DNA methylation landscapes: provocative insights from epigenomics

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Abstract
DNA methylation is an epigenetic mark that is associated with gene silencing. Novel high-throughput techniques have begun to generate much larger scale maps of DNA methylation than were previously available. The new information has broadly confirmed several conclusions that were based on analysis of specific regions of the genome. For example, many promoters in mammalian genome are marked by unmethylated CpG islands. This new data shows, however, that CpG islands are often found at intergenic regions and can acquire methylation in somatic cells. Evidence for tissue-specific CpG methylation patterns revives the idea that gene expression might be controlled by altered methylation of regulatory elements. An unexpected finding is that the bodies of active genes in plants and animals are often heavily methylated. The function of gene-body methylation is presently unknown, but might serve to suppress intragenic transcription initiation. Emerging high-throughput DNA sequencing technologies promise to provide complete DNA methylation maps that will transform our understanding of this epigenetic mark.