Identification and expression of a transforming growth factor beta (TGF-β) homologue in the tropical liver fluke Fasciola gigantica.

Liver flukes, Fasciola spp., are veterinary and medically important parasites infecting numerous species of economically important animals in addition to humans on a global scale. The components of transforming growth factor beta (TGF-β) signalling are widely distributed throughout the animal kingdom and are considerably conserved. Through shared common signal transduction mechanisms, crosstalk of TGF-β signalling between a host and the parasite during infection is possible. Herein, we have identified and undertaken the molecular characterisation of a putative TGF-β homologue from the tropical liver fluke F. gigantica (FgTLM). A FgTLM cDNA was 3557 bp in length, it encoded for 620 amino acid polypeptide which consisted of 494 amino acids of prodomain and 126 amino acids comprising the mature protein. FgTLM displayed characteristic structures of mammalian TGF-β ligands that were unique to the inhibin-β chain, monomer of activin. A phylogenetic analysis revealed the high degree of conservation with TGF-β molecules from trematode species. Interestingly, the sequence of amino acid in the active domain of FgTLM was completely identical to FhTLM from F. hepatica. FgTLM expressed throughout the lifecycle of F. gigantica but was highly expressed in developmental active stages. The dynamics of expression of FgTLM during the developmental stages of F. gigantica was comparable to the pattern of TGF-β expression in F. hepatica. Our findings demonstrated that FgTLM exhibits a high level of similarity to FhTLM in the context of both amino acid sequence and the life stage expression patterns. These similarities underline the possibility that the FgTLM molecule might have the same properties and functions as FhTLM in biological processes of the immature parasites and host immune evasion. Consequently, the specific biological functions of FgTLM on either parasite or relevant hosts need to be defined experimentally.