4 or FIG. 5.
An isolated opsin polypeptide of the present disclosure functions as a light-activated proton channel, e.g., a subject isolated opsin functions as a proton pump.
In some embodiments, a subject DChR1 opsin is modified to include an ER export sequence and/or a trafficking sequence, as described in detail below. Thus, in some embodiments, a subject DChR1 opsin comprises, in order from amino terminus to carboxyl terminus, a DChR1 opsin; and an ER export sequence. In some embodiments, a subject DChR1 opsin comprises, in order from amino terminus to carboxyl terminus, a DChR1 opsin; a trafficking sequence; and an ER export sequence. In some embodiments, a subject DChR1 opsin comprises, in order from amino terminus to carboxyl terminus, a DChR1 opsin; a trafficking sequence; an intervening sequence; and an ER export sequence. Suitable ER export sequences, trafficking sequences, and intervening sequences are described in detail below.
The present disclosure provides a composition comprising a subject opsin polypeptide. A subject opsin polypeptide composition can comprise, in addition to a subject opsin polypeptide, one or more of: a salt, e.g., NaCl, MgCl2, KCl, MgSO4, etc.; a buffering agent, e.g., a Tris buffer, N-(2-Hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid) (HEPES), 2-(N-Morpholino)ethanesulfonic acid (MES), 2-(N-Morpholino)ethanesulfonic acid sodium salt (MES), 3-(N-Morpholino)propanesulfonic acid (MOPS), N-tris[Hydroxymethyl]methyl-3-aminopropanesulfonic acid (TAPS), etc.; a solubilizing agent; a detergent, e.g., a non-ionic detergent such as Tween-20, etc.; a protease inhibitor; glycerol; and the like.
Nucleic Acids
The present disclosure provides a nucleic acid comprising a nucleotide sequence encoding a subject opsin. A nucleotide sequence encoding a subject opsin can be operably linked to one or more regulatory elements, such as a promoter and enhancer, that allow expression of the nucleotide sequence in the intended target cells (e.g., a cell that is genetically modified to synthesize the encoded opsin).
In some embodiments, a DChR1-encoding nucleotide sequence has at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, or 100%, nucleotide sequence identity to a contiguous stretch of from about 1800 nucleotides to about 1900 nucleotides, from about 1900 nucleotides to about 2000 nucleotides, from about 2000 nucleotides to about 2100 nucleotides, or from about 2100 nucleotides to 2163 nucleotides, of the nucleotide sequence depicted in FIG. 4. In some cases, the nucleotide sequence is codon-optimized for expression in a mammalian cell.
Suitable promoter and enhancer elements are known in the art. For expression in a bacterial cell, suitable promoters include, but are not limited to, lacI, lacZ, T3, T7, gpt, lambda P and trc. For expression in a eukaryotic cell, suitable promoters include, but are not limited to, light and/or heavy chain immunoglobulin gene promoter and enhancer elements; cytomegalovirus immediate early promoter; herpes simplex virus thymidine kinase promoter; early and late SV40 promoters; promoter present in long terminal repeats from a retrovirus; mouse metallothionein-I promoter; and various art-known tissue specific promoters.
In some embodiments, e.g., for expression in a yeast cell, a suitable promoter is a constitutive promoter such as an ADH1 promoter, a PGK1 promoter, an ENO promoter, a PYK1 promoter and the like; or a regulatable promoter such as a GAL1 promoter, a GAL10 promoter, an ADH2 promoter, a PHOS promoter, a CUP1 promoter, a GALT promoter, a MET25 promoter, a METS promoter, a CYC 1 promoter, a HISS promoter, an ADH1 promoter, a PGK promoter, a GAPDH promoter, an ADC1 promoter, a TRP1 promoter, a URA3 promoter, a LEU2 promoter, an ENO promoter, a TP1 promoter, and AOX1 (e.g., for use in Pichia). Selection of the appropriate vector and promoter is well within the level of ordinary skill in the art.
Suitable promoters for use in prokaryotic host cells include, but are not limited to, a bacteriophage T7 RNA polymerase promoter; a trp promoter; a lac operon promoter; a hybrid promoter, e.g., a lac/tac hybrid promoter, a tac/trc hybrid promoter, a trp/lac promoter, a T7/lac promoter; a trc promoter; a tac promoter, and the like; an araBAD promoter; in vivo regulated promoters, such as an ssaG promoter or a related promoter (see, e.g., U.S. Patent Publication No. 20040131637), a pagC promoter (Pulkkinen and Miller, J. Bacteriol., 1991: 173(1): 86-93; Alpuche-Aranda et al., PNAS, 1992; 89(21): 10079-83), a nirB promoter (Harborne et al. (1992) Mol. Micro. 6:2805-2813), and the like (see, e.g., Dunstan et al. (1999) Infect. Immun. 67:5133-5141; McKelvie et al. (2004) Vaccine 22:3243-3255; and Chatfield et al. (1992) Biotechnol. 10:888-892); a sigma70 promoter, e.g., a consensus sigma70 promoter (see, e.g., GenBank Accession Nos. AX798980, AX798961, and AX798183); a stationary phase promoter, e.g., a dps promoter, an spy promoter, and the like; a promoter derived from the pathogenicity island SPI-2 (see, e.g., WO96/17951); an actA promoter (see, e.g., Shetron-Rama et al. (2002) Infect. Immun. 70:1087-1096); an rpsM promoter (see, e.g., Valdivia and Falkow (1996). Mol. Microbiol. 22:367); a tet promoter (see, e.g., Hillen, W. and Wissmann, A. (1989) In Saenger, W. and Heinemann, U. (eds), Topics in Molecular and Structural Biology, Protein—Nucleic Acid Interaction. Macmillan, London, UK, Vol. 10, pp. 143-162); an SP6 promoter (see, e.g., Melton et al. (1984) Nucl. Acids Res. 12:7035); and the like. Suitable strong promoters for use in prokaryotes such as Escherichia coli include, but are not limited to Trc, Tac, T5, T7, and PLambda Non-limiting examples of operators for use in bacterial host cells include a lactose promoter operator (LacI repressor protein changes conformation when contacted with lactose, thereby preventing the Lad repressor protein from binding to the operator), a tryptophan promoter operator (when complexed with tryptophan, TrpR repressor protein has a conformation that binds the operator; in the absence of tryptophan, the TrpR repressor protein has a conformation that does not bind to the operator), and a tac promoter operator (see, for example, deBoer et al. (1983) Proc. Natl. Acad. Sci. U.S.A. 80:21-25).
A nucleotide sequence encoding a subject opsin can be present in an expression vector and/or a cloning vector. An expression vector can include a selectable marker, an origin of replication, and other features that provide for replication and/or maintenance of the vector.
Large numbers of suitable vectors and promoters are known to those of skill in the art; many are commercially available for generating a subject recombinant constructs. The following vectors are provided by way of example. Bacterial: pBs, phagescript, PsiX174, pBluescript SK, pBs KS, pNH8a, pNH16a, pNH18a, pNH46a (Stratagene, La Jolla, Calif., USA); pTrc99A, pKK223-3, pKK233-3, pDR540, and pRITS (Pharmacia, Uppsala, Sweden). Eukaryotic: pWLneo, pSV2cat, pOG44, PXR1, pSG (Stratagene) pSVK3, pBPV, pMSG and pSVL (Pharmacia).
Expression vectors generally have convenient restriction sites located near the promoter sequence to provide for the insertion of nucleic acid sequences encoding a protein of interest (e.g., an opsin). A selectable marker operative in the expression host may be present. Suitable expression vectors include, but are not limited to, viral vectors (e.g. viral vectors based on vaccinia virus; poliovirus; adenovirus (see, e.g., Li et al., Invest Opthalmol Vis Sci 35:2543 2549, 1994; Borras et al., Gene Ther 6:515 524, 1999; Li and Davidson, PNAS 92:7700 7704, 1995; Sakamoto et al., H Gene Ther 5:1088 1097, 1999; WO 94/12649, WO 93/03769; WO 93/19191; WO 94/28938; WO 95/11984 and WO 95/00655); adeno-associated virus (see, e.g., Ali et al., Hum Gene Ther 9:81 86, 1998, Flannery et al., PNAS 94:6916 6921, 1997; Bennett et al., Invest Opthalmol Vis Sci 38:2857 2863, 1997; Jomary et al., Gene Ther 4:683 690, 1997, Rolling et al., Hum Gene Ther 10:641 648, 1999; Ali et al., Hum Mol Genet 5:591 594, 1996; Srivastava in WO 93/09239, Samulski et al., J. Vir. (1989) 63:3822-3828; Mendelson et al., Virol. (1988) 166:154-165; and Flotte et al., PNAS (1993) 90:10613-10617); SV40; herpes simplex virus; human immunodeficiency virus (see, e.g., Miyoshi et al., PNAS 94:10319 23, 1997; Takahashi et al., J Virol 73:7812 7816, 1999); a retroviral vector (e.g., Murine Leukemia Virus, spleen necrosis virus, and vectors derived from retroviruses such as Rous Sarcoma Virus, Harvey Sarcoma Virus, avian leukosis virus, human immunodeficiency virus, myeloproliferative sarcoma virus, and mammary tumor virus); and the like.
Also provided herein is a recombinant vector comprising a subject polynucleotide encoding a subject opsin or any variant thereof. A subject recombinant vector also include vectors comprising a polynucleotide which encodes an RNA (e.g., an mRNA) that when transcribed from the polynucleotides of the vector will result in the accumulation of a subject opsin on the plasma membranes of target animal cells. Vectors which may be used include, without limitation, lentiviral, HSV, adenoviral, and andeno-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.
In some embodiments, the vector is a recombinant AAV vector. AAV vectors are DNA viruses of relatively small size that can integrate, in a stable and sites-pecific 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.) p 5-14, 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.) p 15-23, Hudder Arnold, London, UK (2006), the disclosures 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 International Patent Application Publication No.: 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. 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: WO 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 herein incorporated by reference in their entirety). 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). A replication defective recombinant AAV 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.
In some embodiments, a subject recombinant vector is 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.
In some cases, a subject opsin nucleic acid comprises a nucleotide sequence encoding the opsin, where the nucleotide sequence is operably linked to a neuron-specific transcription control element.
Neuron-specific promoters and other control elements (e g, enhancers) are known in the art. Suitable neuron-specific control sequences include, but are not limited to, a neuron-specific enolase (NSE) promoter (see, e.g., EMBL HSENO2, X51956; see also, e.g., U.S. Pat. Nos. 6,649,811, and 5,387,742); an aromatic amino acid decarboxylase (AADC) promoter; a neurofilament promoter (see, e.g., GenBank HUMNFL, L04147); a synapsin promoter (see, e.g., GenBank HUMSYNIB, M55301); a thy-1 promoter (see, e.g., Chen et al. (1987) Cell 51:7-19; and Llewellyn et al. (2010) Nat. Med. 16:1161); a serotonin receptor promoter (see, e.g., GenBank S62283); a tyrosine hydroxylase promoter (TH) (see, e.g., Nucl. Acids. Res. 15:2363-2384 (1987) and Neuron 6:583-594 (1991)); a GnRH promoter (see, e.g., Radovick et al., Proc. Natl. Acad. Sci. USA 88:3402-3406 (1991)); an L7 promoter (see, e.g., Oberdick et al., Science 248:223-226 (1990)); a DNMT promoter (see, e.g., Bartge et al., Proc. Natl. Acad. Sci. USA 85:3648-3652 (1988)); an enkephalin promoter (see, e.g., Comb et al., EMBO J. 17:3793-3805 (1988)); a myelin basic protein (MBP) promoter; a CMV enhancer/platelet-derived growth factor-β promoter (see, e.g., Liu et al. (2004) Gene Therapy 11:52-60); a motor neuron-specific gene Hb9 promoter (see, e.g., U.S. Pat. No. 7,632,679; and Lee et al. (2004) Development 131:3295-3306); and an alpha subunit of Ca(2+)-calmodulin-dependent protein kinase II (CaMKIIα) promoter (see, e.g., Mayford et al. (1996) Proc. Natl. Acad. Sci. USA 93:13250).
Host Cells
The present disclosure provides isolated genetically modified host cells (e.g., in vitro cells) that are genetically modified with a subject nucleic acid. In some embodiments, a subject isolated genetically modified host cell can produce an opsin of the present disclosure.
Suitable host cells include eukaryotic host cells, such as a mammalian cell, an insect host cell, a yeast cell; and prokaryotic cells, such as a bacterial cell. Introduction of a subject nucleic acid into the host cell can be effected, for example by calcium phosphate precipitation, DEAE dextran mediated transfection, liposome-mediated transfection, electroporation, or other known method.
Suitable mammalian cells include primary cells and immortalized cell lines. In some cases, the mammalian cell is a neuron, e.g., a non-immortalized (primary) neuron. In other cases, the mammalian cell is an immortalized cell line.
Suitable mammalian cell lines include human cell lines, non-human primate cell lines, rodent (e.g., mouse, rat) cell lines, and the like. Suitable mammalian cell lines include, but are not limited to, HeLa cells (e.g., American Type Culture Collection (ATCC) No. CCL-2), CHO cells (e.g., ATCC Nos. CRL9618, CCL61, CRL9096), 293 cells (e.g., ATCC No. CRL-1573), Vero cells, NIH 3T3 cells (e.g., ATCC No. CRL-1658), Huh-7 cells, BHK cells (e.g., ATCC No. CCL10), PC12 cells (ATCC No. CRL1721), COS cells, COS-7 cells (ATCC No. CRL1651), RAT1 cells, mouse L cells (ATCC No. CCLI.3), human embryonic kidney (HEK) cells (ATCC No. CRL1573), HLHepG2 cells, and the like.
In some embodiments, the cell is a neuronal cell or a neuronal-like cell. The cells can be of human, non-human primate, mouse, or rat origin, or derived from a mammal other than a human, non-human primate, rat, or mouse. Suitable cell lines include, but are not limited to, a human glioma cell line, e.g., SVGp12 (ATCC CRL-8621), CCF-STTG1 (ATCC CRL-1718), SW 1088 (ATCC HTB-12), SW 1783 (ATCC HTB-13), LLN-18 (ATCC CRL-2610), LNZTA3WT4 (ATCC CRL-11543), LNZTA3WT11 (ATCC CRL-11544), U-138 MG (ATCC HTB-16), U-87 MG (ATCC HTB-14), H4 (ATCC HTB-148), and LN-229 (ATCC CRL-2611); a human medulloblastoma-derived cell line, e.g., D342 Med (ATCC HTB-187), Daoy (ATCC HTB-186), D283 Med (ATCC HTB-185); a human tumor-derived neuronal-like cell, e.g., PFSK-1 (ATCC CRL-2060), SK-N-DZ (ATCCCRL-2149), SK-N-AS (ATCC CRL-2137), SK—N—FI (ATCC CRL-2142), IMR-32 (ATCC CCL-127), etc.; a mouse neuronal cell line, e.g., BC3H1 (ATCC CRL-1443), EOC1 (ATCC CRL-2467), C8-D30 (ATCC CRL-2534), C8-S (ATCC CRL-2535), Neuro-2a (ATCC CCL-131), NB41A3 (ATCC CCL-147), SW10 (ATCC CRL-2766), NG108-15 (ATCC HB-12317); a rat neuronal cell line, e.g., PC-12 (ATCC CRL-1721), CTX TNA2 (ATCC CRL-2006), C6 (ATCC CCL-107), F98 (ATCC CRL-2397), RG2 (ATCC CRL-2433), B35 (ATCC CRL-2754), R3 (ATCC CRL-2764), SCP (ATCC CRL-1700), OA1 (ATCC CRL-6538).
