VISUAL SENSITIVITY AND INTERPHOTORECEPTOR RETINOID-BINDING PROTEIN INTHE MOUSE - REGULATION BY VITAMIN-A

Interphotoreceptor retinoid binding protein (IRBP) is a retinoid and f atty acid binding glycoprotein secreted by rod and cone photoreceptors in all vertebrates, IRBP is believed to serve as a carrier for retino ids in the bleaching and regeneration cycle of rhodopsin. IRBP protein has been found to be decreased in vitamin A-deprived rats; it is rapi dly recovered after retinol repletion, To understand the mechanism for this recovery, we determined whether vitamin A affects transcription and translation of the IRBP gene, Wild-type and transgenic mice harbor ing the IRBP promoter-CAT reporter fusion gene were maintained on a re tinol-deficient diet supplemented with retinoic acid (-A) or on a cont rol diet (+A) for up to 60 wk postweaning, Some of the -A mice were gi ven retinol repletion for 7 days (-A+A), Electroretinography analysis revealed alterations in waveform and a 2 log unit decrease in b-wave s ensitivity in the -A mice over a broad range of stimulus wavelengths, Retinol repletion effected a full recovery, Immunochemistry showed a s ignificant decrease in the immunogold-labeled IRBP between the retinal pigment epithelium and the outer segments of the -A mice compared wit h +A and -A+A mice, Northern blots showed no differences in the amount s of IRBP or CAT mRNA between these three treatment groups, These resu lts suggest that the regulation of IRBP by retinol is not transcriptio nal.