Identification and characterization of 3 integrin in Crassostrea hongkongensis

Crassostrea hongkongensis is a main oyster species farmed in South China Sea offshore area, and commonly suffers from vibriosis. Vibrio parahaemolyticus is one of the principal pathogens that causes the oyster vibriosis. The integrin from C. hongkongensis was studied for its function against V. parahaemolyticus in the current work. The full-length cDNA sequence was 3274 bp with an open reading frame (ORF) of 2397 bp that encoded a polypeptide of 798 amino acids. The polypeptide included typical domains of beta integrin (such as INB domain, three EGF-like domains, and highly conserved NPX[Y/F] motif), and phylogenetically clustered with beta 3 integrins of other invertebrates, thereby, designated as ChInt beta 3. The mRNA transcripts of ChInt beta 3 were significantly higher in the heart, hemocytes, adductor muscle and hepatopancreas than those in gills and mantle of C. hongkongensis. Following stimulation with V. parahaemolyticus, the mRNA expression level of ChInt beta 3 was significantly up-regulated in both hemocytes and hepatopancreas. The recombinant ChInt beta 3 had significantly agglutinating activity on Escherichia coli, V. parahaemolyticus, Bacillus amyloliquefaciens, Pichia pastoris and the red blood cells of rabbit. In the one hand, the survival rate (83.33 +/- 5.77%) of the oyster after V. parahaemolyticus infection at 30 days was significantly higher in the ChInt beta 3 overexpression group than those in the physiological saline control group (26.67 +/- 20.82%) (p < 0.01) and the overexpressed GFP group (26.67 +/- 5.77%) (p < 0.01); in the other hand, the cumulative survival duration of C. hongkongensis was significantly shorter in the RNAi treatment group (197.6 +/- 2.77 h) than that in the control group (247.2 +/- 36.24 h) (p < 0.01). The results indicated that ChInt beta 3 was involved in the recognition and clearance of V. parahaemolyticus through cell adhesion, and contributed to the further understanding of the function of ChInt beta 3 against infection of pathogens.