Cadmium exposure affects on the expression of metallothionein 2 gene in grass carp ( Ctenopharyngodon idellus )

The metallothionein 2 ( mt2 ) genomic gene with 667 bp was cloned from the grass carp ( Ctenopharyngodon idellus ). The structure of mt2 gene was similar with the reported vertebrae mt gene, containing three exons interrupted by two introns. Only one MRE mortify was found in the 5′ flanking region at proximal cluster which was quite different from the previous reports. The number of deduced amino acid was 60, characterized by cysteine-rich. The basal levels and the transcriptional responses of mt2 gene in different organs to cadmium (Cd) were measured using the quantitative real-time PCR (qRT-PCR). In the kidney, the constructive level of the mt2 mRNA was the highest, while the lowest expression level was detected in the skin. The induced impacts of Cd on mt2 mRNA expression were various from tissues. In the liver, gill and skin, the gene was quickly induced at 6 h. After a transient suppression, the expression levels of mt2 mRNA were increased in the intestine and spleen at 12 h, and mt2 mRNA expressed upwards in the bone at 24 h. In the kidney and bone, the expressions elevated only after 48 h Cd induction. The inducibility of mt2 gene to Cd demonstrated that it played a significant role during the metal toxicant detoxification in grass carp and the mt2 gene in the liver was most sensitive to Cd induction.