title: The anaphase-promoting complex/cyclosome inhibitor Emi2 is essential for meiotic but not mitotic cell cycles.
abstract: Vertebrate oocytes awaiting fertilization are arrested at metaphase of meiosis II by cytostatic factor (CSF). This arrest is due to inhibition of the anaphase-promoting complex/cyclosome, in part by a newly identified protein, Emi2 (xErp1). Emi2 is required for maintenance of CSF arrest in egg extracts, but its function in CSF establishment in oocytes and the normal embryonic cell cycle is unknown. Here we show that during oocyte maturation, Emi2 appears only after metaphase I, and its level peaks at CSF arrest (metaphase II). In M phase, Emi2 undergoes a phosphorylation-dependent electrophoretic shift. Microinjection of antisense oligonucleotides against Emi2 into stage VI oocytes blocks progression through meiosis II and the establishment of CSF arrest. Recombinant Emi2 rescues CSF arrest in these oocytes and also causes CSF arrest in egg extracts and in blastomeres of two-cell embryos. Fertilization triggers rapid, complete degradation of Emi2, but it is resynthesized in the first embryonic cell cycle to reach levels 5-fold lower than during CSF arrest. However, depletion of the protein from cycling egg extracts does not prevent mitotic cell cycle progression. Thus, Emi2 plays an essential role in meiotic but not mitotic cell cycles.
authors.affiliation: Howard Hughes Medical Institute (HHMI) and Department of Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80262, USA.
authors.forename: Junjun
authors.initials: J
authors.lastname: Liu
authors.forename: Bryn
authors.initials: B
authors.lastname: Grimison
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Lewellyn
authors.forename: James L
authors.initials: JL
authors.lastname: Maller
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D044783:F-Box Proteins / Q000378:metabolism*; D008540:Meiosis / Q000502:physiology*; D008938:Mitosis / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000037:antagonists & inhibitors*; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism*
chemical_list: D044783:F-Box Proteins; C498166:FBXO43 protein, Xenopus; D029867:Xenopus Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome