Variations in gene expression levels in four European zebra mussel, Dreissena polymorpha, populations in relation to metal bioaccumulation: A field study

• Expression levels of nine genes were analyzed in zebra mussels from four rivers.
• Mussels with the lowest metal levels had the highest in gene expression.
• Different confounding factors were pointed out (size, season, trophic resources).
• This work highlights the relevance of using molecular biomarkers in field studies.

The present study was performed to validate the suitability of using gene expression in zebra mussels, Dreissena polymorpha, for biomonitoring of freshwater environment. Mussels were collected in four French rivers (Meuse, Moselle, Oise and Vilaine) in spring and autumn. Relative gene expression of 9 candidate genes involved in cellular metabolic activities (Cytochrome-c-oxidase – cox, and ATP synthase – atp), detoxification process (Metallothionein – mt and Glutathion-S-Transferase – gst), oxidative stress (Catalase – cat, Superoxyde Dismutase – sod and Glutathion peroxidase – gpx) and digestive functions (Amylase – amy and Cellulase – ghf) were measured in digestive gland. Metal bioaccumulation in tissues and morphometric parameters were also analyzed to interpret molecular responses. All our results are consistent with different physiological reactions to environmental condition between zebra mussel populations. In spring, the levels of mt, sod, gpx, cat, atp, amy and ghf relative expression were significantly higher in mussels with the lowest metal bioaccumulation (the Meuse) compared to at least one of the other sites. In autumn, this higher expression levels in Meuse River were still observed for gpx, cat, atp and amy. This study has also pointed out different sources of variability in gene expression (individual size, season, trophic resources and origin of mussels) which are inevitable in natural fluctuant environment. This underlines the importance to take them into account in field study to propose a correct interpretation of biomarker responses.