Rhodopsin Gene Correction and Gene Knockout in Rod Cells

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Strategies for correction and knockout of the rhodopsin gene in rod photoreceptor cells will be tested to determine what it takes to manipulate the structure and expression of deleterious genes in terminally differentiated neurons. We seek to understand the fundamental cellular processes that allow targeted gene repair and mutation in these cells, as well as those that can control expression of toxic proteins. In the process of gaining this understanding, we aim to develop effective methods for treating autosomal dominant retinitis pigmentosa (ADRP) caused by defects in the rhodopsin gene. Successful therapies for ADRP will provide a paradigm for treatment of dominant eye diseases and other neurodegenerative disorders. Mice are a natural choice for these studies because their eye physiology resembles that of humans;ADRP disease genes cause retinal degeneration in mice more quickly than in humans and large animals, allowing rapid testing of efficacy; and mouse genomes can be readily manipulated. Previously, we fused the complete human rhodopsin genethe ultimate target for therapytothe GFP gene to generate a visible marker for rhodopsin expression that localizes properly to rod outer segments. Here, we propose to use our existing wild type rhodopsin-GTP mice and generate four new mouse lines carrying mutant human rhodopsin-GFP genes to provide targets for various kinds of genetic manipulation. These modified human rhodopsin-GFP genes will include three defined ADRP mutationsP23H, Q64ter, and Q344terand a gene that carries an internal duplication. Adeno-associated virus vectors will be used to deliver novel reagents for rhodopsin correction and knockout. For gene correction, we will test segments of rhodopsin DNA in the presence and absence of genes for zinc-finger nucleases (ZFNs) that have been rationally designedto cleave near the target mutations. For gene knockout, we will test exon-specific ZFNs to mutate the rhodopsin-GFP gene directly, and intron- specific ZFNs designed to stimulate incorporation of a 'killer' exon that will poison expression of the rhodopsin gene. Assays for rhodopsin gene correction and knockout will utilize the fluorescent properties of the humanrhodopsin-GFPtarget gene.