Suitable yeast cells include, but are not limited to, Pichia pastoris, Pichia finlandica, Pichia trehalophila, Pichia koclamae, Pichia membranaefaciens, Pichia opuntiae, Pichia thermotolerans, Pichia salictaria, Pichia guercuum, Pichia pijperi, Pichia stiptis, Pichia methanolica, Pichia sp., Saccharomyces cerevisiae, Saccharomyces sp., Hansenula polymorpha, Kluyveromyces sp., Kluyveromyces lactis, Candida albicans, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae, Trichoderma reesei, Chrysosporium lucknowense, Fusarium sp., Fusarium gramineum, Fusarium venenatum, Neurospora crassa, Chlamydomonas reinhardtii, and the like.
Suitable prokaryotic cells include, but are not limited to, any of a variety of laboratory strains of Escherichia coli, Lactobacillus sp., Salmonella sp., Shigella sp., and the like. See, e.g., Carrier et al. (1992) J. Immunol. 148:1176-1181; U.S. Pat. No. 6,447,784; and Sizemore et al. (1995) Science 270:299-302. Examples of Salmonella strains which can be employed in the present invention include, but are not limited to, Salmonella typhi and S. typhimurium. Suitable Shigella strains include, but are not limited to, Shigella flexneri, Shigella sonnei, and Shigella disenteriae. Typically, the laboratory strain is one that is non-pathogenic. Non-limiting examples of other suitable bacteria include, but are not limited to, Bacillus subtilis, Pseudomonas pudita, Pseudomonas aeruginosa, Pseudomonas mevalonii, Rhodobacter sphaeroides, Rhodobacter capsulatus, Rhodospirillum rubrum, Rhodococcus sp., and the like. In some embodiments, the host cell is Escherichia coli. 
Variant Opsins with Enhanced Membrane Trafficking
The present disclosure provides variant opsins with improved membrane trafficking properties. The present disclosure also provides nucleic acids encoding the variant opsins. In particular, a subject variant opsin is a hyperpolarizing opsin that includes an endoplasmic reticulum (ER) export sequence, a trafficking sequence (TS), or both an ER export sequence and a TS. The presence of the ER export sequence and/or the TS provides for enhanced membrane (e.g., plasma membrane) localization and ER export. In some cases, a subject variant opsin comprises one or more additional amino acids, which may be disposed between the TS and the ER and/or between the opsin and the TS.
Thus, in some cases, a variant opsin comprises, in order from amino terminus to carboxyl terminus: an opsin polypeptide; a trafficking sequence; and an ER export sequence.
Hyperpolarizing Opsins
Opsin amino acid sequences that are suitable for inclusion in a subject variant opsin include, e.g., an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 8A (Halorubrum sodomense archaerhodopsin-3).
Opsin amino acid sequences that are suitable for inclusion in a subject variant opsin include, e.g., an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 9A (Halorubrum sodomense strain TP009 archaerhodopsin).
Opsin amino acid sequences that are suitable for inclusion in a subject variant opsin include, e.g., an amino acid sequence having at least about 85%, or 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 200 amino acids to about 225 amino acids, from about 225 amino acids to about 250 amino acids, from about 250 amino acids to about 275 amino acids, from about 275 amino acids to about 300 amino acids, or from about 300 amino acids to 313 amino acids, of the amino acid sequence depicted in FIG. 10A (Leptosphaeria maculans opsin).
Endoplasmic Reticulum Export Sequences
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) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO: 2); etc.); NANSFCYENEVALTSK (SEQ ID NO: 3); FXYENE (SEQ ID NO: 4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO: 5); 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.
Trafficking Sequences
Trafficking sequences that are suitable for use in a modified opsin of the present disclosure 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:
1) the signal peptide of hChR2 (e.g., MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO: 6))
2) the β2 subunit signal peptide of the neuronal nicotinic acetylcholine receptor (e.g., MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO: 7));
3) a nicotinic acetylcholine receptor signal sequence (e.g., MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO: 8));
4) a nicotinic acetylcholine receptor signal sequence (e.g., MRGTPLLLVVSLFSLLQD (SEQ ID NO: 9));
5) a signal sequence of human inward rectifier potassium channel Kir2.1 (e.g., KSRITSEGEYIPLDQIDINV (SEQ ID NO: 10)).
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.
Additional Sequences
As noted above, in some embodiments, a subject variant opsin comprises one or more amino acids in addition to the opsin, the TS, and the ER export sequence. For example, in some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: an opsin; a TS; an intervening amino acid sequence; and an ER export signal sequence.
Suitable intervening amino acid sequences include, e.g., linkers; epitope tags; fluorescent proteins; peptides that provide for ease of purification; cleavable linker peptides; and the like.
Suitable fluorescent proteins that can be included in a subject variant opsin include, but are not limited to, a green fluorescent protein from Aequoria victoria or a mutant or derivative thereof e.g., as described in U.S. Pat. Nos. 6,066,476; 6,020,192; 5,985,577; 5,976,796; 5,968,750; 5,968,738; 5,958,713; 5,919,445; 5,874,304; e.g., Enhanced GFP, many such GFP which are available commercially, e.g., from Clontech, Inc.; a red fluorescent protein; a yellow fluorescent protein; mCherry; any of a variety of fluorescent and colored proteins from Anthozoan species, as described in, e.g., Matz et al. (1999) Nature Biotechnol. 17:969-973; and the like.
Exemplary Variant Opsins
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 8A (Halorubrum sodomense archaerhodopsin-3); and b) an ER export sequence. For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO:1); VLGSL (SEQ ID NO:2); VLGSL (SEQ ID NO:2); etc.); NANSFCYENEVALTSK (SEQ ID NO:3); and FXYENE (SEQ ID NO:4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO:5).
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 8A (Halorubrum sodomense archaerhodopsin-3); b) a fluorescent protein; and c) an ER export sequence. For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO:2); VLGSL (SEQ ID NO:2); etc.); NANSFCYENEVALTSK (SEQ ID NO:3); and FXYENE (SEQ ID NO:4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO:5).
In some embodiments, a subject variant opsin comprises an amino acid sequence having at least about 85%, or at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to the amino acid sequence depicted in FIG. 7A.
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 8A (Halorubrum sodomense archaerhodopsin-3); b) a TS sequence; and c) an ER export sequence. For example, a TS sequence 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 selected from: MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO:6); MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO:7); MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO:8); MRGTPLLLVVSLFSLLQD (SEQ ID NO: 9); and KSRITSEGEYIPLDQIDINV (SEQ ID NO:10). For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO:1); VLGSL (SEQ ID NO:2); etc.); NANSFCYENEVALTSK (SEQ ID NO:3); and FXYENE (SEQ ID NO:4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO:5).
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 8A (Halorubrum sodomense archaerhodopsin-3); b) a TS sequence; c) a fluorescent protein; and d) an ER export sequence. For example, a TS sequence 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 selected from: MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO:6); MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO:7); MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO:8); MRGTPLLLVVSLFSLLQD (SEQ ID NO:9); and KSRITSEGEYIPLDQIDINV (SEQ ID NO:10). For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO:1); VLGSL (SEQ ID NO:2); etc.); NANSFCYENEVALTSK (SEQ IDNO:3); and FXYENE (SEQ ID NO:4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO:5).
In some embodiments, a subject variant opsin comprises an amino acid sequence having at least about 85%, or at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to the amino acid sequence depicted in FIG. 7B.
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 9A (Halorubrum sodomense strain TP009 opsin); b) a TS sequence; and c) an ER export sequence. For example, a TS sequence 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 selected from: MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO:6); MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO:7); MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO:8); MRGTPLLLVVSLFSLLQD (SEQ ID NO:9); and KSRITSEGEYIPLDQIDINV (SEQ ID NO:10). For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO:1); VLGSL (SEQ ID NO:2); etc.); NANSFCYENEVALTSK (SEQ ID NO:3); and FXYENE (SEQ ID NO:4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO:5).
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 220 amino acids, from about 220 amino acids to about 230 amino acids, from about 230 amino acids to about 240 amino acids, or from about 240 amino acids to 257 amino acids, of the amino acid sequence depicted in FIG. 9A (Halorubrum sodomense strain TP009 opsin); b) a TS sequence; c) a fluorescent protein; and d) an ER export sequence. For example, a TS sequence 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 selected from: MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO: 6); MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO: 7); MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO: 8); MRGTPLLLVVSLFSLLQD (SEQ ID NO: 9); and KSRITSEGEYIPLDQIDINV (SEQ ID NO: 10). For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO: 2); etc.); NANSFCYENEVALTSK (SEQ ID NO: 3); and FXYENE (SEQ ID NO: 4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO: 5).
In some embodiments, a subject variant opsin comprises an amino acid sequence having at least about 85%, or at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to the amino acid sequence depicted in FIG. 7C.
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 225 amino acids, from about 225 amino acids to about 250 amino acids, from about 250 amino acids to about 275 amino acids, from about 275 amino acids to about 300 amino acids, or from about 300 amino acids to 313 amino acids, of the amino acid sequence depicted in FIG. 10A (Leptosphaeria maculans opsin); and b) an ER export sequence. For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO: 2); etc.); NANSFCYENEVALTSK (SEQ ID NO: 3); and FXYENE (SEQ ID NO: 4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO: 5).
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 225 amino acids, from about 225 amino acids to about 250 amino acids, from about 250 amino acids to about 275 amino acids, from about 275 amino acids to about 300 amino acids, or from about 300 amino acids to 313 amino acids, of the amino acid sequence depicted in FIG. 10A (Leptosphaeria maculans opsin); b) a fluorescent protein; and c) an ER export sequence. For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO: 2); etc.); NANSFCYENEVALTSK (SEQ ID NO: 3); and FXYENE (SEQ ID NO: 4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO: 5).
In some embodiments, a subject variant opsin comprises an amino acid sequence having at least about 85%, or at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to the amino acid sequence depicted in FIG. 7D.
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 225 amino acids, from about 225 amino acids to about 250 amino acids, from about 250 amino acids to about 275 amino acids, from about 275 amino acids to about 300 amino acids, or from about 300 amino acids to 313 amino acids, of the amino acid sequence depicted in FIG. 10A (Leptosphaeria maculans opsin); b) a TS sequence; and c) an ER export sequence. For example, a TS sequence 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 selected from: MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO: 6); MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO: 7); MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO: 8); MRGTPLLLVVSLFSLLQD (SEQ ID NO: 9); and KSRITSEGEYIPLDQIDINV (SEQ ID NO: 10). For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO: 2); etc.); NANSFCYENEVALTSK (SEQ ID NO: 3); and FXYENE (SEQ ID NO: 4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO: 5).
In some embodiments, a subject variant opsin comprises, in order from amino terminus to carboxyl terminus: a) a hyperpolarizing opsin comprising an amino acid sequence having at least about 85%, or 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 200 amino acids to about 225 amino acids, from about 225 amino acids to about 250 amino acids, from about 250 amino acids to about 275 amino acids, from about 275 amino acids to about 300 amino acids, or from about 300 amino acids to 313 amino acids, of the amino acid sequence depicted in FIG. 10A (Leptosphaeria maculans opsin); b) a TS sequence; c) a fluorescent protein; and d) an ER export sequence. For example, a TS sequence 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 selected from: MDYGGALSAVGRELLFVTNPVVVNGS (SEQ ID NO: 6); MAGHSNSMALFSFSLLWLCSGVLGTEF (SEQ ID NO: 7); MGLRALMLWLLAAAGLVRESLQG (SEQ ID NO: 8); MRGTPLLLVVSLFSLLQD (SEQ ID NO: 9); and KSRITSEGEYIPLDQIDINV (SEQ ID NO: 10). For example, the ER export sequence is selected from VXXSL (where X is any amino acid) (e.g., VKESL (SEQ ID NO: 1); VLGSL (SEQ ID NO: 2); etc.); NANSFCYENEVALTSK (SEQ ID NO: 3); and FXYENE (SEQ ID NO: 4) (where X is any amino acid), e.g., FCYENEV (SEQ ID NO: 5).
In some embodiments, a subject variant opsin comprises an amino acid sequence having at least about 85%, or at least about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%, amino acid sequence identity to the amino acid sequence depicted in FIG. 7E.
Nucleic Acids
The present disclosure provides nucleic acids comprising a nucleotide sequence encoding a subject variant opsin. A nucleotide sequence encoding a subject variant opsin can be operably linked to one or more regulatory elements, such as a promoter and enhancer, that allow expression of the nucleotide sequence in the intended target cells (e.g., a cell that is genetically modified to synthesize the encoded variant opsin). In some cases, the variant opsin-encoding nucleotide sequence is operably linked to a transcriptional control element(s) that provides for neuron-specific expression. In some cases, a nucleotide sequence encoding a subject variant opsin is codon-optimized for expression in a mammalian cell.
Suitable promoter and enhancer elements are known in the art. For expression in a bacterial cell, suitable promoters include, but are not limited to, lacI, lacZ, T3, T7, gpt, lambda P and trc. For expression in a eukaryotic cell, suitable promoters include, but are not limited to, light and/or heavy chain immunoglobulin gene promoter and enhancer elements; cytomegalovirus immediate early promoter; herpes simplex virus thymidine kinase promoter; early and late SV40 promoters; promoter present in long terminal repeats from a retrovirus; mouse metallothionein-I promoter; and various art-known tissue specific promoters.
In some embodiments, e.g., for expression in a yeast cell, a suitable promoter is a constitutive promoter such as an ADH1 promoter, a PGK1 promoter, an ENO promoter, a PYK1 promoter and the like; or a regulatable promoter such as a GAL1 promoter, a GAL10 promoter, an ADH2 promoter, a PHOS promoter, a CUP1 promoter, a GALT promoter, a MET25 promoter, a METS promoter, a CYC 1 promoter, a HISS promoter, an ADH1 promoter, a PGK promoter, a GAPDH promoter, an ADC1 promoter, a TRP1 promoter, a URA3 promoter, a LEU2 promoter, an ENO promoter, a TP1 promoter, and AOX1 (e.g., for use in Pichia). Selection of the appropriate vector and promoter is well within the level of ordinary skill in the art.
