Molecular identification and expression analysis of cathepsins O and S 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 maintenance of cellular homeostasis. Rock bream (Oplegnathus fasciatus) cathepsin O and S (RbCTSO and RbCTSS, respectively) cDNAs were identified by expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCTSO cDNA (1698 bp) contained an open reading frame (ORF) of 1017 bp encoding 338 amino acids. The full-length RbCTSS cDNA was 1401 bp in length and contained an ORF of 1014 bp encoding 337 amino acids. RbCTSO was significantly expressed in the liver, peripheral blood lymphocytes (PBLs) and spleen. On the other hand, RbCTSS showed significant expression in the liver, trunk kidney, muscle and gills. Real-time RT-PCR was used to examine RbCTSO and RbCTSS mRNA expression in several tissues (kidney, spleen, liver and gill) under conditions of bacterial and viral challenge. Experimental infection of rock bream with Streptococcus iniae and red sea bream iridovirus (RSIV) resulted in significant increases in RbCTSO and RbCTSS mRNA levels in the tissues.