Transcriptional up-regulation of disk abalone selenium dependent glutathione peroxidase by H 2O 2 oxidative stress and Vibrio alginolyticus bacterial infection

Abstract

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 223TGA 225 that corresponds to selenocysteine (Sec) amino acid as U 75. 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 ( 97LGFPCNQF 104), an active site motif ( 183WNFEKF 188) 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 H 2O 2 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 H 2O 2 oxidative stress and Vibrio alginolyticus infection. Therefore, AbSe-GPx may be involved in a protective role against H 2O 2 oxidative stress and immune defence against bacterial infection.