Chemoattraction between adult Schistosoma mansoni worms
Ghaleb, Amr Medhat
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My doctoral research addressed questions about the nature of the attraction between adult Schistosoma mansoni worms, which are parasitic blood flukes trematodes of man. This research represented one of the sincere attempts to identify and to purify a mate attractant factor from these organisms. My main objectives were (a) to develop an improved bioassay to assess the behavior of S. mansoni male and female worms towards each other, (b) to look further into the nature of the mechanism by which male and female schistosome worms find each other in the definitive vertebrate host, (c) to explore the nature of the chemotactic factor(s) released by either or both sexes to attract the opposite sex and the dynamics of the attraction, and (d) to characterize, isolate and sequence one of the factors. Most of this work focused on the female-released male-attractant factor(s). Using a combination of bioassays, size fractionations, chromatographic and chemical and enzymatic treatments, I have shown that there is mutual attraction between the opposite sexes of adult S. mansoni worms and absence of same sex attraction. The females were attracted to possibly more than one male-released factors; a <30kDa and a >30kDa factors. Males, were attracted to a <10kDa female released factor(s). The attractant factors were heat-labile and dead worms from both sexes were still attractive. Male-attractant factor(s), was not in the female vomitus, and TLC showed the absence of lipids and carbohydrates. Male-attractant factor(s) were found to be sensitive to proteases and to be hydrophilic in nature. The results are consistent with the hypothesis that the female-released male-attracting factor(s) has a protein/peptide component of a hydrophilic nature. Using RP-HPLC and specific chemical treatments I have identified, purified and characterized for the first time a 3260 Da peptide released by S. mansoni adult females that plays a role in attracting the males. I also succeeded, using MALDI peptide-MS and MALDI-TOF/TOF, in getting a partial amino acid sequence <QVHHQK> of that peptide. Although I did not identify a homologous sequence in the available schistosomiasis database, completion of the S. mansoni genome will allow eventual identification of the complete peptide.