Kubiak Jacek Z, Bazile Franck, Pascal Aude, Richard-Parpaillon Laurent, Polanski Zbigniew, Ciemerych Maria A, Chesnel Franck
CNRS/University of Rennes 1, Institute of Genetics & Development, Rennes cedex, France.
Folia Histochem Cytobiol. 2008;46(1):5-9. doi: 10.2478/v10042-008-0001-z.
Temporal regulation of M-phases of the cell cycle requires precise molecular mechanisms that differ among different cells. This variable regulation is particularly clear during embryonic divisions. The first embryonic mitosis in the mouse lasts twice as long as the second one. In other species studied so far (C. elegans, Sphaerechinus granularis, Xenopus laevis), the first mitosis is also longer than the second, yet the prolongation is less pronounced than in the mouse. We have found recently that the mechanisms prolonging the first embryonic M-phase differ in the mouse and in Xenopus embryos. In the mouse, the metaphase of the first mitosis is specifically prolonged by the unknown mechanism acting similarly to the CSF present in oocytes arrested in the second meiotic division. In Xenopus, higher levels of cyclins B participate in the M-phase prolongation, however, without any cell cycle arrest. In Xenopus embryo cell-free extracts, the inactivation of the major M-phase factor, MPF, depends directly on dissociation of cyclin B from CDK1 subunit and not on cyclin B degradation as was thought before. In search for other mitotic proteins behaving in a similar way as cyclins B we made two complementary proteomic screens dedicated to identifying proteins ubiquitinated and degraded by the proteasome upon the first embryonic mitosis in Xenopus laevis. The first screen yielded 175 proteins. To validate our strategy we are verifying now which of them are really ubiquitinated. In the second one, we identified 9 novel proteins potentially degraded via the proteasome. Among them, TCTP (Translationally Controlled Tumor Protein), a 23-kDa protein, was shown to be partially degraded during mitosis (as well as during meiotic exit). We characterized the expression and the role of this protein in Xenopus, mouse and human somatic cells, Xenopus and mouse oocytes and embryos. TCTP is a mitotic spindle protein positively regulating cellular proliferation. Analysis of other candidates is in progress.
细胞周期M期的时间调控需要精确的分子机制，而不同细胞的分子机制有所不同。这种可变调控在胚胎分裂过程中尤为明显。小鼠的第一次胚胎有丝分裂持续时间是第二次的两倍。在迄今为止研究的其他物种（秀丽隐杆线虫、粒球海胆、非洲爪蟾）中，第一次有丝分裂也比第二次长，但延长程度不如小鼠明显。我们最近发现，延长小鼠和非洲爪蟾胚胎第一次M期的机制有所不同。在小鼠中，第一次有丝分裂的中期通过一种未知机制特异性延长，该机制类似于存在于第二次减数分裂阻滞的卵母细胞中的细胞静止因子（CSF）。在非洲爪蟾中，细胞周期蛋白B的较高水平参与了M期的延长，但不会导致任何细胞周期停滞。在非洲爪蟾胚胎无细胞提取物中，主要M期因子MPF的失活直接取决于细胞周期蛋白B与CDK1亚基的解离，而不是像之前认为的那样取决于细胞周期蛋白B的降解。为了寻找其他行为与细胞周期蛋白B相似的有丝分裂蛋白，我们进行了两项互补的蛋白质组学筛选，专门用于鉴定非洲爪蟾第一次胚胎有丝分裂时被蛋白酶体泛素化和降解的蛋白质。第一次筛选产生了175种蛋白质。为了验证我们的策略，我们现在正在核实其中哪些真的被泛素化了。在第二次筛选中，我们鉴定出9种可能通过蛋白酶体降解的新蛋白质。其中，23 kDa的蛋白质翻译控制肿瘤蛋白（TCTP）在有丝分裂期间（以及减数分裂退出期间）被证明会部分降解。我们对该蛋白在非洲爪蟾、小鼠和人类体细胞、非洲爪蟾和小鼠卵母细胞及胚胎中的表达和作用进行了表征。TCTP是一种有丝分裂纺锤体蛋白，对细胞增殖起正向调节作用。对其他候选蛋白的分析正在进行中。
