Dolichol phosphate is a rate-limiting factor in mannosyl transferase activity of adult male worms of Schistosoma mansoni

An historical and genomic view of schistosome conjugal biology with emphasis on sex-specific gene expression

The genetic programmes associated with the sexual biology of dioecious schistosomes remain a critically important but significantly understudied area of parasitology. Throughout the last four decades, progress has been slow in describing the gross antigenic and proteomic differences linked to sexually mature schistosomes and in characterizing some of the sex-associated transcripts and regulatory mechanisms induced during developmental maturation. These investigations have been severely hindered by the lack of complete EST/genomic information, as well as corresponding post- and functional-genomic tools for studying these pathogenic parasites. As near complete transcriptomes forSchistosoma japonicumandS. mansonihave recently been reported, and both DNA microarrays and post-transcriptional gene silencing have been applied to schistosomes, the tools and techniques for the high-throughput identification and characterization of transcripts involved in conjugal biology are now readily available. Here, an historical review is presented that summarizes some of the most significant findings associated with schistosome sex and sexual maturation during the last several decades. Following this discussion is a current overview of some modern day genomic approaches used to study schistosomes, which illustrates how major advances in the field of conjugal biology will be achieved.

The N-terminus moiety of the cystatin SmCys from Schistosoma mansoni regulates its inhibitory activity in vitro and in vivo

The complete sequence of SmCys, a cystatin expressed by Schistosoma mansoni, was obtained. Constructs of SmCys consisting of deletions of 10 and 20 amino acid residues from the N-terminal of the full length recombinant protein, were cloned in the pQE-30 vector, expressed in Escherichia coli and assayed for inhibitory activity against papain. Kinetic analysis showed that SmCys -10 and SmCys -20 had K(i) values of 0.7391 and 4.9154, respectively, as compared to 0.0647, displayed by the full length recombinant. Protease inhibition by SmCys was also observed in vivo. When the recombinant products were incubated during 7 days with live schistosomula in the presence of red blood cells, only the full length product could completely inhibit the formation of haemozoin, a dark pigment formed as a by-product of haemoglobin digestion. The sequence data of the recombinant SmCys proteins were used for the construction of molecular models, which were then subjected to molecular dynamics for 2ns. In comparison to the full length, the models corresponding to the truncated constructs, showed a distinctive change on the surface charge distribution. This parameter was more pronounced in SmCys -20, which also displayed a significant displacement of the inhibitory domain, a result which could explain the kinetic data in terms of the loss of attachment sites. These changes correlated well with the progressive lack of inhibition observed for the recombinant deletion constructs, in vitro and in vivo.

Dolichol phosphate mannose synthase is differentially expressed in male and female worms of Schistosoma mansoni

The cDNA encoding the Schistosoma mansoni dolichol phosphate mannose synthase was completely sequenced, displaying the highest homology with Cricetulus griseus and Saccharomyces pombe genes. The Schistosome enzyme had a K(m) of 0.127 microM, a value that is within the range of those reported for several other species. Thin-layer chromatography of the radiolabelled schistosome lipid intermediate showed it was identical to dolichol-phosphate (C80-C105). Expression of dolichol phosphate mannose synthase of S. mansoni (SmDPMS) was analysed by Northern blot and quantified by semi-quantitative RT-PCR with cDNA from mature and immature male and female worms. Northern blot analysis revealed a single 1-kb band. Both approaches confirmed a higher level of expression in mature female worms, as compared to immature and male worms.