Analysis of dauer pathway genes in the parasitic nematode Trichinella spiralis
Trichinella spiralis is a parasitic nematode of mammalian skeletal muscle. Its life cycle includes two stages where developmental progression appears to be inhibited until a specific host niche is encountered. The newborn larva, released within the host intestine depends upon entry to skeletal muscle for continued development. The muscle larva encapsulates within skeletal muscle and further reproductive development is dependent upon ingestion by a new host. Developmental arrest has been extensively characterised in Caenorhabditis elegans, where an alternative L3 larva, the dauer larva, is formed in response to environmental conditions refractive to continued reproductive development. Using the wealth of genetic information regarding C. elegans dauer formation, putative periods of arrest were examined in T. spiralis. TGF-b-like and insulin-like signalling pathways are critical mediators of C. elegans dauer formation. A T. spiralis TGF-b-ligand was identified and designated ts-tll-1. Sequencing and analysis revealed ts-tll-1 to be similar to vertebrate bone morphogenetic proteins and C. elegans DBL-1, is involved in body size regulation. EST mining identified putative type I and II TGF-b receptors and a subtilsin-like proprotein convertase, suggesting conservation of TGF-b-like signalling in T. spiralis. A partial Trichinella gene encoding an orthologue of the C. elegans insulin-like, tyrosine kinase receptor, DAF-2, was identified by degenerate PCR and designated ts-tkr. ts-tkr is most similar to C. elegans daf-2 within the highly conserved tyrosine kinase domain. Two alternative transcripts of ts-tkr were identified by 3’ RACE, which differed in their 3’ UTRs. Semi-quantitative RT-PCR analysis suggested ts-tkr expression was greatest in adult worms, implying a role in promoting reproductive development. Semi-quantitative RT-PCR was also to assess the expression of selected housekeeping and ES protein encoding genes during the T. spiralis life cycle. While transcription in the C. elegans dauer is depressed, there was no obvious transcriptional repression in Trichinella newborn or muscle larva.