Cloning and expression analysis of the 2-CRD galectin gene (ScGL) from Sinonovacula constricta

The galectin gene from Sinonovacula constricta (named ScGL) was cloned using RACE method. The full length cDNA sequence of ScGL was 1 282 bp, which contains 35 bp 5'UTR, 329 bp 3'UTR and 918 bp open reading frame (ORF) that encoded 305 amino acid residues. Analysis of amino acid sequences showed that ScGL lacks a transmembrane domain and contains 2 CRD unlike the galectin containing one CRD that has been identified in S. constricta. Multiple sequence alignment and phylogenetic analysis showed that ScGL shared a hige degree of conservation with galectin of other species and had the similarity identity with Ruditapes philippinesis (65%), 39.74% and 44.76% identical with two galectins reported in S. constricta. ScGL was expressed in inclusion bodies with a calculated molecular mass of 34.4 ku. Quantitative real-time PCR detection results indicated that the ScGL gene was expressed widely in gill, intestine, labial palpus, mantle, exhalent siphon, inhalent siphon, foot and visceral mass, and high expression level was observed in the intestinal, visceral mass, labial palpus and foot, and the lowest expression in the exhalent siphon, and inhalent siphon. After Staphylococcus aureus challenge, the expression of ScGL in the digestive gland was significantly up-regulated at 3 and 48 hpi (hours past infection). Upon Vibrio anguillarum and S. aureus challenge, the expression of ScGL was significantly up-regulated in the gill respectively at 6 and 48 hpi. The result suggests that ScGL might participate in the innate immune response of S. constricta triggered by pathogens. The study provides the basis for further research of the ScGL in S. constricta immunity.