(en)Disclosed herein are methods and compositions for treating ocular disorders.

1.ApplicationNumber: US-201213367216-A
1.PublishNumber: US-2012204282-A1
2.Date Publish: 20120809
3.Inventor: ZHANG H. STEVE

4.Inventor Harmonized: ZHANG H STEVE(US)

5.Country: US
6.Claims:
(en)Disclosed herein are methods and compositions for treating ocular disorders.

7.Description:
(en)CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims the benefit of U.S. Provisional Application No. 61/462,580, filed Feb. 4, 2011, the disclosure of which is hereby incorporated by reference in its entirety.


STATEMENT OF RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH
Not applicable.
TECHNICAL FIELD
The present disclosure is in the field of gene editing.
BACKGROUND
Retinitis pigmentosa (RP) refers to a diverse group of hereditary diseases affecting two million people worldwide that lead to incurable blindness. RP is one of the most common forms of inherited retinal degeneration, and there are multiple genes whose mutation can lead to RP. More than 100 mutations in 44 genes expressed in rod photoreceptors have thus far been identified, accounting for 15% of all types of retinal degeneration, most of which are missense mutations and are usually autosomal dominant.
The typical disease progression for most forms of RP is a presentation of night blindness followed by a loss of the peripheral visual field (tunnel vision). The night blindness can precede the tunnel vision by years or even decades. Some patients with RP do not become legally blind until their fourth or fifth decade, and some maintain limited vision throughout their lives. In more severe forms of RP, vision can be lost in childhood. At the molecular level, in RP patients, rod photoreceptors in the retina die early whereas mutant light-insensitive, morphologically altered cone receptors persist longer.
Rhodopsin is a pigment of the retina that is involved in the first events in the perception of light. It is made of the protein moiety opsin covalently linked to a retinal cofactor. Rhodopsin is encoded by the RHO gene, and the protein has a molecular weight of approximately 40 kD and spans the membrane of the rod cell. The retinal cofactor absorbs light as it enters the retina and becomes photoexcited, causing it to undergo a change in molecular configuration, and dissociates from the opsin. This change initiates the process that eventually causes electrical impulses to be sent to the brain along the optic nerve. In relation to RP, more than 80 mutations in the rhodopsin gene have been identified that account for 30% of all Autosomal Dominant Retinitis Pigmentosa (ADRP) in humans (Dryja et al (2000) Invest Opthalmol Vis Sci 41: 3124-3127).
Recently, it has been shown in a murine model of RP that expression of an archaebacterial halorhodopsin in light insensitive cones restored light sensitivity and was able to activate all retinal come pathways. These transgenic mice were then able to perform light mediated behaviors (see Busskamp et al (2010) Sciencexpress 10.1126/science.1190897).
Three point mutations in the human rhodopsin gene (P23H, Q64X and Q344X) are known to cause ADRP in humans. See, e.g., Olsson et al. (1992) Neuron 9(5):815-30. The P23H mutation is the most common rhodopsin mutation in the United States. Due to problems with protein folding, P23H rhodopsin only partially reconstitutes with retinal in vitro (Liu et al (1996) Proc Nat'l Acad Sci 93:4554-4559), and mutant rhodopsin expressed in transgenics causes retinal degeneration (Goto et al (1995) Invest Opthalmol Vis Sci 36:62-71).
Thus, there remains a need for compositions and methods for the treatment of RP.
SUMMARY
Disclosed herein are methods and compositions for treating RP. In particular, provided herein are methods and compositions for modulating expression of a gene comprising a rhodopsin so as to treat retinitis pigmentosa, for example, modulating expression of a RHO mutant allele so as to treat RP.
Thus, in one aspect, engineered DNA binding domains (e.g., zinc finger proteins or TAL effector (TALE) proteins) that modulate expression of a RHO allele are provided. Engineered zinc finger proteins or TALEs are non-naturally occurring zinc finger or TALE proteins whose DNA binding domains (e.g., recognition helices or RVDs) have been altered (e.g., by selection and/or rational design) to bind to a pre-selected target site. Any of the zinc finger proteins described herein may include 1, 2, 3, 4, 5, 6 or more zinc fingers, each zinc finger having a recognition helix that binds to a target subsite in the selected sequence(s) (e.g., gene(s)). Similarly, any of the TALE proteins described herein may include any number of TALE RVDs), In some embodiments, at least one recognition helix (or RVD) is non-naturally occurring. In certain embodiments, the zinc finger proteins have the recognition helices shown in Table 1. In other embodiments, the DNA-binding proteins (zinc fingers or TALEs) bind to the target sequences shown in Table 2.
In one aspect, repressors are provided which are capable of preferentially binding to mutated rhodopsin, but have reduced affinity for wild-type sequence. In some embodiments, the ZFP-TFs or TALE-TFs are used to repress expression of the dominant mutant allele. In some instances, the point mutation is selected from the mutant genes encoding the P23H, Q64X or Q344X rhodopsin proteins. In certain embodiments, ZFP repressors are provided which are capable of repressing both alleles of a rhodopsin gene. The function of rhodopsin can be restored by reducing expression of the dominant mutant allele and/or by reintroducing a wild type (wt) rhodopsin gene.
In certain embodiments, the DNA-binding proteins as described herein can be placed in operative linkage with a regulatory domain (or functional domain) as part of a fusion protein. In certain embodiments, the functional domain is a transcriptional repression domain. By selecting a repression domain for fusion with the DNA binding domain, such fusion proteins can be used to repress gene expression. In some embodiments, a fusion protein comprising a ZFP or TALE targeted to a RHO gene (e.g., mutant RHO allele) as described herein fused to a transcriptional repression domain that can be used to down-regulate RHO (e.g., mutant RHO) expression is provided. In certain embodiments, the activity of the regulatory domain is regulated by an exogenous small molecule or ligand such that interaction with the cell's transcription machinery will not take place in the absence of the exogenous ligand. Such external ligands control the degree of interaction of the ZFP- or TALE-TF with the transcription machinery. In other embodiments, the functional (regulatory) domain comprises a transcriptional activation domain. The regulatory domain(s) may be operatively linked to any portion(s) of one or more of the RHO-binding proteins, including between one or more RHO-binding proteins, exterior to one or more RHO-binding proteins and any combination thereof.
In some embodiments, the functional domain comprises a nuclease domain. Thus, the engineered DNA binding proteins as described herein can be placed in operative linkage with nuclease (cleavage) domains as part of a fusion protein to make a zinc finger nuclease (ZFN) or a TALE-nuclease (TALEN). In some embodiments, the ZFNs or TALENs are targeted to a RHO mutation or the vicinity of a RHO mutation (e.g., within about 100 bps of the mutation). In other embodiments, the ZFNs or TALENs are used in conjunction with a donor nucleic acid comprising part or all of a wild-type RHO sequence such that the cleavage induced by the ZFN or TALEN drives homology driven recombination (HDR) at the site of the RHO mutation or via non-homologous end joining (NHEJ) driven end capture, resulting in a gene correction. In some embodiments, at least one nuclease is used to target a RHO sequence upstream of naturally occurring RHO mutations, the resultant DNA cleavage can be repaired by a donor nucleic acid containing wild type RHO sequence through homology-base repair, so that a wild type copy of the RHO sequence is inserted upstream of the mutations, wild type rhodopsin protein is expressed, and the expression of mutant protein is blocked. In further embodiments, the donor nucleic acid further comprises a marker gene such as a fluorescent protein (e.g. GFP) such that integration of the wild-type sequence will also result in the tagging of the correct protein for screening purposes.
In some other embodiments, the nucleases are used to target a RHO sequence upstream of naturally occurring RHO mutations without using a donor nucleic acid. Non-homology based repair of the nuclease-mediated DNA break produces insertion/deletion of bases and frameshift mutations that lead to early termination of translation. Nonsense-mediated decay of mRNA will prevent the expression of mutant rhodopsin proteins, which allows the function of rhodopsin to be restored by reintroducing a wild type rhodopsin gene.
In some aspects, the nucleases (e.g., ZFNs or TALENs) are used in vivo. In some embodiments, expression vectors comprising the nucleases and the donors are introduced into retinal cells. In other embodiments, the nucleases are introduced into retinal cells as polypeptides and may be used in conjunction with the donor nucleic acid of choice. In some embodiments, the nucleases are introduced as mRNAs. In some embodiments, the nucleases may be introduced into the retinal cells by subretinal injections. The donor nucleic acids may be co-introduced in these injections.
In any of the methods described herein, the nuclease can be one or more zinc finger nucleases, one or more homing endonucleases (meganucleases) and/or one or more TAL-effector domain nucleases (“TALENs”).
In certain embodiments, such nuclease fusions may be utilized for targeting mutant RHO alleles in stem cells such as induced pluripotent stem cells (iPSC), human embryonic stem cells (hES), mesenchymal stem cells (MSC) or neuronal stem cells wherein the activity of the nuclease fusion will result in an RHO allele containing a wild type sequence. In certain embodiments, pharmaceutical compositions comprising the modified stem cells are provided. In other embodiments, the modified cells are administered to a subject (ex vivo therapy), for example via retinal injection(s).
In yet another aspect, a polynucleotide encoding any of the proteins described herein is provided. Such polynucleotides can be administered to a subject in which it is desirable to treat an ocular disorder.
In still further aspects, the invention provides methods and compositions for the generation of specific model systems for the study of ocular disorders such as RP. In certain embodiments, models in which mutant RHO alleles are generated in embryonic stem cells for the generation of cell and animal lines comprising mutated rhodopsins using a nuclease (e.g., ZFN or TALEN) driven targeted integration via HDR or NHEJ are provided. In certain embodiments, the model systems comprise in vitro cell lines, while in other embodiments, the model systems comprise transgenic animals.
In yet another aspect, a gene delivery vector comprising any of the polynucleotides described herein is provided. In certain embodiments, the vector is an adenovirus vector (e.g., an Ad5/F35 vector), a lentiviral vector (LV) including integration competent or integration-defective lentiviral vectors, or an adenovirus associated viral vector (AAV). Thus, also provided herein are adenovirus (Ad) vectors, LV or adenovirus associate viral vectors (AAV) comprising a sequence encoding at least one nuclease (e.g., ZFN or TALEN) and/or a donor sequence for targeted integration into a target gene. In certain embodiments, the Ad vector is a chimeric Ad vector, for example an Ad5/F35 vector. In certain embodiments, the lentiviral vector is an integrase-defective lentiviral vector (IDLY) or an integration competent lentiviral vector. In certain embodiments the vector is pseudo-typed with a VSV-G envelope, or with other envelopes.
In some embodiments, model systems are provided for ocular disorders (e.g., RP) wherein the target alleles (e.g., mutant RHO) are tagged with expression markers. In certain embodiments, the mutant alleles (e.g., mutant RHO) are tagged. In some embodiments, the wild type allele (e.g., wild-type RHO) is tagged, and in additional embodiments, both wild type and mutant alleles are tagged with separate expression markers. In certain embodiments, the model systems comprise in vitro cell lines, while in other embodiments, the model systems comprise animals (e.g., transgenic animals).
Additionally, pharmaceutical compositions containing the nucleic acids and/or proteins (ZFPs, TALEs, or fusion proteins comprising the ZFPs or TALEs) are also provided. For example, certain compositions include a nucleic acid comprising a sequence that encodes one of the DNA binding domain proteins described herein operably linked to a regulatory sequence, combined with a pharmaceutically acceptable carrier or diluent, wherein the regulatory sequence allows for expression of the nucleic acid in a cell. In certain embodiments, the DNA binding domains encoded are specific for a mutant RHO allele. Protein based compositions include one of more proteins as disclosed herein and a pharmaceutically acceptable carrier or diluent.
In yet another aspect also provided is an isolated cell comprising any of the proteins, polynucleotides and/or compositions as described herein.
In another aspect, provided herein are methods for treating and/or preventing ocular disorders using the compositions disclosed herein. In certain embodiments, the methods involve treatment of RP. In some embodiments, the methods involve compositions where the polynucleotides and/or proteins may be delivered using a viral vector, a non-viral vector (e.g., plasmid) and/or combinations thereof. In other embodiments, the compositions are delivered to retinal cells by sub-retinal injection. In some embodiments, the methods involve compositions comprising stem cell populations comprising a protein or altered with the nuclease of the invention.
These and other aspects will be readily apparent to the skilled artisan in light of disclosure as a whole.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 , panels A to C, depict generation of transgenic mice comprising a human Q344X-GFP transgene. FIG. 1A shows a schematic of the donor DNA used to introduce the human RHO mutant allele. “5′m” and “3′m” are the homology arms containing homology with the murine RHO gene. “HPRT-mini” indicates the selection marker. “H0344ter-EGFP” indicates the human mutant RHO allele fused to GFP. “LoxP” indicates the LoxP sites flanking the selection marker. FIG. 1B is a photograph of one of the chimeric mice containing the transgene. FIG. 1C is a gel displaying PCR amplifications of the murine and human RHO genes from progeny of the chimeric mice, and demonstrates the germline transmission of the transgene.
FIG. 2 , panels A and B, depict the effects on the photoreceptor layer in the indicated RP animals. FIG. 2A depicts photomicrographs of the photoreceptor layer for mice that were homozygous for the murine RHO allele (+/+), heterozygous for the murine allele and the human transgene (Q344X-hRHO-GFP/+), and homozygous for the human transgene (Q344X-hRHO-GFP/Q344X-hRHO-GFP). As can be seen in the photographs, the morphology of the photoreceptor layer is altered in the mice homozygous for the transgene. FIG. 2B is a graph displaying the thickness of the photoreceptor layer (ONL) over time for the three types of animals. As can be seen, the wt and heterozygous animals (depicted by the circles and squares) maintain a stable layer over time while the layer in the mice homozygous for the mutant human transgene degenerates rapidly (triangles).
FIG. 3 , panels A to C, depict rhodopsin expression in the indicated animals. FIG. 3A shows a Northern blot of retinal tissues demonstrating rhodopsin expression in +/+homozygotes, Q344X-hRHO-GFP/+heterozygotes, and Q344X-hRHO-GFP/Q344X-hRHO-GFP homozygotes. The probe used for these studies was the human rhodopsin cDNA. FIG. 3B shows a Western blot against proteins expressed in the retinas. The samples for the +/+homozygotes and the Q344X-hRHO-GFP/+heterozygotes were derived from tissue equivalent to one tenth of a retina, while the sample for the Q344X-hRHO-GFP/Q344X-hRHO-GFP homozygote contained proteins derived from 2 retinas. This demonstrates a decreased expression of the rhodopsin protein. FIG. 3C depicts a quantitation of this observation, and demonstrates that rhodopsin was undetectable in the retinas from the Q344X-hRHO-GFP/Q344X-hRHO-GFP homozygotes.
FIG. 4 depicts a schematic of the Q344X-hRHO-GFP knock in construct as well as the rescue or donor construct. Also shown are the sequences for the ZFN target site in the transgene (wild-type shown as “WT” (SEQ ID NO:36) and resistant is SEQ ID NO:37). The ZFN target sequence in the donor has been altered with silent mutations as shown to render the donor resistant to ZFN cleavage.
FIG. 5 shows a photomicrograph demonstrating GFP expression in retina whole mounts from the heterozygous animals treated with the ZFN and donor molecules. These data demonstrate that the nonsense mutation has been corrected in some cells, and demonstrates in vivo gene correction in the eye.



