ELUCIDATION THE EPIGENETIC AND TRANSCRIPTIONAL LANDSCAPE OF SPINOCEREBELLAR TYPE 7 RETINAL DEGENERATION - PROJECT SUMMARY SPINOCEREBELLAR ATAXIA TYPE 7 (SCA7) IS A RARE, INHERITED NEURODEGENERATIVE DISORDER CHARACTERIZED BY PROGRESSIVE VISION LOSS AND CEREBELLAR ATAXIA. THE DEFINING FEATURE OF SCA7, SETTING IT APART FROM OVER 40 OTHER SCAS, IS ITS RETINAL DEGENERATION, SPECIFICALLY A CONE-ROD DYSTROPHY, AS EVIDENCED BY DYSFUNCTIONAL CONE PHOTORECEPTORS IN PATIENT ELECTRORETINOGRAMS. THE DISORDER IS CAUSED BY A CAG-POLYGLUTAMINE (POLYQ) REPEAT EXPANSION IN THE ATAXIN-7 (ATXN7) GENE. ATXN7 IS A CORE COMPONENT OF THE MAMMALIAN ACETYLTRANSFERASE TRANSCRIPTION COACTIVATOR COMPLEX, AND POLYQ EXPANSION HAS DEMONSTRATED EPIGENETIC DYSREGULATION. THIS CONDITION, PART OF A WIDER GROUP OF POLYQ DISEASES, PRESENTS A SIGNIFICANT CHALLENGE DUE TO ITS COMPLEX PATHOPHYSIOLOGY INVOLVING TRANSCRIPTIONAL DYSREGULATION, WHICH CLASSIFIED THESE DISORDERS AS TRANSCRIPTIONOPATHIES. DESPITE THIS CLASSIFICATION, THE MECHANISMS LINKING MUTANT ATXN7 TO RETINAL CELL DYSFUNCTION AND DEGENERATION REMAIN POORLY UNDERSTOOD. THIS PROJECT AIMS TO DEFINE THE TRANSCRIPTIONAL AND EPIGENETIC ARCHITECTURE UNDERLYING SCA7 RETINAL DEGENERATION USING AN INTEGRATIVE MULTIOMIC APPROACH. WE WILL APPLY SINGLE-CELL RNA-SEQ AND ATAC-SEQ TO RETINAL CELLS FROM SCA7 KNOCK-IN MICE AT PRESYMPTOMATIC AND SYMPTOMATIC STAGES TO MAP ENHANCER-DRIVEN GENE REGULATORY NETWORKS (GRNS) DISRUPTED DURING DISEASE PROGRESSION. TO COMPLEMENT AND EXTEND THESE FINDINGS IN A HUMAN CONTEXT, WE WILL GENERATE RETINAL ORGANOIDS (ROS) FROM SCA7 PATIENT-DERIVED AND ISOGENIC IPSC LINES. THESE IN VITRO MODELS WILL BE STRUCTURALLY AND FUNCTIONALLY CHARACTERIZED TO EVALUATE PHOTORECEPTOR ORGANIZATION, OUTER SEGMENT INTEGRITY, AND VISUAL CYCLE FUNCTION. SINGLE-CELL MULTIOMIC ANALYSIS AT KEY DEVELOPMENTAL MILESTONES WILL IDENTIFY HUMAN-SPECIFIC TRANSCRIPTION FACTOR REGULONS AND REGULATORY ELEMENTS ALTERED BY ATXN7 EXPANSION. CANDIDATE REGULATORS WILL THEN BE TARGETED WITH CRISPRI/A OR PHARMACOLOGIC AGENTS TO ASSESS THEIR POTENTIAL TO RESTORE PHOTORECEPTOR STRUCTURE AND FUNCTION. BY INTEGRATING IN VIVO AND IN VITRO SYSTEMS, THIS RESEARCH WILL DEFINE THE GENE REGULATORY CIRCUITRY DISRUPTED IN SCA7 AND IDENTIFY MECHANISTIC DRIVERS OF CONE-ROD DYSTROPHY. THESE INSIGHTS WILL NOT ONLY INFORM NOVEL THERAPEUTIC STRATEGIES FOR SCA7 BUT MAY ALSO BE BROADLY RELEVANT TO OTHER POLYQ DISORDERS AND INHERITED RETINOPATHIES. ULTIMATELY, THIS WORK SEEKS TO BRIDGE BASIC MECHANISMS OF TRANSCRIPTIONAL DYSFUNCTION WITH THERAPEUTIC DEVELOPMENT IN NEURODEGENERATION. BY IDENTIFYING MODIFIABLE GENE REGULATORY NODES, THIS RESEARCH MAY LAY THE GROUNDWORK FOR FUTURE PRECISION THERAPIES.