| Summary: | The release of genome sequence information is revolutionising the study of helminth parasites by providing important datasets for comparative genomics, allowing the comprehensive analysis of signalling pathways that regulate nematode development. Much of the current knowledge of nematode signalling pathways is based on studies of the free-living model Caenorhabditis elegans. The recent availability of the Trichinella spiralis genome sequence presented an opportunity to study signalling pathways of this, and other, parasitic nematodes, providing a phylum-wide overview of a given signalling pathway. The transforming growth factor-β (TGF-β) ligands are a superfamily of structurally related polypeptides that regulate a wide range of cellular processes in animal tissues. Since the discovery that the TGF-β daf-7 regulates the developmentally-arrested dauer stage in C. elegans, there is the potential for TGF-β signalling to regulate developmental arrest, parasite development and even host-parasite communication in T. spiralis and other nematodes. In the present study, thirteen genes encoding putative TGF-β signalling components, from T. spiralis, have been identified and characterised. Phylogenetic analysis suggests that daf-7 is not conserved beyond C. elegans and that functional extrapolation from C. elegans biology to distantly-related nematodes is difficult. Furthermore, the analysis herein shows a high level of divergence among parasitic nematode TGF-βs. Since the last common ancestor of T. spiralis and C. elegans was the ancestor of the entire nematode phylum, these comparisons allow speculation on the TGF-β signalling networks of the ancestral nematode and provide information on the emergence of TGF-β signalling in animals. ES products from T. spiralis are shown to be capable of interacting directly with mammalian cell receptors and utilise their receptors to control gene expression in vitro. This presents the possibility that these TGF-β ligands may play a part in the formation and maintenance of the host-parasite complex.
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