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GREATER THAN 99% of ovarian follicles undergo a degenerative process called atresia during reproductive life. Extending earlier morphological analysis, recent studies have demonstrated that apoptotic cell death is the molecular mechanism underlying follicle atresia. The use of DNA 3′-end-labeling methods allows quantitation and identification of internucleosomal degradation of DNA after gel fractionation as well as in situ analysis of specific cell types undergoing DNA fragmentation in histological sections. Using rats as the experimental model, gonadotropins, epidermal growth factor (EGF)/transforming growth factor-α (TGFα), basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I), and estrogens have been identified as follicle survival factors capable of suppressing apoptotic DNA fragmentation, whereas androgens, interleukin-6 (IL-6), and GnRH are potential atretogenic factors. This review summarizes the historical background of studies on follicle atresia and selection as well as recent advances in the intraovarian hormonal mechanisms that control follicle apoptosis. It is suggested that during the penultimate stage of follicle development, exposure to a survival factor (probably FSH) is responsible for follicle selection.
Hsueh et al. (Thu,) studied this question.