Transcription-driven establishment of DNA methylation at the PWS/AS imprinted region

Genomic imprinting is a process that dictates parent-of-origin-specific gene expression. The human Prader-Willi/Angelman syndrome (PWS/AS) region on chromosome 15 contains two key imprinted control regions: PWS-SRO and AS-SRO. PWS-SRO acquires maternal-specific methylation, while AS-SRO initiates transcription in oocytes. To investigate if transcription across PWS-SRO can trigger de novo DNA methylation, researchers employed a human induced pluripotent stem cell (iPSC) system.

By replacing the endogenous AS-SRO with a doxycycline-inducible promoter that activates transcription across PWS-SRO, they were able to observe robust activation upon doxycycline treatment. This activation, as confirmed by splicing to SNRPN exon 2, was similar to the structure of oocyte-derived transcripts. Importantly, the study found that DNA methylation up to 10% was observed only following directed differentiation into the endodermal lineage, suggesting that differentiation-dependent cues, reminiscent of the oocyte environment, are necessary for de novo DNA methylation establishment at the PWS/AS locus.

This in vitro system offers a controlled platform to dissect the molecular mechanisms and chromatin dynamics involved in imprint establishment.