Toxicopathology and expression of a CYP1-like gene in gills and digestive gland of wild Mediterranean mussel (Mytilus galloprovincialis) from sites with different contamination profiles and exposed to B[a]P

Even though CYP mixed-function oxidases (MFOs) are well-conserved among eumetazoans, the regulation of putative ‘CYP1-like’ genes in molluscs, which in vertebrates relies chiefly on the aryl hydrocarbon receptor (AhR) pathway, remains under debate. We isolated the full coding sequence of a CYP1-like MFO from the Mediterranean mussel and analysed its transcription in gills and digestive glands in the laboratory and in situ. Acute waterborne exposure to benzo[ a ]pyrene (B[ a ]P), a known mutagen and AhR agonist in vertebrates, at the tested concentrations (up to 100 ng L −1 ) did not significantly modulate the CYP1-like expression in either tissue, despite evidence for DNA damage and histopathological alterations. However, wild mussels collected from estuarine sites with previously described distinct contamination profiles showed different expression patterns in the gills, suggesting that CYP1-like transcription may be influenced by environmental variables other than known AhR agonists in vertebrates, even though these may cause adverse effects. They also indicate that comparisons with vertebrate models should be made with caution, given possible differences in phase I bioactivation and its regulation between lophotrochozoans and higher eumetazoans. • A CYP1-like gene is expressed in Mytilus gills and digestive glands. • The gene shows sequence similarity to the vertebrate CYP1/2 cluster. • Mussel from mixed-contamination estuarine areas had elevated CYP expression in gills. • Different contamination patterns in situ led to differential expression. • 72 h laboratory exposure to B[ a ]P did not induce CYP expression despite effects.