Kyozuka Keiichiro, Chun Jong T, Puppo Agostina, Gragnaniello Gianni, Garante Ezio, Santella Luigia
Research Center for Marine Biology, Asamushi, Tohoku University, 039-3501 Japan.
Dev Biol. 2008 Aug 15;320(2):426-35. doi: 10.1016/j.ydbio.2008.05.549. Epub 2008 Jun 6.
Before successful fertilization can occur, oocytes must undergo meiotic maturation. In starfish, this can be achieved in vitro by applying 1-methyladenine (1-MA). The immediate response to 1-MA is the fast Ca2+ release in the cell cortex. Here, we show that this Ca2+ wave always initiates in the vegetal hemisphere and propagates through the cortex, which is the space immediately under the plasma membrane. We have observed that alteration of the cortical actin cytoskeleton by latrunculin-A and jasplakinolide can potently affect the Ca2+ waves triggered by 1-MA. This indicates that the cortical actin cytoskeleton modulates Ca2+ release during meiotic maturation. The Ca2+ wave was inhibited by the classical antagonists of the InsP(3)-linked Ca2+ signaling pathway, U73122 and heparin. To our surprise, however, these two inhibitors induced remarkable actin hyper-polymerization in the cell cortex, suggesting that their inhibitory effect on Ca2+ release may be attributed to the perturbation of the cortical actin cytoskeleton. In post-meiotic eggs, U73122 and jasplakinolide blocked the elevation of the vitelline layer by uncaged InsP(3), despite the massive release of Ca2+, implying that exocytosis of the cortical granules requires not only a Ca2+ rise, but also regulation of the cortical actin cytoskeleton. Our results suggest that the cortical actin cytoskeleton of starfish oocytes plays critical roles both in generating Ca2+ signals and in regulating cortical granule exocytosis.
在成功受精发生之前，卵母细胞必须经历减数分裂成熟。在海星中，通过施加1-甲基腺嘌呤（1-MA）可在体外实现这一过程。对1-MA的即时反应是细胞皮层中快速的Ca2+释放。在此，我们表明这种Ca2+波总是在植物半球起始并通过皮层传播，皮层是紧邻质膜下方的空间。我们观察到，用Latrunculin-A和jasplakinolide改变皮层肌动蛋白细胞骨架可有效影响由1-MA触发的Ca2+波。这表明皮层肌动蛋白细胞骨架在减数分裂成熟过程中调节Ca2+释放。Ca2+波受到InsP(3)连接的Ca2+信号通路的经典拮抗剂U7??和肝素的抑制。然而，令我们惊讶的是，这两种抑制剂在细胞皮层中诱导了显著的肌动蛋白超聚合，表明它们对Ca2+释放的抑制作用可能归因于皮层肌动蛋白细胞骨架的扰动。在减数分裂后的卵中，尽管Ca2+大量释放，U73122和jasplakinolide通过未笼蔽的InsP(3)阻止了卵黄膜的升高，这意味着皮层颗粒的胞吐作用不仅需要Ca2+升高，还需要皮层肌动蛋白细胞骨架的调节。我们的结果表明，海星卵母细胞的皮层肌动蛋白细胞骨架在产生Ca2+信号和调节皮层颗粒胞吐作用中都起着关键作用。
