Molecular Mechanisms of Sperm-Egg Interactions in the Ascidians

海鞘是雌雄同体的，许多种类是自不育的。利用两种自交不育的单生海鞘（Ciona cocidiansas）模式系统--海鞘（Ciona cocidiansas）（Enterogona）和罗氏盐萼海鞘（Halocynthia roretzi）（侧耳属Pleurogona），研究了精卵相互作用的分子机制。玻璃海鞘中的α-L-岩藻糖苷酶）和卵黄外壳（VC）的相应糖链介导海鞘精子与同源VC的结合。一些实验证据进一步支持了这一假设，在玻璃海鞘和盐辛西娅。In H. roretzi，我们已经纯化了约70 kDa的主要VC糖蛋白。它具有末端岩藻糖残基，可能作为精子受体。从玻璃海鞘精子中分离纯化出一种VC溶素，并证明其能消化VC最外层的薄层。研究还表明，一种Zn^<++>依赖性金属蛋白酶参与了精子的形成， ...更多信息 通过对玻璃海鞘卵巢卵母细胞的体外受精试验，我们发现玻璃海鞘自身不育是由其上的卵泡细胞的产物控制的，可能是一种糖蛋白。当具有萌发囊泡的完全发育的卵巢卵母细胞在室温下在海水中孵育时，它们在20分钟内经历萌发囊泡破裂并变得可育，并且最终在最多3小时的孵育内获得自身不育。当它们在孵育前通过轻轻摇动去除卵泡细胞时，即使在3小时后，它们中的大多数仍然保持自能生殖。如果将无卵泡细胞的卵母细胞与游离卵泡细胞一起孵育，则它们既成为自身不育的卵母细胞，也成为卵泡细胞完整的卵母细胞。这是被精子中的胰凝乳蛋白酶溶素消化的层。因此，顶体反应的诱导可能是精子与VC的同种识别所调控的位点。少

The ascidians are hermaphrodite and many species are seif-sterile. Using two species of self-sterile solitary ascidiansas model systems, Ciona intestinalis (Enterogona) and Halocynthia roretzi (Pleurogona), molecular mechanisms underlying the sperm-egg interactions were studied.We postulated previously that a sperm glycosidase (e.g., alpha-L-fucosidase in Ciona) and corresponding sugar chains of the vitelling coat (VC) mediate the binding of ascidian sperm to the homologous VC. Several lines of experimental evidence has further supported this hypothesis in both Ciona and Halocynthia. In H. roretzi, we have purified the major VC glycoprotein of about 70 kDa. It has terminal fucose residues and presumably serves as a sperm-receptor. Its amino acid sequence was partially revealed.A chymotrypsin-like protease was purified from Ciona sperm as a VC-lysin and proved to digest the outermost thin layer of the VC. It was also shown that a Zn^<++>-dependent metalloprotease is involved in sperm-eg … More g fusion in Ciona.By using in vitro fertilization assay of oocytes from Ciona ovaries, we have found that self-sterility is controlled by products, presumably a glycoprotein, of the overlying follicle cells. When fully-grown ovarian oocytes with a germinal vesicle were incubated in sea water at room temperature, they underwent germinal vesicle breakdown within 20 minutes and became fertile, and eventually acquired self-sterility within a maximum of 3 hours of incubation. When they were deprived of follicle cells by gentle shaking before incubation, most of them remained self-fertile even after 3 hours. If follicle cell-free oocytes were incubated with the free follicle cells, they became self-sterile as well as follicle cell-intact oocytes.The acquisition of self-sterility was accompanied by an ultrastructural change in the VC fixed with tannic acid : an electron-dense, thin layer appeared on the outer surface of the VC after 3 hours of incubation. This was the layer digested by the chymotryptic lysin in the sperm. Therefore it is suggested that the induction of acrosome reaction is the site modulated by allo-recognition between sperm and VC. Less