Suitable promoters for use in prokaryotic host cells include, but are not limited to, a bacteriophage T7 RNA polymerase promoter; a trp promoter; a lac operon promoter; a hybrid promoter, e.g., a lac/tac hybrid promoter, a tac/trc hybrid promoter, a trp/lac promoter, a T7/lac promoter; a trc promoter; a tac promoter, and the like; an araBAD promoter; in vivo regulated promoters, such as an ssaG promoter or a related promoter (see, e.g., U.S. Patent Publication No. 20040131637), a pagC promoter (Pulkkinen and Miller, J. Bacteriol., 1991: 173(1): 86-93; Alpuche-Aranda et al., PNAS, 1992; 89(21): 10079-83), a nirB promoter (Harborne et al. (1992) Mol. Micro. 6:2805-2813), and the like (see, e.g., Dunstan et al. (1999) Infect. Immun. 67:5133-5141; McKelvie et al. (2004) Vaccine 22:3243-3255; and Chatfield et al. (1992) Biotechnol. 10:888-892); a sigma70 promoter, e.g., a consensus sigma70 promoter (see, e.g., GenBank Accession Nos. AX798980, AX798961, and AX798183); a stationary phase promoter, e.g., a dps promoter, an spy promoter, and the like; a promoter derived from the pathogenicity island SPI-2 (see, e.g., WO96/17951); an actA promoter (see, e.g., Shetron-Rama et al. (2002) Infect. Immun. 70:1087-1096); an rpsM promoter (see, e.g., Valdivia and Falkow (1996). Mol. Microbiol. 22:367); a tet promoter (see, e.g., Hillen, W. and Wissmann, A. (1989) In Saenger, W. and Heinemann, U. (eds), Topics in Molecular and Structural Biology, Protein—Nucleic Acid Interaction. Macmillan, London, UK, Vol. 10, pp. 143-162); an SP6 promoter (see, e.g., Melton et al. (1984) Nucl. Acids Res. 12:7035); and the like. Suitable strong promoters for use in prokaryotes such as Escherichia coli include, but are not limited to Trc, Tac, T5, T7, and PLambda. Non-limiting examples of operators for use in bacterial host cells include a lactose promoter operator (LacI repressor protein changes conformation when contacted with lactose, thereby preventing the Lad repressor protein from binding to the operator), a tryptophan promoter operator (when complexed with tryptophan, TrpR repressor protein has a conformation that binds the operator; in the absence of tryptophan, the TrpR repressor protein has a conformation that does not bind to the operator), and a tac promoter operator (see, for example, deBoer et al. (1983) Proc. Natl. Acad. Sci. U.S.A. 80:21-25).
A nucleotide sequence encoding a subject opsin can be present in an expression vector and/or a cloning vector. An expression vector can include a selectable marker, an origin of replication, and other features that provide for replication and/or maintenance of the vector.
Large numbers of suitable vectors and promoters are known to those of skill in the art; many are commercially available for generating a subject recombinant constructs. The following vectors are provided by way of example. Bacterial: pBs, phagescript, PsiX174, pBluescript SK, pBs KS, pNH8a, pNH16a, pNH18a, pNH46a (Stratagene, La Jolla, Calif., USA); pTrc99A, pKK223-3, pKK233-3, pDR540, and pRITS (Pharmacia, Uppsala, Sweden). Eukaryotic: pWLneo, pSV2cat, pOG44, PXR1, pSG (Stratagene) pSVK3, pBPV, pMSG and pSVL (Pharmacia).
Expression vectors generally have convenient restriction sites located near the promoter sequence to provide for the insertion of nucleic acid sequences encoding a protein of interest (e.g., a variant opsin). A selectable marker operative in the expression host may be present. Suitable expression vectors include, but are not limited to, viral vectors (e.g. viral vectors based on vaccinia virus; poliovirus; adenovirus (see, e.g., Li et al., Invest Opthalmol Vis Sci 35:2543 2549, 1994; Borras et al., Gene Ther 6:515 524, 1999; Li and Davidson, PNAS 92:7700 7704, 1995; Sakamoto et al., H Gene Ther 5:1088 1097, 1999; WO 94/12649, WO 93/03769; WO 93/19191; WO 94/28938; WO 95/11984 and WO 95/00655); adeno-associated virus (see, e.g., Ali et al., Hum Gene Ther 9:81 86, 1998, Flannery et al., PNAS 94:6916 6921, 1997; Bennett et al., Invest Opthalmol Vis Sci 38:2857 2863, 1997; Jomary et al., Gene Ther 4:683 690, 1997, Rolling et al., Hum Gene Ther 10:641 648, 1999; Ali et al., Hum Mol Genet 5:591 594, 1996; Srivastava in WO 93/09239, Samulski et al., J. Vir. (1989) 63:3822-3828; Mendelson et al., Virol. (1988) 166:154-165; and Flotte et al., PNAS (1993) 90:10613-10617); SV40; herpes simplex virus; human immunodeficiency virus (see, e.g., Miyoshi et al., PNAS 94:10319 23, 1997; Takahashi et al., J Virol 73:7812 7816, 1999); a retroviral vector (e.g., Murine Leukemia Virus, spleen necrosis virus, and vectors derived from retroviruses such as Rous Sarcoma Virus, Harvey Sarcoma Virus, avian leukosis virus, human immunodeficiency virus, myeloproliferative sarcoma virus, and mammary tumor virus); and the like.
Also provided herein is a recombinant vector comprising a subject polynucleotide encoding a subject variant opsin or any variant thereof. A subject recombinant vector also include vectors comprising a polynucleotide which encodes an RNA (e.g., an mRNA) that when transcribed from the polynucleotides of the vector will result in the accumulation of a subject opsin on the plasma membranes of target animal cells. Vectors which may be used include, without limitation, lentiviral, HSV, adenoviral, and andeno-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.
In some embodiments, the vector is 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.) p 5-14, 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.) p 15-23, Hudder Arnold, London, UK (2006), the disclosures 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 International Patent Application Publication No.: 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. 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: WO 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 herein incorporated by reference in their entirety). 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). A replication defective recombinant AAV 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.
In some embodiments, a subject recombinant vector is 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.
As noted above, in some cases, a subject variant opsin-encoding nucleotide sequence is operably linked to a neuron-specific promoter. Neuron-specific promoters and other control elements (e.g., enhancers) are known in the art. Suitable neuron-specific control sequences include, but are not limited to, a neuron-specific enolase (NSE) promoter (see, e.g., EMBL HSENO2, X51956; see also, e.g., U.S. Pat. Nos. 6,649,811 and 5,387,742); an aromatic amino acid decarboxylase (AADC) promoter; a neurofilament promoter (see, e.g., GenBank HUMNFL, L04147); a synapsin promoter (see, e.g., GenBank HUMSYNIB, M55301); a thy-1 promoter (see, e.g., Chen et al. (1987) Cell 51:7-19); a serotonin receptor promoter (see, e.g., GenBank S62283); a tyrosine hydroxylase promoter (TH) (see, e.g., Nucl. Acids. Res. 15:2363-2384 (1987) and Neuron 6:583-594 (1991)); a GnRH promoter (see, e.g., Radovick et al., Proc. Natl. Acad. Sci. USA 88:3402-3406 (1991)); an L7 promoter (see, e.g., Oberdick et al., Science 248:223-226 (1990)); a DNMT promoter (see, e.g., Bartge et al., Proc. Natl. Acad. Sci. USA 85:3648-3652 (1988)); an enkephalin promoter (see, e.g., Comb et al., EMBO J. 17:3793-3805 (1988)); a myelin basic protein (MBP) promoter; a CMV enhancer/platelet-derived growth factor-β promoter (see, e.g., Liu et al. (2004) Gene Therapy 11:52-60); a motor neuron-specific gene Hb9 promoter (see, e.g., U.S. Pat. No. 7,632,679; and Lee et al. (2004) Development 131:3295-3306); and an alpha subunit of Ca(2+)-calmodulin-dependent protein kinase II (CaMKIIα) promoter (see, e.g., Mayford et al. (1996) Proc. Natl. Acad. Sci. USA 93:13250).
Utility
A subject opsin finds use in modulating the voltage potential of a cell. A subject opsin finds use in therapeutic and drug screening applications. A subject opsin finds use in generating disease models.
Modulating the Voltage Potential of a Cell
For example, a subject opsin is useful for modulating the voltage potential of a cell, e.g., a neuron. The cell can be in vitro or in vivo. Thus, e.g., the present disclosure provides a method for adjusting the voltage potential of cells, subcellular regions, or extracellular regions, the method generally involving: introducing a nucleic acid comprising a nucleotide sequence encoding a subject opsin (e.g., a light-driven proton pump) into at least one target cell, subcellular region, or extracellular region, the opsin operating to change transmembrane potential in response to a specific wavelength of light; and causing the expression of the nucleic acid by exposing the target cell, subcellular region, or extracellular region to the specific wavelength of light in a manner designed to cause the voltage potential of the target cell, subcellular region, or extracellular region to increase or decrease.
In some cases, a subject method further involves the step of increasing or decreasing the voltage potential of the target cell, subcellular region, or extracellular region until it is hyperpolarized. Where the target cell, subcellular region, or extracellular region is a neuron, the hyperpolarization achieves neural silencing.
In some cases, a subject method further involves the step of using a plurality of different opsins (e.g., light-activated proton pumps) responsive to different wavelengths of light to achieve multi-color neural silencing by the steps of: expressing each opsin (e.g., light-activated proton pump) in a different population of cells; and illuminating the cells with different colors of light.
The present disclosure provides a method for adjusting the pH of a cell, subcellular region, or extracellular region, the method generally involving: introducing a nucleic acid comprising a nucleotide sequence encoding a subject opsin (e.g., light-driven proton pump) into at least one target cell, subcellular region, or extracellular region, the opsin operating to change cell, subcellular region, or extracellular region pH in response to a specific wavelength of light; and causing the expression of the nucleic acid by exposing the target cell, subcellular region, or extracellular region to the specific wavelength of light in a manner designed to cause the pH of the target cell, subcellular region, or extracellular region to increase or decrease.
The present disclosure provides method for causing cells, subcellular regions, or extracellular regions to release protons as chemical transmitters, the method generally involving: introducing a nucleic acid comprising a nucleotide sequence encoding a subject opsin (e.g., light-driven proton pump) into at least one target cell, subcellular region, or extracellular region, the opsin operating to cause proton release in response to a specific wavelength of light; and causing the expression of the nucleic acid by exposing the target cell, subcellular region, or extracellular region to the specific wavelength of light in a manner designed to cause the target cell, subcellular region, or extracellular region to release protons.
Target Cell-Modulating Applications
In some embodiments, a target cell is genetically modified with a subject nucleic acid (e.g., a nucleic acid comprising a nucleotide sequence encoding an opsin, e.g., a variant opsin). In some cases, target cells are neurons located in the brain of a mammal. The target cells are genetically modified to express a photosensitive opsin, for example, a subject opsin (e.g., a subject variant opsin), as described above. Light can then be used to stimulate the neurons. Depending upon a number of factors, such as the location within the brain and the frequency and length of stimulation, different objectives can be achieved. For instance, current techniques for deep brain stimulus (DBS) use electrodes to apply a current directly to the targeted area of the brain. The frequency of the electrical stimulus is sometimes referred to as either low-frequency DBS or high-frequency DBS. Studies have suggested that high-frequency DBS inhibits the generation of impulses from the stimulated cells, while low-frequency DBS facilitates the generation of impulses from the stimulated cells. The frequencies that produce the effects of high-frequency of low-frequency DBS have also been shown to vary depending upon the specific area of the brain being stimulated. According to one example of high-frequency DBS, the neurons are stimulated using electrodes supplying current pulses at frequencies around 100 Hz or more. Such a frequency has been shown to be effective in certain applications, as discussed further herein.
A specific example of DBS is used for the treatment of Parkinson's disease. In this application, DBS is often applied to the globus pallidus interna, or the subthalamic nucleus within a patient's brain. By implanting a biological arrangement that modifies the cells to respond to light, a light flashing light can be used in place of electrodes. Thus, the targeted neuron cells and external electrical signal need not be directly applied to the targeted cells. Moreover, light can often travel from its point of origin farther than electricity, thereby increasing the effective area relative to the stimulation source and only those neurons that have been photosensitized are stimulated.
As with the electrode-based DBS methods, one embodiment of the present invention can be implemented using high-frequency DBS to inhibit neuron generated impulses. While high-frequency DBS has been accomplished at frequencies around 100 Hz, high-frequency DBS using various embodiments of the present disclosure may not necessarily require the same frequency. For instance, it may be possible to reproduce the inhibiting effects of high-frequency DBS at lower frequencies (e.g., 50 Hz) when using light activated techniques. For example, activation of a hyperpolarizing opsin can result in hyperpolarization and resistance to action potential generation. Various frequencies can be used depending upon the particular application (e.g., the targeted portion of the brain and the desired effect), and the stimulation modality being applied.
Consistent with another example embodiment of the present invention, gene transfer vectors inducing the expression of photosensitive bio-molecules are used to target a specific type of cell. For instance, viral-based proteins (e.g., lentiviruses, adeno-associated viruses or retroviruses) can be created to target specific types of cells, based upon the proteins that they uniquely express. The targeted cells are then infected by the viral-based gene-transfer proteins, and begin to produce a new type of ion channel (for example a subject opsin; a subject variant opsin), thereby becoming photosensitive. This can be particularly useful for stimulating the targeted cells without stimulating other cells that are in proximity to the targeted cells. For example, neurons of disparate length, diameter, chronaxie, other membrane properties, electrical insulation, neurotransmitter output, and overall function, lie in close proximity to one another, and thus, can be inadvertently stimulated when using electrodes to provide the stimulation of the neurons. See, e.g., Gradinaru et al. (2007) J. Neurosci. 27(52): 14231-14238, Zhang et al. (2007) Nature 446: 633-639, Zhang et al. (2007) Nature Reviews Neuroscience Vol. 8: 577-581.
The present disclosure provides an implantable arrangement for in vivo use. A light-emitting diode, laser or similar light source is included for generating light. A biological portion that modifies target cells to include light responsive molecules which facilitate stimulation of the target cells in response to light generated by the light source.
Another embodiment of the present invention employs an arrangement for stimulating target cells using a photosensitive protein that allows the target cells to be stimulated in response to light. A biological delivery device is used for implanting vectors that modify the target cells to include the photosensitive protein. An implantation component (e.g., an implantable component comprising a recombinant expression vector encoding a subject opsin), is used for implanting a light generating device near the target cells. A control device is used for activating the light generating device to generate light to be received by the target cells, thereby stimulating the target cells in response to the generated light.
For example, light can be delivered to a site internal to an organism (e.g., a mammal). A light generator, such as an an implantable device that generates light in vivo, is used. A subject opsin (e.g., a subject variant opsin) present in target cells at the site provides for stimulation of the target cells in response to light generated by the light generator, which light strikes the target cells. The light generator can be a small electronic device on the order of a few millimeters in size. The small size is particularly useful for minimizing the intrusiveness of the device and associated implantation procedure. In another instance, the light generator can include a fiber optic device that can be used to transmit light from an external source to the target cells. For example, the target cells are modified to contain light-activated proton pump/channel proteins.
A subject light-sensitive protein can be implanted using a number of different methods. Example methods include, but are not limited to, the use of various delivery devices, such as gelatin capsules, liquid injections and the like. Such methods also include the use of stereotactic surgery techniques such as frames or computerized surgical navigation systems to implant or otherwise access areas of the body.
