Elevated temperature triggers increase in global DNA methylation, 5-methylcytosine expression levels, apoptosis and NOx levels in the gonads of Atlantic sea urchin.

Global warming is one of the greatest threats to living organisms. Among them, marine invertebrates are severely impacted on reproductive fitness by rising seawater surface temperatures due to climate change (e.g., massive heat waves). In this study, we used highly sensitive radioimmunoassay, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), in situ TUNEL assay, luminescence assay, and colorimetric assay techniques to investigate the impacts of high temperatures on global DNA methylation, cellular apoptosis, and nitrative stress in gonads of Atlantic sea urchin (Arbacia punctulata, a commercially important species). Young adult sea urchins were exposed to 24, 28, and 32 °C for one week in a controlled laboratory setting. High temperatures (28 and 32 °C) markedly increased global DNA methylation (around 1.1-1.5-fold in testes and ~ 1.7-fold in ovaries) and 5-methylcytosine (5-mC) levels in gonads (around 2.7- to ~5.1-fold in ovaries and ~ 3.5- to ~6.2-fold in testes) compared with controls (24 °C). The number of apoptotic nuclei in gonads was much higher in high-temperature groups. The caspase activity also increased significantly (P < 0.05) in gonads in high-temperature groups. Nitrate/nitrites (NOx, a biomarker of reactive nitrogen species) levels were increased around 2.6- to ~5.2-fold in testes and ~ 1.9- to ~3.8-fold in ovaries in high-temperature groups. Collectively, these outcomes indicate that high temperatures drastically induce global DNA methylation, 5-mC expression levels, cellular apoptosis, and NOx levels in the gonads of Atlantic sea urchin.