Epigenome modulation potentially provides a mechanism for organisms to adapt, within and between generations. However, neither the extent to which this occurs, nor the mechanisms involved are known. Here we investigate DNA methylation variation in Swedish Arabidopsis thaliana accessions grown at two different temperatures. Environmental effects were limited to transposons, where CHH methylation was found to increase with temperature. Genome-wide association studies (GWAS) revealed that the extensive CHH methylation variation was strongly associated with genetic variants in both cis and trans, including a major trans-association close to the DNA methyltransferase CMT2. Unlike CHH methylation, CpG gene body methylation (GBM) was not affected by growth temperature, but was instead correlated with the latitude of origin. Accessions from colder regions had higher levels of GBM for a significant fraction of the genome, and this was associated with increased transcription for the genes affected. GWAS revealed that this effect was largely due to trans-acting loci, many of which showed evidence of local adaptation.DOI: http://dx.doi.org/10.7554/eLife.05255.001

Summary During germ cell and preimplantation development, mammalian cells undergo nearly complete reprogramming of DNA methylation patterns. We profiled the methylomes of human and chimp sperm as a basis for comparison to methylation patterns of ES cells. While the majority of promoters escape methylation in both ES cells and sperm, the corresponding hypomethylated regions show substantial structural differences. Repeat elements are heavily methylated in both germ and somatic cells; however, retrotransposons from several subfamilies evade methylation more effectively during male germ cell development, while other subfamilies show the opposite trend. Comparing methylomes of human and chimp sperm revealed a subset of differentially methylated promoters and strikingly divergent methylation in retrotransposon subfamilies, with an evolutionary impact that is apparent in the underlying genomic sequence. Thus, the features that determine DNA methylation patterns differ between male germ cells and somatic cells, and elements of these features have diverged between humans and chimpanzees.

DNA methylation is implicated in a surprising diversity of regulatory, evolutionary processes and diseases in eukaryotes. The introduction of whole-genome bisulfite sequencing has enabled the study of DNA methylation at a single-base resolution, revealing many new aspects of DNA methylation and highlighting the usefulness of methylome data in understanding a variety of genomic phenomena. As the number of publicly available whole-genome bisulfite sequencing studies reaches into the hundreds, reliable and convenient tools for comparing and analyzing methylomes become increasingly important. We present MethPipe, a pipeline for both low and high-level methylome analysis, and MethBase, an accompanying database of annotated methylomes from the public domain. Together these resources enable researchers to extract interesting features from methylomes and compare them with those identified in public methylomes in our database.

SUMMARY DNA methylation has been implicated as an epigenetic component of mechanisms that stabilize cell-fate decisions. Here, we have characterized the methylomes of human female hematopoietic stem/progenitor cells (HSPCs) and mature cells from the myeloid and lymphoid lineages. Hypomethylated regions (HMRs) associated with lineage-specific genes were often methylated in the opposing lineage. In HSPCs, these sites tended to show intermediate, complex patterns that resolve to uniformity upon differentiation, by increased or decreased methylation. Promoter HMRs shared across diverse cell types typically display a constitutive core that expands and contracts in a lineage-specific manner to fine-tune the expression of associated genes. Many newly identified intergenic HMRs, both constitutive and lineage specific, were enriched for factor binding sites with an implied role in genome organization and regulation of gene expression, respectively. Overall, our studies represent an important reference data set and provide insights into directional changes in DNA methylation as cells adopt terminal fates.

Motivation: Post-translational modifications to histones have several well known associations with regulation of gene expression. While some modifications appear concentrated narrowly, covering promoters or enhancers, others are dispersed as epigenomic domains. These domains mark contiguous regions sharing an epigenomic property, such as actively transcribed or poised genes, or heterochromatically silenced regions. While high-throughput methods like ChIP-Seq have led to a flood of high-quality data about these epigenomic domains, there remain important analysis problems that are not adequately solved by current analysis tools.Results: We present the RSEG method for identifying epigenomic domains from ChIP-Seq data for histone modifications. In contrast with other methods emphasizing the locations of ‘peaks’ in read density profiles, our method identifies the boundaries of domains. RSEG is also able to incorporate a control sample and find genomic regions with differential histone modifications between two samples.Availability: RSEG, including source code and documentation, is freely available at http://smithlab.cmb.usc.edu/histone/rseg/.Contact: anrewds@usc.eduSupplementary information: Supplementary data are available at Bioinformatics online.