Effects of heavy metals on transcription levels of antioxidant and stress responsive genes of Javanese medaka Oryzias javanicus

Abstract

The differential expression of eight genes representing stressor biomarkers (OjaCAT, OjaCYP1A, OjaG6PD, OjaGPx, OjaGR, OjaGST, OjaSOD, and OjaUB) was investigated by real-time quantitative PCR in liver of Javanese medaka, Oryzias javanicus, after exposure to Ag, Cd, Cu, Zn, Cr and Ni at various concentrations. The level of OjaCAT mRNA increased in a dose-dependent manner on 24-h exposure to Cd, Cu and Zn. However, after Ag, Cr and Ni exposure, a significant decrease in OjaCAT levels was observed. OjaCYP1A mRNA levels decreased drastically on exposure to all heavy metals tested. OjaG6PD mRNA levels showed a dramatic increment after 24-h exposure to Cu and Zn at low doses. However, mRNA levels decreased at high concentrations of Cu and Zn. In the case of Ag, Cd, Cr and Ni exposure, no prominent expression changes were observed. OjaGPx mRNA levels in liver were induced by Ag, Cd, Cu and Zn exposure, but suppressed by Cr and Ni exposure. Exposure to all heavy metals tested upregulated mRNA levels of OjaGR. OjaGST mRNA expression was upregulated by all heavy metals tested in a dose-dependent manner. OjaSOD mRNA levels increased on exposure to Ag, Cd, Zn and Cr, but no responses could be observed after Cu and Ni exposure. Positive induction of OjaUB expression was observed for all doses of heavy metal exposure. The induction and repression pattern of each gene level to the different heavy metals will provide multi-biomarker system for biomonitoring of aquatic environments.