Two novel homologs of simple C-type lectin in grass carp (Ctenopharyngodon idellus): Potential role in immune response to bacteria

C-type lectins play important roles in glycoprotein metabolism, multicellular integration and immunity. Based on their overall domain structure, they can be classified as different groups which possess different physiological functions. In this study, two novel simple C-type lectins were identified from grass carp (Ctenopharyngodon idellus), an important cultured fish in China. GcCL1 and gcCL2 share an essentially identical gene structure, a conserved promoter region shorter than 300 bp and an amino acid identity of 81.2%. Phylogenetic analysis indicated they may be products of gene duplication and could be classified as a new clade of group VII C-type lectins. Both of them were expressed in the eleven tissues examined, with the spleen having the highest abundance of transcript. The gcCL1 transcript was more abundant than gcCL2 in the majority of tissue samples from 2-yr-old grass carps, and was lower than those of gcCL2 before 15 days post-hatching. The expression of both genes was significantly up-regulated in spleen, muscle, skin, gills and hepatopancreas after induction by Aeromonas hydrophila. This is the first report that the expression of group VII C-type lectins could be induced by a pathogen, and indicates these lectins may be involved in the immune response to bacteria in fish.