STAGE-SPECIFIC EXPRESSION AND PHOSPHORYLATION OF RETINOBLASTOMA PROTEIN (PRB) IN THE RAT SEMINIFEROUS EPITHELIUM

To assess the potential role of retinoblastoma protein (pRb) in the re gulation of cell cycle during spermatogenesis, the expression of retin oblastoma (Rb) mRNA and protein, as well as the phosphorylation stares of pRb, in the rat seminiferous epithelial cycle, were studied. Two t ranscripts, 5.4 kb and 3.4 kb long, were detected in total RNA from th e adult rat testis and only the 5.4 kb transcript was detected in poly (A)(+)-RNA from 8, 14 End 23-day old rat testes by Northern hybridiza tion. Polysome analysis revealed that only a small portion of both Rb transcripts could be efficiently translated. By in situ hybridization, Rb mRNA was localized to germ cells from stage V pachytene spermatocy tes to step 13 spermatids along the epithelial cycle. pRb immunoreacti vity was detected in Sertoli cells and spermatogonia al all stages, as well as in the elongated steps 14-19 spermatids by immunohistochemist ry. The amount of pRb and the phosphorylation status varied in a stage -specific manner in Western blots. These results show that pRb is expr essed in the rat seminiferous epithelium in a cyclic fashion and sugge st that it is involved in the regulation of proliferation of spermatog onia and maintenance of the differentiation status of Sertoli cells an d spermatids. (C) 1997 Elsevier Science Ireland Ltd.