Wells K E, Cordingley J S
Department of Molecular Biology, University of Wyoming, Laramie 82071.
Exp Parasitol. 1991 Oct;73(3):295-310. doi: 10.1016/0014-4894(91)90101-2.
The protein precursors of the schistosome eggshell are synthesized and packaged into secretory vesicles in the vitelline cells. These vesicles appear to contain an emulsion of eggshell precursor material. Evidence is presented to show that these secretory vesicles are acidic as in other systems and that this acidity stabilizes the emulsion and prevents the eggshell cross-linking reactions from occurring. Alkalinizing treatments trigger eggshell formation within the secretory vesicles as shown by (1) the induction of autofluorescence and (2) by electron microscopy which shows that the eggshell precursors have aggregated within the secretory vesicles into spherical particles bearing microspines. These aggregates formed in the secretory vesicles were isolated and shown to have the same protease resistance and amino acid composition as authentic eggshell. The calcium ionophore A23187 induces scattered autofluorescence in intact female worms which electron micrographs show to be due to exocytosis of eggshell material. Based on these observations we propose a model for the formation of schistosome eggshell and suggest that it may apply to all trematodes in which the eggshell precursors are present as stable emulsions in the secretory vesicles of the vitelline cells.
血吸虫卵壳的蛋白质前体在卵黄细胞中合成并包装到分泌小泡中。这些小泡似乎含有卵壳前体物质的乳液。有证据表明，这些分泌小泡与其他系统中的一样呈酸性，这种酸性稳定了乳液并防止卵壳交联反应的发生。碱化处理会触发分泌小泡内的卵壳形成，这表现为：（1）自发荧光的诱导；（2）电子显微镜观察显示卵壳前体在分泌小泡内聚集成带有微刺的球形颗粒。在分泌小泡中形成的这些聚集体被分离出来，显示出与真实卵壳相同的蛋白酶抗性和氨基酸组成。钙离子载体A23187会在完整的雌虫中诱导分散的自发荧光，电子显微镜照片显示这是由于卵壳物质的胞吐作用所致。基于这些观察结果，我们提出了一个血吸虫卵壳形成的模型，并表明它可能适用于所有卵壳前体以稳定乳液形式存在于卵黄细胞分泌小泡中的吸虫。