DETAILED DESCRIPTION
Disclosed herein are compositions and methods for modulating rhodopsin expression, for treating and/or preventing ocular disorders such as retinitis pigmentosa and for developing cell and animal models for such ocular disorders. In particular, RHO-modulating transcription factors or nucleases comprising DNA binding domains such as zinc finger proteins (ZFP TFs) or TAL effector domains (TALEs) and methods utilizing such proteins are provided for use in treating RP. For example, ZFP-TFs which repress expression of a mutant RHO allele are provided. In addition, zinc finger nucleases (ZFNs) or TALENs that modify the genomic structure of the genes associated with these disorders are provided. For example, nucleases that are able to specifically alter sequences of a mutant form of RHO are provided. These include compositions and methods using engineered zinc finger proteins, i.e., non-naturally occurring proteins which bind to a predetermined nucleic acid target sequence.
Thus, the methods and compositions described herein provide methods for treatment of ocular disorders, and these methods and compositions can comprise zinc finger and/or TALE transcription factors capable of modulating target genes as well as engineered nucleases (ZFNs and/or TALENs).
General
Practice of the methods, as well as preparation and use of the compositions disclosed herein employ, unless otherwise indicated, conventional techniques in molecular biology, biochemistry, chromatin structure and analysis, computational chemistry, cell culture, recombinant DNA and related fields as are within the skill of the art. These techniques are fully explained in the literature. See, for example, Sambrook et al. MOLECULAR CLONING: A LABORATORY MANUAL , Second edition, Cold Spring Harbor Laboratory Press, 1989 and Third edition, 2001; Ausubel et al., CURRENT PROTOCOLS IN MOLECULAR BIOLOGY , John Wiley & Sons, New York, 1987 and periodic updates; the series METHODS IN ENZYMOLOGY , Academic Press, San Diego; Wolfe, CHROMATIN STRUCTURE AND FUNCTION , Third edition, Academic Press, San Diego, 1998; METHODS IN ENZYMOLOGY , Vol. 304, “Chromatin” (P. M. Wassarman and A. P. Wolffe, eds.), Academic Press, San Diego, 1999; and METHODS IN MOLECULAR BIOLOGY , Vol. 119, “Chromatin Protocols” (P. B. Becker, ed.) Humana Press, Totowa, 1999.
DEFINITIONS
The terms “nucleic acid,” “polynucleotide,” and “oligonucleotide” are used interchangeably and refer to a deoxyribonucleotide or ribonucleotide polymer, in linear or circular conformation, and in either single- or double-stranded form. For the purposes of the present disclosure, these terms are not to be construed as limiting with respect to the length of a polymer. The terms can encompass known analogues of natural nucleotides, as well as nucleotides that are modified in the base, sugar and/or phosphate moieties (e.g., phosphorothioate backbones). In general, an analogue of a particular nucleotide has the same base-pairing specificity; i.e., an analogue of A will base-pair with T.
The terms “polypeptide,” “peptide” and “protein” are used interchangeably to refer to a polymer of amino acid residues. The term also applies to amino acid polymers in which one or more amino acids are chemical analogues or modified derivatives of a corresponding naturally-occurring amino acids.
“Binding” refers to a sequence-specific, non-covalent interaction between macromolecules (e.g., between a protein and a nucleic acid). Not all components of a binding interaction need be sequence-specific (e.g., contacts with phosphate residues in a DNA backbone), as long as the interaction as a whole is sequence-specific. Such interactions are generally characterized by a dissociation constant (K d ) of 10 −6 M −1 or lower. “Affinity” refers to the strength of binding: increased binding affinity being correlated with a lower K d .
A “binding protein” is a protein that is able to bind non-covalently to another molecule. A binding protein can bind to, for example, a DNA molecule (a DNA-binding protein), an RNA molecule (an RNA-binding protein) and/or a protein molecule (a protein-binding protein). In the case of a protein-binding protein, it can bind to itself (to form homodimers, homotrimers, etc.) and/or it can bind to one or more molecules of a different protein or proteins. A binding protein can have more than one type of binding activity. For example, zinc finger proteins have DNA-binding, RNA-binding and protein-binding activity.
A “zinc finger DNA binding protein” (or binding domain) is a protein, or a domain within a larger protein, that binds DNA in a sequence-specific manner through one or more zinc fingers, which are regions of amino acid sequence within the binding domain whose structure is stabilized through coordination of a zinc ion. The term zinc finger DNA binding protein is often abbreviated as zinc finger protein or ZFP.
Zinc finger binding domains or TALEN can be “engineered” to bind to a predetermined nucleotide sequence, for example via engineering (altering one or more amino acids) of the recognition helix region of a naturally occurring zinc finger or by engineering the RVDs of a TALEN protein. Therefore, engineered zinc finger proteins or TALENs are proteins that are non-naturally occurring. Non-limiting examples of methods for engineering zinc finger or TALEN proteins are design and selection. A designed zinc finger or TALEN protein is a protein not occurring in nature whose design/composition results principally from rational criteria. Rational criteria for design include application of substitution rules and computerized algorithms for processing information in a database storing information of existing ZFP designs and binding data. See, for example, U.S. Pat. Nos. 6,140,081; 6,453,242; and 6,534,261; see also WO 98/53058; WO 98/53059; WO 98/53060; WO 02/016536; WO 03/016496 and WO 2011/146121.
A “selected” zinc finger or TALEN protein is a protein not found in nature whose production results primarily from an empirical process such as phage display, interaction trap or hybrid selection. See e.g., U.S. Pat. No. 5,789,538; U.S. Pat. No. 5,925,523; U.S. Pat. No. 6,007,988; U.S. Pat. No. 6,013,453; U.S. Pat. No. 6,200,759; WO 95/19431; WO 96/06166; WO 98/53057; WO 98/54311; WO 00/27878; WO 01/60970; WO 01/88197; WO 02/099084 and WO 2011/146121 (U.S. Patent Publication No. 20110301073).
“Recombination” refers to a process of exchange of genetic information between two polynucleotides. For the purposes of this disclosure, “homologous recombination (HR)” refers to the specialized form of such exchange that takes place, for example, during repair of double-strand breaks in cells via homology-directed repair mechanisms. This process requires nucleotide sequence homology, uses a “donor” molecule to template repair of a “target” molecule (i.e., the one that experienced the double-strand break), and is variously known as “non-crossover gene conversion” or “short tract gene conversion,” because it leads to the transfer of genetic information from the donor to the target. Without wishing to be bound by any particular theory, such transfer can involve mismatch correction of heteroduplex DNA that forms between the broken target and the donor, and/or “synthesis-dependent strand annealing,” in which the donor is used to resynthesize genetic information that will become part of the target, and/or related processes. Such specialized HR often results in an alteration of the sequence of the target molecule such that part or all of the sequence of the donor polynucleotide is incorporated into the target polynucleotide.
In the methods of the disclosure, one or more targeted nucleases as described herein create a double-stranded break in the target sequence (e.g., cellular chromatin) at a predetermined site, and a “donor” polynucleotide, having homology to the nucleotide sequence in the region of the break, can be introduced into the cell. The presence of the double-stranded break has been shown to facilitate integration of the donor sequence. The donor sequence may be physically integrated or, alternatively, the donor polynucleotide is used as a template for repair of the break via homologous recombination, resulting in the introduction of all or part of the nucleotide sequence as in the donor into the cellular chromatin. Thus, a first sequence in cellular chromatin can be altered and, in certain embodiments, can be converted into a sequence present in a donor polynucleotide. Thus, the use of the terms “replace” or “replacement” can be understood to represent replacement of one nucleotide sequence by another, (i.e., replacement of a sequence in the informational sense), and does not necessarily require physical or chemical replacement of one polynucleotide by another.
In any of the methods described herein, additional pairs of zinc-finger proteins can be used for additional double-stranded cleavage of additional target sites within the cell.
In certain embodiments of methods for targeted recombination and/or replacement and/or alteration of a sequence in a region of interest in cellular chromatin, a chromosomal sequence is altered by homologous recombination with an exogenous “donor” nucleotide sequence. Such homologous recombination is stimulated by the presence of a double-stranded break in cellular chromatin, if sequences homologous to the region of the break are present.
In any of the methods described herein, the first nucleotide sequence (the “donor sequence”) can contain sequences that are homologous, but not identical, to genomic sequences in the region of interest, thereby stimulating homologous recombination to insert a non-identical sequence in the region of interest. Thus, in certain embodiments, portions of the donor sequence that are homologous to sequences in the region of interest exhibit between about 80 to 99% (or any integer therebetween) sequence identity to the genomic sequence that is replaced. In other embodiments, the homology between the donor and genomic sequence is higher than 99%, for example if only 1 nucleotide differs as between donor and genomic sequences of over 100 contiguous base pairs. In certain cases, a non-homologous portion of the donor sequence can contain sequences not present in the region of interest, such that new sequences are introduced into the region of interest. In these instances, the non-homologous sequence is generally flanked by sequences of 50-1,000 base pairs (or any integral value therebetween) or any number of base pairs greater than 1,000, that are homologous or identical to sequences in the region of interest. In other embodiments, the donor sequence is non-homologous to the first sequence, and is inserted into the genome by non-homologous recombination mechanisms.
Any of the methods described herein can be used for partial or complete inactivation of one or more target sequences in a cell by targeted integration of donor sequence that disrupts expression of the gene(s) of interest. Cell lines with partially or completely inactivated genes are also provided.
Furthermore, the methods of targeted integration as described herein can also be used to integrate one or more exogenous sequences. The exogenous nucleic acid sequence can comprise, for example, one or more genes or cDNA molecules, or any type of coding or noncoding sequence, as well as one or more control elements (e.g., promoters). In addition, the exogenous nucleic acid sequence may produce one or more RNA molecules (e.g., small hairpin RNAs (shRNAs), inhibitory RNAs (RNAis), microRNAs (miRNAs), etc.).
“Cleavage” refers to the breakage of the covalent backbone of a DNA molecule. Cleavage can be initiated by a variety of methods including, but not limited to, enzymatic or chemical hydrolysis of a phosphodiester bond. Both single-stranded cleavage and double-stranded cleavage are possible, and double-stranded cleavage can occur as a result of two distinct single-stranded cleavage events. DNA cleavage can result in the production of either blunt ends or staggered ends. In certain embodiments, fusion polypeptides are used for targeted double-stranded DNA cleavage.
A “cleavage half-domain” is a polypeptide sequence which, in conjunction with a second polypeptide (either identical or different) forms a complex having cleavage activity (preferably double-strand cleavage activity). The terms “first and second cleavage half-domains;” “+ and − cleavage half-domains” and “right and left cleavage half-domains” are used interchangeably to refer to pairs of cleavage half-domains that dimerize.
An “engineered cleavage half-domain” is a cleavage half-domain that has been modified so as to form obligate heterodimers with another cleavage half-domain (e.g., another engineered cleavage half-domain). See, also, U.S. Patent Publication Nos. 2005/0064474, 20070218528, 2008/0131962 and 2011/0201055, incorporated herein by reference in their entireties.
The term “sequence” refers to a nucleotide sequence of any length, which can be DNA or RNA; can be linear, circular or branched and can be either single-stranded or double stranded. The term “donor sequence” refers to a nucleotide sequence that is inserted into a genome. A donor sequence can be of any length, for example between 2 and 10,000 nucleotides in length (or any integer value therebetween or thereabove), preferably between about 100 and 1,000 nucleotides in length (or any integer therebetween), more preferably between about 200 and 500 nucleotides in length.
“Chromatin” is the nucleoprotein structure comprising the cellular genome. Cellular chromatin comprises nucleic acid, primarily DNA, and protein, including histones and non-histone chromosomal proteins. The majority of eukaryotic cellular chromatin exists in the form of nucleosomes, wherein a nucleosome core comprises approximately 150 base pairs of DNA associated with an octamer comprising two each of histones H2A, H2B, H3 and H4; and linker DNA (of variable length depending on the organism) extends between nucleosome cores. A molecule of histone H1 is generally associated with the linker DNA. For the purposes of the present disclosure, the term “chromatin” is meant to encompass all types of cellular nucleoprotein, both prokaryotic and eukaryotic. Cellular chromatin includes both chromosomal and episomal chromatin.
A “chromosome,” is a chromatin complex comprising all or a portion of the genome of a cell. The genome of a cell is often characterized by its karyotype, which is the collection of all the chromosomes that comprise the genome of the cell. The genome of a cell can comprise one or more chromosomes.
An “episome” is a replicating nucleic acid, nucleoprotein complex or other structure comprising a nucleic acid that is not part of the chromosomal karyotype of a cell. Examples of episomes include plasmids and certain viral genomes.
A “target site” or “target sequence” is a nucleic acid sequence that defines a portion of a nucleic acid to which a binding molecule will bind, provided sufficient conditions for binding exist. Exemplary target sites for various NT-3 targeted ZFPs are shown in Tables 2 and 3.
An “exogenous” molecule is a molecule that is not normally present in a cell, but can be introduced into a cell by one or more genetic, biochemical or other methods. “Normal presence in the cell” is determined with respect to the particular developmental stage and environmental conditions of the cell. Thus, for example, a molecule that is present only during embryonic development of muscle is an exogenous molecule with respect to an adult muscle cell. Similarly, a molecule induced by heat shock is an exogenous molecule with respect to a non-heat-shocked cell. An exogenous molecule can comprise, for example, a functioning version of a malfunctioning endogenous molecule or a malfunctioning version of a normally-functioning endogenous molecule.
An exogenous molecule can be, among other things, a small molecule, such as is generated by a combinatorial chemistry process, or a macromolecule such as a protein, nucleic acid, carbohydrate, lipid, glycoprotein, lipoprotein, polysaccharide, any modified derivative of the above molecules, or any complex comprising one or more of the above molecules. Nucleic acids include DNA and RNA, can be single- or double-stranded; can be linear, branched or circular; and can be of any length. Nucleic acids include those capable of forming duplexes, as well as triplex-forming nucleic acids. See, for example, U.S. Pat. Nos. 5,176,996 and 5,422,251. Proteins include, but are not limited to, DNA-binding proteins, transcription factors, chromatin remodeling factors, methylated DNA binding proteins, polymerases, methylases, demethylases, acetylases, deacetylases, kinases, phosphatases, integrases, recombinases, ligases, topoisomerases, gyrases and helicases.
An exogenous molecule can be the same type of molecule as an endogenous molecule, e.g., an exogenous protein or nucleic acid. For example, an exogenous nucleic acid can comprise an infecting viral genome, a plasmid or episome introduced into a cell, or a chromosome that is not normally present in the cell. Methods for the introduction of exogenous molecules into cells are known to those of skill in the art and include, but are not limited to, lipid-mediated transfer (i.e., liposomes, including neutral and cationic lipids), electroporation, direct injection, cell fusion, particle bombardment, calcium phosphate co-precipitation, DEAE-dextran-mediated transfer and viral vector-mediated transfer. An exogeneous molecule can also be the same type of molecule as an endogenous molecule but derived from a different species than the cell is derived from. For example, a human nucleic acid sequence may be introduced into a cell line originally derived from a mouse or hamster.
By contrast, an “endogenous” molecule is one that is normally present in a particular cell at a particular developmental stage under particular environmental conditions. For example, an endogenous nucleic acid can comprise a chromosome, the genome of a mitochondrion, chloroplast or other organelle, or a naturally-occurring episomal nucleic acid. Additional endogenous molecules can include proteins, for example, transcription factors and enzymes.
A “fusion” molecule is a molecule in which two or more subunit molecules are linked, preferably covalently. The subunit molecules can be the same chemical type of molecule, or can be different chemical types of molecules. Examples of the first type of fusion molecule include, but are not limited to, fusion proteins (for example, a fusion between a ZFP or TALE DNA-binding domain and one or more functional domains) and fusion nucleic acids (for example, a nucleic acid encoding the fusion protein described supra). Examples of the second type of fusion molecule include, but are not limited to, a fusion between a triplex-forming nucleic acid and a polypeptide, and a fusion between a minor groove binder and a nucleic acid.
Expression of a fusion protein in a cell can result from delivery of the fusion protein to the cell or by delivery of a polynucleotide encoding the fusion protein to a cell, wherein the polynucleotide is transcribed, and the transcript is translated, to generate the fusion protein. Trans-splicing, polypeptide cleavage and polypeptide ligation can also be involved in expression of a protein in a cell. Methods for polynucleotide and polypeptide delivery to cells are presented elsewhere in this disclosure.
A “gene,” for the purposes of the present disclosure, includes a DNA region encoding a gene product (see infra), as well as all DNA regions which regulate the production of the gene product, whether or not such regulatory sequences are adjacent to coding and/or transcribed sequences. Accordingly, a gene includes, but is not necessarily limited to, promoter sequences, terminators, translational regulatory sequences such as ribosome binding sites and internal ribosome entry sites, enhancers, silencers, insulators, boundary elements, replication origins, matrix attachment sites and locus control regions.
“Gene expression” refers to the conversion of the information, contained in a gene, into a gene product. A gene product can be the direct transcriptional product of a gene (e.g., mRNA, tRNA, rRNA, antisense RNA, ribozyme, structural RNA or any other type of RNA) or a protein produced by translation of an mRNA. Gene products also include RNAs which are modified, by processes such as capping, polyadenylation, methylation, and editing, and proteins modified by, for example, methylation, acetylation, phosphorylation, ubiquitination, ADP-ribosylation, myristilation, and glycosylation.
“Modulation” of gene expression refers to a change in the activity of a gene. Modulation of expression can include, but is not limited to, gene activation and gene repression. Genome editing (e.g., cleavage, alteration, inactivation, random mutation) can be used to modulate expression. Gene inactivation refers to any reduction in gene expression as compared to a cell that does not include a ZFP as described herein. Thus, gene inactivation may be partial or complete.
A “region of interest” is any region of cellular chromatin, such as, for example, a gene or a non-coding sequence within or adjacent to a gene, in which it is desirable to bind an exogenous molecule. Binding can be for the purposes of targeted DNA cleavage and/or targeted recombination. A region of interest can be present in a chromosome, an episome, an organellar genome (e.g., mitochondrial, chloroplast), or an infecting viral genome, for example. A region of interest can be within the coding region of a gene, within transcribed non-coding regions such as, for example, leader sequences, trailer sequences or introns, or within non-transcribed regions, either upstream or downstream of the coding region. A region of interest can be as small as a single nucleotide pair or up to 2,000 nucleotide pairs in length, or any integral value of nucleotide pairs.
“Eukaryotic” cells include, but are not limited to, fungal cells (such as yeast), plant cells, animal cells, mammalian cells and human cells (e.g., T-cells).
The terms “operative linkage” and “operatively linked” (or “operably linked”) are used interchangeably with reference to a juxtaposition of two or more components (such as sequence elements), in which the components are arranged such that both components function normally and allow the possibility that at least one of the components can mediate a function that is exerted upon at least one of the other components. By way of illustration, a transcriptional regulatory sequence, such as a promoter, is operatively linked to a coding sequence if the transcriptional regulatory sequence controls the level of transcription of the coding sequence in response to the presence or absence of one or more transcriptional regulatory factors. A transcriptional regulatory sequence is generally operatively linked in cis with a coding sequence, but need not be directly adjacent to it. For example, an enhancer is a transcriptional regulatory sequence that is operatively linked to a coding sequence, even though they are not contiguous.
With respect to fusion polypeptides, the term “operatively linked” can refer to the fact that each of the components performs the same function in linkage to the other component as it would if it were not so linked. For example, with respect to a fusion polypeptide in which a ZFP DNA-binding domain is fused to an activation domain, the ZFP DNA-binding domain and the activation domain are in operative linkage if, in the fusion polypeptide, the ZFP DNA-binding domain portion is able to bind its target site and/or its binding site, while the activation domain is able to upregulate gene expression. When a fusion polypeptide in which a ZFP DNA-binding domain is fused to a cleavage domain, the ZFP DNA-binding domain and the cleavage domain are in operative linkage if, in the fusion polypeptide, the ZFP DNA-binding domain portion is able to bind its target site and/or its binding site, while the cleavage domain is able to cleave DNA in the vicinity of the target site.
A “functional fragment” of a protein, polypeptide or nucleic acid is a protein, polypeptide or nucleic acid whose sequence is not identical to the full-length protein, polypeptide or nucleic acid, yet retains the same function as the full-length protein, polypeptide or nucleic acid. A functional fragment can possess more, fewer, or the same number of residues as the corresponding native molecule, and/or can contain one or more amino acid or nucleotide substitutions. Methods for determining the function of a nucleic acid (e.g., coding function, ability to hybridize to another nucleic acid) are well-known in the art. Similarly, methods for determining protein function are well-known. For example, the DNA-binding function of a polypeptide can be determined, for example, by filter-binding, electrophoretic mobility-shift, or immunoprecipitation assays. DNA cleavage can be assayed by gel electrophoresis. See Ausubel et al., supra. The ability of a protein to interact with another protein can be determined, for example, by co-immunoprecipitation, two-hybrid assays or complementation, both genetic and biochemical. See, for example, Fields et al. (1989) Nature 340:245-246; U.S. Pat. No. 5,585,245 and PCT WO 98/44350.
A “vector” is capable of transferring gene sequences to target cells. Typically, “vector construct,” “expression vector,” and “gene transfer vector,” mean any nucleic acid construct capable of directing the expression of a gene of interest and which can transfer gene sequences to target cells. Thus, the term includes cloning, and expression vehicles, as well as integrating vectors.
A “reporter gene” or “reporter sequence” refers to any sequence that produces a protein product that is easily measured, preferably although not necessarily in a routine assay. Suitable reporter genes include, but are not limited to, sequences encoding proteins that mediate antibiotic resistance (e.g., ampicillin resistance, neomycin resistance, G418 resistance, puromycin resistance), sequences encoding colored or fluorescent or luminescent proteins (e.g., green fluorescent protein, enhanced green fluorescent protein, red fluorescent protein, luciferase), and proteins which mediate enhanced cell growth and/or gene amplification (e.g., dihydrofolate reductase). Epitope tags include, for example, one or more copies of FLAG, His, myc, Tap, HA or any detectable amino acid sequence. “Expression tags” include sequences that encode reporters that may be operably linked to a desired gene sequence in order to monitor expression of the gene of interest.
DNA-Binding Domains
Described herein are compositions comprising a DNA-binding domain that specifically bind to a target site in any gene involved in an ocular disorder, including, but not limited to, RHO. Any DNA-binding domain can be used in the compositions and methods disclosed herein.
The sequence of the human and mouse rhodopsin proteins (both 348 amino acids) encoded by the RHO gene are shown below. The residues corresponding to the P23H, Q64X and Q344X point mutations are underlined and bolded:






