Granulosa cell apoptosis: conservation of cell signaling in an avian ovarian model system.

Ovarian follicle atresia in all vertebrates studied to date is mediated via apoptosis, a process that is often initiated within the granulosa cell layer. While follicle atresia is considered a normal physiological process to insure the greatest chance for ovulation of fertilizable oocytes, abnormally high rates of atresia result in chronic infertility and/or premature termination of fertility (e.g., menopause). Although the vast majority of research to elucidate the molecular ordering of cell signaling during the process of granulosa cell apoptosis has been conducted in mammalian model systems, there is ample evidence to demonstrate that many of the proteins, enzymes and cell-signaling pathways are common to ovarian follicles from avian species. The following review will discuss evidence for the conservation of cellular processes that regulate the fate of granulosa cells from the avian, versus mammalian, ovary during follicle development.