Allelic chromatin structure is a pervasive feature of imprinted domains and functions cooperatively with cis-acting long non-coding RNAs at the Mest-Copg2 locus [ATAC-seq]

Genomic imprinting is an epigenetic phenomenon in which genes exhibit restricted or biased expression from one allele according to parental origin. Imprinted gene expression plays a crucial role in the development, including the brain. Higher-order chromatin structure has long been associated with gene regulation, particularly in the context of spatial enhancer-promoter interactions. Given the characteristic parental allele-biased expression pattern of imprinted genes, a compelling question is whether the three-dimensional organization of parental genomes plays a role in imprinted gene regulation. Using a capture Hi-C approach, we identifiedparental allele-specific higher-order chromatin structures across multiple imprinted domains in the mouse brain. These allele-specific structural features largely stem from annotated imprinting control regions (ICRs), concomitant with allele-specific binding of CTCF. Detailed analysis suggests that transcriptional start sites (TSS) of active and inactive alleles of imprinted genes form distinct chromatin interactions, differing in degree and/or type. CRISPRi screeningrevealed a distal cis-regulatory element that modulates imprinted expression of the Mest-Copg2locus in neurons, and its regulatory mechanism is tightly associated with allele-specific chromatin interactions. Further investigation revealed that both a cis-acting long non-coding RNA and allele-specific enhancer-promoter architecture modulates Mest-Copg2 imprinted expression. Together, this study highlights the interplay between chromatin structure and regulatory landscapes that modulate allele-specific expression of imprinted genes.