Immunocytochemical localization of retinoid-binding proteins in developing normal and RCS rats.

Interstitial retinol-binding protein (IRBP), cellular retinol-binding protein (CRBP), and cellular retinal-binding protein (CRALBP) were localized in developing normal and RCS rat retinas. IRBP is found in the presumptive interphotoreceptor space in normal and RCS rats on P1. It reaches adult levels on P18. In the RCS rat, the level of IRBP decreases after P18 until there is only a small amount of staining on P38. CRBP and CRALBP are localized in the retinal pigment epithelium from P1 to adult. CRALBP is also found in the ciliary body pigment epithelium and in the outer epithelium of the iris during the first week, but decreases during the second week to a very low level as found in the adult. The significance of the early presence of IRBP and the transient appearance of CRALBP in the ciliary body and iris epithelia is discussed.