Transcriptional up-regulation of disk abalone selenium dependent glutathione peroxidase by H2O2 oxidative stress and Vibrio alginolyticus bacterial infection

Selenium dependent glutathione peroxidase (Se-GPx) belongs to the family of selenoprotein, which acts mainly as an antioxidant in the cellular defence system. We have identified Se-GPx full length cDNA from disk abalone (Haliotis discus discus) designated as AbSe-GPx. It has a characteristic codon at 223TGA225 that corresponds to selenocysteine (Sec) amino acid as U75. The full length cDNA consists of 675 bp, an open reading frame encoding 225 amino acids. Sequence characterization revealed that AbSe-GPx contains a characteristic GPx signature motif 2 (97LGFPCNQF104), an active site motif (183WNFEKF188) and essential residues for the enzymatic function. Additionally, the eukaryotic selenocysteine insertion sequence (SECIS) is conserved in the 3′ UTR. The AbSe-GPx amino acid sequence exhibited the highest level of identity (46%) with insect (Ixodes scapularis) GPx, and shares 41% with bivalve (Unio tumidus) Se-GPx. The RT-PCR analysis revealed that AbSe-GPx mRNA was expressed constitutively in gill, mantle, gonad, abductor muscle, digestive tract, and hemocytes in a tissue specific manner. AbSe-GPx mRNA expression was significantly up-regulated in gill and digestive tract tissues after H2O2 injection and Vibrio alginolyticus infection. However, AbSe-GPx expression was not up-regulated after Aroclor 1254 injection. These results indicate that AbSe-GPx mRNA is expressed at a basal level in abalone tissues, which can be up-regulated transcriptionally by H2O2 oxidative stress and Vibrio alginolyticus infection. Therefore, AbSe-GPx may be involved in a protective role against H2O2 oxidative stress and immune defence against bacterial infection.