Epigenetic safeguards are coordinately removed to reverse cell identity [RNA-Seq]

Epigenetic modifications operate in concert to maintain cell identity, yet how these interconnected networks suppress alternative cell fates remains unknown. Here we uncover a link between the removal of repressive histone H3K9 methylation and DNA methylation during the reprogramming of somatic cells to pluripotency. The H3K9me2 demethylase, Kdm3b, transcriptionally controls DNA demethylase Tet1 expression. Unexpectedly, in the absence of Kdm3b, loci that have to be DNA demethylated are trapped in an intermediate hydroxymethylated (5hmC) state and do not resolve to unmethylated cytosine. Ectopic 5hmC trapping precludes the chromatin association of master pluripotency factor, POU5F1, and pluripotent gene activation. Tet1 but not Tet2 is critical for this defining event in the reprogramming process. Taken together we uncover a mechanism of coordinated chromatin modification removal in disrupting cell identity. Overall design: RNA Sequencing of WT or Kdm3b KO stalled intermediates during the conversion to iPSCs .