Redundancy of the effect of TGFbeta1 and beta-NGF on the second meiotic division of rat spermatocytes.

We have previously shown that in cocultures of late pachytene/diplotene spermatocytes (PS/DS) with Sertoli cells, beta-nerve growth factor (beta-NGF) or transforming growth factor (TGFbeta1) regulates the second meiotic division by blocking secondary spermatocytes in metaphase II, and thereby lowers round spermatid formation. In this study, we raised the question if beta-NGF and TGFbeta1 have additional or redundant effects on this step. Hence, we addressed the effect of beta-NGF in combination with TGFbeta1, as compared to those of beta-NGF or TGFbeta1 separately, on the completion of meiosis by rat late PS/DS. Identification and counting of meiotic cells were performed by cytological methods. Under our culture conditions, some late PS/DS differentiated into round spermatids. When beta-NGF in combination with TGFbeta1 was added to the culture medium, the numbers of PS/DS and of secondary spermatocytes were not modified by the treatment. By contrast, the number of round spermatids was about 2-fold lower in treated cultures than in basal cultures, and an increase in metaphase II, but not metaphase I, over basal values was observed. Similar results were found when either beta-NGF or TGFbeta1 was added to the culture medium. These results indicate a redundancy between beta-NGF and TGFbeta1 on the negative regulation of the second meiotic division of rat spermatocytes. This suggests that beta-NGF and TGFbeta1 share some common pathway of regulation of this step. In addition, these results reinforce the view that the adjustment of the number of round spermatids supported by Sertoli cells is a key event of the spermatogenic process.