Cloning, characterisation, and expression analysis of the cathepsin D gene from rock bream (Oplegnathus fasciatus)

Cathepsins are lysosomal cysteine proteases belonging to the papain family, members of which play important roles in normal metabolism for the maintenance of cellular homeostasis. Rock bream (Oplegnathus fasciatus) cathepsin D (RbCTSD) cDNAs were identified by expressed sequence tag analysis of a lipopolysaccharide-stimulated rock bream liver cDNA library. The full-length RbCTSD cDNA (1644 bp) contained an open reading frame of 1191 bp encoding 396 amino acids. Alignment analysis revealed that the active sites and N-glycosylation sites of the deduced protein were well conserved. Phylogenetic analysis revealed that RbCTSD is most closely related to the Mi-iuy croaker (Miichthys miiuy) cathepsin D. RbCTSD was ubiquitously expressed in all the examined tissues, predominantly in muscle and kidneys. RbCTSD mRNA expression was also examined in several tissues under conditions of bacterial and viral challenge. All examined tissues of fish infected with Edwardsiella tarda (E. tarda), Streptococcus iniae (S. iniae), and red sea bream iridovirus (RSIV) showed significant increases in RbCTSD expression compared with the control. In the kidney and spleen, RbCTSD mRNA expression was markedly upregulated following infection with all tested pathogens. These findings indicate that RbCTSD plays an important role in the innate immune response of rock bream. Furthermore, these results provide important information for the identification of other cathepsin D genes in various fish species.