MOLECULAR CLONING, CHARACTERIZATION AND EXPRESSION OF TWO NOVEL LECTINS IN MUD CRAB, SCYLLA PARAMAMOSAIN

C-type lectins are a group of carbohydrate binding proteins which contain one or more Ca2+ dependent carbohydrate recognition domains (CRDs). They have been regarded as one of the most important pattern recognition receptors in invertebrates. In this study, we cloned two novel C-type lectins, namely Sp-lectin3 and Sp-lectin4, from the hepatopancreas of Scylla paramamosain. The predicted amino acid sequences of Sp-lectin3 and Sp-lectin4 possessed several conserved properties of C-type lectins, such as a signal peptide, a single CRD, and a QPD motif (only in Sp-lectin4). The open reading frame of Sp-lectin3 consisted of 5 exons and 4 introns, while that of Sp-lectin4 was composed of 4 exons and 3 introns. In normal cultivated crabs expression of both genes could be detected in almost all the eleven tested tissues and organs, such as hepatopancreas, intestine, gill, haemocytes, and different parts of the reproductive duct. The expression of Sp-lectin3 was highest in hepatopancreas and second highest in ejaculatory ducts; for Sp-lectin4 the highest expression was observed also in hepatopancreas and then in the intestine. We further investigated the expression of Sp-lectin3 and Sp-lectin4 at different developmental stages. The results showed that the expression of both genes increased gradually and reached a peak at the embryonic stage of zoea, then declined sharply at the stage of megalopa, and finally recovered at the stage of crablet. When artificially infected with Vibrio parahaemolyticus, the expression of Sp-lectin3 in ejaculatory ducts was significantly up-regulated at 6h after the infection, and the expression in seminal vesicles was boosted at 12h post infection (P0.05). For Sp-lectin4, the expression was significantly elevated only in hepatopancreas both at 12h and 18h post infection (P0.05). Our results suggested that the two C-type lectins might be involved in the immune response to bacterial infection in Scylla paramamosain. Sp-lectin3 could mainly function in the reproductive system such as the ejaculatory duct and seminal vesicles, while Sp-lectin4 may mainly function in hepatopancreas.