Résumé
Vertebrate oocytes are arrested at metaphase II of meiosis by a cytoplasmic activity termed cytostatic factor or CSF. Only after fertilization this activity will be inhibited and the oocyte will exit meiosis. The nature of the CSF factor has been studied for more than three decades however its identity has remained unknown until recently. The first discoveries on the CSF showed the implication in this activity of the c‐Mos‐MAPK‐Rsk pathway and the Anaphase Promoting Complex (APC). An important insight into the mechanisms controlling metaphase II arrest was subsequently provided by the identification a new APC inhibitor, the Emi1 Related Protein 1 (Erp1). This protein that directly interacts with the APC, inhibits this ubiquitin ligase and stabilizes cyclin B during CSF arrest. Erp1‐APC interaction is regulated via the Rsk‐dependent phosphorylation of Erp1, giving the link between the APC and the c‐Mos‐MAPK‐Rsk pathways on CSF arrest. Moreover, Erp1 is rapidly degraded upon fertilization and this degradation is triggered by a double phosphorylation on Erp1 by CaMKII and Plx1. Finally, Erp1 has also been suggested to be the target of the new identified calcineurin‐dependent pathway that is required for CSF release.