Allele-specific regulation of gene expression through enhancer function and transcriptional elongation control at imprinted loci

Genomic imprinting is a critical developmental process characteristic of parent-of-origin- specific gene expression. Here, we have identified the AFF family protein, Aff3, as a factor that functionally interacts with imprinted loci. Indeed, our genome-wide studies demonstrate that Aff3 specifically binds both imprinting control regions (ICRs) and enhancers within imprinted loci in an allele-specific manner. We have identified the molecular regulators involved in the recruitment of Aff3 to ICRs to impede transcription through the ICR, and provide a mechanism requiring Aff3 within the Super Elongation Complex-like 3 (SEC-L3) in the expression of an imprinted polycistronic transcript spanning the Dlk1-Dio3 locus. Our study also shows that DNA methylation at the ICR reinforces silencing of its related enhancers by controlling the binding and activity of Aff3 in an allele-specific manner. This study provides molecular details about the regulation of dosage-critical imprinted gene expression through Aff3’s function in transcriptional elongation control.