DNA methylation in Daphnia Magna

Daphnia magna is gaining interest as a model for epigenetic research. It is easy to maintain under laboratory conditions and has low genetic diversity due to parthenogenetic reproduction. The D. magna genome is responsive to a wide range of stimuli and genomics resources are being developed for this species. Despite these great advantages, information regarding the epigenome of D. magna and its regulation is still lacking. Thus, the main aim of this work was to describe the methylome of D.magna and investigate its regulation and responsiveness to environmentally relevant exposure conditions. Despite the low levels of global DNA methylation, a defined profile could be identified. DNA methylation in D. magna is sporadic and mainly found at coding regions. These data suggest that D. magna encodes a complete set of genes for DNA methylation reactions. Evidence of direct effects on the DNA methylation profile were found in animals exposed to the DNA methylation inhibitor 5-azacytidine and these changes were persistent after the removal of the stressor. Acute and chronic exposures to environmentally relevant concentrations of stressors (arsenic and hypoxia) also induced changes in gene transcription levels and concentrations of onecarbon pathway metabolites. These findings indicate that the epigenome of D. magna is responsive to changes in the environment, supporting its use as an environmentally relevant model organism for epigenetics research. Furthermore, the maintenance of some of the epigenetic changes in the absence of the initial stressor supports the concept of ‘epigenetic memory’ and its potential use in chemical risk assessment.