Cell cycle control and early embryogenesis: Xenopus laevis maturation and early embryonic cell cycles

Our understanding of how meiotic maturation is regulated in Xenopus laevis continues to flourish. Premature initiation of maturation is prevented by the cAMP-dependent protein kinase, which inhibits the synthesis of Mos and potently blocks activation of cdc25. The autoamplification of maturation promoting factor (MPF) activity can be explained by the ability of MPF to directly activate cdc25. Later, in Meiosis II, the contribution of Mos to cytostatic factor (CSF) appears to be mediated through its activation of the mitogen-activated protein kinase, and cdk2 has been added to the active components of CSF. A model is presented illustrating the pathways of meiotic reinitiation, and indicating gaps in our knowledge.