Release from meiotic arrest in ascidian eggs requires the activity of two phosphatases but not CaMKII
Release from meiotic arrest in ascidian eggs requires the activity of two phosphatases but not CaMKII
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DOI：
10.1242/dev.096578
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发表时间：
2013-11-15
期刊：
影响因子：
4.6
通讯作者：
McDougall, Alex
中科院分区：
文献类型：
--
作者：
Levasseur, Mark;Dumollard, Remi;McDougall, Alex
受精的精子触发了短暂的Ca 2+增加，在绝大多数动物卵子中将卵子从细胞周期停滞中释放出来。在脊椎动物卵中，APC/C-cdc 20抑制剂Erp 1将中期II停滞的释放与Ca 2+瞬变联系起来，其降解由Ca 2+诱导的CaMKII激活触发。相比之下，许多无脊椎动物群体有成熟的卵子，在中期I逮捕，这些物种不具备CaMKII目标Erp 1在他们的基因组。因此，目前尚不清楚细胞周期阻滞在中期I是如何实现的，以及受精Ca 2+瞬变是如何克服绝大多数动物物种的阻滞的。使用活细胞成像与一种新的细胞周期蛋白报告研究细胞周期阻滞和释放在urochordate海鞘，最接近的活无脊椎动物组的脊椎动物，我们已经确定了一个新的信号通路细胞周期恢复中CaMKII不起作用。相反，我们发现，钙激活磷酸酶钙调神经磷酸酶（CN）是卵激活所必需的。此外，我们表明，孤雌激活中期I-逮捕鸡蛋MEK抑制，独立的Ca 2+的增加，需要第二个鸡蛋磷酸酶的活性：PP 2A。此外，PP 2A活性与CN一起是受精期间正常卵子激活所需的。由于海鞘是脊椎动物的姐妹群，我们讨论了这些发现与脊索动物细胞周期阻滞和卵激活。
The fertilising sperm triggers a transient Ca2+ increase that releases eggs from cell cycle arrest in the vast majority of animal eggs. In vertebrate eggs, Erp1, an APC/C-cdc20 inhibitor, links release from metaphase II arrest with the Ca2+ transient and its degradation is triggered by the Ca2+-induced activation of CaMKII. By contrast, many invertebrate groups have mature eggs that arrest at metaphase I, and these species do not possess the CaMKII target Erp1 in their genomes. As a consequence, it is unknown exactly how cell cycle arrest at metaphase I is achieved and how the fertilisation Ca2+ transient overcomes the arrest in the vast majority of animal species. Using live-cell imaging with a novel cyclin reporter to study cell cycle arrest and its release in urochordate ascidians, the closest living invertebrate group to the vertebrates, we have identified a new signalling pathway for cell cycle resumption in which CaMKII plays no part. Instead, we find that the Ca2+-activated phosphatase calcineurin (CN) is required for egg activation. Moreover, we demonstrate that parthenogenetic activation of metaphase I-arrested eggs by MEK inhibition, independent of a Ca2+ increase, requires the activity of a second egg phosphatase: PP2A. Furthermore, PP2A activity, together with CN, is required for normal egg activation during fertilisation. As ascidians are a sister group of the vertebrates, we discuss these findings in relation to cell cycle arrest and egg activation in chordates.