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The schistosome egg: development and secretions

Published online by Cambridge University Press:  07 May 2002

P.D. ASHTON ,
R. HARROP ,
B. SHAH  and
R.A. WILSON
P.D. ASHTON
Affiliation:
Department of Biology, University of York, PO Box 373, York YO10 5YW
R. HARROP
Affiliation:
Department of Biology, University of York, PO Box 373, York YO10 5YW Current address: Oxford BioMedica (UK) Ltd, Medawar Centre, Robert Robinson Avenue, The Oxford Science Park, Oxford OX4 4GA.
B. SHAH
Affiliation:
Department of Biology, University of York, PO Box 373, York YO10 5YW
R.A. WILSON
Affiliation:
Department of Biology, University of York, PO Box 373, York YO10 5YW
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Abstract

We have investigated the development of the schistosome egg and its secretions in order to understand how it migrates through gut tissues and also initiates pathology in the liver. We show by electron microscopy that the subshell envelope is absent in the newly deposited egg, but appears very early and differentiates as development progresses. In the mature egg, this nucleated envelope contains extensive endoplasmic reticulum, suggestive of a protein synthetic capacity. Furthermore, Reynolds' layer only appears between the envelope and the egg-shell in the mature egg and may represent its accumulated secretions. We have biosynthetically labelled and collected the secretions (ESP) released by mature but not immature eggs during culture. Their fractionation by SDS–PAGE reveals a simple pattern of 6 bands, differing markedly in composition from soluble egg antigen preparations. Electrophoresis in casein substrate gels demonstrates the presence of 2 distinct proteases in the egg secretions. By immunocytochemistry, ESP localized predominantly to the envelope of the mature egg, suggesting that this layer rather than the miracidium is the source of egg secretions.

Keywords

schistosome eggultrastructuredevelopmentsecretionprotease
Type
Research article
Information
Parasitology , Volume 122 , Issue 3 , March 2001 , pp. 329 - 338
Copyright
2001 Cambridge University Press

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