Molecular cloning, functional characterization and localization of an annexin from a fish gill fluke Microcotyle sebastis (Platyhelminthes: Monogenea)

The full cDNA of an annexin gene from Microcotyle sebastis (MsANX) was cloned for the first time in monogeneans. The cDNA of MsANX comprises 1199 bp with a 29 bp 5′ untranslated region, an open reading frame of 1062 bp, and a 108 bp 3′ untranslated region. The recombinantly produced MsANX bound phosphatidylserine vesicles in the presence of Ca2+, whereas no MsANX was precipitated in the absence of free Ca2+. Phylogenetically, MsANX formed a cluster with human annexin A13, known as the earliest annexin in vertebrates and expressed mainly in the intestine. The localization of MsANX in M. sebastis was analyzed by Western blotting and immunohistochemistry using the antiserum raised against the recombinant MsANX. In Western blot analysis, rat antiserum bound to a protein corresponding to the MsANX in size when worm crude extracts were used as antigens, but no bands were detected by the antiserum when the excretory/secretory proteins of worms were used as antigens. In immunohistochemistry analysis, significant antibody binding annexin was found in the ovarian region, the pharynx and the intestinal caecum of the worm. Interestingly, the alimentary canal location of MsANX was similar to the location of human annexin A13, and further research is needed to trace evolutionary relationship among helminthic annexins and human annexin A13. Also it remains to be investigated whether immunization of naïve fish with the recombinant MsANX can induce protective immune responses against M. sebastis infection.