Figure 7.

Emi2-Cdc20 in mammalian meiosis and meiotic exit. In this model, suspension of meiosis at mII occurs because Emi2 sequesters Cdc20. This suspension is resolved by an activating stimulus—induced by sperm or parthenogenetic agent such as SrCl₂, for example—that signals to release Cdc20 from Emi2^Cdc20, enabling the generation of active APC^Cdc20. The APC adaptor Cdh1 is implicated in mI, but Cdh1 is inactivated or destroyed by mII. Thus, Cdc20 apparently functions as an obligate signal transduction node connecting the oocyte activating stimulus to meiotic exit. A subpopulation of Emi2 remains following activation to ensure productive cytokinesis. Pb₁ and Pb₂ are first and second polar bodies, respectively.