Infectious diseases have seriously inhibited the aquaculture of mud crab Scylla paramamosain in southeastern China. Identification of the immune molecules and characterization of the defense mechanisms will be pivotal to the reduction of these diseases. Available data show that leucine-rich repeat (LRR) proteins play a crucial role in protein-protein interactions, recognition processes or immune reactions in both invertebrates and vertebrates. In the present study, we cloned and characterized a LRR cDNA from the mud crab Scylla paramamosain (SpLRR) by using the RACE strategy. Bioinformatics analysis predicted that SpLRR contains one open reading frame of 1893 bp and encodes a LRR protein of 630 amino acids with 17 LRR domains and 5 potential N-glycosylation sites. Further, SpLRR and other arthropod LRR proteins could be clustered into one branch in a phylogenetic tree. SpLRR transcripts were detected using RT-PCR from examined tissues including heart, gill, stomach, intestine, muscle and hemocytes, whereas not from hepatopancreas. More importantly, the SpLRR mRNA expression was up-regulated after infection with Vibrio alginolyticus, Beta streptococcus or Poly I: C for 12-48 h, suggesting a novel LRR homolog in crab might be associated with the resistance to pathogens. The result could be important for future investigation of crab immune defense mechanisms.
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