As one example, target cells that have been modified to be photosensitive, e.g., modified to produce a subject opsin (e.g., a subject variant opsin). The target cells are thus photosensitive. Stimulation of the target cells can be controlled by the implantable device. For example, a control circuit can be arranged to respond to an external signal by activating, or deactivating a light source, or by charging the battery that powers light source. In one instance, the external signal is electromagnetic radiation that is received by a control circuit. For example, radio frequency (RP) signals can be transmitted by an external radiofrequency (RF) transmitter and received by a control circuit. In another example, a magnetic field can be used to activate and/or power the control circuit.
A control circuit can be implemented using varying degrees of complexity. In one instance, the circuit is a simple coil that when exposed to a magnetic field generates a current. The current is then used to a power light source. Such an implementation can be particularly useful for limiting the size and complexity as well as increasing the longevity of the device. In another instance, a control circuit can include an RF antenna. Optionally, a battery or similar power source, such as a capacitive element, can be used by a control circuit. While charged, the power source allows the circuitry to continue to operate without need for concurrent energy delivery from outside the body. This can be particularly useful for providing precise control over the light emitted by a light source and for increased intensity of the emitted light. In one embodiment, a light source is implemented using a light-emitting-diode (LED). LEDs have been proven to be useful for low power applications and also to have a relatively fast response to electrical signals.
In another embodiment, a matrix (e.g., which can include a gelatin or similar substance) that contains recombinant expression vectors encoding a subject opsin (e.g., a subject variant opsin), which recombinant expression vectors enter target cells and provide for target cell photosensitivity. In one instance, the vectors are released once implanted into the body. This can be accomplished, for example, by using a containment material that allows the vectors to be released into aqueous solution {e.g., using dehydrated or water soluble materials such as gelatins). The release of the vectors results in the target cells being modified such that they are simulated in response to light from a light source.
In another embodiment, a synthetic mesh that contains the photosensitive cells is used. In one instance, the cells are neurons that have been modified to be photosensitive (e.g., modified to include a subject opsin, e.g., a subject variant opsin. The synthetic mesh can be constructed so as to allow the dendrites and axons to pass through the mess without allowing the entire neuron {e.g., the cell body) to pass. One example of such a mesh has pores that are on the order of 3-7 microns in diameter and is made from polyethylene terephthalate. In another example embodiment, an injection mechanism is used to deliver a subject opsin (e.g., a subject variant opsin), e.g., a recombinant expression vector encoding a subject opsin.
For example, an implantable device can be responsive to a magnetic field. For example, an inductor generates a current/Voltage in response to a magnetic field. The current is passed to a control circuit through a conductive path. In response, a control circuit activates a light source using a conductive path. A light source illuminates a biological portion in order to stimulate the target cells. In one instance, the biological portion includes a gelatin, synthetic mesh, or injection mechanism as discussed above.
In one embodiment, the control portion can be a simple electrical connection, resistive element, or can be removed completely. In such an embodiment, the intensity, duration and frequency of light generated would be directly controlled by the current generated from a magnetic field. This can be particularly useful for creating inexpensive, long lasting and small devices.
In another embodiment, the control portion can be implemented as a more complex circuit. For instance the control circuit may include and otherwise implement different rectifier circuits, batteries, pulse timings, comparator circuits and the like. In a particular example, the control circuit includes an integrated circuit (IC) produced using CMOS or other processes. Integrated circuit technology allows for the use of a large number of circuit elements in a very small area, and thus, a relatively complex control circuit can be implemented for some applications.
As an example, an inductor is a surface mount inductor, such as a 1OOuH inductor part number CF1008-103K supplied by Gowanda Electronics Corp. The light generating portion is a blue LED, such as LEDs in 0603 or 0805 package sizes. A particular example is a blue surface mount LED having part number SML0805, available from LEDtronics, Inc (Torrance, Calif.). Connective paths can be implemented using various electrical conductors, such as conductive epoxies, tapes, solder or other adhesive materials. LEDs emitting light in the appropriate spectrum (as applicable to a subject opsin) are available through commercial sources including this same manufacturer.
The present disclosure provides a method for genetically modifying neurons to express a light-sensitive opsin described herein. For example, a subject opsin can be used to impart photosensitivity upon mammalian nerve cells, by using an expression vector to deliver a nucleic acid encoding a subject opsin into targeted nerve cells, which subsequently produce the encoded opsin. Stimulation of the target cells with light results in hyperpolarization of the target cells.
The present disclosure provides methods for generating an inhibitory neuron-current flow in a neuron, the methods involving modifying the neuron to express a subject opsin; and exposing the neuron to a light stimulus. The present disclosure provides methods for controlling action potential of a neuron, the methods involving modifying the neuron to express a subject opsin; and exposing the neuron to a light stimulus. The present disclosure provides methods for controlling a voltage level across a cell membrane of a cell, the methods involving modifying the cell to express a subject opsin; and exposing the cell to a light stimulus.
The present disclosure provides a system for controlling an action potential of a neuron in vivo. The system includes a delivery device, a light source, and a control device. The delivery device introduces a light responsive protein (a subject opsin) to the neuron, with the light responsive protein producing an inhibitory current. The light source generates light for stimulating the light responsive protein, and the control device controls the generation of light by the light source.
The present disclosure provides methods of treating a disorder. The method targets a group of neurons associated with the disorder; the target neurons are modified to express a subject opsin; the modified target neurons produce an inhibitory current that reduces depolarization of the neurons; the modified neurons are exposed to a light stimulus, thereby reducing depolarization of the neurons.
Drug Screening
Certain embodiments of the present invention can be useful in drug screening. The various light-sensitive proteins, serving to regulate membrane voltage using ion switches that, when activated (or deactivated) in response to light, function as channels or pumps and are referred to hereafter as light-responsive ion switches or light-activated membrane potential switches (LAMPS).
For example, the present disclosure provides for screening for ion-channel and ion-pump affecting compounds. The system introduces one or more drug candidates that could either block or enhance the activity of a subject opsin in a cell modified to synthesize a subject opsin. Light triggers optically responsive ion channels in the cells causing a change in the voltage seen across the cell membrane. The voltage change stimulates voltage-gated ion channels in the cells which will then cause a change in ion concentrations that can be read as optical outputs. These optical signals are detected and used to determine what effect, if any, the drug candidates have on the voltage-gated ion channels. In a more specific embodiment a protein expressing a proton pump is introduced into the cell.
In one instance, the system allows for different drug candidates to be screened without necessitating extensive setup between screenings. For example, an assay may be performed using optics both to stimulate the optically responsive cells and to detect the effectiveness of the drug. The use of optics instead of manual contacts, e.g., using a whole-cell patch clamp, can be particularly useful in increasing the throughput of the assay screening process. For instance, the time between screenings can be reduced by minimizing or eliminating physical manipulations otherwise necessary to stimulate or detect ion flow in the target cells. The cells can also be prepared prior to the screening process because the test equipment need only be optically coupled to the prepared cells. In another instance, throughput may be increased by screening a number of different drugs simultaneously using, for example, an array of photo detectors and a corresponding array of modified cells exposed to different drugs.
Optical stimulation of the modified cells can be altered to determine specific properties of an introduced drug candidate. For example, the intensity of the optical stimulus may be modified to change the corresponding level of depolarization. The level of desired depolarization can be tuned to further characterize the effectiveness of the drug under test. In another example, the optical stimulus may include rapid pulsing of the light. By correlating the temporal relationship between the optical stimulus and the resultant detected fluorescence, the drug may be further characterized in terms of a kinetic response. Thus, the drug may be characterized for a variety of different aspects including, but not limited to, the steady state effect on ion concentrations, a change in the level of depolarization necessary to open voltage gated ion channels, and the effect on repeated depolarization.
In one embodiment, the system allows for simple calibration of the optical stimulation and/or detection. The modified cells may be optically stimulated prior to introduction of the drug candidate. The ion channel responsiveness is detected and recorded. The recorded values may be used as a baseline for comparison to the ion channel responsiveness of the same modified cells after the introduction of the drug under test. The recorded values may also be used to modify the optical stimulus or the sensitivity of the optical detector. Such modifications may be applied to an individual test sample or an array of test samples. For such an array of test samples, each test sample may be individually calibrated by adjusting the corresponding optical stimulus. Similarly, each corresponding photo detector may be individually adjusted.
The amount of time allotted for light delivery may vary, and depends on factors including the level of light-gated proton or ion channel/pump expression, and the density and characteristics of other proton/ionic channel characteristics of that cell population. The amount of time allotted for light receipt may vary, and depends upon factors including the degree of accuracy required for the screening session. The amount of time allotted for well-plate (tray) changing may vary, and depends upon factors including the mechanical speed of the automated apparatus. If fast neurons are used as the cells being tested, the cellular stimulation and LEIA detection process may be accomplished in milliseconds.
The process above may be repeated under varying conditions. For example, a given set of cells may be tested with no drug present, and subsequently with one or more drugs present. The response of electrically-excitable cells under those conditions may be thereby documented, compared and studied. If the invention is implemented with at least one emitter/detector for each well on a tray and at least two concurrently operating devices, continuous operation may be maintained for extended periods of time.
Exemplary screening methods could include the collection of multiple data points without having to switch samples. Because control over the samples is reversible in the same sample preparation by simply turning the activating light on and off with fast shutters, the same samples can be reused. Further, a range of patterns of stimulation can be provided to the same cell sample so that testing can be performed for the effect of drugs without concern with regards to differences across different sample preparations. By modulating the level of excitation (e.g., by ramping the level from no light to a high or maximum intensity), the effect of the drug across a range of membrane potentials can be tested. This permits for the identification of drugs that are efficacious during hyperpolarized, natural, or depolarized membrane potentials.
The cell lines described herein may be a particularly useful for detailed characterization of drug candidates in a high-throughput manner. Optical control is relatively fast, thereby allowing for the testing the drug's activity under more physiological forms of activation. For example, different frequencies of depolarization and/or hyperpolarization may be used to determine how a drug interacts with the channel under physiological forms of neural activity. In some instances, the process may be accomplished without the application of expensive chemical dyes to the cell lines.
In conjunction with the various properties discussed herein, the use of various embodiments of the invention may be particularly useful for improving screening throughput by eliminating the need for cumbersome mechanical manipulation and liquid handling. Various embodiments may also be useful for repeatable the screening assay using the same samples, reducing screening cost by eliminating the need for chemically-based fluorescence reports, producing high temporal precision and low signal artifact (due to the optical nature of the voltage manipulation), modulating the level of depolarization by attenuating the light intensity used for stimulation, and ascertaining the kinetics of the drug's modulation on the ion channel through the use of pulsed light patterns.
The existence of multiple independently controllable excitation proteins and inhibition proteins opens the door for a variety of applications including, but not limited to, applications for treatment of a variety of disorders and the use of a plurality of light-responsive proteins that can be selected so as to respond to a plurality of respective optical wavelengths. Although not always expressly stated, inhibition can be used in combination with, in addition to, or in place of excitation in the applications. The family of single-component proteins has been shown to respond to multiple wavelengths and intensities of light. Aspects of the disclosure allow for further mutations and/or searches for sequences that allow for additional optical wavelengths and/or individually controllable protein channels. Variations on the optical stimulus (e.g., a wavelength, intensity or duration profile) can also be used. For instance, stimulation profiles may exploit overlaps in the excitation wavelengths of two different ion channel proteins to allow excitation of both proteins at the same time. In one such instance, the proteins may have different levels of responsibility. Thus, in a neural application, one set of ion channels may produce spiking at a different success percentage relative to a second set of ion channels. Similarly, the overlaps in inhibition wavelengths of two different ion channels (or pumps) allows for inhibition of both proteins at the same time.
Alternatively, multiple light sources may be used allowing for stimulations of the light responsive proteins in the combination desired, while leaving other proteins unstimulated.
Therapeutic Applications
The present disclosure provides various therapeutic methods.
Addiction is associated with a variety of brain functions, including reward and expectation. Additionally, the driving cause of addiction may vary between individuals. According to one embodiment, addiction, for example nicotine addiction, may be treated with optogenetic stabilization of small areas on the insula. Optionally, functional brain imaging, for example cued-state PET or fMRI, may be used to locate a hyper metabolic focus in order to determine a precise target spot for the intervention on the insula surface.
Optogenetic excitation of the nucleus accumbens and septum may provide reward and pleasure to a patient without need for resorting to use of substances, and hence may hold a key to addiction treatment. Conversely, optogenetic stabilization of the nucleus accumbens and septum may be used to decrease drug craving in the context of addiction. In an alternative embodiment, optogenetic stabilization of hyper metabolic activity observed at the genu of the anterior cingulate (BA32) can be used to decrease drug craving. Optogenetic stabilization of cells within the arcuate nucleus of the medial hypothalamus which contain peptide products of pro-opiomelanocortin (POMC) and cocaine-and-amphetamine-regulating transcript (CART) can also be used to decrease drug addiction behavior.
Optogenetic stimulation of neuroendocrine neurons of the hypothalamic periventricular nucleus that secrete somatostatin can be used to inhibit secretion of growth hormone from the anterior pituitary, for example in acromegaly. Optogenetic stabilization of neuroendocrine neurons that secrete somatostatin or growth hormone can be used to increase growth and physical development. Among the changes that accompany “normal” aging, is a sharp decline in serum growth hormone levels after the 4th and 5th decades. Consequently, physical deterioration associated with aging may be lessened through optogenetic stabilization of the periventricular nucleus.
Optogenetic stabilization of the ventromedial nucleus of the hypothalamus, particularly the pro-opiomelanocortin (POMC) and cocaine-and-amphetamine-reguiating transcript (CART) of the arcuate nucleus, can be used to increase appetite, and thereby treat anorexia nervosa. Alternatively, optogenetic stimulation of the lateral nuclei of the hypothalamus can be used to increase appetite and eating behaviors.
Optogenetic excitation in the cholinergic cells of affected areas including the temporal lobe, the NBM (Nucleus basalis of Meynert) and the posterior cingulate gyrus (BA 31) provides stimulation, and hence neurotrophic drive to deteriorating areas.
Because the affected areas are widespread within the brain, an analogous treatment with implanted electrodes may be less feasible than an opto-genetic approach.
Anxiety disorders are typically associated with increased activity in the left temporal and frontal cortex and amygdala, which trends toward normal as anxiety resolves. Accordingly, the affected left temporal and frontal regions and amygdala may be treated with optogenetic stabilization, so as to dampen activity in these regions.
In normal physiology, photosensitive neural cells of the retina, which depolarize in response to the light that they receive, create a visual map of the received light pattern. Optogenetic ion channels can be used to mimic this process in many parts of the body, and the eyes are no exception. In the case of visual impairment or blindness due to damaged retina, a functionally new retina can be grown, which uses natural ambient light rather than flashing light patterns from an implanted device. The artificial retina grown may be placed in the location of the original retina (where it can take advantage of the optic nerve serving as a conduit back to the visual cortex). Alternatively, the artificial retina may be placed in another location, such as the forehead, provided that a conduit for the depolarization signals are transmitted to cortical tissue capable of deciphering the encoded information from the optogenetic sensor matrix. Cortical blindness could also be treated by simulating visual pathways downstream of the visual cortex. The stimulation would be based on visual data produced up stream of the visual cortex or by an artificial light sensor.
