5. Conclusion
We have investigated salinity-induced DNA methylation and its role in
plasticity and gene expression in gills of euryhaline European sea bass.
This study highlighted that genes with low methylation levels in first
exons, first introns and promoters are generally highly expressed. We
also showed that fresh water triggers an overall hypomethylation of the
genome. Our investigation showed that pathways involved in tight
junctions are highly enriched in upregulated genes displaying
hypomethylated promoters. We also identified other pathways as lipid
metabolism, calcium signaling and regulation of actin cytoskeleton that
were enriched for gene expression and DNA methylation changes in either
promoters or first exons/introns. Numerous key genes involved in
transepithelial ion transport of gill ionocytes also show methylation
and gene expression changes. Interestingly, mitochondria metabolism is
strongly activated, suggesting a modulation of metabolite availability
as substrate for chromatin-modifying enzymes. We recommend further
investigation of methylation dynamics in environmentally challenged fish
in order to determine the role of methylation changes in phenotypic
plasticity, acclimation and adaptation.