Gene structure and expression patterns of Acdaf-1, a TGF-β type I receptor in Ancylostoma caninum

The components of the transforming growth factor β (TGF-β) signaling pathway in parasitic nematodes remain unknown. In this research, a type I receptor for TGF-β was isolated from the hookworm Ancylostoma caninum. The new gene was designated as Acdaf-1, a Caenorhabditis elegans daf-1 homolog. The full-length cDNA of Acdaf-1 encodes a 595-amino-acid protein with an NH₂-terminal signal peptide. This protein has a cytoplasm tail (209-595aa region) which corresponds to the type 1a membrane topology. Between amino acid position 295-500, the protein contains the ATP binding site, substrate binding sites, and PKC-kinase-like domain. Real-time RT-PCR showed that the transcript was expressed in three main stages of A. caninum. It reached the maximal level in the female adult worm stage with lower transcript level in the first and second larvae (L1/L2) and intermediate level in L3 stages as well as in the male worms. After serum activation, the activity of Acdaf-1 was decreased in L3 larvae. These data implied that Acdaf-1 might relate to the infection ability of the larvae. Immunolocalization revealed that AcDAF-1 was present in eggs, intestine, and epidermis cells of larvae (L1, L2, and L3 stages) with strong signal in primordium of the gonads in L3 and was abundant in epidermis, intestine, and ovary of adult worm. These results suggested that Acdaf-1 might be involved in the interaction of the parasite and host relationship and provide a potential target for parasite control.