Treatment of tachycardia may be accomplished with optogenetic stimulation to parasympathetic nervous system fibers including CN X or Vagus Nerve. This causes a decrease in the S A node rate, thereby decreasing the heart rate and force of contraction. Similarly, optogenetic stabilization of sympathetic nervous system fibers within spinal nerves T1 through T4, serves to slow the heart. For the treatment of pathological bradycardia, optogenetic stabilization of the Vagus nerve, or optogenetic stimulation of sympathetic fibers in T1 through T4 will serve to increase heart rate. Cardiac disrhythmias resulting from aberrant electrical foci that outpace the sinoatrial node may be suppressed by treating the aberrant electrical focus with moderate optogenetic stabilization. This decreases the intrinsic rate of firing within the treated tissue, and permits the sinoatrial node to regain its role in pacing the heart's electrical system. In a similar way, any type of cardiac arrhythmia could be treated. Degeneration of cardiac tissue that occurs in cardiomyopathy or congestive heart failure could also be treated using this invention; the remaining tissue could be excited using various embodiments of the invention.
Optogenetic excitation stimulation of brain regions including the frontal lobe, parietal lobes and hippocampi, may increase processing speed, improve memory, and stimulate growth and interconnection of neurons, including spurring development of neural progenitor cells. As an example, one such application of the present invention is directed to optogenetic excitation stimulation of targeted neurons in the thalamus for the purpose of bringing a patient out of a near-vegetative (barely-conscious) state. Growth of light-gated ion channels or pumps in the membrane of targeted thalamus neurons is affected. These modified neurons are then stimulated (e.g., via optics which may also gain access by the same passageway) by directing a flash of light thereupon so as to modulate the function of the targeted neurons and/or surrounding cells.
In an alternative embodiment, optogenetic excitation may be used to treat weakened cardiac muscle in conditions such as congestive heart failure. Electrical assistance to failing heart muscle of CHF is generally not practical, due to the thin-stretched, fragile state of the cardiac wall, and the difficulty in providing an evenly distributed electrical coupling between an electrodes and muscle. For this reason, methods to date for increasing cardiac contractility have involved either pharmacological methods such as Beta agonists, and mechanical approaches such as ventricular assist devices. In this embodiment of the present invention, optogenetic excitation is delivered to weakened heart muscle via light emitting elements on the inner surface of a jacket surround the heart or otherwise against the affected heart wall. Light may be diffused by means well known in the art, to smoothly cover large areas of muscle, prompting contraction with each light pulse.
Optogenetic stabilization in the subgenual portion of the cingulate gyms (Cg25), yellow light may be applied with an implanted device. The goal would be to treat depression by suppressing target activity in manner analogous to what is taught by Mayberg H S et al, “Deep Brain Stimulation for Treatment-Resistant Depression,” Neuron, Vol. 45, 651-660, Mar. 3, 2005, pp. 651-660, which is fully incorporated herein by reference. In an alternative embodiment, an optogenetic excitation stimulation method is to increase activity in that region in a manner analogous to what is taught by Schlaepfer et al., “Deep Brain stimulation to Reward Circuitry Alleviates Anhedonia in Refractory Major Depression,” Neuropsychopharmacology 2007, pp. 1-10, which is fully incorporated herein by reference.
In yet another embodiment, the left dorsolateral prefrontal cortex (LDPFC) is targeted with an optogenetic excitation stimulation method. Pacing the LDLPFC at 5-20 Hz serves to increase the basal metabolic level of this structure which, via connecting circuitry, serves to decrease activity in Cg 25, improving depression in the process. Suppression of the right dorsolateral prefrontal cortex (RDLPFC) is also an effective depression treatment strategy. This may be accomplished by optogenetic stabilization on the RDLPFC, or suppression may also be accomplished by using optogenetic excitation stimulation, and pulsing at a slow rate (e.g. 1 Hz or less) improving depression in the process. Vagus nerve stimulation (VNS) may be improved using an optogenetic approach. Use of optogenetic excitation may be used in order to stimulate only the vagus afferents to the brain, such as the nodose ganglion and the jugular ganglion.
Efferents from the brain would not receive stimulation by this approach, thus eliminating some of the side-effects of VNS including discomfort in the throat, a cough, difficulty swallowing and a hoarse voice. In an alternative embodiment, the hippocampus may be optogenetically excited, leading to increased dendritic and axonal sprouting, and overall growth of the hippocampus. Other brain regions implicated in depression that could be treated using this invention include the amygdala, accumbens, orbitofrontal and orbitomedial cortex, hippocampus, olfactory cortex, and dopaminergic, serotonergic, and noradrenergic projections. Optogenetic approaches could be used to control spread of activity through structures like the hippocampus to control depressive symptoms.
So long as there are viable alpha and beta cell populations in the pancreatic islets of Langerhans, the islets can be targeted for the treatment of diabetes. For example, when serum glucose is high (as determined manually or by closed loop glucose detection system), optogenetic excitation may be used to cause insulin release from the beta cells of the islets of Langerhans in the pancreas, while optogenetic stabilization is used to prevent glucagon release from the alpha cells of the islets of Langerhans in the pancreas. Conversely, when blood sugars are too low (as determined manually or by closed loop glucose detection system), optogenetic stabilization may be used to stop beta cell secretion of insulin, and optogenetic excitation may be used to increase alpha-cell secretion of glucagon.
For treatment of epilepsy, quenching or blocking epileptogenic activity is amenable to optogenetic approaches. Most epilepsy patients have a stereotyped pattern of activity spread resulting from an epileptogenic focus. Optogenetic stabilization could be used to suppress the abnormal activity before it spreads or truncated it early in its course. Alternatively, activation of excitatory tissue via optogenetic excitation stimulation could be delivered in a series of deliberately asynchronous patterns to disrupt the emerging seizure activity. Another alternative involves the activation of optogenetic excitation stimulation in GABAergic neurons to provide a similar result. Thalamic relays may be targeted with optogenetic stabilization triggered when an abnormal EEG pattern is detected.
Another embodiment involves the treatment of gastrointestinal disorders. The digestive system has its own, semi-autonomous nervous system containing sensory neurons, motor neurons and interneurons. These neurons control movement of the GI tract, as well as trigger specific cells in the gut to release acid, digestive enzymes, and hormones including gastrin, cholecystokinin and secretin. Syndromes that include inadequate secretion of any of these cellular products may be treated with optogenetic stimulation of the producing cell types, or neurons that prompt their activity.
Conversely, optogenetic stabilization may be used to treat syndromes in which excessive endocrine and exocrine products are being created. Disorders of lowered intestinal motility, ranging from constipation (particularly in patients with spinal cord injury) to megacolan may be treated with optogenetic excitation of motor neurons in the intestines.
Disorders of intestinal hypermotility, including some forms of irritable bowel syndrome may be treated with optogenetic stabilization of neurons that control motility.
Neurogenic gastric outlet obstructions may be treated with optogenetic stabilization of neurons and musculature in the pylons. An alternative approach to hypomobility syndromes would be to provide optogenetic excitation to stretch-sensitive neurons in the walls of the gut, increasing the signal that the gut is full and in need of emptying.
In this same paradigm, an approach to hypermobility syndromes of the gut would be to provide optogenetic stabilization to stretch receptor neurons in the lower GI, thus providing a “false cue” that the gut was empty, and not in need of emptying. In the case of frank fecal incontinence, gaining improved control of the internal and external sphincters may be preferred to slowing the motility of the entire tract. During periods of time during which a patient needs to hold feces in, optogenetic excitation of the internal anal sphincter will provide for retention. Providing optogenetic stimulation to the external sphincter may be used to provide additional continence. When the patient is required to defecate, the internal anal sphincter, and then external anal sphincter should be relaxed, either by pausing the optogenetic stimulation, or by adding optogenetic stabilization.
Conductive hearing loss may be treated by the use of optical cochlear implants. Once the cochlea has been prepared for optogenetic stimulation, a cochlear implant that flashes light may be used. Sensorineural hearing loss may be treated through optical stimulation of downstream targets in the auditory pathway.
Another embodiment of the present invention is directed toward the treatment of blood pressure disorders, such as hypertension. Baroreceptors and chemoreceptors in regions such as the aorta (aortic bodies and paraaortic bodies) and the carotid arteries (“carotic bodies”) participate in the regulation of blood pressure and respiration by sending afferents via the vagus nerve (CN X), and other pathways to the medulla and pons, particularly the solitary tract and nucleus. Optogenetic excitation of the carotid bodies, aortic bodies, paraortic bodies, may be used to send a false message of “hypertension” to the solitary nucleus and tract, causing it to report that blood pressure should be decreased. Optogenetic excitation or stabilization directly to appropriate parts of the brainstem may also be used to lower blood pressure. The opposite modality causes the optogenetic approach to serve as a pressor, raising blood pressure. A similar effect may also be achieved via optogenetic excitation of the Vagus nerve, or by optogenetic stabilization of sympathetic fibers within spinal nerves T1-T4. In an alternative embodiment, hypertension may be treated with optogenetic stabilization of the heart, resulting in decreased cardiac output and lowered blood pressure. According to another embodiment, optogenetic stabilization of aldosterone-producing cells within the adrenal cortex may be used to decrease blood pressure. In yet another alternative embodiment, hypertension may be treated by optogenetic stabilization of vascular smooth muscle. Activating light may be passed transcutaneousiy to the peripheral vascular bed.
Another example embodiment is directed toward the treatment of hypothalamic-pituitary-adrenal axis disorders. In the treatment of hypothyroidism, optogenetic excitation of parvocellular neuroendocrine, neurons in the paraventricular and anterior hypothalamic nuclei can be used to increase secretion of thyrotropin-releasing hormone (TRH). TRH, in turn, stimulates anterior pituitary to secrete TSH. Conversely, hyperthyroidism may be treated with optogenetic stabilization of the provocellular neuroendocrine neurons. For the treatment of adrenal insufficiency, or of Addison's disease, optogenetic excitation of parvocellular neuroendocrine neurons in the supraoptic nucleus and paraventricular nuclei may be used to increase the secretion of vasopressin, which, with the help of corticotropin-releasing hormone (CRH), stimulate anterior pituitary to secrete ACTH. Cushing syndrome, frequently caused by excessive ACTH secretion, may be treated with optogenetic stabilization of the parvocellular neuroendocrine neurons of supraoptic nucleus via the same physiological chain of effects described above. Neuroendocrine neurons of the arcuate nucleus produce dopamine, which inhibits secretion of prolactin from the anterior pituitary. Hyperprolactinemia can therefore be treated via optogenetic excitation, while hypoprolactinemia can be treated with optogenetic stabilization of the neuroendocrine cells of the arcuate nucleus.
In the treatment of hyperautonomic states, for example anxiety disorders, optogenetic stabilization of the adrenal medulla may be used to reduce norepinephrine output. Similarly, optogenetic stimulation of the adrenal medulla may be used in persons with need for adrenaline surges, for example those with severe asthma, or disorders that manifest as chronic sleepiness.
Optogenetic stimulation of the adrenal cortex will cause release of chemicals including Cortisol, testosterone, and aldosterone. Unlike the adrenal medualla, the adrenal cortex receives its instructions from neuroendocrine hormones secreted from the pituitary and hypothalamus, the lungs, and the kidneys. Regardless, the adrenal cortex is amenable to optogenetic stimulation. Optogenetic stimulation of the cortisol-producing cells of the adrenal cortex may be used to treat Addison's disease. Optogenetic stabilization of cortisol-producing cells of the adrenal cortex may be used to treat Cushing's disease. Optogenetic stimulation of testosterone-producing cells may be used to treat disorders of sexual interest in women: Optogenetic stabilization of those same cells may be used to decrease facial hair in women. Optogenetic stabilization of aldosterone-producing cells within the adrenal cortex may be used to decrease blood pressure. Optogenetic excitation of aldosterone-producing cells within the adrenal cortex may be used to increase blood pressure.
Optogenetic excitation stimulation of specific affected brain regions may be used to increase processing speed, and stimulate growth and interconnection of neurons, including spurring the maturation of neural progenitor cells. Such uses can be particularly useful for treatment of mental retardation.
According to another embodiment, various muscle diseases and injuries can be treated. Palsies related to muscle damage, peripheral nerve damage and to dystrophic diseases can be treated with optogenetic excitation to cause contraction, and optogenetic stabilization to cause relaxation. This latter relaxation via optogenetic stabilization approach can also be used to prevent muscle wasting, maintain tone, and permit coordinated movement as opposing muscle groups are contracted. Likewise, frank spasticity can be treated via optogenetic stabilization.
In areas as diverse as peripheral nerve truncation, stroke, traumatic brain injury and spinal cord injury, there is a need to foster the growth of new neurons, and assist with their integration into a functional network with other neurons and with their target tissue. Re-growth of new neuronal tracts may be encouraged via optogenetic excitation, which serves to signal stem cells to sprout axons and dendrites, and to integrate themselves with the network. Use of an optogenetic technique (as opposed to electrodes) prevents receipt of signals by intact tissue, and serves to ensure that new target tissue grows by virtue of a communication set up with the developing neurons, and not with an artificial signal like current emanating from an electrode.
Obesity can be treated with optogenetic excitation to the ventromedial nucleus of the hypothalamus, particularly the pro-opiomelanocortin (POMC) and cocaine-and-amphetamine-regulating transcript (CART) of the arcuate nucleus. In an alternative embodiment, obesity can be treated via optogenetic stabilization of the lateral nuclei of the hypothalamus. In another embodiment, optogenetic stimulation to leptin-producing cells or to cells with leptin receptors within the hypothalamus may be used to decrease appetite and hence treat obesity.
Destructive lesions to the anterior capsule and analogous DBS to that region are established means of treating severe, intractable obsessive-compulsive disorder 48 (OCD48). Such approaches may be emulated using optogenetic stabilization to the anterior limb of the internal capsule, or to regions such as BA32 and Cg24 which show metabolic decrease as OCD remits.
Chronic pain can be treated using another embodiment of the present disclosure. Electrical stimulation methods include local peripheral nerve stimulation, local cranial nerve stimulation and “sub threshold” motor cortex stimulation. Reasonable autogenic approaches include optogenetic stabilization at local painful sites. Attention to promoter selection would ensure that other sensory and motor fibers would be unaffected.
Selective optogenetic excitation of interneurons at the primary motor cortex also may provide effective pain relief. Also, optogenetic stabilization at the sensory thalamus, (particularly medial thalamic nuclei), periventricular grey matter, and ventral raphe nuclei, may be used to produce pain relief. In an alternative embodiment, optogenetic stabilization of parvalbumin-expres sing cells targeting as targeting strategy, may be used to treat pain by decreasing Substance P production. The release of endogenous opiods may be accomplished by using optogenetic excitation to increase activity in the nucleus accumbens. In an alternative embodiment, when POMC neurons of the arcuate nucleus of the medial hypothalamus are optogenetically excited, beta endorphin are increased, providing viable treatment approaches for depression and for chronic pain.
