Comparative aspects of meiotic cell cycle control in mammals.

This review examines the mechanisms of cell cycle control in mammalian germ cells with respect to species-specific variations in reproductive strategies. While sex-specific variants are evidenced at the level of checkpoint controls, the timing of meiotic progression, and the modulation of meiosis by hormonal cues, local somatic cell influences impose a hierarchical order to both the initiation and completion of gametogenesis. In the particular case of meiosis in females the rules governing entry into meiotic prophase during gonadal development are generally conserved. In contrast, the regulation of meiotic arrest in developing ovarian follicles, the reinitiation of meiosis at ovulation, and the completion of meiosis upon fertilization involves changes in both the cell cycle machinery and execution of external cues. The overall efficiency of meiotic progression is determined by inputs, mediated by cell contact and/or growth factor, which coordinate oogenesis with folliculogenesis and ensure appropriate and species-specific ovulatory outputs (monovular or polyovular). How mechanisms of meiotic cell cycle control can be exploited to improve gamete quality or interfere with fertility is discussed.