Non-apoptotic Role of Cleaved Caspase-3 in Rat Male Germ Cell Development

Germ cells emerge from the epiblast and migrate to the gonads, where they become gonocytes. The gonocytes are the precursors of the spermatogonial stem cells, but little is known about their differentiation. The rigid control of gonocyte proliferation, quiescence and pluripotency marker expression is crucial for spermatogonia development. We have previously suggested that cleaved caspase-3 (Casp3) might play a non-apoptotic role in gonocyte quiescence. Here we describe when rat fetal gonocyte enter mitotic arrest and show that Casp3 inhibition in these cells affects the expression of cell cycle genes. The expression of Ki67, p27Kip, Retinoblastoma 1 (pRb1), NANOG and CASP3 was investigated in 15, 17 and 19 days post coitum rat embryo gonads. The results show that Ki67 and pRB1 proteins are downregulated from 15 days post coitum to 19 days post coitum, whereas p27Kip, NANOG and CASP3 are upregulated. This suggests that rat germ cells start to enter quiescence around 15dpc and that CASP3 and NANOG seem to play a role in this process. CASP3 labelling formed a ring in gonocyte cytoplasm, which is clearly distinct from apoptotic cell labelling, and coincided with NANOG labelling. CASP3 inhibition lead to an increase of Pcna expression and to a decrease of p27kip and p21cip expression. These results suggest that cleaved CASP3 has a role in rat male germ cell development which can be related to the control of the cell cycle genes.