The myoblast methylome: multiple types of associations with chromatin and transcription

Epigenetic changes are implicated in development, repair, and physiology of postnatal skeletal muscle (SkM). We generated methylomes for human myoblasts (SkM progenitor cells) and determined myoblast differentially methylated regions (DMRs) for comparison to the epigenomics and transcriptomics of diverse cell types. Analyses were from global genomic and single-gene perspectives and included reporter gene assays. One atypical finding was the association of promoter-adjacent hypermethylation in myoblasts with transcription turn-on, but at downmodulated levels, for certain genes (e.g., SIM2 and TWIST1). In contrast, brain-specific OLIG2 was in repressed chromatin and silent in most cell types but linked to hypermethylated DMRs specifically in myoblasts. The OLIG2-linked DMRs might be needed because of the overlapping or nearby binding of myogenic differentiation protein 1 (MYOD). We found genome-wide overlap of DMRs with MYOD or CCCTC-binding factor (CTCF) binding sites in myoblasts that is consistent with the importance of MYOD, as well as CTCF, in organizing myoblast transcription-enhancing chromatin interactions. We also observed some gene upregulation correlated with a special association of regional DNA hypomethylation with H3K36me3, H3K27ac, and H3K4me1 enrichment. Our study highlights unusual relationships between epigenetics and gene expression that illustrate the interplay between DNA methylation and chromatin epigenetics in the regulation of transcription.