Abstract

Many organisms respond to environmental conditions by showing plasticity, namely different phenotypes from the same genotype.^1,2 Increasing evidence shows that part of this phenotypic plasticity in animals exposed to environmental factors is mediated by epigenetics.^3,4 Epigenetics refers to potentially heritable changes in gene activity that occur without alterations to DNA sequence. First described as major agents in development and differentiation, epigenetic mechanisms emerged as key components of an organism’s response to environmental changes by modulating gene expression and other genome functions. Many classes of contaminants have been shown to alter DNA methylation (DNAm) in rodents including metals, endocrine disrupting compounds, pesticides and persistent organic pollutants.⁵ Hypo- and hyper-methylation are generalized responses to control gene expression however recent studies have demonstrated that classes of contaminants could mark specific DNAm signatures, that could usefully signal prior environmental exposure.⁶

We collected skin from 6 free-ranging the Mediterranean fin whale (Balenoptera physalus), a zooplanktivorous baleen whale of the Balaenopteridae family, sampled in the Pelagos Sanctuary for Marine Mammals of the Ligurian Sea in the northern Mediterranean. Genomic DNA extracted from the skin of the fin whales and levels of contaminants (organochlorines and phthalate levels) measured in the blubber of the same individuals were used for DNAm profiling through reduced representation bisulfite sequencing (RRBS).

The aims of this study were to determine the DNAm profiles of the methylation contexts (CpGs and non-CpGs) of differently contaminated groups using the RRBS, and to identify potential contaminant exposure related genes. Amount and proportion of methylcytosines in CpG and non-CpG regions (CHH and CHG) was very similar across the 6 samples. The proportion of methylcytosines sites in CpG was n=32,682, the highest among all the sequence contexts (n=3216 in CHH; n=1743 in CHG). The majority of the methylcytosine occurred in the intron regions, followed by exon and promoter regions in CpG, CHH and CHG.

Gene ontology results indicated that DNAm affected genes that take place in cell differentiation and function in cutaneous, vascular and nervous systems. Reorganization of skin tissues is apparently underlined by differential methylation of genes assisting adipogenesis, epidermal cell proliferation and glucose and lipid metabolism, keratinocyte development, maintenance of tight junctions, fibroblast development and activation in wound healing. A selection of genes is currently being tested using digital-PCR on a bigger set of samples collected throughout the years with contamination records.

The identification of cellular response pathways allows a better understanding of the organism biological reaction to a specific environmental challenge and the development of sensitive tools based on the predictive responses. Eco-epigenetics analyses have an extraordinary potential to address growing issues on pollution biomonitoring, ecotoxicity assessment, conservation and management planning.

*Presenting author

Literature Cited

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