Apoptosis and mitosis in gonocytes of the rat testis during foetal and neonatal development

This study was undertaken to determine the extent of apoptosis and mitosis in the Various testicular cell types throughout rat development from foetal day 14.5 to postnatal days 9-10. Apoptotic activity was studied by detecti ng DNA fragmentation (TUNEL method) in situ. A TUNEL-positive reaction was detected in gonocytes, while none of the other testicular cells were labell ed. The morphology of the TUNEL-positive gonocytes was characteristic of ap optotic cells and was different from that observed in experimentally induce d necrosis. The percentage of stained gonocytes peaked on day 15.5-16.5 pos t-conception (dpc), decreased thereafter and no TUNEL-positive gonocytes we re found from foetal day 18.5 onwards. On postnatal day 2, apoptosis resume d and increased to reach a maximum on day 7. Mitosis in the gonocyces, as e valuated by the immunodetection of 5-bromo-2'-deoxyuridine (BrdU) incorpora tion, was present during the same developmental periods but the ratio of Br dU-positive/ TUNEL-positive gonocytes was much greater in the foetal period than in the neonatal period. In an organotypic culture system, the changes in the apoptotic and mitotic activities of the gonocytes in testicular exp lants from foetuses on days 18.5 and 20.5 or from neonates on day 3, cultur ed for two days were similar to those observed in vitro. Addition of LH or FSH did not influence either apoptosis or mitosis in the germ cells. These results suggest that both apoptosis and mitosis of gonocytes are independen t of gonadotrophins and are mainly controlled by intratesticular factors.