Apoptosis and ovarian function: Novel perspectives from the teleosts

Apoptosis is a fundamental mechanism in follicular atresia and postovulator y regression in mammals, but its role in teleost ovarian function is curren tly unknown. This study tested the hypotheses that apoptosis mediates folli cular atresia in teleosts and is inducible in vitro by incubation in serum- free conditions. Vitellogenic follicles from rainbow trout (Oncorhynchus my kiss) and goldfish (Carassius auratus) were incubated overnight in serum-fr ee medium and examined for apoptosis by 3'-end-labeling and/or TUNEL analys is. Primary, postovulatory, and oocytectomized vitellogenic trout follicles and atretic goldfish follicles were evaluated in similar fashion. Overall, goldfish follicles had lower levels of DNA fragmentation than trout follic les. The DNA fragmentation in atretic goldfish follicles was similar to tha t measured in healthy vitellogenic and prematurational follicles; DNA fragm entation did not change after incubation. In the trout, postovulatory and o ocytectomized vitellogenic follicles showed significantly greater in vitro susceptibility to apoptosis than intact vitellogenic follicles, whereas pri mary follicles were least susceptible. The TUNEL analyses revealed that in trout vitellogenic follicles, more thecal/epithelial cells than granulosa c ells showed fragmented DNA in vivo, but incubation (24 h) did not result in increased apoptosis in cells of either type. These results indicate that a poptosis is involved in normal ovarian growth and postovulatory regression in teleosts, but that it does not appear to be an early event in teleost fo llicular atresia.