Characterization of two C-type lectin-like domain (CTLD)-containing proteins from the cDNA library of Chinese mitten crab Eriocheir sinensis.

Chinese mitten crab Eriocheir sinensis is one of the most important aquaculture crustacean species in China. A cDNA library was constructed from mixed tissues of E. sinensis challenged with LPS. Eight genes involved in immune response were identified from 319 single colonies. Among them, two different C-type lectin-like domain (CTLD)-containing proteins were firstly identified in Chinese mitten crab. The full-length cDNA sequences of two C-type lectin-like domain (CTLD)-containing proteins named EsCTLDcp-1 and EsCTLDcp-2 were cloned by 5' RACE. The deduced amino acid sequences of EsCTLDcp-1 and EsCTLDcp-2 possessed several conserved features of C-type lectin subfamily. The tissue distribution of EsCTLDcp-1 and EsCTLDcp-2 was examined by Real-time PCR. In the normal Chinese mitten crab, the expression of EsCTLDcp-2 was detected in all tested tissues such as haemolymph, muscle, intestine, gill, heart, gonad and hepatopancreas, whereas in muscle, intestine, gill, heart and hepatopancreas for EsCTLDcp-1. The highest expressions of EsCTLDcp-1 and EsCTLDcp-2 were both observed in hepatopancreas. LPS significantly induced the expression of EsCTLDcp-1 and EsCTLDcp-2 in the hepatopancreas at the different time points. The induced fold change of EsCTLDcp-1 and EsCTLDcp-2 increased significantly from 2 h for EsCTLDcp-1 and 4 h for EsCTLDcp-2, and reached a maximum at 12 h, then dropped at 24 h. A differential pattern was found in Chinese mitten crab challenged with Chinese mitten crab pathogen Aeromonas hydrophila. The expression of EsCTLDcp-1 increased significantly at 2 h post-challenge crabs with A. hydrophila, then decreased at 4 h and 8 h, after that increased at 12 h and 24 h. The expression of EsCTLDcp-2 was decreased at the all time points. All these data suggest a differential role of EsCTLDcp-1 and EsCTLDcp-2 in the crab innate immune response to bacterial infection.