Human rhodopsin (NCBI Reference Sequence: NP_000530.1, SEQ ID NO: 34):


MNGTEGPNFYVPFSNATGVVRS P FEYPQYYLAEPWQFSMLAAYMFLLIVLGFPINFLTLY



VTV Q HKKLRTPLNYILLNLAVADLFMVLGGFTSTLYTSLHGYFVFGPTGCNLEGFFATLG



GEIALWSLVVLAIERYVVVCKPMSNFRFGENHAIMGVAFTWVMALACAAPPLAGWSRYIP



EGLQCSCGIDYYTLKPEVNNESFVIYMFVVHFTIPMIIIFFCYGQLVFTVKEAAAQQQES



ATTQKAEKEVTRMVIIMVIAFLICWVPYASVAFYIFTHQGSNFGPIFMTIPAFFAKSAAI



YNPVIYIMMNKQFRNCMLTTICCGKNPLGDDEASATVSKTETS Q VAPA



Mouse rhodopsin (NCBI Reference Sequence: NP_663358.1, SEQ ID NO: 35):

MNGTEGPNFYVPFSNVTGVVRS P FEQPQYYLAEPWQFSMLAAYMFLLIVLGFPINFLTL



YVTV Q HKKLRTPLNYILLNLAVTDLFMVFGGFTTTLYTSLHGYFVFGPTGCNLEGFFAT



LGGEIALWSLVVLAIERYVVVCKPMSNFRFGENHAIMGVVFTWIMALACAAPPLVGWSR



YIPEGMQCSCGIDYYTLKPEVNNESFVIYMFVVHFTIPMIVIFFCYGQLVFTVKEAAAQ



QQESATTQKAEKEVTRMVIIMVIFFLICWLPYASVAFYIFTHQGSNFGPIFMTLPAFFA



KSSSIYNPVIYIMLNKQFRNCMLTTLCCGKNPLGDDDASATASKTETS Q VAPA
































In certain embodiments, the DNA binding domain comprises a zinc finger protein. Preferably, the zinc finger protein is non-naturally occurring in that it is engineered to bind to a target site of choice. See, for example, Beerli et al. (2002) Nature Biotechnol. 20:135-141; Pabo et al. (2001) Ann. Rev. Biochem. 70:313-340; Isalan et al. (2001) Nature Biotechnol. 19:656-660; Segal et al. (2001) Curr. Opin. Biotechnol. 12:632-637; Choo et al. (2000) Curr. Opin. Struct. Biol. 10:411-416; U.S. Pat. Nos. 6,453,242; 6,534,261; 6,599,692; 6,503,717; 6,689,558; 7,030,215; 6,794,136; 7,067,317; 7,262,054; 7,070,934; 7,361,635; 7,253,273; and U.S. Patent Publication Nos. 2005/0064474; 2007/0218528; 2005/0267061, all incorporated herein by reference in their entireties.
An engineered zinc finger binding domain can have a novel binding specificity, compared to a naturally-occurring zinc finger protein. Engineering methods include, but are not limited to, rational design and various types of selection. Rational design includes, for example, using databases comprising triplet (or quadruplet) nucleotide sequences and individual zinc finger amino acid sequences, in which each triplet or quadruplet nucleotide sequence is associated with one or more amino acid sequences of zinc fingers which bind the particular triplet or quadruplet sequence. See, for example, co-owned U.S. Pat. Nos. 6,453,242 and 6,534,261, incorporated by reference herein in their entireties.
Exemplary selection methods, including phage display and two-hybrid systems, are disclosed in U.S. Pat. Nos. 5,789,538; 5,925,523; 6,007,988; 6,013,453; 6,410,248; 6,140,466; 6,200,759; and 6,242,568; as well as WO 98/37186; WO 98/53057; WO 00/27878; WO 01/88197 and GB 2,338,237. In addition, enhancement of binding specificity for zinc finger binding domains has been described, for example, in co-owned WO 02/077227.
In addition, as disclosed in these and other references, zinc finger domains and/or multi-fingered zinc finger proteins may be linked together using any suitable linker sequences, including for example, linkers of 5 or more amino acids in length. See, also, U.S. Pat. Nos. 6,479,626; 6,903,185; and 7,153,949 for exemplary linker sequences 6 or more amino acids in length. The proteins described herein may include any combination of suitable linkers between the individual zinc fingers of the protein. In addition, enhancement of binding specificity for zinc finger binding domains has been described, for example, in co-owned WO 02/077227.
Selection of target sites; ZFPs and methods for design and construction of fusion proteins (and polynucleotides encoding same) are known to those of skill in the art and described in detail in U.S. Pat. Nos. 6,140,0815; 789,538; 6,453,242; 6,534,261; 5,925,523; 6,007,988; 6,013,453; 6,200,759; WO 95/19431; WO 96/06166; WO 98/53057; WO 98/54311; WO 00/27878; WO 01/60970 WO 01/88197; WO 02/099084; WO 98/53058; WO 98/53059; WO 98/53060; WO 02/016536 and WO 03/016496.
In addition, as disclosed in these and other references, zinc finger domains and/or multi-fingered zinc finger proteins may be linked together using any suitable linker sequences, including for example, linkers of 5 or more amino acids in length. See, also, U.S. Pat. Nos. 6,479,626; 6,903,185; and 7,153,949 for exemplary linker sequences 6 or more amino acids in length. The proteins described herein may include any combination of suitable linkers between the individual zinc fingers of the protein.
In certain embodiments, the DNA binding domain is an engineered zinc finger protein that binds (in a sequence-specific manner) to a target site in a RHO gene and modulates expression of RHO. The ZFPs can bind selectively to either a mutant RHO allele or a wild-type RHO sequence. RHO target sites typically include at least one zinc finger but can include a plurality of zinc fingers (e.g., 2, 3, 4, 5, 6 or more fingers). Usually, the ZFPs include at least three fingers. Certain of the ZFPs include four, five or six fingers. The ZFPs that include three fingers typically recognize a target site that includes 9 or 10 nucleotides; ZFPs that include four fingers typically recognize a target site that includes 12 to 14 nucleotides; while ZFPs having six fingers can recognize target sites that include 18 to 21 nucleotides. The ZFPs can also be fusion proteins that include one or more regulatory domains, which domains can be transcriptional activation or repression domains.
Specific examples of RHO-targeted ZFPs are disclosed in Table 1. The first column in this table is an internal reference name (number) for a ZFP and corresponds to the same name in column 1 of Table 2. “F” refers to the finger and the number following “F” refers which zinc finger (e.g., “F1” refers to finger 1).





TABLE 1



RHO-targeted zinc finger proteins




SBS


#
Design










F1
F2
F3
F4
F5
F6



23950
QSGALAR
RSDHLTT
RSDVLSE
QSGSLTR
QSGALAR
RSDNLRE


(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID


NO: 1)
NO: 2)
NO: 3)
NO: 4)
NO: 1)
NO: 5)



22529
TSGSLSR
QSGDLTR
RSDALST
DRSTRTK
N/A
N/A


(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID




NO: 6)
NO: 7)
NO: 8)
NO: 9)





22524
QSGDLTR
DRSDLSR
NSDDLIE
TSSHLSR
RSDALAR
N/A


(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID



NO: 7)
NO: 10)
NO: 11)
NO: 12)
NO: 13)




23947
DRSDLSR
RSDNLTR
QSSNLAR
DRSNLTR
N/A
N/A


(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID




NO: 10)
NO: 14)
NO: 15)
NO: 16)





23966
RSDVLSE
RNQHRKT
ERGTLAR
RSDHLTT
DRSNLSR
QSGHLSR


(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID


NO: 3)
NO: 17)
NO: 18)
NO: 2)
NO: 19)
NO: 20)



23974
DRSDLSR
QSSDLRR
QSSDLSR
RSDNLRE
DRSSRKR
N/A


(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID
(SEQ ID



NO: 10)
NO: 21)
NO: 22)
NO: 5)
NO: 23)
















































The sequence and location for the target sites of these proteins are disclosed in Table 2. Table 2 shows target sequences for the indicated zinc finger proteins. Nucleotides in the target site that are contacted by the ZFP recognition helices are indicated in uppercase letters; non-contacted nucleotides indicated in lowercase.





TABLE 2



Target sites for RHO-ZFPs




SBS #
Target Site



23950
gcCAGGTAGTACTGTGGGTActcgaagg_(SEQ ID NO: 24)



22529
gaGCCATGGCAGTTctccatgctggccg_(SEQ ID NO: 25)



22524
caGTGGGTTCTtGCCGCAgcagatggtg_(SEQ ID NO: 26)



23947
gtGACGATGAGGCCtctgctaccgtgtc_(SEQ ID NO: 27)



23966
ggGGAGACAGGGCAAGGCTGgcagagag_(SEQ ID NO: 28)



23974
atGTCCAGGCTGCTGCCtcggtcccatt_(SEQ ID NO: 29)































