Grimison Bryn, Liu Junjun, Lewellyn Andrea L, Maller James L
Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80262, USA.
Curr Biol. 2006 Oct 10;16(19):1968-73. doi: 10.1016/j.cub.2006.08.055.
Cytostatic factor (CSF) arrests vertebrate eggs in metaphase of meiosis II through several pathways that inhibit activation of the anaphase-promoting complex/cyclosome (APC/C). In Xenopus, the Mos-MEK1-MAPK-p90(Rsk) cascade utilizes spindle-assembly-checkpoint components to effect metaphase arrest. Another pathway involves cyclin E-Cdk2, and sustained cyclin E-Cdk2 activity in egg extracts causes metaphase arrest in the absence of Mos; this latter finding suggests that an independent pathway contributes to CSF arrest. Here, we demonstrate that metaphase arrest with cyclin E-Cdk2, but not with Mos, requires the spindle-checkpoint kinase monopolar spindles 1 (Mps1), a cyclin E-Cdk2 target that is also implicated in centrosome duplication. xMps1 is synthesized and activated during oocyte maturation and inactivated upon CSF release. In egg extracts, CSF release by calcium was inhibited by constitutively active cyclin E-Cdk2 and delayed by wild-type xMps1. Ablation of cyclin E by antisense oligonucleotides blocked accumulation of xMps1, suggesting that cyclin E-Cdk2 controls Mps1 levels. During meiosis II, activated cyclin E-Cdk2 significantly inhibited the APC/C even in the absence of the Mos-MAPK pathway, but this inhibition was not sufficient to suppress S phase between meiosis I and II. These results uniquely place xMps1 downstream of cyclin E-Cdk2 in mediating a pathway of APC/C inhibition and metaphase arrest.
细胞静止因子（CSF）通过多种抑制后期促进复合物/细胞周期体（APC/C）激活的途径，将脊椎动物卵母细胞阻滞在减数分裂II中期。在非洲爪蟾中，Mos-MEK1-MAPK-p90（Rsk）级联利用纺锤体组装检查点成分来实现中期阻滞。另一条途径涉及细胞周期蛋白E-Cdk2，卵提取物中持续的细胞周期蛋白E-Cdk2活性在没有Mos的情况下会导致中期阻滞；后一发现表明，一条独立的途径有助于CSF阻滞。在此，我们证明，细胞周期蛋白E-Cdk2介导的中期阻滞需要纺锤体检查点激酶单极纺锤体1（Mps1），而Mos介导的中期阻滞则不需要，Mps1是细胞周期蛋白E-Cdk2的一个靶点，也与中心体复制有关。xMps1在卵母细胞成熟过程中合成并激活，在CSF释放时失活。在卵提取物中，组成型活性细胞周期蛋白E-Cdk2抑制了钙介导的CSF释放，野生型xMps1则延迟了这种释放。反义寡核苷酸对细胞周期蛋白E的消除阻止了xMps1的积累，表明细胞周期蛋白E-Cdk2控制着Mps1的水平。在减数分裂II期间，即使在没有Mos-MAPK途径的情况下，激活的细胞周期蛋白E-Cdk2也能显著抑制APC/C，但这种抑制不足以抑制减数分裂I和II之间的S期。这些结果独特地将xMps1置于细胞周期蛋白E-Cdk2下游，介导APC/C抑制和中期阻滞途径。
