AN EARLY DECREASE IN INTERPHOTORECEPTOR RETINOID-BINDING PROTEIN GENEEXPRESSION IN ABYSSINIAN CATS HOMOZYGOUS FOR HEREDITARY ROD-CONE DEGENERATION

Levels of interphotoreceptor retinoid-binding protein (IRBP) protein a nd message in retinas of Abyssinian cats homozygous for progressive ro d-cone degeneration were determined at early ages, well before the ons et of clinical retinal degeneration. IRBP gene expression was assessed by immunochemical quantitation of IRBP protein, and by Northern blott ing and slot-blotting of total RNA using a human IRBP cDNA probe. Morp hology was assessed by electron microscopy and immunocytochemistry. Le vels of both IRBP protein and message in affected Abyssinian cat retin as were significantly reduced below normal as early as 4 weeks of age at the earliest stage of retinal disorientation. Opsin mRNA was more a bundant in affected Abyssininian cat retinas than in control retinas. This was at least 1 year before the onset of clinical symptoms. The re duction in IRBP gene expression to levels significantly below normal w ell before the onset of retinal degeneration in affected Abyssinian ca t retinas indicates that this represents a primary defect or at least an early problem that could itself cause adverse effects.