School of Biomedical Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.
Development. 2009 Dec;136(24):4077-81. doi: 10.1242/dev.042143. Epub 2009 Nov 11.
Mature mammalian eggs are ovulated arrested at meiotic metaphase II. Sperm break this arrest by an oscillatory Ca(2+) signal that is necessary and sufficient for the two immediate events of egg activation: cell cycle resumption and cortical granule release. Previous work has suggested that cell cycle resumption, but not cortical granule release, is mediated by calmodulin-dependent protein kinase II (CamKII). Here we find that mouse eggs contain detectable levels of only one CamKII isoform, gamma 3. Antisense morpholino knockdown of CamKIIgamma3 during oocyte maturation produces metaphase II eggs that are insensitive to parthenogenetic activation by Ca(2+) stimulation and insemination. The effect is specific to this morpholino, as a 5-base-mismatch morpholino is without effect, and is rescued by CamKIIgamma3 or constitutively active CamKII cRNAs. Although CamKII-morpholino-treated eggs fail to exit metaphase II arrest, cortical granule exocytosis is not blocked. Therefore, CamKIIgamma3 plays a necessary and sufficient role in transducing the oscillatory Ca(2+) signal into cell cycle resumption, but not into cortical granule release.
成熟的哺乳动物卵在减数分裂中期 II 时被排出并被阻止。精子通过一个震荡的 Ca(2+)信号打破这种阻滞，这个信号对于卵激活的两个直接事件是必要和充分的：细胞周期恢复和皮质颗粒释放。先前的工作表明，细胞周期恢复，但皮质颗粒释放不是由钙调蛋白依赖性蛋白激酶 II（CamKII）介导的。在这里，我们发现小鼠卵中只含有可检测到的一种 CamKII 同工型，γ 3。在卵母细胞成熟过程中用抗 CamKIIγ3 反义 morpholino 进行敲低会产生对 Ca(2+)刺激和授精引起的孤雌激活不敏感的中期 II 期卵。这种作用是针对这种 morpholino 的，因为 5 个碱基错配的 morpholino 没有效果，并且可以被 CamKIIγ3 或组成性激活的 CamKII cRNA 挽救。尽管 CamKII-morpholino 处理的卵不能退出中期 II 阻滞，但皮质颗粒外排没有被阻断。因此，CamKIIγ3 在将振荡的 Ca(2+)信号转导为细胞周期恢复中起着必要和充分的作用，但在皮质颗粒释放中不起作用。