In certain embodiments, the DNA-binding domain comprises a naturally occurring or engineered (non-naturally occurring) TAL effector DNA binding domain. See, e.g., U.S. Patent Publication No. 20110301073, incorporated by reference in its entirety herein. The plant pathogenic bacteria of the genus Xanthomonas are known to cause many diseases in important crop plants. Pathogenicity of Xanthomonas depends on a conserved type III secretion (T3S) system which injects more than 25 different effector proteins into the plant cell. Among these injected proteins are transcription activator-like effectors (TALE) which mimic plant transcriptional activators and manipulate the plant transcriptome (see Kay et al (2007) Science 318:648-651). These proteins contain a DNA binding domain and a transcriptional activation domain. One of the most well characterized TALEs is AvrBs3 from Xanthomonas campestgris pv. Vesicatoria (see Bonas et al (1989) Mol Gen Genet 218: 127-136 and WO2010079430). TALEs contain a centralized domain of tandem repeats, each repeat containing approximately 34 amino acids, which are key to the DNA binding specificity of these proteins. In addition, they contain a nuclear localization sequence and an acidic transcriptional activation domain (for a review see Schornack S, et al (2006) J Plant Physiol 163(3): 256-272). In addition, in the phytopathogenic bacteria Ralstonia solanacearum two genes, designated brg11 and hpx17 have been found that are homologous to the AvrBs3 family of Xanthomonas in the R. solanacearum biovar 1 strain GMI1000 and in the biovar 4 strain RS1000 (See Heuer et al (2007) Appl and Envir Micro 73(13): 4379-4384). These genes are 98.9% identical in nucleotide sequence to each other but differ by a deletion of 1,575 bp in the repeat domain of hpx17. However, both gene products have less than 40% sequence identity with AvrBs3 family proteins of Xanthomonas.
Specificity of these TALEs depends on the sequences found in the tandem repeats. The repeated sequence comprises approximately 102 bp and the repeats are typically 91-100% homologous with each other (Bonas et al, ibid). Polymorphism of the repeats is usually located at positions 12 and 13 and there appears to be a one-to-one correspondence between the identity of the hypervariable diresidues at positions 12 and 13 with the identity of the contiguous nucleotides in the TALE's target sequence (see Moscou and Bogdanove, (2009) Science 326:1501 and Boch et al (2009) Science 326:1509-1512). Experimentally, the code for DNA recognition of these TALEs has been determined such that an HD sequence at positions 12 and 13 leads to a binding to cytosine (C), NG binds to T, NI to A, C, G or T, NN binds to A or G, and IG binds to T. These DNA binding repeats have been assembled into proteins with new combinations and numbers of repeats, to make artificial transcription factors that are able to interact with new sequences and activate the expression of a non-endogenous reporter gene in plant cells (Boch et al, ibid). Engineered TAL proteins have been linked to a FokI cleavage half domain to yield a TAL effector domain nuclease fusion (TALEN) exhibiting activity in a yeast reporter assay (plasmid based target). Christian et al ((2010)< Genetics epub 10.1534/genetics.110.120717). See, also, U.S. Patent Publication No. 20110301073, incorporated by reference in its entirety.
Alternatively, the DNA-binding domain may be derived from a nuclease. For example, the recognition sequences of homing endonucleases and meganucleases such as I-SceI, I-CeuI, PI-PspI, PI-Sce, I-SceIV, I-CsmI, I-PanI, I-SceII, I-PpoI, I-SceIII, I-CreI, I-TevI, I-TevII and I-TevIII are known. See also U.S. Pat. No. 5,420,032; U.S. Pat. No. 6,833,252; Belfort et al. (1997) Nucleic Acids Res. 25:3379-3388; Dujon et al. (1989) Gene 82:115-118; Perler et al. (1994) Nucleic Acids Res. 22, 1125-1127; Jasin (1996) Trends Genet. 12:224-228; Gimble et al. (1996) J. Mol. Biol. 263:163-180; Argast et al. (1998) J. Mol. Biol. 280:345-353 and the New England Biolabs catalogue. In addition, the DNA-binding specificity of homing endonucleases and meganucleases can be engineered to bind non-natural target sites. See, for example, Chevalier et al. (2002) Molec. Cell 10:895-905; Epinat et al. (2003) Nucleic Acids Res. 31:2952-2962; Ashworth et al. (2006) Nature 441:656-659; Paques et al. (2007) Current Gene Therapy 7:49-66; U.S. Patent Publication No. 20070117128.
Fusion Proteins
Fusion proteins comprising DNA-binding proteins (e.g., ZFPs or TALEs) as described herein and a heterologous regulatory (functional) domain (or functional fragment thereof) are also provided. Common domains include, e.g., transcription factor domains (activators, repressors, co-activators, co-repressors), silencers, oncogenes (e.g., myc, jun, fos, myb, max, mad, rel, ets, bcl, myb, mos family members etc.); DNA repair enzymes and their associated factors and modifiers; DNA rearrangement enzymes and their associated factors and modifiers; chromatin associated proteins and their modifiers (e.g. kinases, acetylases and deacetylases); and DNA modifying enzymes (e.g., methyltransferases, topoisomerases, helicases, ligases, kinases, phosphatases, polymerases, endonucleases) and their associated factors and modifiers. U.S. Patent Application Publication Nos. 20050064474; 20060188987 and 2007/0218528 for details regarding fusions of DNA-binding domains and nuclease cleavage domains, incorporated by reference in their entireties herein
Suitable domains for achieving activation include the HSV VP16 activation domain (see, e.g., Hagmann et al., J. Virol. 71, 5952-5962 (1997)) nuclear hormone receptors (see, e.g., Torchia et al., Curr. Opin. Cell. Biol. 10:373-383 (1998)); the p65 subunit of nuclear factor kappa B (Bitko & Barik, J. Virol. 72:5610-5618 (1998) and Doyle & Hunt, Neuroreport 8:2937-2942 (1997)); Liu et al., Cancer Gene Ther. 5:3-28 (1998)), or artificial chimeric functional domains such as VP64 (Beerli et al., (1998) Proc. Natl. Acad. Sci. USA 95:14623-33), and degron (Molinari et al., (1999) EMBO J. 18, 6439-6447). Additional exemplary activation domains include, Oct 1, Oct-2A, Sp1, AP-2, and CTF1 (Seipel et al., EMBO J. 11, 4961-4968 (1992) as well as p300, CBP, PCAF, SRC1 PvALF, AtHD2A and ERF-2. See, for example, Robyr et al. (2000) Mol. Endocrinol. 14:329-347; Collingwood et al. (1999) J. Mol. Endocrinol. 23:255-275; Leo et al. (2000) Gene 245:1-11; Manteuffel-Cymborowska (1999) Acta Biochim. Pol. 46:77-89; McKenna et al. (1999) J. Steroid Biochem. Mol. Biol. 69:3-12; Malik et al. (2000) Trends Biochem. Sci. 25:277-283; and Lemon et al. (1999) Curr. Opin. Genet. Dev. 9:499-504. Additional exemplary activation domains include, but are not limited to, OsGAI, HALF-1, C1, AP1, ARF-5, -6, -7, and -8, CPRF1, CPRF4, MYC-RP/GP, and TRAB1. See, for example, Ogawa et al. (2000) Gene 245:21-29; Okanami et al. (1996) Genes Cells 1:87-99; Goff et al. (1991) Genes Dev. 5:298-309; Cho et al. (1999) Plant Mol. Biol. 40:419-429; Ulmason et al. (1999) Proc. Natl. Acad. Sci. USA 96:5844-5849; Sprenger-Haussels et al. (2000) Plant J. 22:1-8; Gong et al. (1999) Plant Mol. Biol. 41:33-44; and Hobo et al. (1999) Proc. Natl. Acad. Sci. USA 96:15,348-15,353.
It will be clear to those of skill in the art that, in the formation of a fusion protein (or a nucleic acid encoding same) between a DNA-binding domain and a functional domain, either an activation domain or a molecule that interacts with an activation domain is suitable as a functional domain. Essentially any molecule capable of recruiting an activating complex and/or activating activity (such as, for example, histone acetylation) to the target gene is useful as an activating domain of a fusion protein. Insulator domains, localization domains, and chromatin remodeling proteins such as ISWI-containing domains and/or methyl binding domain proteins suitable for use as functional domains in fusion molecules are described, for example, in co-owned U.S. Patent Applications 2002/0115215 and 2003/0082552 and in co-owned WO 02/44376.
Exemplary repression domains include, but are not limited to, KRAB A/B, KOX, TGF-beta-inducible early gene (TIEG), v-erbA, SID, MBD2, MBD3, members of the DNMT family (e.g., DNMT1, DNMT3A, DNMT3B), Rb, and MeCP2. See, for example, Bird et al. (1999) Cell 99:451-454; Tyler et al. (1999) Cell 99:443-446; Knoepfler et al. (1999) Cell 99:447-450; and Robertson et al. (2000) Nature Genet. 25:338-342. Additional exemplary repression domains include, but are not limited to, ROM2 and AtHD2A. See, for example, Chem et al. (1996) Plant Cell 8:305-321; and Wu et al. (2000) Plant J. 22:19-27.
Fusion molecules are constructed by methods of cloning and biochemical conjugation that are well known to those of skill in the art. Fusion molecules comprise a DNA-binding domain and a functional domain (e.g., a transcriptional activation or repression domain). Fusion molecules also optionally comprise nuclear localization signals (such as, for example, that from the SV40 medium T-antigen) and epitope tags (such as, for example, FLAG and hemagglutinin). Fusion proteins (and nucleic acids encoding them) are designed such that the translational reading frame is preserved among the components of the fusion.
Fusions between a polypeptide component of a functional domain (or a functional fragment thereof) on the one hand, and a non-protein DNA-binding domain (e.g., antibiotic, intercalator, minor groove binder, nucleic acid) on the other, are constructed by methods of biochemical conjugation known to those of skill in the art. See, for example, the Pierce Chemical Company (Rockford, Ill.) Catalogue. Methods and compositions for making fusions between a minor groove binder and a polypeptide have been described. Mapp et al. (2000) Proc. Natl. Acad. Sci. USA 97:3930-3935.
In certain embodiments, the target site bound by the DNA binding domain is present in an accessible region of cellular chromatin. Accessible regions can be determined as described, for example, in co-owned International Publication WO 01/83732. If the target site is not present in an accessible region of cellular chromatin, one or more accessible regions can be generated as described in co-owned WO 01/83793. In additional embodiments, the DNA-binding domain of a fusion molecule is capable of binding to cellular chromatin regardless of whether its target site is in an accessible region or not. For example, such DNA-binding domains are capable of binding to linker DNA and/or nucleosomal DNA. Examples of this type of “pioneer” DNA binding domain are found in certain steroid receptor and in hepatocyte nuclear factor 3 (HNF3). Cordingley et al. (1987) Cell 48:261-270; Pina et al. (1990) Cell 60:719-731; and Cirillo et al. (1998) EMBO J. 17:244-254.
The fusion molecule may be formulated with a pharmaceutically acceptable carrier, as is known to those of skill in the art. See, for example, Remington's Pharmaceutical Sciences, 17th ed., 1985; and co-owned WO 00/42219.
The functional component/domain of a fusion molecule can be selected from any of a variety of different components capable of influencing transcription of a gene once the fusion molecule binds to a target sequence via its DNA binding domain. Hence, the functional component can include, but is not limited to, various transcription factor domains, such as activators, repressors, co-activators, co-repressors, and silencers.
Additional exemplary functional domains are disclosed, for example, in co-owned U.S. Pat. No. 6,534,261 and US Patent Application Publication No. 2002/0160940.
Functional domains that are regulated by exogenous small molecules or ligands may also be selected. For example, RheoSwitch® technology may be employed wherein a functional domain only assumes its active conformation in the presence of the external RheoChem™ ligand (see for example US 20090136465). Thus, the ZFP may be operably linked to the regulatable functional domain wherein the resultant activity of the ZFP-TF is controlled by the external ligand.
Nucleases
In certain embodiments, the fusion protein comprises a DNA-binding binding domain and cleavage (nuclease) domain. As such, gene modification can be achieved using a nuclease, for example an engineered nuclease. Engineered nuclease technology is based on the engineering of naturally occurring DNA-binding proteins. For example, engineering of homing endonucleases with tailored DNA-binding specificities has been described. Chames et al. (2005) Nucleic Acids Res 33(20):e178; Arnould et al. (2006) J. Mol. Biol. 355:443-458. In addition, engineering of ZFPs has also been described. See, e.g., U.S. Pat. Nos. 6,534,261; 6,607,882; 6,824,978; 6,979,539; 6,933,113; 7,163,824; and 7,013,219.
In addition, ZFPs and TALEs have been fused to nuclease domains to create ZFNs—a functional entity that is able to recognize its intended nucleic acid target through its engineered (ZFP or TALE) DNA binding domain and cause the DNA to be cut near the ZFP/TALE binding site via the nuclease activity. See, e.g., Kim et al. (1996) Proc Nat'l Acad Sci USA 93(3):1156-1160; U.S. Patent Publication No. 20110301073. ZFNs and TALENs have been used for genome modification in a variety of organisms. See, for example, United States Patent Publications 20030232410; 20050208489; 20050026157; 20050064474; 20060188987; 20060063231; 20110301073 and International Publication WO 07/014,275.
Thus, the methods and compositions described herein are broadly applicable and may involve any nuclease of interest. Non-limiting examples of nucleases include meganucleases, TALENs and zinc finger nucleases (ZFNs). The nuclease may comprise heterologous DNA-binding and cleavage domains (e.g., zinc finger nucleases; TALENs; meganuclease DNA-binding domains with heterologous cleavage domains) or, alternatively, the DNA-binding domain of a naturally-occurring nuclease may be altered to bind to a selected target site (e.g., a meganuclease that has been engineered to bind to site different than the cognate binding site).
