Conservation and divergence in eukaryotic DNA methylation

Abstract

Cytosine methylation is a common DNA modification found in most eukaryotic organisms including plants, animals, and fungi (1, 2). The addition of a methyl group to cytosine nucleotides in DNA does not change the primary DNA sequence, but the covalent modification of DNA by methylation can impact gene expression and activity in a heritable fashion. This type of epigenetic regulation through DNA methylation appears to be a critical process, in an evolutionary sense, with highly conserved enzymes mediating the process (3). In humans, aberrant DNA methylation has been associated with diseases, including cancer (4). To study cytosine methylation patterns across the genome, researchers have used microarray hybridization or direct sequencing of bisulfite-treated DNA (5). However, mapping methylation of individual cytosines in a given genome has been a challenging task and, accordingly, comparative analysis of genome methylation patterns across species has not been performed. Several new studies have addressed this gap in our understanding of the evolution of cytosine methylation (6, 7). Feng et al. in PNAS (7) used next-generation sequencing to investigate the DNA methylation patterns in eight divergent species, including green algae, flowering plants, insects, and vertebrates. Their data allowed a comprehensive comparison of whole-genome methylation profiles across the plant and animal kingdoms, revealing both conserved and divergent features of DNA methylation in eukaryotes.