Epigenetic effects of environmental contaminants on the skin of the fin whale (Balenoptera physalus) in the Mediterranean basin

The phenotypic plasticity of many organisms is mediated in part by epigenetics, the heritable changes in gene activity that occur without any alterations to DNA sequence. A major mechanism is the DNA methylation (DNAm). Hypo- and hypermethylation are generalized responses to control gene expression but recent studies have demonstrated that classes of contaminants could mark specific DNAm signatures, therefore be used to assess prior environmental exposure. We sampled skin and blubber from 6 fin whale (Balenoptera physalus) individuals living in the northern Mediterranean Sea. Blubber was analyzed for Organochlorines levels while genomic DNA extracted from the skin of the animals with the lowest (mean value = 19 µg/g lipid basis, l.b.) (group 1, n=3) and the highest (mean value = 53 µg/g l.b.) (group 2, n=3) levels of contaminants were used for DNAm profiling through reduced representation bisulfite sequencing (RRBS). We tested the hypothesis that the differences in the methylation patterns observed comparing the 2 groups are linked to environmental contaminant exposure and load in the whale tissues.While pronounced variations in CHH and CHG methylation (where H is any base except G) were not observed, the CpGs showed 32683 differentially methylated Cs in promoters and/or exon/intron regions of genes (p <0.05, mean coverage = 8.5), accounting for 13% of the whole set. Gene Ontology indicated that DNAm affected genes dealt with cell differentiation and function in nervous, endocrine, immune, circulatory and muscular systems. qPCR on a larger set of skin samples with known contamination loads correlated differential expression of selected genes with DNAm changes. Eco-epigenetics have extraordinary potential to advance our understanding of biological responses to environmental challenges, and yield sensitive tools for pollution biomonitoring and ecotoxicity assessment.