Mammalian homolog of Drosophila retinal degeneration B rescues the mutant fly phenotype

Mutations in the Drosophila rdgB gene, which encodes a transmembrane phosphatidylinositol transfer protein (PITP), cause a light-enhanced retinal degeneration. Cloning of mammalian rdgB orthologs (mrdgB) reveal predicted proteins that are 39% identical to rdgB, with highest homology in the N- terminal PITP domain (62%) and in a region near the C terminus (65%). The human mrdgB gene spans ~12 kb and maps to 11q13.1, a locus where several retinal diseases have also been mapped. Murine mrdgB maps to a syntenic region on the proximal region of chromosome 19. MrdgB is specifically expressed in the retina and brain. In the retina, MrdgB protein is localized photoreceptor inner segments and the outer and inner plexiform layers. Expression of murine mrdgB in mutant flies fully rescues both the rdgB- dependent retinal degeneration and abnormal electroretinogram. These results suggest the existence of similarities between the invertebrate and mammalian retina that were not previously appreciated and also identify mrdgB as a candidate gene for retinal diseases that map to 11q13.1.