Mechanism of monoallelic expression and allelic rheostat role of DNA methylation

Thousands of mammalian genes show epigenetically controlled unequal transcription of the parental alleles. Genes subject to autosomal monoallelic expression (MAE) display mitotically stable allelic choice, leading to persistent transcriptional differences between clonal cell lineages. Mechanism of MAE mitotic maintenance is unknown. Using a new screening-by-sequencing strategy, we uncovered a key role for DNA methylation in MAE maintenance. Subset of MAE loci were insensitive to DNA demethylation, suggesting mechanistic heterogeneity of MAE. Genome-wide analyses indicate that MAE is part of a more general mode of gene regulation and reveal a previously unappreciated interplay of genetic and epigenetic control of allele-specific transcription. While cis-acting regulation defines a common underlying state for all cells, DNA methylation plays the role of an allele-specific rheostat and determines multiple regulatory states distinguishing between developmentally equivalent clonal cell lineages. Our findings imply that allele-specific analyses of clonal cell populations can unmask long- term transcriptional responses to drug-driven perturbations.