Ovarian regression and apoptosis in the South American teleost Leporinus taeniatus Lutken (Characiformes, Anostomidae) from the Sao Francisco Basin

Involution and resorption of both postovulatory and atretic follicles were analysed in piau-jejo Leporinus taeniatus (Characiformes. Anostomidae) in order it) evaluate the role of apoptosis during ovarian regression. Histological and ultrastructural analyses showed hallmarks of apoptosis in the granulosa: aggregation of' compacted chromatin against the nuclear envelope, cell shrinkage, surface blebbing, loss of cell adhesion and cell fragmentation into apoptotic bodies, Protein synthesis activity preceded the onset of the cell death. The breakdown of' the basement membrane led to the detachment of the granulosa cells into the follicular lumen, TUNEL-positive reactions were detected in in situ DNA fragmentation of granulosa of both postovulatory and atretic follicles. Apoptosis increased in a time-dependent manner contributing to reduction of the follicular areas. The apoptotic index (per cent of apoptotic cells) of the granulosa increased in postovulatory follicles soon after spawning, then these follicles degenerated and only remnants were observed at 7 days. In contrast, the granulosa cells reabsorbed the yolk during follicular atresia and the apoptotic index increased only in the late stage of regression. The results' indicated apoptosis as the major mechanism to rapidly eliminate postovulatory follicles and being an essential process in the ovarian regression after spawning.