In certain embodiments, the nuclease is a meganuclease (homing endonuclease). Naturally-occurring meganucleases recognize 15-40 base-pair cleavage sites and are commonly grouped into four families: the LAGLIDADG family, the GIY-YIG family, the His-Cyst box family and the HNH family. Exemplary homing endonucleases include I-SceI, I-CeuI, PI-PspI, PI-Sce, I-SceIV, I-CsmI, I-PanI, I-SceII, I-PpoI, I-SceIII, I-CreI, I-TevI, I-TevII and I-TevIII. Their recognition sequences are known. See also U.S. Pat. No. 5,420,032; U.S. Pat. No. 6,833,252; Belfort et al. (1997) Nucleic Acids Res. 25:3379-3388; Dujon et al. (1989) Gene 82:115-118; Perler et al. (1994) Nucleic Acids Res. 22, 1125-1127; Jasin (1996) Trends Genet. 12:224-228; Gimble et al. (1996) J. Mol. Biol. 263:163-180; Argast et al. (1998) J. Mol. Biol. 280:345-353 and the New England Biolabs catalogue.
DNA-binding domains from naturally-occurring meganucleases, primarily from the LAGLIDADG family, have been used to promote site-specific genome modification in plants, yeast, Drosophila, mammalian cells and mice, but this approach has been limited to the modification of either homologous genes that conserve the meganuclease recognition sequence (Monet et al. (1999), Biochem. Biophysics. Res. Common. 255: 88-93) or to pre-engineered genomes into which a recognition sequence has been introduced (Route et al. (1994), Mol. Cell. Biol. 14: 8096-106; Chilton et al. (2003), Plant Physiology. 133: 956-65; Puchta et al. (1996), Proc. Natl. Acad. Sci. USA 93: 5055-60; Rong et al. (2002), Genes Dev. 16: 1568-81; Gouble et al. (2006), J. Gene Med. 8(5):616-622). Accordingly, attempts have been made to engineer meganucleases to exhibit novel binding specificity at medically or biotechnologically relevant sites (Porteus et al. (2005), Nat. Biotechnol. 23: 967-73; Sussman et al. (2004), J. Mol. Biol. 342: 31-41; Epinat et al. (2003), Nucleic Acids Res. 31: 2952-62; Chevalier et al. (2002) Molec. Cell 10:895-905; Epinat et al. (2003) Nucleic Acids Res. 31:2952-2962; Ashworth et al. (2006) Nature 441:656-659; Paques et al. (2007) Current Gene Therapy 7:49-66; U.S. Patent Publication Nos. 20070117128; 20060206949; 20060153826; 20060078552; and 20040002092). In addition, naturally-occurring or engineered DNA-binding domains from meganucleases have also been operably linked with a cleavage domain from a heterologous nuclease (e.g., FokI).
In other embodiments, the DNA-binding domain comprises a naturally occurring or engineered (non-naturally occurring) TAL effector DNA binding domain. The plant pathogenic bacteria of the genus Xanthomonas are known to cause many diseases in important crop plants. Pathogenicity of Xanthomonas depends on a conserved type III secretion (T3S) system which injects more than 25 different effector proteins into the plant cell. Among these injected proteins are transcription activator-like (TAL) effectors which mimic plant transcriptional activators and manipulate the plant transcriptome (see Kay et al (2007) Science 318:648-651). These proteins contain a DNA binding domain and a transcriptional activation domain. One of the most well characterized TAL-effectors is AvrBs3 from Xanthomonas campestgris pv. Vesicatoria (see Bonas et al (1989) Mol Gen Genet 218: 127-136 and WO2010079430). TAL-effectors contain a centralized domain of tandem repeats, each repeat containing approximately 34 amino acids, which are key to the DNA binding specificity of these proteins. In addition, they contain a nuclear localization sequence and an acidic transcriptional activation domain (for a review see Schornack S, et al (2006) J Plant Physiol 163(3): 256-272). In addition, in the phytopathogenic bacteria Ralstonia solanacearum two genes, designated brg11 and hpx17 have been found that are homologous to the AvrBs3 family of Xanthomonas in the R. solanacearum biovar 1 strain GMI1000 and in the biovar 4 strain RS1000 (See Heuer et al (2007) Appl and Envir Micro 73(13): 4379-4384). These genes are 98.9% identical in nucleotide sequence to each other but differ by a deletion of 1,575 bp in the repeat domain of hpx17. However, both gene products have less than 40% sequence identity with AvrBs3 family proteins of Xanthomonas . See, e.g., U.S. Provisional Application Nos. 61/395,836 and 61/401,429, filed May 17, 2010 and Aug. 21, 2010, respectively.
Specificity of these TAL effectors depends on the sequences found in the tandem repeats. The repeated sequence comprises approximately 102 bp and the repeats are typically 91-100% homologous with each other (Bonas et al, ibid). Polymorphism of the repeats is usually located at positions 12 and 13 and there appears to be a one-to-one correspondence between the identity of the hypervariable diresidues at positions 12 and 13 with the identity of the contiguous nucleotides in the TAL-effector's target sequence (see Moscou and Bogdanove, (2009) Science 326:1501 and Boch et al (2009) Science 326:1509-1512). Experimentally, the natural code for DNA recognition of these TAL-effectors has been determined such that an HD sequence at positions 12 and 13 leads to a binding to cytosine (C), NG binds to T, NI to A, C, G or T, NN binds to A or G, and ING binds to T. These DNA binding repeats have been assembled into proteins with new combinations and numbers of repeats, to make artificial transcription factors that are able to interact with new sequences and activate the expression of a non-endogenous reporter gene in plant cells (Boch et al, ibid). Engineered TAL proteins have been linked to a FokI cleavage half domain to yield a TAL effector domain nuclease fusion (TALEN) exhibiting activity in a yeast reporter assay (plasmid based target). Christian et al ((2010)< Genetics epub 10.1534/genetics.110.120717).
In other embodiments, the nuclease is a zinc finger nuclease (ZFN). ZFNs comprise a zinc finger protein that has been engineered to bind to a target site in a gene of choice and cleavage domain or a cleavage half-domain.
As described in detail above, zinc finger and/or TALE binding domains can be engineered to bind to a sequence of choice. See, for example, Beerli et al. (2002) Nature Biotechnol. 20:135-141; Pabo et al. (2001) Ann. Rev. Biochem. 70:313-340; Isalan et al. (2001) Nature Biotechnol. 19:656-660; Segal et al. (2001) Curr. Opin. Biotechnol. 12:632-637; Choo et al. (2000) Curr. Opin. Struct. Biol. 10:411-416; U.S. Patent Publication No. 20110301073. An engineered zinc finger or TALE binding domain can have a novel binding specificity, compared to a naturally-occurring zinc finger or TALE protein. Engineering methods include, but are not limited to, rational design and various types of selection. Rational design includes, for example, using databases comprising triplet (or quadruplet) nucleotide sequences and individual zinc finger amino acid sequences, in which each triplet or quadruplet nucleotide sequence is associated with one or more amino acid sequences of zinc fingers which bind the particular triplet or quadruplet sequence. See, for example, co-owned U.S. Pat. Nos. 6,453,242 and 6,534,261, incorporated by reference herein in their entireties.
Exemplary selection methods, including phage display and two-hybrid systems, are disclosed in U.S. Pat. Nos. 5,789,538; 5,925,523; 6,007,988; 6,013,453; 6,410,248; 6,140,466; 6,200,759; and 6,242,568; as well as WO 98/37186; WO 98/53057; WO 00/27878; WO 01/88197 and GB 2,338,237. In addition, enhancement of binding specificity for zinc finger binding domains has been described, for example; in co-owned WO 02/077227.
Selection of target sites; DNA binding proteins binding to these target sites and methods for design and construction of fusion proteins (and polynucleotides encoding same) are known to those of skill in the art and described in detail in U.S. Patent Application Publication Nos. 20050064474; 20060188987 and 20110301073, incorporated by reference in their entireties herein.
In addition, as disclosed in these and other references, zinc finger domains and/or multi-fingered zinc finger proteins may be linked together using any suitable linker sequences, including for example, linkers of 5 or more amino acids in length (e.g., TGEKP (SEQ ID NO:30), TGGQRP (SEQ ID NO:31), TGQKP (SEQ ID NO:32), and/or TGSQKP (SEQ ID NO:33)). See, e.g., U.S. Pat. Nos. 6,479,626; 6,903,185; and 7,153,949 for exemplary linker sequences 6 or more amino acids in length. The proteins described herein may include any combination of suitable linkers between the individual zinc fingers of the protein. See, also, U.S. Provisional Patent Application No. 61/343,729.
Nucleases such as ZFNs, TALENs and/or meganucleases also comprise a nuclease (cleavage domain, cleavage half-domain). As noted above, the cleavage domain may be heterologous to the DNA-binding domain, for example a zinc finger DNA-binding domain and a cleavage domain from a nuclease or a meganuclease DNA-binding domain and cleavage domain from a different nuclease. Heterologous cleavage domains can be obtained from any endonuclease or exonuclease. Exemplary endonucleases from which a cleavage domain can be derived include, but are not limited to, restriction endonucleases and homing endonucleases. See, for example, 2002-2003 Catalogue, New England Biolabs, Beverly, Mass.; and Belfort et al. (1997) Nucleic Acids Res. 25:3379-3388. Additional enzymes which cleave DNA are known (e.g., S1 Nuclease; mung bean nuclease; pancreatic DNase I; micrococcal nuclease; yeast HO endonuclease; see also Linn et al. (eds.) Nucleases , Cold Spring Harbor Laboratory Press, 1993). One or more of these enzymes (or functional fragments thereof) can be used as a source of cleavage domains and cleavage half-domains.
Similarly, a cleavage half-domain can be derived from any nuclease or portion thereof, as set forth above, that requires dimerization for cleavage activity. In general, two fusion proteins are required for cleavage if the fusion proteins comprise cleavage half-domains. Alternatively, a single protein comprising two cleavage half-domains can be used. The two cleavage half-domains can be derived from the same endonuclease (or functional fragments thereof), or each cleavage half-domain can be derived from a different endonuclease (or functional fragments thereof). In addition, the target sites for the two fusion proteins are preferably disposed, with respect to each other, such that binding of the two fusion proteins to their respective target sites places the cleavage half-domains in a spatial orientation to each other that allows the cleavage half-domains to form a functional cleavage domain, e.g., by dimerizing. Thus, in certain embodiments, the near edges of the target sites are separated by 5-8 nucleotides or by 15-18 nucleotides. However any integral number of nucleotides or nucleotide pairs can intervene between two target sites (e.g., from 2 to 50 nucleotide pairs or more). In general, the site of cleavage lies between the target sites.
Restriction endonucleases (restriction enzymes) are present in many species and are capable of sequence-specific binding to DNA (at a recognition site), and cleaving DNA at or near the site of binding. Certain restriction enzymes (e.g., Type IIS) cleave DNA at sites removed from the recognition site and have separable binding and cleavage domains. For example, the Type IIS enzyme Fok I catalyzes double-stranded cleavage of DNA, at 9 nucleotides from its recognition site on one strand and 13 nucleotides from its recognition site on the other. See, for example, U.S. Pat. Nos. 5,356,802; 5,436,150 and 5,487,994; as well as Li et al. (1992) Proc. Natl. Acad. Sci. USA 89:4275-4279; Li et al. (1993) Proc. Natl. Acad. Sci. USA 90:2764-2768; Kim et al. (1994a) Proc. Natl. Acad. Sci. USA 91:883-887; Kim et al. (1994b) J. Biol. Chem. 269:31,978-31,982. Thus, in one embodiment, fusion proteins comprise the cleavage domain (or cleavage half-domain) from at least one Type IIS restriction enzyme and one or more zinc finger binding domains, which may or may not be engineered.
An exemplary Type IIS restriction enzyme, whose cleavage domain is separable from the binding domain, is Fok I. This particular enzyme is active as a dimer. Bitinaite et al. (1998) Proc. Natl. Acad. Sci. USA 95: 10,570-10,575. Accordingly, for the purposes of the present disclosure, the portion of the FokI enzyme used in the disclosed fusion proteins is considered a cleavage half-domain. Thus, for targeted double-stranded cleavage and/or targeted replacement of cellular sequences using zinc finger-Fok I fusions, two fusion proteins, each comprising a FokI cleavage half-domain, can be used to reconstitute a catalytically active cleavage domain. Alternatively, a single polypeptide molecule containing a zinc finger binding domain and two FokI cleavage half-domains can also be used. Parameters for targeted cleavage and targeted sequence alteration using zinc finger-Fok I fusions are provided elsewhere in this disclosure.
A cleavage domain or cleavage half-domain can be any portion of a protein that retains cleavage activity, or that retains the ability to multimerize (e.g., dimerize) to form a functional cleavage domain.
Exemplary Type IIS restriction enzymes are described in International Publication WO 07/014,275, incorporated herein in its entirety. Additional restriction enzymes also contain separable binding and cleavage domains, and these are contemplated by the present disclosure. See, for example, Roberts et al. (2003) Nucleic Acids Res. 31:418-420.
