DISTRIBUTION AND LEVELS OF CELLULAR RETINOL-BINDING AND CELLULAR RETINOIC ACID-BINDING PROTEIN IN VARIOUS TYPES OF RAT TESTIS CELLS

The distribution and levels of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP) were measured in rat testicular peritubular and Sertoli cells and in isolated rat pachytene spermatocytes and spermatids. Two Sertoli cell preparations, one containing some germ cells and another that had been osmotically shocked to destroy germ cells, were examined. CRBP and CRABP levels were measured by specific and sensitive radioimmunoassays. Testicular peritubular cell cytosol preparations were found to contain high levels of CRBP (1.48 .+-. 0.87 .mu.g CRBP/mg protein) but CRABP could not be detected. The mean CRBP level in Sertoli cell preparations that contained some germ cells was 0.93 .+-. 0.24 .mu.g CRBP/mg protein; this value was similar to the level of 1.11 .+-. 0.20 .mu.g CRBP/mg protein measured for Sertoli cells free of germ cells. The level of CRABP found in Sertoli cell preparations containing germ cells (0.81 .+-. 0.32 .mu.g CRABP/mg protein) was approximately five times greater than was observed in Sertoli cells free of germ cells (0.16 .+-. 0.03 .mu.g CRABP/mg protein). CRABP and CRABP levels in cultured Sertoli cells were not affected by time in culture for up to five days of culture. Pachytene spermatocytes and spermatids were very enriched in CRABP (0.72 .+-. 0.26 .mu.g CRABP/mg protein for spermatocytes and 0.65 .+-. 0.21 .mu.g CRABP/ml protein for spermatids). A search for a high molecular weight retinol-binding protein did not demonstrate the existence of such a protein in Sertoli cell-conditioned medium. In summary, these studies provide quantitative information about the distribution of the cellular retinoid-binding proteins in the cell types that compose the rat testis. The data delineate the high enrichment of CRBP is Sertoli cells and that of CRABP in germ cells.