Certain personality disorders, including the borderline and antisocial types, demonstrate focal deficits in brain disorders including “hypofrontality.” Direct or indirect optogenetic excitation of these regions is anticipated to produce improvement of symptoms. Abnormal bursts of activity in the amygdala are also known to precipitate sudden, unprompted flights into rage: a symptom of borderline personality disorder, as well as other conditions, which can benefit from optogenetic stabilization of the amygdala. Optogenetic approaches could improve communication and synchronization between different parts of the brain, including amygdala, striatum, and frontal cortex, which could help in reducing impulsiveness and improving insight.
The amygdalocentric model of post-traumatic-stress disorder (PTSD) proposes that it is associated with hyperarousal of the amygdala and insufficient top-down control by the medial prefrontal cortex and the hippocampus. Accordingly, PTSD may be treated with optogenetic stabilization of the amygdale or hippocampus.
Schizophrenia is characterized by abnormalities including auditory hallucinations. These might be treated by suppression of the auditory cortex using optogenetic stabilization. Hypofrontality associated with schizophrenia might be treated with optogenetic excitation in the affected frontal regions. Optogenetic approaches could improve communication and synchronization between different parts of the brain which could help in reducing mis attribution of self-generated stimuli as foreign.
Optogenetic stabilization of cells within the arcuate nucleus of the medial hypothalamus, which contain peptide products of pro-opiomelanocortin (POMC) and cocaine-and-amphetamine-regulating transcript (CART), can be used to reduce compulsive sexual behavior. Optogenetic excitation of cells within the arcuate nucleus of the medial hypothalamus which contain peptide products of pro-opiomelanocortin (POMC) and cocaine-and-amphetamine-regulating transcript (CART) may be used to increase sexual interest in the treatment of cases of disorders of sexual desire. In the treatment of disorders of hypoactive sexual desire testosterone production by the testes and the adrenal glands can be increased through optogenetic excitation of the pituitary gland. Optogenetic excitation of the nucleus accumbens can be used for the treatment of anorgasmia.
The suprachiasmatic nucleus secretes melatonin, which serves to regulate sleep/wake cycles. Optogenetic excitation to the suprachiasmic nucleus can be used to increase melatonin production, inducing sleep, and thereby treating insomnia. Orexin (hypocretin) neurons strongly excite numerous brain nuclei in order to promote wakefulness. Optogenetic excitation of orexin-producing cell populations can be used to treat narcolepsy, and chronic daytime sleepiness.
Optogenetic stimulation of the supraoptic nucleus may be used to induce secretion of oxytocin, can be used to promote parturition during childbirth, and can be used to treat disorders of social attachment.
Like muscular palsies, the motor functions that have been de-afferented by a spinal cord injury may be treated with optogenetic excitation to cause contraction, and optogenetic stabilization to cause relaxation. This latter relaxation via optogenetic stabilization approach may also be used to prevent muscle wasting, maintain tone, and permit coordinated movement as opposing muscle groups are contracted. Likewise, frank spasticity may be treated via optogenetic stabilization. Re-growth of new spinal neuronal tracts may be encouraged via optogenetic excitation, which serves to signal stem cells to sprout axons and dendrites, and to integrate themselves with the network.
Stroke deficits include personality change, motor deficits, sensory deficits, cognitive loss, and emotional instability. One strategy for the treatment of stroke deficits is to provide optogenetic stimulation to brain and body structures that have been deafferented from excitatory connections. Similarly, optogenetic stabilization capabilities can be imparted on brain and body structures that have been deafferented from inhibitory connections.
Research indicates that the underlying pathobiology in Tourette's syndrome is a phasic dysfunction of dopamine transmission in cortical and subcortical regions, the thalamus, basal ganglia and frontal cortex. In order to provide therapy, affected areas are preferably first identified using techniques including functional brain imaging and magnetoencephalography (MEG). Whether specifically identified or not, optogenetic stabilization of candidate tracts may be used to suppress motor tics. Post-implantation empirical testing of device parameters reveals which sites of optogenetic stabilization, and which are unnecessary to continue.
In order to selectively excite/inhibit a given population of neurons, for example those involved in the disease state of an illness, several strategies can be used to target the optogenetic proteins/molecules to specific populations.
For various embodiments of the present invention, genetic targeting may be used to express various optogenetic proteins or molecules. Such targeting involves the targeted expression of the optogenetic proteins/molecules via genetic control elements such as promoters (e.g., Parvalbumin, Somatostatin, Cholecystokinin, GFAP), enhancers/silencers (e.g., Cytomaglovirus Immediate Early Enhancer), and other transcriptional or translational regulatory elements (e.g., Woodchuck Hepatitis Virus Post-transcriptional Regulatory Element). Permutations of the promoter+enhancer+regulatory element combination can be used to restrict the expression of optogenetic probes to genetically-defined populations.
Various embodiments of the present invention may be implemented using spatial/anatomical targeting. Such targeting takes advantage of the fact that projection patterns of neurons, virus or other reagents carrying genetic information (DNA plasmids, fragments, etc.), can be focally delivered to an area where a given population of neurons project to. The genetic material will then be transported back to the bodies of the neurons to mediate expression of the optogenetic probes. Alternatively, if it is desired to label cells in a focal region, viruses or genetic material may be focally delivered to the interested region to mediate localized expression.
Gene Delivery Systems
Various gene delivery systems are useful in implementing one or more embodiments of the present disclosure. One such delivery system is Adeno-Associated Virus (AAV). AAV can be used to deliver a promoter+optogenetic probe (opsin) cassette to a specific region of interest. As used herein, “optogenetic probe” refers to an opsin, e.g., an opsin, or a variant opsin, of the present disclosure. The choice of promoter will drive expression in a specific population of neurons. For example, using the CaMKIIα promoter will drive excitatory neuron specific expression of optogenetic probes. AAV will mediate long-term expression of the optogenetic probe (opsin) for at least one year or more. To achieve more specificity, AAV may be pseudotyped with specific serotypes 1, 2, 3, 4, 5, 6, 7, and 8, with each having different tropism for different cell types. For instance, serotype 2 and 5 is known to have good neuron-specific tropism.
Another gene delivery mechanism is the use of a retrovirus. HIV or other lentivirus-based retroviral vectors may be used to deliver a promoter+optogenetic probe cassette to a specific region of interest. Retroviruses may also be pseudo-typed with the Rabies virus envelope glycoprotein to achieve retrograde transport for labeling cells based on their axonal projection patterns. Retroviruses integrate into the host cell's genome, therefore are capable of mediating permanent expression of the optogenetic probes. Non-lentivirus based retroviral vectors can be used to selectively label dividing cells.
Gutless Adenovirus and Herpes Simplex Virus (HSV) are two DNA-based viruses that can be used to deliver promoter+optogenetic probe cassette into specific regions of the brain as well. HSV and Adenovirus have much larger packaging capacities and therefore can accommodate much larger promoter elements and can also be used to deliver multiple optogenetic probes or other therapeutic genes along with optogenetic probes.
Focal Electroporation can also be used to transiently transfect neurons. DNA plasmids or fragments can be focally delivered into a specific region of the brain. By applying mild electrical current, surrounding local cells will receive the DNA material and expression of the optogenetic probes.
In another instance, lipofection can be used by mixing genetic material with lipid reagents and then subsequently injected into the brain to mediate transfection of the local cells.
Various embodiments involve the use of various control elements. In addition to genetic control elements, other control elements (particularly promoters and enhancers whose activities are sensitive to chemical, magnetic stimulation or infrared radiation) can be used to mediate temporally-controlled expression of the optogenetic probes. For example, a promoter whose transcriptional activity is subject to infrared radiation allows one to use focused radiation to fine tune the expression of optogenetic probes in a focal region at only the desired time.
Parkinson's Disease can be treated by expressing optogenetic stabilization in the glutamatergic neurons in either the subthalamic nucleus (STN) or the globus pallidus interna (GPi) using an excitatory-specific promoter such as CaMKIIα, and apply optogenetic stabilization. Unlike electrical modulation in which all cell-types are affected, only glutamatergic STN neurons would be suppressed.
Disease Models
Aspects of the present disclosure provide for testing a model of a neural circuit or disease. The model can define output response of the circuit as a function of input signals. The output response can be assessed using a number of different measurable characteristics. For instance, characteristics can include an electrical response of downstream neurons and/or behavioral response of a patient. To test the model, optogenetic probes are expressed at an input position for the model. The optogenetic probes are stimulated and the output characteristics are monitored and compared to an output predicted by the model.
In certain implementations, the use of optogenetic probes allows for fine tuning of models defined using electrical probes. As electrical probes provide only limited ability to direct the stimulus and thus are not well suited for stimulus of certain areas without also directly stimulating nearby areas. Optogenetic probes disclosed herein provide a mechanism for more precise selection of the stimulus location. For instance, the stimulus from the optogenetic probes can be directed to very specific types of circuits/cells, such as afferent fibers. The following description provides an example implementation consistent with such an embodiment and is meant to show the feasibility and wide-ranging applicability for aspects of present invention.
According to one embodiment of the present disclosure, the invention may be used in animal models of DBS, for example in Parkinsonian rats, to identify the target cell types responsible for therapeutic effects (an area of intense debate and immense clinical importance). This knowledge alone may lead to the development of improved pharmacological and surgical strategies for treating human disease.
One such application involves long-term potentiation (LTP) and/or long-term depression (LTD) between two neural groups. By targeting the expression of a subject opsin to different neural populations and stimulating each with a different frequency of light, LTP or LTD can be accomplished between the two groups. Each group can be individually controlled using the respective wavelength of light. This can be particularly useful for applications in which the spatial arrangement of the two groups presents issues with individual control using the same wavelength of light. Thus, the light delivery device(s) are less susceptible to exciting the wrong neural group and can be less reliant upon precise spatial location of the optical stimulus.
The delivery of the proteins to cells in vivo can be accomplished using a number of different deliver devices, methods and systems. On such delivery device is an implantable device that delivers a nucleotide sequence for modifying cells in vivo, such as a viral-vector. The implantable device can also include a light delivery mechanism. The light delivery can be accomplished using, for example, light-emitting diodes (LEDs), fiber optics and/or Lasers.
EXAMPLES
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Celsius, and pressure is at or near atmospheric. Standard abbreviations may be used, e.g., bp, base pair(s); kb, kilobase(s); pl, picoliter(s); s or sec, second(s); min, minute(s); h or hr, hour(s); aa, amino acid(s); kb, kilobase(s); bp, base pair(s); nt, nucleotide(s); i.m., intramuscular(ly); i.p., intraperitoneal(ly); s.c., subcutaneous(ly); and the like.
Example 1
Hyperpolarizing Opsins
Materials and Methods
All experiments were conducted under protocols approved by the Stanford Administrative Panel on Laboratory Animal Care.
Molecular Cloning
Lentiviral constructs contained BamHI between the promoter and the opsin, NotI between the opsin and the fluorophore, and EcoRI between the fluorophore and the WPRE. Opsin-eYFP fragments were polymerase chain reaction (PCR)-amplified to add AscI and NheI, using gtggcgcgccctattacttgtacagctcgtccatg (SEQ ID NO:11) (for all opsins), tatgctagccaccatggactatggcggcgc (SEQ ID NO: 12) (for the ChR2 mutants), and gttatgctagcgccaccatgtcgcggaggccatggc (SEQ ID NO:13) (for ChIEF), and then ligated to an AAV-Ef1α-DIO backbone cut with those sites.
Mac and Arch were obtained from Addgene as green fluorescent protein (GFP) fusion genes, and switched to enhanced yellow fluorescent protein (eYFP) for consistency. Humanized ArchT was synthesized by DNA2.0. Mac, Arch, and ArchT were enhanced to the 2.0 versions using the endoplasmic reticulum (ER) export element alone and to the 3.0 versions with both the ER export motif and the trafficking signal as described previously33.
All constructs were fully sequenced to check for accuracy and all AAV vectors were tested for in vitro expression prior to viral production. Complete sequence information is on the website: www(dot)optogenetics(dot)org.
Hippocampal Neuron Culture and Calcium Phosphate Transfections
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 papain (Worthington), and plated onto glass coverslips pre-coated with 1:30 Matrigel (Beckton Dickinson Labware). Cultures were maintained in a 5% CO2 humid incubator with Neurobasal-A medium (Invitrogen) containing 1.25% fetal bovine serum (FBS) (Hyclone), 4% B-27 supplement (Gibco), 2 mM Glutamax (Gibco), and 2 mg/mL 5-Fluoro-2′-deoxyuridine (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, 2M 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 mM at room temperature (RT), the mix was added drop-wise into each well (from which the growth medium had been removed and replaced with pre-warmed MEM) and transfection proceeded for 45-60 minutes at 37° C., after which each well was washed with 3×1 mL warm MEM before the original growth medium was returned.
Stereotactic Injections
Adeno-associated virus (AAV) serotype 2/5 was produced by the University of Carolina Chapel Hill Vector Core. Genomic titers were 1.5×1012 cfu mL−1 for ChETAA, ChETATR, and ChIEF, and 4×1012 cfu mL−1 for eYFP, eNpHR3.0, and eArch3.0. 1 μL of virus was stereotactically injected bilaterally into the medial prefrontal cortex of 3-4 week-old mice at +1.7 anteroposterior, 0.4 mediolateral, and 2.5 dorsoventral (in mm from bregma).
Whole-Cell Electrophysiology Recordings
Recordings in cultured neurons were performed 4-6 days post-transfection in Tyrode's solution (320 mOsm): 125 mM NaCl, 2 mM KCl, 2 mM CaCl2, 2 mM MgCl2, 30 mM glucose, and 25 mM HEPES, titrated to pH 7.3-7.4 with NaOH. Tyrode was perfused at a rate of 1-2 ml, min−1 and was kept at room temperature (20-22° C.). Intracellular solution (300 mOsm) contained 130 mM K-gluconate, 10 mM KCl, 10 mM HEPES, 10 mM EGTA, and 2 mM MgCl2, titrated to pH 7.3 with KOH. Characterization of excitatory opsins was done with bath-applied tetrodotoxin (TTX) (1 μM; Sigma-Aldrich) and intracellular QX-314 chloride (1 mM; Tocris Bioscience). In vitro patching of hyperpolarizing opsins and current clamp recordings for depolarizing opsins were performed in the presence of synaptic transmission blockers 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 μM; Sigma-Aldrich) and D(−)-2-amino-5-phosphonovaleric acid (APV; 25 μM, Sigma-Aldrich) as well as gabazine for the current clamp experiments (10 μM; Sigma-Aldrich). All recordings of cultured neurons were performed on an upright Leica DM-LFSA microscope.
