Caspase activity in newt spermatogonial apoptosis induced by prolactin and cycloheximide.

We previously showed in vivo and in vitro, that among the spermatogenic stages of the newt, prolactin (PRL) induces apoptosis specifically in the penultimate stage of secondary spermatogonia. In the current report, we demonstrate in vitro that cycloheximide (CHX), an inhibitor of protein synthesis, induces morphological apoptotic changes similar to those caused by PRL, such as chromatin condensation and apoptotic body formation. Next, we found that Z-VAD-fmk, an inhibitor of various caspases, suppressed the apoptosis induced by PRL and CHX, but ICE inhibitor Ac-YVAD-CHO or caspase-3 inhibitor Ac-DEVD-CHO did not. As high caspase activity was present in extracts of testes treated with CHX, we suggest that an unidentified caspase induces the morphological changes of apoptosis in newt spermatogonia.