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Mapping of variable DNA methylation across multiple cell types defines a dynamic regulatory landscape of the human genome

ABSTRACT: DNA methylation is an important epigenetic modification involved in many biological processes and diseases. Many studies have mapped DNA methylation changes associated with embryogenesis, cell differentiation and cancer at a genome-wide scale. Our understanding of genome-wide DNA methylation changes in a developmental or disease-related context has been steadily growing. However, the investigation of which CpGs are variably methylated in different normal cell or tissue types is still limited. Here we present an in-depth analysis of 54 single-CpG-resolution DNA methylomes of normal human cell types by integrating high-throughput sequencing-based methylation data. We find that the percentage of unmethylated CpGs is relatively fixed regardless of cell type. However, which CpGs are unmethylated is cell-type specific. We categorize the 26 million human autosomal CpGs based on their methylation levels across multiple cell types to identify variably methylated CpGs. Among all the autosomal CpGs, 22.6% exhibit variable DNA methylation across cell types included in our study. These variably methylated CpGs form 66 thousand variably methylated regions (VMRs), encompassing 11% of the genome. By integrating a multitude of genomic data, we found that VMRs enrich for histone modifications indicative of enhancers, suggesting their role as regulatory elements marking cell type specificity. VMRs enrich for transcription factor binding sites in a tissue-dependent manner. Importantly, they enrich for GWAS variants, suggesting VMRs could potentially be implicated in disease and complex traits. Taken together, our results highlight the link among CpG methylation variation, genetic variation and disease risk in a tissue-specific manner for many human cell types.

ORGANISM(S): Homo sapiens

PROVIDER: GSE69894 | GEO | 2016/04/06

SECONDARY ACCESSION(S): PRJNA287045

REPOSITORIES: GEO

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Project description:Methylation of DNA at CpG dinucleotides represents one of the most important epigenetic mechanisms involved in the control of gene expression in vertebrate cells. In this report, we conducted high-throughput nucleosome reconstitution experiments on 572 KB of human DNA and 668 KB of mouse DNA that was unmethylated or methylated in order to investigate the effects of this epigenetic modification on the positioning and stability of nucleosomes. The DNA loci from both species contained the genes that encode the serum albumin family, the MYC protein, and the tumor suppressor p53. The results demonstrated that a small subset of nucleosomes positioned by nucleotide sequence was sensitive to methylation where the modification increased the affinity of these sequences for the histone octamer. The features that distinguished these nucleosomes from the bulk of the methylation-insensitive nucleosomes were an increase in the frequency of CpG dinucleotides and a unique rotational orientation of CpGs such that their minor grooves tended to face toward the histones in the nucleosome rather than away. We propose that these features serve to enhance the affinity of methylated DNA for the histone octamer and that this effect could be involved in gene regulatory mechanisms such as silencing. These methylation-sensitive nucleosomes were preferentially associated with exons as compared to introns while unmethylated CpG islands near transcription start sites became enriched in nucleosomes upon methylation. The results of this study suggest that the effects of DNA methylation on nucleosome stability in vitro can recapitulate what has been observed in the cell and provide a direct link between DNA methylation and the structure and function of chromatin. For the human data, there were 3 unmethylated nucleosome replicates, 2 methylated nucleosome replicates, an unmethylated MNase control, and an unmethylated sonicated control. For the mouse data, there were 2 unmethylated nucleosome replicates, 2 methylated nucleosome replicates, an unmethylated MNase control, a methylated MNase control, and an unmethylated sonicated control.

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Mapping of variable DNA methylation across multiple cell types defines a dynamic regulatory landscape of the human genome

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