Regulation of expression of multixenobiotic resistance (MXR) genes by environmental factors in the blue mussel Mytilus edulis.

Marine organisms and especially those living in tidal zones are confronted with dramatic changes in their environment such as temperature fluctuations on a daily and/or seasonal basis. In the present study, we investigated whether these parameters affect expression of multixenobiotic resistance (MXR)-related genes that serve as a first line of defense against a broad spectrum of natural and man-made toxicants. Expression of MXR-related genes seems to be an appropriate biomarker to determine hazardous effects of chemicals in contaminated marine habitats. The interference of natural environmental factors in the expression of biomarkers is an important issue with respect to the use of biomarkers in monitoring biological effects of pollutants, making interpretations difficult. We studied the effects of temperature, salinity and oxygen supply (anaerobiosis) on expression of MXR-related genes in gills and digestive gland of the blue mussel Mytilus edulis in order to differentiate between pollution-induced stress and responses to natural environmental variations. We found changes in expression levels of P-glycoprotein (pgp), major vault protein (mvp), topoisomerase II (topoII), heat shock protein 70 (hsp70), but not of the multidrug resistance-related protein (mrp2) genes, in laboratory experiments in relation to high temperature, low salinity and anaerobiosis but not low temperature. These effects of environmental factors have to be considered in sampling strategies for monitoring programmes to prevent false interpretation of results.