Cloning and expression of a GST-pi gene in Mytilus galloprovincialis. Attempt to use the GST-pi transcript as a biomarker of pollution

Glutathione S-transferase is involved in the detoxication of many chemical compounds. Northern blot analysis of mRNA GST gene from the mussel Mytilus galloprovincialis shows the presence of a transcript of 850 bp (GenBank accession no. Gi:22094808 and AF527010). The cDNA cloned sequence is constituted by an ORF of 621 bp encoding for a protein of 23,700 Da present in the gills and digestive gland of M galloprovincialis. The sequence, called Mg (M. galloprovincialis) GST-p, is clearly related to the pi class GST. M. galloprovincialis treated with Cd (200 μg/L) and BaP (100 μg/L) or co-treated with Cd and BaP take up cadmium in the gills (16.2 ± 4.2 and 12.6 ± 1.2 μg Cd/g dry wt. after exposure to Cd and Cd + BaP, respectively) and in the digestive gland. The transcription of GST-pi gene, by semi-quantitative RT-PCR, shows the lowest value in the digestive glands of mussels exposed to BaP, whereas the treatment with cadmium and the co-treatment with cadmium and BaP evoke GST-pi gene expression higher than controls. Mussels collected from six sites along the south coast of Portugal show different GST-pi transcription levels, some of which are related to their pollutant content.