Cloning of a river pufferfish (Takifugu obscurus) metallothionein cDNA and study of its induction profile in cadmium-exposed fish.

We report here the full-length cDNA sequence of metallothionein (MT) gene from an anadromous river pufferfish, Takifugu obscurus (order: Tetradotiformes; family: Tetradontidae). Phylogenetic relationship analysis revealed that the identified MT has high sequence similarity with many Perciformes fish species. The tissue distribution and concentration- and time-dependent expression of MT mRNA were studied in fish exposed to cadmium. Liver showed the highest level of MT gene expression followed by other tissues (brain, gill and kidney) in response to cadmium exposure. Muscle showed a weak expression response of MT gene. Time-course study revealed highest early phase (at 6h) expression in the brain and late persistence of induction in the intestine. MT mRNA expression showed a concentration-dependent expression in all the tissues. However, induction in brain and liver occurred at much lower concentrations as compared to other tissues. Our results demonstrate that MT in T. obscurus is induced by cadmium exposure which indicates that it plays a functionally conserved function of metal detoxification.