Authors

Discussion

Lipid rafts are microdomains present in plasma membranes that are rich in cholesterol and sphingolipids. As lipid rafts are thought to play an important role in signal transduction, the presence of lipid rafts in the tegument of Schistosoma mansoni schistosomules (somules) and their potential role in molecular communication with the host was investigated. Twenty-four hour in vitro-cultured somules were stimulated with human epidermal growth factor (EGF) and stained for lipid rafts. Confocal laser scanning microscopy revealed that lipid raft clusters were present in the tegument of somules and were preferentially localized towards the anterior cone of the parasite. Furthermore, a number of lipid raft-associated proteins were detected by western blotting/immunofluorescence including flotillin, Ras, and Gq that were predominantly expressed in the parasite tegument; Ras and Gq were also localised in structures like the acetabulum and cephalic ganglia. Epidermal growth factor receptors (EGFRs) were mapped on somules using fluorescence-labelled EGF and were discovered towards the anterior cone of the parasite, consistent with the localisation of lipid rafts. Next, detergent resistant membranes were prepared and proteomic analysis carried out to reveal which proteins are present in these structures. A total of 287 proteins were identified in both triton-insoluble (TI) and triton-soluble (TS) fractions, of which 41 were specifically identified in the TI fraction only. Current experiments on the effect of raft disruption using methyl-beta-cyclodextrin (MBCD) on signalling pathways suggest that cholesterol levels modulate phosphorylation/activation of protein kinase C (PKC), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38 MAPK) and Akt pathways. Future work aims to further characterise the lipid rafts and elucidate their importance to schistosome survival and host-parasite interactions.