Mad2 is required for inhibiting securin and cyclin B degradation following spindle depolymerisation in meiosis I mouse oocytes
Mad2 is required for inhibiting securin and cyclin B degradation following spindle depolymerisation in meiosis I mouse oocytes
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DOI：
10.1530/rep.1.00856
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发表时间：
2005-12-01
期刊：
影响因子：
3.8
通讯作者：
Herbert, M
中科院分区：
文献类型：
--
作者：
Homer, HA;McDougall, A;Herbert, M
Mad2是纺锤体组装检查点（SAC）的关键组成部分，通过隔离Cdc20抑制后期促进复合物/环小体（APC/C）活性，从而调节securin和cyclin B的破坏。在有丝分裂期间，纺锤体解聚合由于抑制securin和cyclin B的破坏而诱导强烈的Mad2依赖性阻滞。与有丝分裂不同的是，小鼠卵母细胞暴露于纺锤体解聚合时所经历的减数分裂I期阻滞的分子细节仍未完全表征。值得注意的是，Mad2的作用和后期标记物securin的命运尚未被探索。如前所述，我们发现诺可达唑的纺锤体解聚合抑制第一极体挤出（PBE），并稳定小鼠卵母细胞中周期蛋白B和周期蛋白依赖性激酶1的活性。在这里，我们表明，周期蛋白B在诺可达唑中的稳定可以持续数小时，并与安可达唑的稳定有关。这些影响是sac介导的，因为在被morpholino反义耗尽大部分Mad2的卵母细胞中，securin和cyclin B不稳定，15%的卵母细胞发生PBE。这反映了APC/C的过早激活，因为缺乏APC/C降解信号的细胞周期蛋白B的突变形式在缺乏mad2的卵母细胞中是稳定的。此外，同源物在nococlaozole诱导的延长减数分裂I阻滞（bbbb18 h）期间不会分离，这表明非分裂机制本身不足以解决哺乳动物卵母细胞臂内聚的问题。总之，当所有着丝点缺乏附着和张力时，小鼠卵母细胞会产生强大的mad2依赖性减数分裂I阻滞，从而抑制安全蛋白和细胞周期蛋白B的破坏。
Mad2 is a pivotal component of the spindle assembly checkpoint (SAC) which inhibits anaphase promoting complex/cyclosome (APC/C) activity by sequestering Cdc20 thereby regulating the destruction of securin and cyclin B. During mitosis, spindle depolymerisation induces a robust Mad2-dependent arrest due to inhibition of securin and cyclin B destruction. In contrast to mitosis, the molecular details underpinning the meiosis I arrest experienced by mouse oocytes exposed to spindle depolymerisation remain incompletely characterised. Notably, the role of Mad2 and the fate of the anaphase-marker, securin, are unexplored. As shown previously, we find that spindle depolymerisation by nocodazole inhibits first polar body extrusion (PBE) and stabilises cyclin B and cyclin-dependent kinase 1 activity in mouse oocytes. Here we show that stabilisation of cyclin B in nocodazole can be sustained for several hours and is associated with stabilisation of securin. These effects are SAC-mediated as, in oocytes depleted of the majority of Mad2 by morpholino antisense, securin and cyclin B are destabilised and 15% of oocytes undergo PBE. This reflects premature APC/C activation as a mutant form of cyclin B lacking its APC/C degradation signal is stable in Mad2-depleted oocytes. Moreover, homologues do not disjoin during the prolonged meiosis I arrest (> 18 h) induced by nococlaozole indicating that a non-cleavage mechanism is insufficient on its own for resolution of arm cohesion in mammalian oocytes. In conclusion, when all kinetochores lack attachment and tension, mouse oocytes mount a robust Mad2-dependent meiosis I arrest which inhibits the destruction of securin and cyclin B.