Molecular Mechanisms Underlying Self-Sterility In Ascidian Gametes

海鞘是雌雄同体的，许多种类是自我不育的。在自育单生海鞘中，只有异源，而无自源。精子可以与卵磷脂（VC）结合。据推测，VC的聚焦蛋白和精子的- L聚焦酶介导了这种结合，但控制配子之间异体识别的分子尚不清楚。在另一种自我不育的孤独海鞘中。异种精子和自体精子都通过相似的机制结合VC，即利用聚焦I蛋白和- L - f - ucos I酶。因为失去VC的卵母细胞是自我受精的。在这个物种中，自体精子似乎不能穿透VC。通过对芪脂娜卵巢卵母细胞的体外受精实验，我们发现自体不育是由产品促成或控制的。可能是一种糖蛋白。上面的卵泡细胞。将发育完全的卵巢卵母细胞和生发囊泡放入室温海水中孵育。它们在20分钟内经历了生发囊泡的破裂，并变得有生育能力。并最终获得自我，在最多3小时的孵育。在孵育前用轻摇法除去卵泡细胞，大多数在孵育3小时后仍能自我受精。将无卵泡细胞的卵母细胞与游离卵泡细胞孵育。它们变成了自我不育以及卵泡细胞完整的卵母细胞。自不育的获得伴随着单宁酸固定VC的超微结构变化：电子密度。孵育3小时后，VC外表面出现薄层。在无卵泡细胞的卵母细胞中，只有当卵母细胞与自由卵泡细胞孵育时，才能观察到这一层。我们纯化了一种类似凝血酶的蛋白酶，作为一种卵泡溶解素。有趣的是，从琼脂精中纯化的酶可以消化电子致密层。这些观察结果表明，在卵子发生过程中，卵泡细胞合成一种自我不育控制因子（可能是一种糖蛋白）。在生发囊泡破裂后，它被分泌以一种赋予卵母细胞自我不育的方式包裹在VC上。异体识别分子是否包含在VC的最外层电子致密层中是一个有趣的问题。少

The ascidians are hermaphrodite and many species are self-sterile. In the self-sterile solitary ascidian Ciona intestinalis, only heterologous, but no autologous. spermatozoa can bind to the vitelline coat (VC). It is postulated that fucosyl proteins of the VC and a- L- fucosidase of sperm mediate the binding, yet the molecules controlling allorecognition between the gametes remain unknown. In another self-sterile solitary ascidian Halocynthia roretzi. both heterologous and autologous spermatozoa bind to the VC by a similar mechanism us ing fucosy I proteins and a - L - f ucos i dase. Because the oocytes deprived of the VC are self-fertile. the autologous spermatozoa seem incapable of penetrating the VC in this species.By using in vitro fertilization assay of oocytes from Qi-Qna ovaries, we have found that self-sterility is contributed or controlled by products. presumably a glycoprotein. of the overlying follicle cells. When fully-grown ovarian oocytes with a germinal vesicle were inc … More ubated 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 cellfree oocytes were incubated with the free follicle cells. they became selfsterile 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 layer was similarly observed in follicle cell-free oocytes only when they had been incubated with the free follicle cells. We have purified a chymoteypsin-like protease as a VC-lysin in Ciona spermatozoa. Interestingly, the enzyme purified from Ciona spermatozoa digested the electron-dense layer.These observations suggest that, during oogenesis, follicle-cells synthesize a self-sterility controlling factor (probably a glycoprotein) which. following germinal vesicle breakdown, is secreted to coat the VC in a way that confers self-sterility to the oocytes. It is an interesting question to ask whether the allorecognition molecule (s) is contained in the outermost electrondense layer of the VC or not. Less