CELLULAR RETINALDEHYDE-BINDING PROTEIN IS EXPRESSED BY OLIGODENDROCYTES IN OPTIC-NERVE AND BRAIN

Cellular retinaldehyde-binding protein (CRALBP) is abundant in the ret inal pigment epithelium and Muller glial cells of the retina, where it forms complexes with endogenous Il-cis-retinoids. We examined the dis tribution of CRALBP in extraretinal tissues using polyclonal antibodie s (pAb) and monoclonal antibodies (mAb). A protein was detected by imm unoblot analysis in extracts of bovine and rat brain and optic nerve b ut not in several other tissues. This protein had electrophoretic, chr omatographic, and retinoid-binding properties identical to those of CR ALBP from bovine retina. Comparison of the masses of tryptic peptides and of partial amino acid sequences derived from brain and retinal CRA LBP indicated that the two proteins are probably identical. Immunopero xidase cytochemistry and double labeling immuno fluorescence revealed CRALBP(+) cells in brain that resembled oligondendrocytes and not astr ocytes, microglial cells, or pinealocytes. In Ii-day-old rat brain, ap proximately 11% of the CRALBP( +) cells were labeled with the Rip anti body, a marker for oligodendroglia. In developing rat optic nerve, the temporal appearance of CRALBP(+) cells corresponded to that of oligod endrocytes and not that of astrocytes. In adult rat and mouse optic ne rves, the CRALBP(+) somata showed the same distribution as oligodendro cytes. No endogenous retinoids were associated with CRALBP isolated fr om dark-dissected adult bovine brain. The results suggest that CRALBP has functions in addition to retinoid metabolism and visual pigment re generation. (C) 1997 Wiley-Liss, Inc.