Gene expression during mammalian spermatogenesis. I. Evidence for stage-specific synthesis of polypeptides in vivo

Following intratesticular injection of [35S]methionine or [3H]leucine, four testicular cell types (pachytene spermatocytes, round spermatids, elongating spermatids and residual bodies) were purified from mouse testicular cell suspensions by unit gravity sedimentation and equilibrium density gradient centrifugation through Percoll. Measurement of the amount of radiolabeled amino acid incorporated into protein in the testicular cells revealed that for a constant number of cells, pachytene spermatocytes incorporated 5.4 times more isotope than round spermatids, which incorporated 2.4 times more isotope than elongating spermatids. Analysis by two-dimensional gel electrophoresis of the polypeptides synthesized in vivo in the four testicular cell types demonstrated qualitative and quantitative changes in protein synthesis during spermatogenesis. At the level of detection provided by the electrophoretic methods used, pachytene spermatocytes and round spermatids synthesized approximately equivalent numbers of polypeptides while the number of polypeptides synthesized in elongating spermatids and residual bodies was decreased. Quantitative changes for polypeptides ranging in molecular weight from 16,500 to 82,000 were detected during spermatogenesis. For each cell type examined, a minimum of 5% of the polypeptides appear to be either unique or greatly enriched. These studies indicate that the expression of a sizable number of polypeptides is specific to certain stages of spermatogenesis.