Department of Research Infrastructures for Marine Biological Resources, Stazione Zoologica Anton Dohrn, Napoli, Italy.
Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, Napoli, Italy.
Biosystems. 2021 Aug;206:104448. doi: 10.1016/j.biosystems.2021.104448. Epub 2021 May 28.
The sea urchin Arbacia lixula coexist with Paracentrotus lividus in the Mediterranean, but the two sea urchin species are quite different from each other. Concerning the female gamete, A. lixula eggs are much darker than those of P. lividus due to the characteristic pigmentation. Upon insemination, the fertilization envelope formed by A. lixula eggs is remarkably thinner than that of P. livius eggs, which implies that the cortical organization of the eggs in the two species may be quite different. In this communication, we examined the phenotypic plasticity of A. lixula eggs in the changing osmolality. The plasma membrane, cortical actin cytoskeleton and vesicles are extensively altered in the eggs exposed to 40% seawater for 15 min. When fertilized, the Ca response in these eggs was significantly compromised and the sperm often failed to enter the eggs. Remarkably, the pattern of the Ca response was restored when these eggs were transferring back to the natural seawater before fertilization, while the actin cytoskeleton partially reverted to the original state. Nonetheless, these eggs restored in seawater failed to regain the innate sperm receptivity that allows only one sperm to enter in natural seawater. Thus, the ability to guide monospermic fertilization is lost by water entry into the eggs, and the eggs incorporated either multiple or no sperm. On the other hand, eggs briefly exposed to hypertonic seawater exhibited no evident morphological anomaly. Nonetheless, the monospermic eggs that experienced a brief exposure (15 min) to hypertonic seawater prior to fertilization in natural seawater displayed a subtly altered sperm-induced Ca response and morpho-functional anomaly around the pluteus stage. Our results suggest that A. lixula eggs attain only a limited extent of cytological plasticity, and that the osmolality shock affects the physical nature of the egg surface which in turn affects the developmental programming.
地中海中的石鳖（Arbacia lixula）与扁形动物（Paracentrotus lividus）共生，但这两种海胆在很多方面都存在显著差异。就雌性配子而言，由于特征性的色素沉着，石鳖的卵子比扁形动物的卵子颜色深得多。受精时，石鳖卵子形成的受精膜比扁形动物卵子的受精膜薄得多，这意味着这两种物种的卵子皮质组织可能有很大的不同。在本通讯中，我们研究了石鳖卵子在渗透压变化下的表型可塑性。暴露在 40%海水中 15 分钟后，卵子中的质膜、皮质肌动蛋白细胞骨架和小泡广泛改变。当受精时，这些卵子中的 Ca 反应显著受损，精子常常无法进入卵子。值得注意的是，当这些卵子在受精前转移回天然海水中时，Ca 反应模式得到了恢复，而肌动蛋白细胞骨架部分恢复到原始状态。尽管如此，在海水中恢复的这些卵子无法恢复其内在的精子接受能力，即只允许一个精子进入天然海水中。因此，水进入卵子会导致引导单精受精的能力丧失，卵子中会包含多个或没有精子。另一方面，短暂暴露于高渗海水中的卵子没有表现出明显的形态异常。然而，在天然海水中受精前短暂暴露（15 分钟）于高渗海水中的单精卵子表现出微妙改变的精子诱导 Ca 反应和幼体阶段的形态功能异常。我们的结果表明，石鳖卵子仅获得有限程度的细胞学可塑性，渗透压冲击会影响卵子表面的物理性质，进而影响发育编程。
