Stazione Zoologica Anton Dohrn, Naples, Italy.
Sci China Life Sci. 2011 Aug;54(8):733-43. doi: 10.1007/s11427-011-4202-x. Epub 2011 Jul 24.
Since the first demonstration of sperm entry into the fertilized eggs of Mediterranean sea urchin Paracentrotus lividus by Hertwig (1876), enormous progress and insights have been made on this topic. However, the precise molecular mechanisms underlying fertilization are largely unknown. The two most dramatic changes taking place in the zygote immediately after fertilization are: (i) a sharp increase of intracellular Ca(2+) that initiates at the sperm interaction site and traverses the egg cytoplasm as a wave, and (ii) the concomitant dynamic rearrangement of the actin cytoskeleton. Traditionally, this has been studied most extensively in the sea urchin eggs, but another echinoderm, starfish, whose eggs are much bigger and transparent, has facilitated experimental approaches using microinjection and fluorescent imaging methodologies. Thus in starfish, it has been shown that the sperm-induced Ca(2+) increase in the fertilized egg can be recapitulated by several Ca(2+)-evoking second messengers, namely inositol 1,4,5-trisphosphate (InsP3), cyclic ADP-ribose (cADPr) and nicotinic acid adenine dinucleotide phosphate (NAADP), which may play distinct roles in the generation and propagation of the Ca(2+) waves. Interestingly, it has also been found that the dynamic rearrangement of the actin cytoskeleton in the fertilized eggs plays pivotal roles in guiding monospermic sperm entry and in the fine modulation of the intracellular Ca(2+) signaling. As it is well known that Ca(2+) regulates the structure of the actin cytoskeleton, our finding that Ca(2+) signaling can be reciprocally affected by the state of the actin cytoskeleton raises an intriguing possibility that actin and Ca(2+) signaling may form a 'positive feedback loop' that accelerates the downstream events of fertilization. Perturbation of the cortical actin networks also inhibits cortical granules exocytosis. Polymerizing actin bundles also compose the 'acrosome process,' a tubular structure protruding from the head of fertilizing sperm. Hence, actin, which is one of the most strictly conserved proteins in eukaryotes, modulates almost all major aspects of fertilization.
自从赫特维希（Hertwig）（1876 年）首次展示地中海扁形虫 Paracentrotus lividus 的受精卵中的精子进入卵母细胞以来，在这个主题上已经取得了巨大的进展和深入的了解。然而，受精的确切分子机制在很大程度上仍是未知的。受精后卵母细胞中立即发生的两个最显著的变化是：（i）在精子相互作用部位起始并沿细胞质作为波传播的细胞内 Ca（2+）的急剧增加，以及（ii）肌动蛋白细胞骨架的同时动态重排。传统上，这在海胆卵中得到了最广泛的研究，但另一种棘皮动物，海星，其卵更大且透明，这促进了使用微注射和荧光成像方法的实验方法。因此，在海星中，已经表明受精的卵母细胞中精子诱导的 Ca（2+）增加可以通过几种 Ca（2+）诱发的第二信使，即肌醇 1,4,5-三磷酸（InsP3）、环 ADP-核糖（cADPr）和烟酰胺腺嘌呤二核苷酸磷酸（NAADP）来再现，它们可能在 Ca（2+）波的产生和传播中发挥不同的作用。有趣的是，还发现受精的卵母细胞中肌动蛋白细胞骨架的动态重排在指导单精子进入和精细调节细胞内 Ca（2+）信号方面起着关键作用。由于众所周知 Ca（2+）调节肌动蛋白细胞骨架的结构，我们发现 Ca（2+）信号可以被肌动蛋白细胞骨架的状态反向影响，这提出了一个有趣的可能性，即肌动蛋白和 Ca（2+）信号可能形成一个“正反馈回路”，加速受精的下游事件。皮质肌动蛋白网络的扰动也抑制皮质颗粒的胞吐作用。聚合的肌动蛋白束还构成了“顶体突起”，这是从受精精子头部伸出的管状结构。因此，肌动蛋白作为真核生物中最严格保守的蛋白质之一，调节着受精的几乎所有主要方面。
