CELLULAR-LOCALIZATION OF MESSENGER-RNAS FOR RETINOIC ACID RECEPTOR-ALPHA, CELLULAR RETINOL-BINDING PROTEIN, AND CELLULAR RETINOIC ACID-BINDING PROTEIN IN RAT TESTIS - EVIDENCE FOR GERM CELL-SPECIFIC MESSENGER-RNAS

In the present study we have examined the cellular localization and developmental changes of mRNAs for retinoid-binding proteins in rat testis. We demonstrate that mRNA (0.7 kb) for cellular retinol-binding protein (CRBP) is expressed only in Sertoli cells and peritubular cells. The mRNA for CRBP could not be detected in other testicular cells. In contrast, mRNA for cellular retinoic acid-binding protein (CRABP) was detected primarily in germ cells and to a small extent in tumor Leydig cells. The mRNA for CRABP in germ cells revealed distinct size heterogeneity and three distinct mRNA species were observed (1.0, 1.8, and 1.9 kb), in contrast to previous data for somatic cells where only the 1.0-kb mRNA has been reported. Messenger RNAs for retinoic acid receptor-alpha (RAR-alpha) were detected in both somatic and haploid germ cells. The highest level of RAR-alpha was seen in Sertoli cells, round spermatids, and tumor Leydig cells. Lower, but distinct, levels were observed in peritubular cells. Furthermore, we observed germ cell-specific species of RAR-alpha mRNA (4 kb and approximately 7 kb). The smallest mRNA for RAR-alpha (2.7 kb) in somatic cells was absent in germ cells. The levels of mRNAs for the various retinoid-binding proteins in whole testis obtained from rats of various ages confirmed this cellular localization. The mRNAs for CRBP, the small molecular size (2.7 kb) mRNA for RAR-alpha (localized to somatic cells), and the 1-kb mRNA for CRABP showed an age-dependent decrease. In contrast, the 1.8-kb and 1.9-kb mRNAs for CRABP (localized to germ cells) revealed a dramatic increase as a function of age. The 3.4-kb mRNA and RAR-alpha (present in both germ cells and somatic cells) did not change with age. Thus, the mRNAs for retinoid-binding proteins revealed distinct cell-specific expression. Furthermore germ cell-specific mRNA species for retinoid-binding proteins were demonstrated.