Department of Research Infrastructures for Marine Biological Resources, Stazione Zoologica Anton Dohrn, 80121 Napoli, Italy.
Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton Dohrn, 80121 Napoli, Italy.
Cells. 2024 Sep 2;13(17):1477. doi: 10.3390/cells13171477.
Sea urchin eggs are covered with layers of extracellular matrix, namely, the vitelline layer (VL) and jelly coat (JC). It has been shown that sea urchin eggs' JC components serve as chemoattractants or ligands for the receptor on the fertilizing sperm to promote the acrosome reaction. Moreover, the egg's VL provides receptors for conspecific sperm to bind, and, to date, at least two sperm receptors have been identified on the surface of sea urchin eggs. Interestingly, however, according to our previous work, denuded sea urchin eggs devoid of the JC and VL do not fail to become fertilized by sperm. Instead, they are bound and penetratedby multiple sperm, raising the possibility that an alternative pathway independent of the VL-residing sperm receptor may be at work. In this research, we studied the roles of the JC and VL using intact and denuded eggs and the synthetic polyamine BPA-C8. BPA-C8 is known to bind to the negatively charged macromolecular complexes in the cells, such as the JC, VL, and the plasma membrane of echinoderm eggs, as well as to the actin filaments in fibroblasts. Our results showed that, when added to seawater, BPA-C8 significantly repressed the Ca wave in the intact eggs at fertilization. In eggs deprived of the VL and JC, BPA-C8 binds to the plasma membrane and increases fibrous structures connecting microvilli, thereby allowing the denuded eggs to revert towards monospermy at fertilization. However, the reduced Ca signal in denuded eggs was nullified compared to the intact eggs because removing the JC and VL already decreased the Ca wave. BPA-C8 does not cross the VL and the cell membrane of unfertilized sea urchin eggs to diffuse into the cytoplasm at variance with the fibroblasts. Indeed, the jasplakinolide-induced polymerization of subplasmalemmal actin filaments was inhibited in the eggs microinjected with BPA-C8, but not in the ones bath-incubated with the same dose of BPA-C8.
海胆卵被层层细胞外基质包裹，即卵黄层（VL）和凝胶层（JC）。已经表明，海胆卵的 JC 成分作为趋化因子或配体，与受精精子上的受体结合，促进顶体反应。此外，卵的 VL 为同种精子提供结合受体，迄今为止，已经在海胆卵的表面鉴定出至少两种精子受体。然而，有趣的是，根据我们之前的工作，没有 JC 和 VL 的裸露海胆卵并没有阻止精子受精。相反，它们被多个精子结合并穿透，这表明可能存在一种独立于 VL 上的精子受体的替代途径。在这项研究中，我们使用完整和裸露的卵以及合成多胺 BPA-C8 研究了 JC 和 VL 的作用。BPA-C8 已知与细胞中的带负电荷的大分子复合物结合，如 JC、VL 和棘皮动物卵的质膜以及成纤维细胞中的肌动蛋白丝。我们的结果表明，当添加到海水中时，BPA-C8 在受精时显著抑制完整卵中的 Ca 波。在缺乏 VL 和 JC 的卵中，BPA-C8 与质膜结合，并增加连接微绒毛的纤维结构，从而使裸露的卵在受精时恢复到单精子受精。然而，与完整的卵相比，裸露的卵中的 Ca 信号减少，因为去除 JC 和 VL 已经降低了 Ca 波。BPA-C8 不能穿过未受精的海胆卵的 VL 和质膜扩散到细胞质中，与成纤维细胞不同。事实上，在微注射 BPA-C8 的卵中，jasplakinolide 诱导的亚质膜肌动蛋白丝聚合被抑制，但在孵育相同剂量 BPA-C8 的卵中则没有。
