Sexual dimorphism in the regulation of mammalian meiosis

This chapter focuses on sexual dimorphism in the regulation of the progress and tempo of the cell cycle during meiosis that emphasizes both common and sexually dimorphic features of oogenesis and spermatogenesis. Meiosis is overtly sexually dimorphic in mammals, with several key features that differ between males and females. In females, meiosis is initiated once, more or less synchronously in a finite and limited pool of cells, but in males, meiosis is initiated continuously in cells derived from a mitotically proliferating stem cell population. In females, the progress of meiosis is arrested at the end of the first meiotic prophase and reinitiated at a later time period when an extremely small number of cells are selected for growth and meiotic maturation, stimulated by hormonal signaling. In contrast, in males, meiosis and gametogenesis proceed continuously without cell cycle arrest or interruption. In spite of the genetic difference between the meiotic and mitotic cell cycles, evidence suggests remarkable similarity between the two in the regulation of the transition from prophase, or the end of the G2 phase of the cell cycle, to metaphase. Meiotic prophase is initiated in oogenic cells in the fetal mouse ovary over a period of several days, beginning at day 13.5 of gestation. In the fetal testis, the spermatogenic cells cease mitotic proliferation but do not enter meiosis. © 1998 Academic Press Inc.