Liu Junjun, Grimison Bryn, Lewellyn Andrea L, Maller James L
Howard Hughes Medical Institute (HHMI) and Department of Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80262, USA.
J Biol Chem. 2006 Nov 17;281(46):34736-41. doi: 10.1074/jbc.M606607200. Epub 2006 Sep 18.
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.
等待受精的脊椎动物卵母细胞会被细胞静止因子（CSF）阻滞在减数分裂II中期。这种阻滞是由于后期促进复合体/细胞周期体受到抑制，部分原因是一种新发现的蛋白质Emi2（xErp1）。Emi2是维持卵提取物中CSF阻滞所必需的，但它在卵母细胞中CSF建立以及正常胚胎细胞周期中的功能尚不清楚。在此我们表明，在卵母细胞成熟过程中，Emi2仅在减数分裂I中期之后出现，其水平在CSF阻滞（减数分裂II中期）时达到峰值。在M期，Emi2会发生磷酸化依赖性的电泳迁移。向VI期卵母细胞显微注射针对Emi2的反义寡核苷酸会阻断减数分裂II进程以及CSF阻滞的建立。重组Emi2可挽救这些卵母细胞中的CSF阻滞，并且还会在卵提取物和二细胞胚胎的卵裂球中引起CSF阻滞。受精会触发Emi2快速、完全降解，但它会在第一个胚胎细胞周期中重新合成，其水平比CSF阻滞期间低5倍。然而，从循环的卵提取物中耗尽该蛋白质并不会阻止有丝分裂细胞周期的进程。因此，Emi2在减数分裂而非有丝分裂细胞周期中发挥着重要作用。