Recordings of eYFP, eNpHR3.0, and eArch3.0-expressing pyramidal cells were performed in acute slices from wild-type C57BL/6 mice 6-7 weeks after virus injection. ACSF contained CNQX, APV, and gabazine. Intracellular solution (280 mOsm) contained 135 mM K-gluconate, 5 mM KCl, 10 mM HEPES, 0.1 mM EGTA, 2 mM MgCl2, 2 mM Mg-ATP, and 0.2 mM Na2-GTP, titrated to pH 7.4 with KOH. Pyramidal cells were identified by morphology and characteristic electrophysiological properties. Recordings were performed on an upright Olympus BX51 microscope. For all patching experiments, borosilicate glass (Sutter Instruments) pipette resistances were 3-6 MΩ. For cell-attached electrophysiology recordings, upon obtaining GΩ seals, holding potential was set so that no net current flowed across the membrane; the same stimulation protocol used for whole-cell spiking experiments. After the cell-attached recording had been performed, we applied suction to the pipette to break into the cell and repeated the same experiments in whole-cell to provide a direct within-cell comparison. No exogenous retinal co-factor was added to neurons in any preparation.
Light Delivery
All experiments were performed using single-photon activation. For cultured neurons, light was emitted from a 300 W DG-4 lamp (Sutter Instruments, Novato, Calif.) and was delivered through a 40×, 0.8NA water-immersion objective. Pulsed input signals were delivered to the DG-4 from pClamp (Axon Instruments) via a BNC connection. The delay from the DG-4 trigger signal to full light output was measured using an amplified photodetector (Thorlabs) as  ̃1 ms, with a 200 us rise-time. All measurements of time-to-peak and latency were corrected for this delay.
For light sensitivity measurements, light was passed through a 470/40 nm filter (for blue-light sensitive excitatory opsins) or a 562/40 nm filter (for C1V1s and all inhibitory opsins), and then through a series of neutral-density (ND) filters to achieve power densities ranging from  ̃0.1 to 20 mW mm−2 Other properties were studied at  ̃5 mW mm−2 For these experiments, the light was passed through a Lambda 10-3 filter wheel (Sutter Instruments) with a 10-position wheel for filters of different wavelengths, ND-normalized to generate closely-matched power densities. Filters were: 406/15; 427/20; 445/20; 470/20; 494/20; 520/15; 542/20; 560/25; 590/20. Inhibitory spectra also used a 607/45 filter. Functional performance of depolarizing tools in culture used a 470/40 nm filter (for blue-light sensitive excitatory tools) or a 562/40 nm filter (for C1VTs), and then ND filters to achieve power densities of 2, 6, and 20 mW mm−2.
For experiments investigating fast depolarizing tools in slice, light was emitted from the same 300 W DG-4 lamp (Sutter Instruments) and delivered through a 40×, 0.8NA water-immersion objective. Light was passed through a 470/40 nm filter and adjusted to achieve a light power density of 5.1 mW mm−2 For experiments investigating hyperpolarizing tools in slice, a 40×/0.8 NA LUMPlanFL/IR Objective (Olympus), XCite halogen light source (EXPO) was used. Light was passed through a 589/15 filter (eNpHR3.0) or a 560/14 filter (eArch3.0). For experiments comparing the photocurrent and hyperpolarization magnitudes under matched conditions, light power density was adjusted to  ̃5 mW mm−2 For the remaining experiments light was adjusted across a range of light power densities (5-10 mW mm2 for eNpHR3.0; 0.25-5 mW mm−2 for eArch3.0) in order to achieve a comparable range of photocurrents for both opsins.
All experiments contained at least 30 s of dark between sweeps in order to allow recovery to baseline. All filters are given here as wavelength in nm/bandwidth in nm. All light power densities were measured coming out of the 40× objective, at approximately the sample distance.
Data Analysis
Analyses of physiological results were performed using ClampFit software (Axon Instruments) or custom software written in MATLAB (Mathworks).
Access resistance (Ra) and input resistance (Rin) were monitored continually and data was only included when Ra was <30 MΩ and Rin was >90 MΩ Any traces containing escaped spikes were excluded from analyses of peak photocurrent or of kinetics, but steady-state photocurrents were still measured when possible. For current clamp recordings in culture, only cells that fit those criteria and had leak currents >−150 pA (holding at −65 mV) were included for analysis. For current clamp recordings in acute slice, only cells that fit those criteria and had resting potentials <−55 mV were included for analysis.
To identify the peak photocurrent, traces were smoothed using the robust Loess method with a filter width of 2 ms and the peak was defined as the extremum from laser onset to 200 ms post laser onset, less the baseline current (from the average over 500 ms prior to laser onset). Visual inspection ensured that no escape spikes or other anomalies occurred. Time-to-peak was measured from laser onset to this marked peak time. The steady-state photocurrent was determined by fitting a monoexponential curve to the smoothed waveform from 2 ms after the peak to the laser offset time. Steady-state current was taken from the parameters of this fit. τoff and τdes were calculated using ClampFit. The trace was first smoothed using a lowpass Gaussian filter with a −3 dB cutoff at 1,000 Hz; then a monoexponential curve was fit to the smoothed waveform. All curves were visually inspected for goodness of fit.
Photocurrent properties of the depolarizing tools ChR2, ChETAA, and ChIEF were characterized in vitro using both the lentiviral and the adenoassociated virus (AAV) constructs. For parameters that depend on single-molecule properties (steady-state: peak ratio, action spectrum, light sensitivity, and kinetics), values were pooled across experiments after confirming that datasets were not statistically different. Photocurrent properties of the hyperpolarizing tools were assessed in two separate rounds of experiments. eNpHR3.0 photocurrent magnitudes were statistically different between the two datasets, so we only combine datasets when considering normalized values, or intrinsic single-molecule properties (action spectrum, light sensitivity, and kinetics) after confirming that eNpHR3.0 performed similarly across datasets.
Whole-cell spikes were defined as rising above a high threshold (−20 mV for the comparison of fast depolarizing opsins in slice; 0 mV for all other comparisons) and then dropping below a low threshold (−30 mV). Subsequent spikes that occurred within 2 ms of a prior spike were ignored. To detect spikes elicited by light, a window of time from 1-50 ms after the pulse onset was defined. Above 20 Hz, this window was truncated to 1 ms after the current pulse onset to 1 ms after the subsequent pulse onset. The window around the last light pulse was truncated to the same length. Cell-attached spikes were identified using the threshold function in ClampFit. Very small, broad events were not included as spikes. Where the spike data was ambiguous, the trace was inspected manually. For each whole-cell pulse train we calculated the proportion of light pulses that elicited ≧1 spike (pulse efficacy) and that elicited >1 spike (multiple spike likelihood).
Plateau potentials were defined as the offset of the spike waveform from the baseline. For the depolarizing tools in vitro, all cells that fired≧one spike were included for analysis. For the fast-spiking cells in slice, only traces that had 100% pulse efficacy were included for analysis. Temporal stationarity, the extent to which spiking is sustained at the same reliability over time, was calculated by dividing the light pulses into quartiles and computing the pulse efficacy each quartile. Latency and latency spread across pulse trains were determined as follows: For each light pulse, we measured the time delta from the light pulse onset to the spike time. Latency is the average of these time deltas, and latency spread is the standard deviation of these time deltas. Note that latency spread therefore is a measure of how variable the latencies are within each cell, whereas the error bars on latency are the standard error of mean latencies across cells. Traces in which the cell fired <5 action potentials were excluded from analysis.
Statistical Analysis
All statistical analysis was performed using Graphpad Prism version 5.04 for Windows (GraphPad Software, www(dot)graphpad(dot)com). For two-sample comparisons of a single variable (such as kinetics of ChETAA vs. ChIEF in slice) it was first tested whether the data followed a Gaussian distribution (Shapiro-Wilk normality test). If the data were detectably non-Gaussian, a non-parametric Mann-Whitney test was performed. If the data well-approximated a Gaussian, an independent, two-sample t-test (equal variance) was performed. In the case of unequal variance (determined by an F test), Welch's correction was applied. All tests were two-tailed with confidence levels of 95%.
For multi-way comparisons of a single variable (such as kinetics of all depolarizing opsins in culture) it was first tested whether the data followed a Gaussian distribution (Shapiro-Wilk normality test). In cases in which distributions were detectably non-Gaussian, a square root transformation was used to stabilize the variance and make the data approximately normal; all data were then compared against one specified “control”, correcting for family-wise error using Dunnett's test. If the transformed data were still non-Gaussian, we used the non-parametric Dunn's test. In all cases, overall significance levels of alpha=0.05 (95% confidence interval) were maintained. Comparisons between larger numbers of opsins will therefore have a more conservative alpha (more stringent requirement for significance). This may also result in different significance values assigned to the same comparison, depending on how many comparisons are being performed in parallel. In particular, since some of the same ChR2 and ChETAA data were included in two comparisons, discrepancies in reported significance values can be attributed to the total number of opsins included in each set of comparisons.
For comparisons across multiple variables (such as spiking performance across frequencies), two-way ANOVAs were performed, followed by post-tests between pairs or against a specified “control”. A conservative Bonferroni's correction was used to control the false positive rate. To test the relationship between two opsin properties (such as τoff vs. EPD50), a nonparametric, two-tailed Spearman correlation with a confidence level of 95% was performed. To estimate the slope, a least-squares regression (either linear or linear on log-log transformed data), minimizing relative distance squared (1/Y^2) was performed.
To test the dependency of an opsin property on an experimental condition (e.g. photocurrent vs. light power density), regressions were performed, as follows. First, for analysis of time-to-peak vs. light power density, we performed linear regression on log-log transformed data was performed; and it was compared whether, for each opsin, the best-fit slope differs significantly from 0. Second, for analysis of recovery from desensitization, a non-linear regression was used to fit the mean photocurrent recovery data with a two-phase association curve, constraining Y0=0 and plateau=1. This fit was used to generate the curves and the R-squared values. In a separate analysis, we fit the data for each individual cell, to calculate the time required for 50% recovery. Third, for analysis of light sensitivities, the raw population means was fit with a one-site specific binding curve: Y=Bmax*X/(Kd+X). In a separate analysis, the photocurrents for each cell were normalized; and the population means and standard errors for each opsin were plotted. This population data was fit the same way to generate the curves and the R-squared values. For each individual cell, a Kd (equilibrium binding constant), which we refer to as EPD50 (50% effective light power density), was obtained.
Population significance thresholds were always set at P<0.05 (*), P<0.01 (**), and P<0.001 (***) for the entire family of comparisons. All graphs are shown as mean±standard error of the mean (s.e.m.).
Immunohistochemistry
6 or 4 weeks post-injection, mice were perfused transcardially with PBS followed by 4% paraformaldehyde (PFA). After an overnight post-fix in PFA, brains were equilibrated in 30% sucrose in PBS for at least 24 hours. 40 μm sections were obtained using a frozen microtome, DAPI-stained (1:50,000), and coverslipped with PVA-DABCO (Sigma-Aldrich). Transfected primary hippocampal cultures were fixed for 15 min with 4% PFA. For staining with KDEL (SEQ ID NO: 14), cultures were then permeabilized for 30 min with 0.4% saponin in 2% normal donkey serum (NDS). Primary antibody incubations were performed overnight at 4° C. using a monoclonal antibody marking endogenous ER-resident proteins containing the KDEL (SEQ ID NO:14) retention signal (anti-KDEL 1:200, Abcam). Secondary antibodies (Jackson Laboratories) were applied in 2% NDS for 1 hour at room temperature.
Equipment and Settings
All images were obtained on a Leica confocal microscope (DM600B) as 1024×1024 resolution (pixel dimensions=3.03 μm2). Images were acquired using the following objectives: 10×/0.40 NA (air), 40×/1.25 NA (oil), and 63×/1.4 NA (oil). Excitation and emission wavelengths were as follows: eYFP in FIG. 1b, 514 nm/512-600 nm; eYFP for all other figures, 488 nm/500-545 nm; GFP, 488 nm/500-600 nm; CyS, 633 nm/650-750 nm. The following figures used line-averaging: FIG. 1b and FIG. 2a. Consistent settings were used for all images in each given figure panel. The brightness and contrast of all eYFP images for FIG. 1b were uniformly and identically modified in Photoshop (Adobe). All other images were unprocessed after acquisition.
Quantification of Fluorescence Levels in Transfected Cells
Fluorescence images were acquired from the same cells that were patched to enable quantification of expression levels and photocurrent/fluorescence relationships. Images were acquired with Metamorph, maintaining constant settings, and processed off-line using ImageJ. Hand-drawn ROIs encompassed the soma and proximal dendrites.
Results
Hyperpolarizing Tools and Properties
Various hyperpolarizing optogenetic tools were compared head-to-head. Although each experiment will have its own unique set of requirements for hyperpolarizing photocurrent properties, some common guiding principles initially seem clear. First, in most experimental applications, hyperpolarizing photocurrents will need to be sufficiently large to robustly and safely inhibit spiking even in the presence of excitatory inputs. Second, higher light sensitivity will likely enable modulation of larger volumes of tissue, the use of lower light powers, and/or less invasive light delivery. Third, precise, time-locked inhibition will presumably require photocurrents with rapid onset and offset, while longer-term inhibition will require photocurrents that are stable, with minimal desensitization. Finally the nature of the action spectrum will dictate feasibility of combining with other light-activated reagents in the same preparation32,33.
The first hyperpolarizing tool shown to be efficacious in neurons was the N. pharaonic halorhodopsin (NpHR), a yellow light-activated chloride pump that has now been used in preparations ranging across mammalian brain slice32, freely moving worms32, cultured neurons32,34, and behaving mammals35-38. Two versions modified for enhanced membrane targeting in mammalian neurons, termed eNpHR2.039 and eNpHR3.033 have since been reported. The outward proton pumps Arch40 (from Halorubrum sodomense), ArchT41 (from Halorubrum strain TP009), eBR33 (from Halobacterium) and Mac40 (from Leptosphaeria maculans) have also recently been shown to achieve successful neuronal inhibition. eNpHR3.0 has larger photocurrents than eNpHR2.0, and Arch has larger photocurrents than eNpHR2.040, but no direct comparison between eNpHR3.0 and Arch or any of the proton pumps has yet been reported. Below is presented a direct comparison of the most potent hyperpolarizing opsins (FIG. 1a), including novel membrane trafficking-enhanced versions of proton pumps resulting in the highest expression levels and inhibitory photocurrents yet described. Properties were charaterized in vitro; then the functional performance of two of the most promising candidates in acute slice was tested.
Each hyperpolarizing tool was fused in-frame with enhanced yellow fluorescence protein (eYFP), cloned the opsins into an identical lentiviral backbone with the excitatory CaMKIIα promoter (FIG. 1a); and the opsins were expressed in cultured neurons (FIG. 1b). eNpHR3.0 was well-targeted to the membrane, but Arch, ArchT, and Mac all showed intracellular accumulations reminiscent of the endoplasmic reticulum (ER)-aggregations observed with NpHR1.039. The same accumulations were also observed in the GFP versions of the constructs; the GFP and YFP 1.0 versions had similar photocurrents. ER-aggregation was confirmed by co-staining with the ER marker KDEL (SEQ ID NO: 14) (FIG. 1b). Trafficking modifications applied to eNpHR3.0 were applied to Arch, ArchT, and Mac. These novel trafficking-enhanced versions, which are termed (by analogy with NpHR version progression) eArch3.0, eArchT3.0, and eMac3.0, had markedly reduced intracellular labeling and improved membrane-localization with labeling of cellular processes (FIG. 1b). Intermediate “2.0” versions were potent but not as successful as the 3.0 versions.
