Abstract
Cathepsin D is a soluble lysosomal aspartic proteinase of the pepsin superfamily that plays a crucial role in immune response. In this study, a novel cathepsin D of noble scallop Chlamys nobilis (named as CnCD) was cloned and its immune response to three different immunostimulants, including polyinosinic polycytidylic acid, lipo-polysaccharide and Vibrio parahaemolyticus, was investigated in golden scallops and brown scallops of C. nobilis with different carotenoids content. The full-length cDNA of CnCD is 1844 bp, containing a 63-bp 5′ terminal untranslated region (5′-UTR), a 1212-bp ORF encoding 403 amino acids and a 569-bp 3′-UTR. The predicted protein sequence of CnCD is composed of a signal peptide, a propeptide domain and a mature domain, and has a conserved bilobal structure. Phylogenetic analysis showed the CnCD was clustered into invertebrate group, and especially close to mollusc. Tissue distribution analysis of CnCD showed it was widely distributed in all tested tissues with higher levels in intestine, haemocytes and hepatopancreas. After immunostimulants challenged, CnCD transcripts were significantly up-regulated compared with the control group, indicating the CnCD plays important roles in immune response. Furthermore, the expression levels of CnCD in golden scallops were significantly higher than that of brown ones at most time points, suggesting carotenoids in golden scallops are important in promoting the immune response against pathogens. These results suggested that CnCD plays important roles in the immune defence against pathogens and the carotenoids can enhance the immune ability by up-regulating immune-related genes in noble scallop.
Published Version
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