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Background  Smad proteins are essential cellular mediators within the transforming growth factor-β (TGF-β) superfamily. They directly transmit incoming signals from the cell surface receptors to the nucleus. In spite of their functional importance, almost nothing is known about Smad proteins in parasitic nematodes including  Haemonchus contortus , an important blood-sucking nematode of small ruminants.    Methods  Based on genomic and transcriptome data for  H. contortus  and using bioinformatics methods, a Smad homologue (called  Hco - daf-8 ) was inferred from  H .  contortus  and the structural characteristics of this gene and its encoded protein  Hco -DAF-8 established. Using real-time PCR and immunofluorescence assays, temporal transcriptional and spatial expression profiles of  Hco - daf-8  were studied. Gene rescue in  Caenorhabditis elegans  was then applied to assess the function of  Hco-daf-8  and a specific inhibitor of human Smad3 (called SIS3) was employed to evaluate the roles of  Hco -DAF-8 in  H. contortus  development.    Results  The features of  Hco- DAF-8 (502 amino acids), including conserved R-Smad domains and residues of the L3-loop that determine pathway specificity, are consistent with a TGF-β type I receptor-activated R-Smad. The  Hco-daf-8  gene was transcribed in all developmental stages of  H. contortus  studied, with a higher level of transcription in the fourth-stage larval (L4) females and the highest level in adult males.  Hco -DAF-8 was expressed in the platymyarian muscular cells, intestine and reproductive system of adult stages. Gene rescue experiments showed that  Hco-daf-8  was able to partially rescue gene function in a  daf-8  deficient mutant strain of  C. elegans , leading to a resumption of normal development. In  H. contortus , SIS3 was shown to affect  H. contortus  development from the exsheathed third-stage larvae (L3s) to L4s  in vitro .    Conclusions  These findings suggest that  Hco -DAF-8, encoded by the gene  Hco-daf-8 , is an important cellular mediator of  H. contortus  development  via  the TGF-β signalling pathway. They provide a basis for future explorations of  Hco -DAF-8 and associated pathways in  H. contortus  and other important parasitic nematodes.

Identification and characterization of an R-Smad homologue (Hco-DAF-8) from Haemonchus contortus