TET activity propagates transcriptional memory through embryonic dormancy [CUT&TAG]

Dormancy is an essential biological process for the propagation of many life forms through generations and stressful conditions. Early embryos of many mammals are preservable for weeks to months within the uterus under dormancy, which can be induced in vitro through mTOR inhibition. Dormancy features silencing of the genome and abundant heterochromatin formation, which conflicts with the permissive and uncommitted genomic profile of pluripotent cells. Cellular strategies to maintain pluripotency in the fate of this conflict are not known. Here we probed chromatin regulation during embryonic stem cells’ (ESC) entry into dormancy to identify mechanisms that ensure nsure faithful propagation of cellular identity through dormancy. We show a global increase in DNA methylation and loss of chromatin accessibility in dormant ESCs and find that TET DNA demethylases are essential to counteract this trend at key pluripotency regulatory elements. Perturbation of TET activity compromises transcriptional programs and embryo survival through dormancy; whereas its enhancement improves survival rates. We propose that key regulatory elements are bookmarked coordinately by TETs and transcription factors in dormancy for maintenance of cellular identity. Our results reveal the first essential chromatin regulator in establishing mammalian dormancy and paves the way to building its temporal regulatory code in embryonic and adult tissues.