Expression of two metallothionein genes in different brain regions of common carp.

The expression pattern of two metallothionein (MT) genes in response to temperature shock and exposure to Cd(2+) was investigated in the brain of common carp ( Cyprinus carpio ), in whole-animal experiments. The changes in the levels of MT-1 and MT-2 mRNA in the olfactory lobe, midbrain and cerebellum were followed by semiquantitative RT-PCR. The inducibility of the two MT genes was brain region and stressor-specific. Cd(2+) affected mostly the expression of MT-2, while the level of the MT-1 transcript did not change significantly in any of the brain regions examined. Moreover, the MT-2 expression was regulated spatially; MT-2 was induced significantly more strongly in the olfactory lobe than in the cerebellum or midbrain. A sudden temperature drop mainly affected the expression of the MT-1 gene; after 5 h of cold shock, the MT-1 mRNA level was about 25% of the basal value in the cerebellum and the midbrain region. The MT-2 expression did not change significantly during this treatment.