Regulation of ovarian follicle atresia.

The majority of ovarian follicles undergo atresia, a hormonally controlled apoptotic process. Monitoring apoptotic DNA fragmentation provides a quantitative and sensitive endpoint to study the hormonal regulation of atresia in ovarian follicles. During follicle development, gonadotropins, together with local ovarian growth factors (IGF-I, EGF/TGF-alpha, basic FGF) and cytokine (interleukin-1 beta), as well as estrogens, activate different intracellular pathways to rescue follicles from apoptotic demise. In contrast, TNF-alpha, Fas ligand, presumably acting through receptors with a death domain, and androgens are atretogenic factors. These diverse hormonal signals probably converge on selective intracellular pathways (including genes of the bcl-2 and ICE families) to regulate apoptosis. With a constant loss of follicles from the original stockpile, the ovary provides a unique model for studying the hormonal regulation of apoptosis.