RPGR Interacts With a Novel Ciliary IQ Domain Protein Nephrocystin 5, Mutated in Senior–Loken Syndrome (Nephronophthisis With Retinitis Pigmentosa)

Abstract

Abstract: : Purpose: Mutations in RPGR (Retinitis Pigmentosa GTPase Regulator) are the most frequent cause of X–linked RP. Multiple alternatively spliced isoforms of RPGR, including a retina–enriched isoform RPGR–ORF15, are widely expressed. We hypothesize that different RPGR isoforms perform distinct functions in photoreceptors depending upon their subcellular localization. The goal of this study is to identify RPGR–interacting proteins in order to gain insights into the function(s) of RPGR. Methods: Various fractions of bovine retina extract were prepared and immuno–precipitation was carried out using RPGR–ORF15^CP antibody. The proteins were separated by SDS–PAGE, followed by MS/MS analysis and/or immunoblotting. Results: We have identified KIAA0036, a novel coiled–coil, IQ domain protein mutated in Senior–Loken Syndrome, as part of the RPGR–multi–complex(es) in the retina. This protein, now called nephrocystin 5, co–localizes with RPGR–ORF15 to the connecting cilium of human and mouse photoreceptors and to the primary cilia of renal epithelial cells. We demonstrate that calmodulin, an interacting partner of KIAA0036, is also present in the RPGR–containing complex (es) in the retina. Conclusions: RPGR thus interacts with a complex of other proteins in the photoreceptor cilium. At least one of these proteins (NPHP5) is essential for photoreceptor cell viability in its own right.

Keywords: retina: distal (photoreceptors, horizontal cells, bipolar cells) • photoreceptors • retina