You Zhou

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The surface layer of Schistosoma mansoni is an anucleated syncytium, covered by an apical plasma membrane (APM) and an overlying envelope (En), and is connected with the subsyncytial cell bodies via the membrane-bound cytoplasmic connections (MCC). This syncytium is considered as an adaptation for rapid and synchronous renewal of the surface membranes which play an important role in evasion of the host's immune system.;The present studies demonstrated the effects of the third complement component (C{dollar}\sb3{dollar}) and serotonin (5HT) on the synthesis of the discoid bodies (DBs) and multilamellar bodies (MLBs), and major syncytial inclusion bodies in vitro. With short-time incubations (20 or 40 min), 5HT stimulated synthesis of the DBs by 2 fold, while C{dollar}\sb3{dollar} accelerated synthesis of the MLBs by 2 fold. However, when microtubules (MTs) within the MCC were disrupted with colchicine, the DBs and MLBs synthesized in response to 5HT or C{dollar}\sb3{dollar} accumulated in the cell bodies, suggesting that the transport of the organelles to the syncytium is dependent upon the MTs in the MCC. The present study also revealed the presence of the MTs in the syncytium. These MTs are organized in a radial crisscross array, interacting with the APM and spines, and may play an important role in regulating the distribution and exocytosis of the membrane precursor organelles once in the surface syncytium.;The present study demonstrated the presence of ring-shaped F-actin associated with the surface sensory receptors. These F-actin structures can be characterized into two types according to their size, density, and distribution: the F-actin rings, found in the syncytia of both the male and female worms, appear to be more dense and larger in size than the other type of F-actin structures located only at the central regions of the male dorsal syncytial tubercles.;The surface spines, another major syncytial component, consist of bundles of microfilaments (MFs) having identical polarity. These MFs interact with both the APM and basal membrane via some electron-dense material(s) which is commonly seen in many other cell systems. MF-networks or scattered MFs having various polarities were also observed in the syncytial cytoplasm.;Consistent with the demonstrations showing the presence of the syncytial MFs and MTs, actin and tubulin were detected in the syncytial materials of the parasites by electrophoretic and immunoblotting analysis. Two other major polypeptides, with relative masses of 180 and 75 kDa, were also characterized in association with the spine MFs using immunofluorescence confocal laser scanning and immunogold labelling electron microscopy.



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