The schistosome egg: development and secretions

We hare investigated the development of the schistosome egg and its secreti ons in order to understand how it migrates through gut tissues and also ini tiates pathology in the liver. We show by electron microscopy that the subs hell envelope is absent in the newly deposited egg, but appears very early and differentiates as development progresses. In the mature egg, this nucle ated envelope contains extensive endoplasmic reticulum, suggestive of a pro tein synthetic capacity. Furthermore, Reynolds' layer only appears between the envelope and the egg-shell in the mature egg and may represent its accu mulated secretions. We have biosynthetically labelled and collected the sec retions (ESP) released by mature but not immature eggs during culture. Thei r fractionation by SDS-PAGE reveals a simple pattern of 6 bands, differing markedly in composition from soluble egg antigen preparations. Electrophore sis in casein substrate gels demonstrates the presence of 2 distinct protea ses in the egg secretions. By immunocytochemistry, ESP localized predominan tly to the envelope of the mature egg, suggesting that this layer rather th an the miracidium is the source of egg secretions.