In certain embodiments, the cleavage domain comprises one or more engineered cleavage half-domain (also referred to as dimerization domain mutants) that minimize or prevent homodimerization, as described, for example, in U.S. Patent Publication Nos. 20050064474 and 20060188987 20060188987; 20080131962; 20090305346 and 20110201055, and in International Patent Publication WO2005/014791, the disclosures of all of which are incorporated by reference in their entireties herein. Amino acid residues at positions 446, 447, 479, 483, 484, 486, 487, 490, 491, 496, 498, 499, 500, 531, 534, 537, and 538 of Fok I are all targets for influencing dimerization of the Fok I cleavage half-domains. Exemplary engineered cleavage half-domains of Fok I that form obligate heterodimers include a pair in which a first cleavage half-domain includes mutations at amino acid residues at positions 490 and 538 of Fok I and a second cleavage half-domain includes mutations at amino acid residues 486 and 499.
Thus, in one embodiment, a mutation at 490 replaces Glu (E) with Lys (K); the mutation at 538 replaces Iso (I) with Lys (K); the mutation at 486 replaced Gln (Q) with Glu (E); and the mutation at position 499 replaces Iso (I) with Lys (K). Specifically, the engineered cleavage half-domains described herein were prepared by mutating positions 490 (E→K) and 538 (I→K) in one cleavage half-domain to produce an engineered cleavage half-domain designated “E490K:I538K” and by mutating positions 486 (Q→E) and 499 (I→L) in another cleavage half-domain to produce an engineered cleavage half-domain designated “Q486E:I499L”. The engineered cleavage half-domains described herein are obligate heterodimer mutants in which aberrant cleavage is minimized or abolished. See, e.g., U.S. Patent Publication Nos. 2008/0131962 and 2011/0201055, the disclosures of which are incorporated by reference in their entireties for all purposes.
In certain embodiments, the engineered cleavage half-domain comprises mutations at positions 486, 499 and 496 (numbered relative to wild-type FokI), for instance mutations that replace the wild type Gln (Q) residue at position 486 with a Glu (E) residue, the wild type Iso (I) residue at position 499 with a Leu (L) residue and the wild-type Asn (N) residue at position 496 with an Asp (D) or Glu (E) residue (also referred to as a “ELD” and “ELE” domains, respectively). In other embodiments, the engineered cleavage half-domain comprises mutations at positions 490, 538 and 537 (numbered relative to wild-type FokI), for instance mutations that replace the wild type Glu (E) residue at position 490 with a Lys (K) residue, the wild type Iso (I) residue at position 538 with a Lys (K) residue, and the wild-type His (H) residue at position 537 with a Lys (K) residue or a Arg (R) residue (also referred to as “KKK” and “KKR” domains, respectively). In other embodiments, the engineered cleavage half-domain comprises mutations at positions 490 and 537 (numbered relative to wild-type FokI), for instance mutations that replace the wild type Glu (E) residue at position 490 with a Lys (K) residue and the wild-type His (H) residue at position 537 with a Lys (K) residue or a Arg (R) residue (also referred to as “KIK” and “KIR” domains, respectively). (See U.S. Patent Publication No. 20110201055).
Engineered cleavage half-domains described herein can be prepared using any suitable method, for example, by site-directed mutagenesis of wild-type cleavage half-domains (Fok I) as described in U.S. Patent Publication Nos. 20050064474 and 20080131962.
Alternatively, nucleases may be assembled in vivo at the nucleic acid target site using so-called “split-enzyme” technology (see e.g. U.S. Patent Publication No. 20090068164). Components of such split enzymes may be expressed either on separate expression constructs, or can be linked in one open reading frame where the individual components are separated, for example, by a self-cleaving 2A peptide or IRES sequence. Components may be individual zinc finger binding domains or domains of a meganuclease nucleic acid binding domain.
In some embodiments, the DNA binding domain is an engineered domain from a TAL effector similar to those derived from the plant pathogens Xanthomonas (see Boch et al, (2009) Science 326: 1509-1512 and Moscou and Bogdanove, (2009) Science 326: 1501) and Ralstonia (see Heuer et al (2007) Applied and Environmental Microbiology 73(13): 4379-4384).
Nucleases (e.g., ZFNs) can be screened for activity prior to use, for example in a yeast-based chromosomal system as described in WO 2009/042163 and 20090068164. Nuclease expression constructs can be readily designed using methods known in the art. See, e.g., United States Patent Publications 20030232410; 20050208489; 20050026157; 20050064474; 20060188987; 20060063231; and International Publication WO 07/014,275. Expression of the nuclease may be under the control of a constitutive promoter or an inducible promoter, for example the galactokinase promoter which is activated (de-repressed) in the presence of raffinose and/or galactose and repressed in presence of glucose.
Delivery
The proteins (e.g., ZFPs or TALEs), polynucleotides encoding same and compositions comprising the proteins and/or polynucleotides described herein may be delivered to a target cell by any suitable means including, for example, by injection of ZFP TF, TALE, TALEN or ZFN mRNA. Suitable cells include but not limited to eukaryotic and prokaryotic cells and/or cell lines. Non-limiting examples of such cells or cell lines generated from such cells include COS, CHO (e.g., CHO-S, CHO-K1, CHO-DG44, CHO-DUXB11, CHO-DUKX, CHOK1SV), VERO, MDCK, WI38, V79, B14AF28-G3, BHK, HaK, NS0, SP2/0-Ag14, HeLa, HEK293 (e.g., HEK293-F, HEK293-H, HEK293-T), and perC6 cells as well as insect cells such as Spodoptera fugiperda (Sf), or fungal cells such as Saccharomyces, Pichia and Schizosaccharomyces . In certain embodiments, the cell line is a CHO-K1, MDCK or HEK293 cell line. Suitable cells also include stem cells such as, by way of example, embryonic stem cells, induced pluripotent stem cells, hematopoietic stem cells, neuronal stem cells and mesenchymal stem cells.
Methods of delivering proteins comprising DNA binding domains as described herein are described, for example, in U.S. Pat. Nos. 6,453,242; 6,503,717; 6,534,261; 6,599,692; 6,607,882; 6,689,558; 6,824,978; 6,933,113; 6,979,539; 7,013,219; and 7,163,824, the disclosures of all of which are incorporated by reference herein in their entireties.
Zinc finger or TALE proteins as described herein may also be delivered using vectors containing sequences encoding one or more of the zinc finger or TALE protein(s). Any vector systems may be used including, but not limited to, plasmid vectors, retroviral vectors, lentiviral vectors, adenovirus vectors, poxvirus vectors; herpesvirus vectors and adeno-associated virus vectors, etc. See, also, U.S. Pat. Nos. 6,534,261; 6,607,882; 6,824,978; 6,933,113; 6,979,539; 7,013,219; and 7,163,824, incorporated by reference herein in their entireties. Furthermore, it will be apparent that any of these vectors may comprise one or more zinc finger protein-encoding sequences. Thus, when one or more ZFPs are introduced into the cell, the ZFPs may be carried on the same vector or on different vectors. When multiple vectors are used, each vector may comprise a sequence encoding one or multiple ZFPs.
Conventional viral and non-viral based gene transfer methods can be used to introduce nucleic acids encoding engineered ZFPs in cells (e.g., mammalian cells) and target tissues. Such methods can also be used to administer nucleic acids encoding ZFPs to cells in vitro. In certain embodiments, nucleic acids encoding ZFPs are administered for in vivo or ex vivo gene therapy uses. Non-viral vector delivery systems include DNA plasmids, naked nucleic acid, and nucleic acid complexed with a delivery vehicle such as a liposome or poloxamer. Viral vector delivery systems include DNA and RNA viruses, which have either episomal or integrated genomes after delivery to the cell. For a review of gene therapy procedures, see Anderson, Science 256:808-813 (1992); Nabel & Felgner, TIBTECH 11:211-217 (1993); Mitani & Caskey, TIBTECH 11:162-166 (1993); Dillon, TIBTECH 11:167-175 (1993); Miller, Nature 357:455-460 (1992); Van Brunt, Biotechnology 6(10):1149-1154 (1988); Vigne, Restorative Neurology and Neuroscience 8:35-36 (1995); Kremer & Perricaudet, British Medical Bulletin 51(1):31-44 (1995); Haddada et al., in Current Topics in Microbiology and Immunology Doerfler and Böhm (eds.) (1995); and Yu et al., Gene Therapy 1:13-26 (1994).
Methods of non-viral delivery of nucleic acids include electroporation, lipofection, microinjection, biolistics, virosomes, liposomes, immunoliposomes, polycation or lipid:nucleic acid conjugates, naked DNA, artificial virions, and agent-enhanced uptake of DNA. Sonoporation using, e.g., the Sonitron 2000 system (Rich-Mar) can also be used for delivery of nucleic acids.
Additional exemplary nucleic acid delivery systems include those provided by Amaxa Biosystems (Cologne, Germany), Maxcyte, Inc. (Rockville, Md.), BTX Molecular Delivery Systems (Holliston, Mass.) and Copernicus Therapeutics Inc, (see for example U.S. Pat. No. 6,008,336). Lipofection is described in e.g., U.S. Pat. Nos. 5,049,386; 4,946,787; and 4,897,355) and lipofection reagents are sold commercially (e.g., Transfectam™ and Lipofectin™). Cationic and neutral lipids that are suitable for efficient receptor-recognition lipofection of polynucleotides include those of Felgner, WO 91/17424, WO 91/16024. Delivery can be to cells (ex vivo administration) or target tissues (in vivo administration).
The preparation of lipid:nucleic acid complexes, including targeted liposomes such as immunolipid complexes, is well known to one of skill in the art (see, e.g., Crystal, Science 270:404-410 (1995); Blaese et al., Cancer Gene Ther. 2:291-297 (1995); Behr et al., Bioconjugate Chem. 5:382-389 (1994); Remy et al. Bioconjugate Chem. 5:647-654 (1994); Gao et al., Gene Therapy 2:710-722 (1995); Ahmad et al., Cancer Res. 52:4817-4820 (1992); U.S. Pat. Nos. 4,186,183, 4,217,344, 4,235,871, 4,261,975, 4,485,054, 4,501,728, 4,774,085, 4,837,028, and 4,946,787).
Additional methods of delivery include the use of packaging the nucleic acids to be delivered into EnGeneIC delivery vehicles (EDVs). These EDVs are specifically delivered to target tissues using bispecific antibodies where one arm of the antibody has specificity for the target tissue and the other has specificity for the EDV. The antibody brings the EDVs to the target cell surface and then the EDV is brought into the cell by endocytosis. Once in the cell, the contents are released (see MacDiarmid et al (2009) Nature Biotechnology 27(7):643).
The use of RNA or DNA viral based systems for the delivery of nucleic acids encoding engineered ZFPs take advantage of highly evolved processes for targeting a virus to specific cells in the body and trafficking the viral payload to the nucleus. Viral vectors can be administered directly to patients (in vivo) or they can be used to treat cells in vitro and the modified cells are administered to patients (ex vivo). Conventional viral based systems for the delivery of ZFPs include, but are not limited to, retroviral, lentivirus, adenoviral, adeno-associated, vaccinia and herpes simplex virus vectors for gene transfer. Integration in the host genome is possible with the retrovirus, lentivirus, and adeno-associated virus gene transfer methods, often resulting in long term expression of the inserted transgene. Additionally, high transduction efficiencies have been observed in many different cell types and target tissues.
The tropism of a retrovirus can be altered by incorporating foreign envelope proteins, expanding the potential target population of target cells. Lentiviral vectors are retroviral vectors that are able to transduce or infect non-dividing cells and typically produce high viral titers. Selection of a retroviral gene transfer system depends on the target tissue. Retroviral vectors are comprised of cis-acting long terminal repeats with packaging capacity for up to 6-10 kb of foreign sequence. The minimum cis-acting LTRs are sufficient for replication and packaging of the vectors, which are then used to integrate the therapeutic gene into the target cell to provide permanent transgene expression. Widely used retroviral vectors include those based upon murine leukemia virus (MuLV), gibbon ape leukemia virus (GaLV), Simian Immunodeficiency virus (SIV), human immunodeficiency virus (HIV), and combinations thereof (see, e.g., Buchscher et al. J. Virol. 66:2731-2739 (1992); Johann et al., J. Virol. 66:1635-1640 (1992); Sommerfelt et al., Virol. 176:58-59 (1990); Wilson et al., J. Virol. 63:2374-2378 (1989); Miller et al., J. Virol. 65:2220-2224 (1991); PCT/US94/05700).
In applications in which transient expression is preferred, adenoviral based systems can be used. Adenoviral based vectors are capable of very high transduction efficiency in many cell types and do not require cell division. With such vectors, high titer and high levels of expression have been obtained. This vector can be produced in large quantities in a relatively simple system. Adeno-associated virus (“AAV”) vectors are also used to transduce cells with target nucleic acids, e.g., in the in vitro production of nucleic acids and peptides, and for in vivo and ex vivo gene therapy procedures (see, e.g., West et al., Virology 160:38-47 (1987); U.S. Pat. No. 4,797,368; WO 93/24641; Kotin, Human Gene Therapy 5:793-801 (1994); Muzyczka, J. Clin. Invest. 94:1351 (1994). Construction of recombinant AAV vectors are described in a number of publications, including U.S. Pat. No. 5,173,414; Tratschin et al., Mol. Cell. Biol. 5:3251-3260 (1985); Tratschin, et al., Mol. Cell. Biol. 4:2072-2081 (1984); Hermonat & Muzyczka, PNAS 81:6466-6470 (1984); and Samulski et al., J. Virol. 63:03822-3828 (1989).
