Upregulation of metallothionein and glucose-6-phosphate dehydrogenase expression in silver sea bream, Sparus sarba exposed to sublethal levels of cadmium

In this study, the induction of metallothionein (MT) and glucose-6-phosphate dehydrogenase (G6PDH) gene expression in response to exposure to cadmium (Cd2+) was investigated in silver sea bream (Sparus sarba) in vivo. In addition, a primary hepatocyte culture has been developed from silver sea bream liver in order to assess the changes in gene expression of MT and G6PDH in hepatocytes directly exposed to Cd2+ in vitro. The sea bream metallothionein gene was cloned and characterized for the development of real-time PCR assays for quantification of MT transcript abundance. G6PDH gene expression was quantified using a real-time PCR assay developed using sequence information from a previously cloned silver sea bream G6PDH gene. In both in vivo and in vitro experiments, MT mRNA was highly inducible following Cd2+ treatment. In addition, Cd2+ exposure caused the upregulation of G6PDH mRNA expression and this suggests the possibility of the involvement of G6PDH in the defense against Cd2+-induced oxidative stress in cells. It is likely that the defense system of silver sea bream to Cd2+ stress includes upregulation of G6PDH in addition to metallothionein.