COEXPRESSION OF THE MESSENGER-RNAS ENCODING RETINOL DEHYDROGENASE ISOZYMES AND CELLULAR RETINOL-BINDING PROTEIN

We used in situ hybridization of adult rat tissue to show that mRNAs e ncoding cellular retinol-binding protein (CRBP) and retinol dehydrogen ase (RoDH) isozymes I/III and II were expressed in hepatocytes uniform ly throughout the liver lobule, but were absent from Kupffer cells and endothelial cells of blood vessels and bile ducts. In kidney, CRBP, R oDH(I), and RoDH(II) were found in the proximal tubules of the cortex. Distal tubules, Henle's loops, collecting ducts, and glomeruli showed little, if any, expression. In testis, CRBP, RoDH(I), and RoDH(II) we re found in Sertoli cells. Expression, albeit weaker, also occurred in spermatogonia and primary spermatocytes. Peritubular cells and other germ cells had even weaker expression. Only CRBP and RoDH(II) mRNA wer e detected in interstitial cells. In lung CRBP, RoDH(I) and RoDH(II) w ere expressed most intensely in the epithelium of the bronchi and bron chioli, but also occurred in the simple columnar epithelial cells of t he alveolar duct and in alveolar type II cells. These data are consist ent with the hypothesis that holo-CRBP serves as substrate for retinoi c acid biosynthesis because they show that the substrate and the enzym e occur in the same cellular loci in vivo. Those data also indicate th at multiple cellular sites of retinoic acid biosynthesis occur through out tissues. Also, the general concordance between mRNA localization a nd CRBP expression patterns, revealed by previous immunocytochemistry studies, supports and extends the conclusion that CRBP mRNA expression correlates with CRBP expression, based earlier on comparing RNA assay s with radioimmunoassays. (C) 1997 Wiley-Liss, Inc.