At least six viral vector approaches are currently available for gene transfer in clinical trials, which utilize approaches that involve complementation of defective vectors by genes inserted into helper cell lines to generate the transducing agent.
pLASN and MFG-S are examples of retroviral vectors that have been used in clinical trials (Dunbar et al., Blood 85:3048-305 (1995); Kohn et al., Nat. Med. 1:1017-102 (1995); Malech et al. PNAS 94:22 12133-12138 (1997)). PA317/pLASN was the first therapeutic vector used in a gene therapy trial. (Blaese et al., Science 270:475-480 (1995)). Transduction efficiencies of 50% or greater have been observed for MFG-S packaged vectors. (Ellem et al., Immunol Immunother. 44(1):10-20 (1997); Dranoff et al., Hum. Gene Ther. 1:111-2 (1997).
Recombinant adeno-associated virus vectors (rAAV) are a promising alternative gene delivery systems based on the defective and nonpathogenic parvovirus adeno-associated type 2 virus. All vectors are derived from a plasmid that retains only the AAV 145 bp inverted terminal repeats flanking the transgene expression cassette. Efficient gene transfer and stable transgene delivery due to integration into the genomes of the transduced cell are key features for this vector system. (Wagner et al., Lancet 351:9117 1702-3 (1998), Kearns et al., Gene Ther. 9:748-55 (1996)). Other AAV serotypes, including AAV1, AAV3, AAV4, AAV5, AAV6 and AAV8, can also be used in accordance with the present invention.
Replication-deficient recombinant adenoviral vectors (Ad) can be produced at high titer and readily infect a number of different cell types. Most adenovirus vectors are engineered such that a transgene replaces the Ad E1a, E1b, and/or E3 genes; subsequently the replication defective vector is propagated in human 293 cells that supply deleted gene function in trans. Ad vectors can transduce multiple types of tissues in vivo, including nondividing, differentiated cells such as those found in liver, kidney and muscle. Conventional Ad vectors have a large carrying capacity. An example of the use of an Ad vector in a clinical trial involved polynucleotide therapy for antitumor immunization with intramuscular injection (Sterman et al., Hum. Gene Ther. 7:1083-9 (1998)). Additional examples of the use of adenovirus vectors for gene transfer in clinical trials include Rosenecker et al., Infection 24:1 5-10 (1996); Sterman et al., Hum. Gene Ther. 9:7 1083-1089 (1998); Welsh et al., Hum. Gene Ther. 2:205-18 (1995); Alvarez et al., Hum. Gene Ther. 5:597-613 (1997); Topf et al., Gene Ther. 5:507-513 (1998); Sterman et al., Hum. Gene Ther. 7:1083-1089 (1998).
Packaging cells are used to form virus particles that are capable of infecting a host cell. Such cells include 293 cells, which package adenovirus, and ψ2 cells or PA317 cells, which package retrovirus. Viral vectors used in gene therapy are usually generated by a producer cell line that packages a nucleic acid vector into a viral particle. The vectors typically contain the minimal viral sequences required for packaging and subsequent integration into a host (if applicable), other viral sequences being replaced by an expression cassette encoding the protein to be expressed. The missing viral functions are supplied in trans by the packaging cell line. For example, AAV vectors used in gene therapy typically only possess inverted terminal repeat (ITR) sequences from the AAV genome which are required for packaging and integration into the host genome. Viral DNA is packaged in a cell line, which contains a helper plasmid encoding the other AAV genes, namely rep and cap, but lacking ITR sequences. The cell line is also infected with adenovirus as a helper. The helper virus promotes replication of the AAV vector and expression of AAV genes from the helper plasmid. The helper plasmid is not packaged in significant amounts due to a lack of ITR sequences. Contamination with adenovirus can be reduced by, e.g., heat treatment to which adenovirus is more sensitive than AAV.
In many gene therapy applications, it is desirable that the gene therapy vector be delivered with a high degree of specificity to a particular tissue type. Accordingly, a viral vector can be modified to have specificity for a given cell type by expressing a ligand as a fusion protein with a viral coat protein on the outer surface of the virus. The ligand is chosen to have affinity for a receptor known to be present on the cell type of interest. For example, Han et al., Proc. Natl. Acad. Sci. USA 92:9747-9751 (1995), reported that Moloney murine leukemia virus can be modified to express human heregulin fused to gp70, and the recombinant virus infects certain human breast cancer cells expressing human epidermal growth factor receptor. This principle can be extended to other virus-target cell pairs, in which the target cell expresses a receptor and the virus expresses a fusion protein comprising a ligand for the cell-surface receptor. For example, filamentous phage can be engineered to display antibody fragments (e.g., FAB or Fv) having specific binding affinity for virtually any chosen cellular receptor. Although the above description applies primarily to viral vectors, the same principles can be applied to nonviral vectors. Such vectors can be engineered to contain specific uptake sequences which favor uptake by specific target cells.
Gene therapy vectors can be delivered in vivo by administration to an individual patient, typically by systemic administration (e.g., intravenous, intraperitoneal, intramuscular, subdermal, or intracranial infusion) or topical application, as described below. Alternatively, vectors can be delivered to cells ex vivo, such as cells explanted from an individual patient (e.g., lymphocytes, bone marrow aspirates, tissue biopsy) or universal donor hematopoietic stem cells, followed by reimplantation of the cells into a patient, usually after selection for cells which have incorporated the vector. Vectors may also be administered to retinal tissue through the use of a biodegradable or non-biodegradable intraocular drug delivery system or matrix. (See for example U.S. Pat. No. 6,331,313 or Hatefli and Amsden (2002) Journal of Controlled Release, 80, 1-3: 9-28).
Ex vivo cell transfection for diagnostics, research, or for gene therapy (e.g., via re-infusion of the transfected cells into the host organism) is well known to those of skill in the art. In a preferred embodiment, cells are isolated from the subject organism, transfected with a ZFP nucleic acid (gene or cDNA), and re-infused back into the subject organism (e.g., patient). Various cell types suitable for ex vivo transfection are well known to those of skill in the art (see, e.g., Freshney et al., Culture of Animal Cells, A Manual of Basic Technique (3rd ed. 1994)) and the references cited therein for a discussion of how to isolate and culture cells from patients).
In one embodiment, stem cells are used in ex vivo procedures for cell transfection and gene therapy. The advantage to using stem cells is that they can be differentiated into other cell types in vitro, or can be introduced into a mammal (such as the donor of the cells) where they will engraft in the bone marrow. Methods for differentiating CD34+ cells in vitro into clinically important immune cell types using cytokines such a GM-CSF, IFN-γ and TNF-α are known (see Inaba et al., J. Exp. Med. 176:1693-1702 (1992)).
Stem cells are isolated for transduction and differentiation using known methods. For example, stem cells are isolated from bone marrow cells by panning the bone marrow cells with antibodies which bind unwanted cells, such as CD4+ and CD8+ (T cells), CD45+ (panB cells), GR-1 (granulocytes), and Tad (differentiated antigen presenting cells) (see Inaba et al., J. Exp. Med. 176:1693-1702 (1992)).
Stem cells that have been modified may also be used in some embodiments. For example, neuronal stem cells that have been made resistant to apoptosis may be used as therapeutic compositions where the stem cells also contain the ZFP TFs of the invention. Resistance to apoptosis may come about, for example, by knocking out BAX and/or BAK using BAX- or BAK-specific ZFNs (see, U.S. patent application Ser. No. 12/456,043) in the stem cells, or those that are disrupted in a caspase, again using caspase-6 specific ZFNs for example. These cells can be transfected with the ZFP TFs that are known to regulate mutant or wild-type RHO.
Vectors (e.g., retroviruses, adenoviruses, liposomes, etc.) containing therapeutic nucleic acids as described herein can also be administered directly to an organism for transduction of cells in vivo. Alternatively, naked DNA can be administered. Administration is by any of the routes normally used for introducing a molecule into ultimate contact with blood or tissue cells including, but not limited to, injection, infusion, topical application and electroporation. Suitable methods of administering such nucleic acids are available and well known to those of skill in the art, and, although more than one route can be used to administer a particular composition, a particular route can often provide a more immediate and more effective reaction than another route.
Methods for introduction of DNA into hematopoietic stem cells are disclosed, for example, in U.S. Pat. No. 5,928,638. Vectors useful for introduction of transgenes into hematopoietic stem cells, e.g., CD34 + cells, include adenovirus Type 35.
Vectors suitable for introduction of transgenes into immune cells (e.g., T-cells) include non-integrating lentivirus vectors. See, for example, Ory et al. (1996) Proc. Natl. Acad. Sci. USA 93:11382-11388; Dull et al. (1998) J. Virol. 72:8463-8471; Zuffery et al. (1998) J. Virol. 72:9873-9880; Follenzi et al. (2000) Nature Genetics 25:217-222.
Pharmaceutically acceptable carriers are determined in part by the particular composition being administered, as well as by the particular method used to administer the composition. Accordingly, there is a wide variety of suitable formulations of pharmaceutical compositions available, as described below (see, e.g., Remington's Pharmaceutical Sciences, 17th ed., 1989).
As noted above, the disclosed methods and compositions can be used in any type of cell including, but not limited to, prokaryotic cells, fungal cells, Archaeal cells, plant cells, insect cells, animal cells, vertebrate cells, mammalian cells and human cells. Suitable cell lines for protein expression are known to those of skill in the art and include, but are not limited to COS, CHO (e.g., CHO-S, CHO-K1, CHO-DG44, CHO-DUXB11), VERO, MDCK, W138, V79, B14AF28-G3, BHK, HaK, NS0, SP2/0-Ag14, HeLa, HEK293 (e.g., HEK293-F, HEK293-H, HEK293-T), perC6, insect cells such as Spodoptera fugiperda (Sf), and fungal cells such as Saccharomyces, Pischia and Schizosaccharomyces . Progeny, variants and derivatives of these cell lines can also be used.
Applications
The disclosed compositions and methods can be used for any application in which it is desired to modulate genes associated with ocular disorders and/or to correct mutations in genes associated with these disorders. In particular, these methods and compositions can be used where modulation of a RHO allele is desired, including but not limited to, therapeutic and research applications.
Diseases and conditions which RHO repressing ZFP or TALE TFs can be used as therapeutic agents include, but are not limited to, RP. Additionally, methods and compositions comprising nucleases specific for correcting mutant alleles of RHO can be used as a therapeutic for the treatment of RP.
Methods and compositions for the treatment of RP also include compositions comprising a nuclease specific for a mutant RHO allele and a donor nucleic acid molecule comprising a wt RHO sequence for in vivo gene correction. Donor nucleic acids can alternately contain silent mutations to be resistant to nuclease cleavage. These compositions may be administered through intraocular injection for in situ treatment of retinal cells for example.
Methods and compositions for the treatment of RP also include stem cell compositions wherein a mutant copy of the RHO allele within the stem cells has been modified to a wild-type RHO allele using a RHO-specific nuclease and a donor nucleic acid.
The methods and compositions of the invention are also useful for the design and implementation of in vitro and in vivo models, for example, animal models of ocular disorders, which allows for the study of these disorders.
EXAMPLES
Example 1
Design and Construction of RHO-Targeted Zinc Finger Nucleases (ZFNs)
Zinc finger nucleases targeted to RHO were engineered essentially as described in U.S. Pat. No. 6,534,261. Table 1 shows the recognition helices DNA binding domain of exemplary RHO-targeted ZFPs. The designed DNA-binding domains contain four to six zinc fingers, recognizing specified target sequences (see Table 2). Nucleotides in the target site that are contacted by the ZFP recognition helices are indicated in uppercase letters; non-contacted nucleotides indicated in lowercase.
The Cel-I assay (Surveyor™, Transgenomics. Perez et al, (2008) Nat. Biotechnol. 26: 808-816 and Guschin et al, (2010) Methods Mol Biol. 649:247-56), was used where PCR-amplification of the target site was followed by quantification of insertions and deletions (indels) using the mismatch detecting enzyme Cel-I (Yang et al, (2000) Biochemistry 39, 3533-3541) which provides a lower-limit estimate of DSB frequency.
The results for the RHO-specific pairs are presented below in Table 3, which also discloses the location of the cleavage site, and specific RHO mutations in the vicinity of the cleavage site that may be modified by ZFN-driven DNA repair.