Because only those proteins expressed on the membrane can contribute to the measured photocurrent, it was anticipated that this improved opsin trafficking should increase photocurrent size. Indeed, all three enhanced proton pumps had dramatically increased photocurrents (P<0.001; FIG. 1c). While the 1.0 versions of the proton pumps had significantly smaller photocurrents than eNpHR3.0, eArch3.0 and eArchT3.0 photocurrents were significantly larger (P<0.001 for each comparison; FIG. 1c). eNpHR3.0-expressing cells had the dimmest fluorescence, but the greatest photocurrent per fluorescence, of these tools.
Although maximal eMac3.0 photocurrents were the smallest among the enhanced opsins (and significantly smaller than eNpHR3.0; P<0.05), Mac has been reported to have an activation spectrum sufficiently blue-shifted to allow dual-inhibition in combination with eNpHR3.064. After verifying that membrane trafficking did not change the spectra, the spectra of the enhanced pumps were compared, and plotted with ChR2, for reference (FIG. 1d). eNpHR3.0 was red-shifted (peaking at 560-590 nm) relative to the three proton pumps (peaking at 520-560 nm), exhibiting the least overlap with ChR2; no functionally relevant differences were seen among the proton pumps.
The temporal precision of hyperpolarizing photocurrents was investigated by quantifying on-kinetics (τon) and off-kinetics (τoff) at the beginning and end of a 1 s light pulse. All pumps activated rapidly, with proton pumps activating significantly faster than eNpHR3.0 (all within the range of 1.5-3 ms, FIG. 1e). Both Mac variants had much slower off-kinetics compared with the other pumps (P<0.001; FIG. 1e).
The light sensitivity of the hyperpolarizing pumps was assessed by measuring photocurrents across a range of light power densities ranging from  ̃0.05 to  ̃20 mW mm−2 (FIG. 1f); due to small photocurrents, Mac 1.0 was eliminated from this and subsequent analyses.) As expected, the 3.0 pumps had much larger operational light sensitivity (that is, by absolute current magnitude) than the 1.0 counterparts, although trafficking-enhancement did not affect the population sensitivity (normalized current magnitudes or EPD50). eMac3.0 was the most sensitive (EPD50=1.9±0.4 mW mm−2 vs. 5.4±0.2 mW mm−2 for eNpHR3.0; P<0.001). Off-kinetics and population light sensitivity were therefore inversely correlated for the hyperpolarizing tools, reminiscent of the pattern observed for depolarizing tools.
Given that many behavioral neuroscience experiments may require prolonged inhibition on the order of minutes, the stability of the hyperpolarizing photocurrents was investigated. While all pump photocurrents decayed across 60 s of continuous light, eNpHR3.0 currents were the most persistent and the large 3.0 proton pump currents (eArch3.0 and eArchT3.0) had the largest drop-off in vitro. All pumps recovered photocurrents with similar efficacy under these cultured-neuron conditions.
FIG. 1: Properties of hyperpolarizing tools. (a) NpHR is an inward chloride pump (halorhodopsin type; HR), while Arch, ArchT, and Mac are outward proton pumps (bacteriorhodopsin type; BR). 3.0 versions include a trafficking sequence (TS) between opsin and fluorophore and the 2.0-type endoplasmic reticulum export sequence (ER) after the fluorophore. (b) Confocal images of 1.0 and 3.0 versions (green) expressed in culture and immunolabeled with an ER marker (anti-KDEL (SEQ ID NO: 14); red). Horizontal scale bar represents 25 μm. (c) Representative traces and raw photocurrents in response to 1 s light for 1.0 (open bars) vs. 3.0 versions (closed bars) for Arch (n=15-19), ArchT (n=14-16), and Mac (n=8-12). Vertical and horizontal scale bars represent 500 pA and 500 ms, respectively. Photocurrents were normalized to eNpHR3.0 values from within the same experiment to enable direct comparisons across opsins (n=8-35). (d) Action spectra for 3.0 versions (n=7-20) alongside ChR2 (black). (e) τon and τoff=7-35). Vertical and horizontal scale bars represent 200 pA and 5 ms, respectively. (f) EPD50 for all hyperpolarizing opsins (n=5-14). Raw photocurrent vs. light power density plotted alongside within-experiment eNpHR3.0 (n=5-14). All population data is plotted as mean±s.e.m. Stars indicate significance level: * P<0.05, ** P<0.01, *** P<0.001. Unless otherwise indicated, eNpHR3.0 was activated with 590 nm light, while all other tools were activated with 560 nm light, both at  ̃5 mW mm2.
Hyperpolarizing Tools: Inhibiting Spikes in in Acute Slice
To further investigate the characteristics of prolonged photocurrents under conditions more relevant to in vivo experiments, and to test the functional ability of hyperpolarization to stably inhibit spiking, acute slice preparations were used. For this analysis, one of each broad class of hyperpolarizing tool (namely, the chloride pump eNpHR3.0 against one of the proton pumps) was compared. The enhanced counterpart of the best-established proton pump (Arch1.0) to date, namely eArch3.0 was used. To express eNpHR3.0 and eArch3.0 in vivo, an adeno-associated viral vector (AAV serotype 2⁄5), with the opsin-eYFP fusion gene under control of the CaMKIIα promoter, was stereotactically injected. Under matched conditions, eArch3.0 expressed much more strongly based on fluorescence, both at the injection site and in axons at downstream targets such as the basolateral amygdala (BLA; FIG. 2a). Compared with eYFP-transduced controls, cells expressing both opsins had similar baseline input resistances (FIG. 2b) and resting potentials, but slightly higher membrane capacitance, as has previously been observed for opsin-expressing HEK cells42. Also as expected from the in vitro work (FIG. 1), at matched light power densities (5 mW mm−2) eArch3.0 had significantly larger photocurrents (P=0.01), averaging 1680±360 pA vs. 450±70 pA for eNpHR3.0 (FIG. 2c). Under current-clamp, eArch3.0-mediated hyperpolarization was also significantly larger (−94±12 mV vs.−41±4 mV, P=0.005; FIG. 2d); smaller differences in hyperpolarization compared with photocurrent could be due to voltage-dependent slowing of photocycle turnover in proton pumps.
Because photocurrent stability and cell responses to hyperpolarization may depend on photocurrent magnitudes, a set of experiments was carried using non-matched light power densities (5-10 mW mm−2 for eNpHR3.0; 0.25-5 mW mm−2 for eArch3.0) to obtain a similar range of photocurrents for the two tools. Cells were illuminated for 60 s under voltage clamp, and measured the start and end photocurrent for each cell. These data were well-fit by linear regression (eNpHR3.0 R2=0.68, eArch3.0 R2=0.88) with eArch3.0 having significantly higher slope (F1,36=22.2, P<0.001), reflecting the fact that, for cells with similar onset photocurrents, eArch3.0-expressing cells had more photocurrent remaining at the end of the light pulse under these slice conditions, as seen in the illustrative traces and in contrast with the pattern of stability observed in vitro.
The ability of eArch3.0 and eNpHR3.0 to inhibit spiking in current clamp was assessed. Spiking was elicited with modestly suprathreshold current injections at 5 Hz, with 30 s baseline (pre-light), 60 s light, and 30 s post-light. Both pumps successfully blocked spikes throughout the duration of the prolonged light stimulation (FIG. 2e). We observed that from both groups some cells became unstable after prolonged hyperpolarization especially by >50 mV, failing to spike to current injections or rebounding to a more depolarized resting potential after light offset. These factors were quantified for each cell and plotted each against the degree of hyperpolarization (FIG. 20. Under more moderate (>50 mV) hyperpolarizations, no consistent or lasting effects on excitability or membrane resistance were observed.
FIG. 2: Performance of hyperpolarizing tools. (a) Confocal images of eNpHR3.0 and eArch3.0 expression at the injection site in medial prefrontal cortex (mPFC) and the downstream basolateral amygdala (BLA). Scale bars represent 250 μm and 25 μm. DAPI staining (white) delineates cell bodies. (b) Mean input resistances for opsin-expressing cells and eYFP-controls (n=10-22). (c) Representative traces and mean onset photocurrents for eArch3.0 and eNpHR3.0 in response to 60 s 5 mW mm−2 light pulses (n=8-10). Vertical and horizontal scale bars represent 400 pA and 10 s, respectively. (d) Mean peak hyperpolarization generated by eArch3.0 and eNpHR3.0 with 60 s 5 mW mm−2 light pulses (n=6-10). (e) Suppression of current injection-evoked spiking in reliably-firing cells by 60 s of continuous light in cells expressing eNpHR3.0 or eArch3.0. Cells were illuminated with light power densities set to achieve approximately matched hyperpolarization. Vertical and horizontal scale bars represent 40 mV and 20 s, respectively. (f) Relationship between hyperpolarization magnitude and cell stability. Post-light recovery of evoked spiking (relative to pre-light performance) and change in resting potential plotted against light-evoked hyperpolarization. All population data is plotted as mean±s.e.m. Stars indicate significance level: * P<0.05, ** P<0.01, *** P<0.001. eNpHR3.0 was activated with 590 nm light, while eArch3.0 was activated with 560 nm light.
Example 2
Cloning and Characterization of Dunaliella salina Opsin
Typically found in hyper-saline environments such as evaporation salt fields, the unicellular (oval with two flagella) green alga Dunaliella salina is salt tolerant. Despite belonging to the same order as the green algae Chlamydomonas reinhardtii and Volvox carteri, Dunaliella can appear reddish due to the accumulation of high levels of carotenoid molecules (FIG. 3A). We hypothesized that a Dunaliella ChR might have unusual properties and engaged in efforts to clone ChRs from this flagellated algal species.
Despite high homology with other known ChRs, the DChR1 sequence contained several notable features (FIG. 3B). First, one of the residues that is thought to contribute to the complex counterion of the RSB, E123 in ChR2 as discussed above, is replaced by Ala in the DChR1 TM3 (FIG. 3B,C); from structural modeling (FIG. 3C), it was expected that the counterion function is assumed by E309 in DChR1, a position that plays only a minor role in BR (D212) or Anabaena sensory rhodopsin (ASR) (Vogeley et al., 2004). Even more remarkably, DChR1 photocurrents were exclusively carried by protons, unlike any other known ChR, and were completely unaffected by changes in the extracellular cation composition (FIG. 3D). Consequently, the photocurrent was highly sensitive to changes in the pH environment and completely vanished at high pH (FIG. 3E).
Full understanding of structure-function relationships will require high-resolution crystal structures in multiple photocycle states. However, directed mutagenesis studies here demonstrate that DChR1 has a different counterion arrangement and ion selectivity compared to other known ChRs. The strict H+ selectivity of DChR1 was not mediated by the unusual protonated retinal Schiff base (RSBH) counter ion, as substitution of A178 with the more typical putative counterion Glu as found in ChR2 only red-shifted the activation spectrum (FIG. 3F, from 475 to 510 nm) with minimal effect on current amplitude or kinetics. Similarly, replacing E309 with Asp caused a slight spectral shift and a slight current increase, whereas replacing the charged E309 by Ala rendered the protein almost totally inactive (FIG. 3F).
Given typical electrochemical proton gradients, the DChR1 H+ current direction is opposite in direction to the H+ current generated by bacteriorhodopsin (BR) pump activity; therefore, DChR1 and BR could enable interventions such as bidirectional control of cellular pH, for example in manipulating the pH of intracellular compartments (mitochondria and synaptic vesicles). DChR1 therefore defines a novel class of microbial opsin—a light-activated proton channel—unlike any other microbial opsin including ChR1 and ChR2. These findings illustrate the diversity of function likely to be present within the vast array of microbial opsin genomes.
FIG. 3. Characterization of a Channelrhodopsin from Dunaliella salina. 
A. The halophilic unicellular alga Dunaliella salina. B. Sequence homology between the algal channelrhodopsins and BR within the third transmembrane helix. The typically conserved E123 position has been replaced with an Ala in DChR1 (and is shown on a yellow background), conserved residues are shown on a blue background, and amino acids likely interacting with the chromophore are shown in red. C. Lack of a proton acceptor in DChR1, compared with BR and Chlamydomonas ChR2 (CChR2). ASR (Anabaena sensory rhodopsin) has been crystallized with a mixture of all-trans retinal seen as an overlay (Vogeley et al., 2004). D. DChR1 photocurrents are unaffected by changes in the extracellular cation composition (sole cation present in each condition shown on category X axis). Cation exchange was performed in 5 mM Mops-NMG, 0.1 mM MgCl2 with 100 mM LiCl, KCl, NaCl, Guanidium chloride or NMG chloride (pH 7.5). We used a human-codon adapted DChR sequence (amino acid residues 1-339) as a template for capped RNA synthesis by T7 RNA polymerase (mMessage mMachine, Ambion). Oocyte preparation, injection of capped RNA were carried out as described previously (Berthold et al. 2008), and two-electrode voltage clamp was performed with a Turbo Tec-05 (NPI Electronic) or a GeneClamp 500 (Molecular Devices) amplifier on an oocyte after 3-7 days of the capped RNA injection. Continuous light was provided by a 75-W Xenon lamp (Jena Instruments) and delivered to the oocytes via a 3-mm light guide. The light passed through a 500 25-nm broadband filter (Balzers) with an intensity of 46 mW/cm2. E. In contrast, DChR1 photocurrent is highly sensitive to changes in the pH environment. Solutions contained 100 mM NMG-chloride, 0.1 mM MgCl2, 0.1 mM CaCl2 with 5 mM glycine (pH 9.0), 5 mM Mops-NMG (pH 7.5), 5 mM citrate (pH 6, 5.5, 5.0, 4.6, 4.2). F. Introduction or alteration of a proton acceptor (A178E or E309D) into the DChR1 retinal-binding pocket causes a pronounced red-shift in the absorption spectrum. We applied 10-ns laser flashes as described previously (Berthold et al. 2008); solutions for action spectra recording contained 100 mM NaCl, 0.1 mM MgCl2, 0.1 mM CaCl2 and 5 mM citrate (pH 4.2).
A nucleotide sequence endoding D. salina DChR1 is presented in FIG. 4. The DChR1-encoding nucleotide sequence was codon-optimized for mammalian expression; the codon-optimized nucleotide sequence is depicted in FIG. 5. FIG. 6 provides an amino acid sequence of D. salina DChR1.
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While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.

## Claims

1. An isolated fusion polypeptide comprising, in order from N-terminus to C-terminus:
a) an opsin polypeptide comprising an amino acid sequence having at least 90% amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:28;
b) a membrane trafficking signal comprising the amino acid sequence KSRITSEGEYIPLDQIDINV (SEQ ID NO: 10); and
c) an endoplasmic reticulum (ER) export signal comprising the amino acid sequence FCYENEV (SEQ ID NO:5).

2. The fusion polypeptide of claim 1, wherein the polypeptide further comprises a fluorescent protein disposed between (a) and (b).

3. The fusion polypeptide of claim 1, wherein the opsin polypeptide comprises an amino acid sequence having at least 95% amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:28.

4. The fusion polypeptide of claim 1, wherein the opsin polypeptide comprises an amino acid sequence having at least 98% amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:28.