Tissue-specific regulation of metallothionein and metallothionein mRNA accumulation in the Antarctic notothenioid, Notothenia coriiceps

The distribution of metallothionein and metallothionein mRNA was examined in brain, liver and kidney of the red-blooded Antarctic fish Notothenia coriiceps. Basal levels of metallothionein were detected by silver saturation assay; the analysis showed large differences in the metallothionein content, with an increasing amount in kidney, liver and brain, respectively. Reverse transcriptase-mediated polymerase chain reaction was used to amplify two distinct metallothionein cDNA species from RNA extracted from the three tissues examined. Northern blot analysis revealed a high constitutive expression of metallothionein mRNA in kidney, in spite of the low metallothionein content found in this tissue. The analysis of the distribution of the two metallothionein transcripts, termed MT-1 and MT-2, in the tissues showed that the MT-2 transcript was the major form of the metallothionein mRNA in kidney and brain, whilst in liver the expression levels of the two metallothionein transcripts were comparable. This tissue-specific expression of isometallothioneins in the Antarctic fish suggests the presence of an organ-specific regulation of the metallothionein genes.