TABLE 3



Activity of RHO-specific ZFN pairs









Target




ZFN pair
location
RHO Mutation
% NHEJ











23950/22529
Exon 1
Q64X
8.7%


22524/23947
Exon 5
Q344X
11.5%


23966/23974
Intron 1

9.3%




























Example 2
In Vivo Repair of the Q344X RHO Mutation in a Murine Model, of RP
The Q344X mutation in rhodopsin was described in 1997 by Kremer et al (see Graefes Arch Clin Exp Opthalmol 235(9): 575-583) and has a stop codon at position 344, located in exon 5 resulting in a non-functioning rhodopsin protein.
To investigate the potential for correcting this mutation in vivo, a murine model was generated in which the mice had one wild type murine rhodopsin allele and one human allele containing the Q344X mutation. Photoreceptor cells are terminally differentiated neurons that are capable of repairing double strand breaks by either NHEJ or HDR. In addition, the human allele for insertion was fused with a sequence encoding eGFP such that correction of the mutation would result in read through of the GFP sequence. The transgene (Q344X-hRho-GFP) shown in FIG. 1A was introduced into murine embryonic stem cells using standard methodology. The insert contained a HPRT gene to allow for selection of the stem cells containing an integrated transgene, and homology regions with the murine RHO gene, but the HPRT sequence was flanked by LoxP sites for its subsequent removal.
The transgenic chimeric mice are shown in FIG. 1B . These chimeras were then bred and demonstrated germline transmission as illustrated in FIG. 1C . Thus the human transgene comprising the mutated RHO-GFP fusion was inserted into the murine genome.
The retinas of the progeny of the chimeric mice were then characterized for photoreceptor morphology and to examine the thickness of the photoreceptor layer in their retinas. Retinas of 4 week old mice were examined by standard protocols, and the results are presented in FIG. 2 . FIG. 2A demonstrates that the photoreceptor layer in mice that were homozygous for the wt murine allele looked similar to that for the heterozygotes carrying on wt murine allele and one Q344X-hRHO-GFP allele. In contrast, those mice that were homozygous for the mutant allele displayed abnormal morphology in the photoreceptor layer, and the thickness of this layer degenerated over time ( FIG. 2B ).
The expression level of the mutant transgene was then analyzed. Using standard methodologies, the mRNA expression was examined and demonstrated that the gene was being expressed (see FIG. 3A ). Next, the protein levels of the rhodopsin were examined by Western analysis using standard techniques. The antibody used recognized the N-terminus of rhodopsin and was able to detect both murine and human rhodopsin. The results are shown in FIG. 3B , and demonstrate that expression at the protein level was decreased in both the heterozygous mice and those that were homozygous for the human transgene. This observation was then quantitated by spectroscopy and demonstrated that the heterozygotes displayed decreased rhodopsin expression, and the mice that were homozygous for the transgene showed no detectable rhodopsin present.
Next, gene correction was performed in the heterozygous mice. FIG. 4 depicts a schematic of the knock-in construct of the Q344X-hRHO-GFP transgene for the murine RHO allele, as well as a schematic of the donor. For this experiment, silent mutations were introduced in the wt human RHO donor DNA such that once incorporated, the corrected sequence would be resistant to cleavage by the 22524/23947 ZFN pair (see FIG. 4 , ZFN recognition sequences: Wt and resistant). The donor further comprised a truncated GFP sequence and coding sequence including parts of exons 4 and 5 to provide homology arms.
The donor nucleic acid and ZFN expression vectors were introduced in AAV constructs via subretinal injection. Heterozygous mice were injected at three weeks of age, and at 5 weeks, retinas were harvested and tissue whole mounts were screened for GFP fluorescence using standard methodology. The tissues were subject to confocal microscopy and projections of a Z-stack are shown in FIG. 5 . Expression of GFP was readily apparent and indicated that the nonsense mutation was corrected.
All patents, patent applications and publications mentioned herein are hereby incorporated by reference in their entirety.
Although disclosure has been provided in some detail by way of illustration and example for the purposes of clarity of understanding, it will be apparent to those skilled in the art that various changes and modifications can be practiced without departing from the spirit or scope of the disclosure. Accordingly, the foregoing descriptions and examples should not be construed as limiting.