Localization of retinoid-binding proteins in developing rat retina.

Antibodies to cellular retinol-binding protein (CRBP) and cellular retinal-binding protein (CRALBP) were obtained from rabbits immunized with antigens purified from bovine retina. Antigens were localized on frozen sections of rat retina using indirect FITC immunofluorescence. In the retinal pigment epithelium of rats from postnatal day 1 (the day of birth) to postnatal day 32, specific staining with anti-CRBP was restricted to the cytoplasm; the nuclei were unstained. In the neurosensory retina, Muller cell endfeet were stained with anti-CRBP at all ages examined. No CRBP reactivity was found in the pigment epithelium of the ciliary body at any age examined. On postnatal days 14 and 32, in addition to Muller cell endfeet and radial processes, two fine laminae in the inner plexiform layer were faintly positive for CRBP. Anti-CRALBP stained the cytoplasm of the RPE and Muller cells in the adult rat. In developing rat retina, in addition to Muller cells and the retinal pigment epithelium, the ciliary body pigment epithelium and the outer epithelium of the iris were stained with anti-CRALBP in the first postnatal week. The intensity of staining of the ciliary body pigment epithelium decreased gradually from postnatal day 8 until postnatal day 14, at which point a clear line of demarcation was found between the positively stained retinal pigment epithelium and the adjacent, lightly stained, pigment epithelial cells of the ciliary body.