Project description:To profile the Daphnia species methylome and to achieve a better understanding of the level of variations in the methylome of Daphnia species, we performed whole genome bisulfite sequencing (WGBSeq) of adult Daphnia magna Bham2 strain and Daphnia pulex Eloise Butler strain (EB45 and EB31 strains). We also analysed the correlation between gene expression and methylation in the two species, using data generated in this study and RNA-seq data from Orsini, et al. 2016. We found that methylation percentage across the genome of Daphnia spp. follows a bimodal distribution. Furthermore, CpG methylation in Daphnia predominantly occurs at coding regions. Although methylation levels significantly decrease towards the 3’ end of a gene with a significant drop in methylation levels from one exon to the neighbouring intron, there is a clear spike in relative methylation levels between exon and intron boundaries, which may be linked to regulation of splicing. We further demonstrate that DNA methylation in Daphnia is responsive to intrinsic and extrinsic factors. We also compared the methylation and gene expression correlations found in Daphnia to publicly available dataset from two other invertebrate species (Apis mellifera and Nasonia vitripennis) and two vertebrate species (Homo sapiens and Mus musculus). We observed that similar to other invertebrates, Daphnia’s genome is sparsely methylated at a lower level and the methylation is predominantly focused at gene body while in vertebrate species the genome is heavily methylated (global methylation). Although the level and distribution of methylation across CpG sites is different between vertebrates and invertebrates it is possible that methylation density at coding regions has the same function between vertebrates and invertebrates. We demonstrate evolutionary conservation of a positive correlation between high methylation density at coding regions and gene expression across vertebrates and invertebrates, leading to potentially ensuring continuous high expression of genes required throughout the life in both vertebrates and invertebrates.
Project description:DNA methylation epigenetic changes were analysed in Daphnia magna exposed for 25-day to chronic gamma irradiation compared to unexposed controls. Generation F0 were exposed to 6.5 μGy/h or 41.3 mG/h and let recoverd until the F3 generation without exposures to ionizing radiations. DNA-methylation patterns were analysed by WGBS on the whole organismes at the generation F0, F2 and F3 in order to detect possible transmission of DNA methylation changes to the progeny.
Project description:Toxic chemical contaminants have variety of detrimental effects on various species and the impact of pollutants on ecosystems has become an urgent issue. However, very limited species have been examined to date and those studies are mainly limited to vertebrates. In this study, we aimed to establish an ecotoxicogenomic bases for Daphnia magna. Based on a daphnia EST database, we made oligonucleotide-based DNA microarray that has high reproducibility. The DNA microarray was applied to evaluate gene expression profiles of daphnid exposed to chemicals. Characteristic gene expression patterns depending on chemicals indicate that the Daphnia microarray can be used for mechanistic understanding of chemical toxicity. Although acute toxicity test or reproductive toxicity test can provide hazardous concentrations of chemicals, they give no information about mode of action. Our study can be a breakthrough for the evaluation of chemical toxicity on environmental organisms. Keywords: Chemical response
Project description:Little is known about the influence that environmental stressors may have on genome-wide methylation patterns, and to what extent epigenetics may be involved in environmental stress response. Yet, studies of methylation patterns under stress could provide crucial insights on stress response and toxicity pathways. Here, we focus on genome-wide methylation patterns in the micro-crustacean Daphnia magna, a model organism in ecotoxicology and risk assessment, exposed to the toxic cyanobacterium Microcystis aeruginosa. Bisulfite sequencing of exposed and control animals highlighted differential methylation patterns in Daphnia upon exposure to Microcystis primarily in exonic regions. These patterns are enriched for serine/threonine amino acid codons and genes related to protein synthesis, transport and degradation. Furthermore, we observed that genes with differential methylation corresponded well with genes susceptible to alternative splicing in response to Microcystis stress. Overall, our results suggest a complex mechanistic response in Daphnia characterized by interactions between DNA methylation and gene regulation mechanisms. These results underscore that DNA methylation is modulated by environmental stress and can also be an integral part of the toxicity response in our study species.
Project description:Background Daphnia species reproduce by cyclic parthenogenesis involving both sexual and asexual reproduction. The sex of the offspring is environmentally determined and mediated via endocrine signalling by the mother. Interestingly, male and female Daphnia can be genetically identical, yet display large differences in behaviour, morphology, lifespan and metabolic activity. Our goal was to integrate multiple omics datasets, including gene expression, splicing, histone modification and DNA methylation data generated from genetically identical female and male Daphnia pulex under controlled laboratory settings with the aim of achieving a better understanding of the underlying epigenetic factors that may contribute to the phenotypic differences observed between the two genders. Results In this study we demonstrate that gene expression level is positively correlated with increased DNA methylation, and histone H3 trimethylation at lysine 4 (H3K4me3) at predicted promoter regions. Conversely, elevated histone H3 trimethylation at lysine 27 (H3K27me3), distributed across the entire transcript length, is negatively correlated with gene expression level. Interestingly, male Daphnia are dominated with epigenetic modifications that globally promote elevated gene expression, while female Daphnia are dominated with epigenetic modifications that reduce gene expression globally. For examples, CpG methylation (positively correlated with gene expression level) is significantly higher in almost all differentially methylated sites in male compared to female Daphnia. Furthermore, H3K4me3 modifications are higher in male compared to female Daphnia in more than 3/4 of the differentially regulated promoters. On the other hand, H3K27me3 is higher in female compared to male Daphnia in more than 5/6 of differentially modified sites. However, both sexes demonstrate roughly equal number of genes that are up-regulated in one gender compared to the other sex. Since, gene expression analyses typically assume that most genes are expressed at equal level among samples and different conditions, and thus cannot detect global changes affecting most genes. Conclusions The epigenetic differences between male and female in Daphnia pulex are vast and dominated by changes that promote elevated gene expression in male Daphnia. Furthermore, the differences observed in both gene expression changes and epigenetic modifications between the genders relate to pathways that are physiologically relevant to the observed phenotypic differences.