PROJECT SUMMARY Mutations in Peripherin 2 (PRPH2) account for a significant portion of inherited retinal diseases (IRD). Delineating the role of PRPH2 in photoreceptor morphogenesis and rim formation is vital to understand how mutations in a single protein could contribute to such diverse group of pathologies, ranging from retinitis pigmentosa (RP) to pattern dystrophy (PD) and macular degeneration (MD). Even patients with intrafamilial mutations can exhibit a notable degree of phenotypic variability, attesting to the complex nature in which PRPH2 functions. My objective in this application is to advance our current knowledge of the role of PRPH2 in outer segment (OS) formation in order to have a better understanding of disease pathogeneses and for future development of effective therapeutic strategies. Over the years, our lab has developed an extensive toolbox of in vitro and in vivo mutant models, and are currently exploring innovative imaging techniques to further our understanding of the role of Prph2 in OS landscape. Thus far, it has been determined that the association between Prph2 and its homologue, Rod OS Protein 1 (Rom1), contributes significantly to the phenotypic variability observed in patients and that lowering Rom1 levels could shift a sever Prph2-assocaited PD phenotype to milder RP. Furthermore, it is know that the proper function of Prph2 at the disc rim is contingent upon proper complex assembly of Prph2-oligomers and Prph2/Rom1-complexes. The central focus of this investigation is to understand how Prph2 and Rom1 function differently in rods and cones with particular interest in Prph2 homo- and Prph2/Rom1 hetero-complex formation/trafficking, and the effects of Prph2 mutations on these processes. We propose two aims to address these goals: Aim 1 will assess the role of Rom1 in cones and the mechanism by which it modulates Prph2-disease phenotypes. By eliminating or overexpressing Rom1 in Prph2-disease models, we will conduct careful biochemical, structural, and functional analyses to assess phenotypic differences, as they pertain to complex assembly and OS trafficking. Aim 2 will investigate the role of interacting partners in the differential behavior of Prph2 in rods vs cones. In order to properly traffic and function in the OS, Prph2 forms membrane microdomains to organize and house a network of proteins that are necessary/specific for the formation of the closed rims in rods and open lamellae/rims in cones. In this aim, we will identify critical Prph2 binding partners and determine how these interactions differ between rods and cones. The outcomes of these studies will elucidate the specific function of Prph2 and Rom1 in rods and cones, determine how modulating Rom1 affects disease phenotypes, and will further our understanding of the role of Prph2 in the closed rim structure in rods and the open rim structures in cones. Given the lack of effective treatments for Prph2-associated diseases, these studies are essential and b...