DNA Methylation Dynamics in Atlantic Salmon (Salmo salar) after being Challenged with High Temperature and Moderate Hypoxia

Abstract

he marine environment is predicted to become warmer and more hypoxic over this century, and these conditions may become a challenge for cultured Atlantic salmon by negatively affecting their growth, immunology and welfare. DNA methylation mediates phenotypically plastic responses in gene expression that can potentially facilitate acclimatization responses. Thus, we measured DNA methylation from salmon that were subjected to: i) control conditions (normoxia, 12°C); ii) an incremental increase in temperature (12°C to 20°C, at 1°C per week) and then held at 20°C for 4 weeks; or iii) the former temperature regimen in combination with moderate hypoxia (~70% air saturation). DNA methylation levels were measured at CpG sites within a ~500 bp region (Promotor, 5’UTR, Exon, Intron) of six important liver biomarker genes (cribp, jund, pkd3, prdx6, serpinh1, and ucp2). Considering both experimental groups, we found 12 CpGs (out of 94 total) across the six genes that were differentially methylated when exposed to 20°C for 3 days, whereas only 6 CpGs from three genes (jund, prdx6 and ucp2) were affected after 4 weeks at 20°C. At both time points, we uncovered distinct DNA methylation profiles for fish of each treatment group, suggesting that high temperature and moderate hypoxia were inducing different CpG methylation changes in the liver of salmon. Further, we report significant relationships between CpG methylation and the mRNA expression of these genes that are complex and dynamic. These changes in DNA methylation may be an important regulatory mechanism allowing Atlantic salmon to quickly respond to new environmental challenges associated with global warming