Replication-independent histone turnover confers regulatory genome for adult heart homeostasis [ChIP-Seq]

Disruption and replacement of nucleosomal histone (histone turnover, HT) take place during transcription and cell division. Here we examined the functional roles for replication-independent HT in directing precise regulatory genome in terminally differentiated cardiomyocytes (CMs) of adult heart. Surprisingly, histone H2B pausing and chasing assay revealed the histone halftime ~2.5 weeks in non-replicating CMs, in sharp contrast to the longer halftime of CMs, despite in the abscence of replication-dependent passive dilution of labeled histones. Regions of high HT identified enhancers of important heart function. Co-occupancy of mutiple cardiac transcription factors in part accounted for enhancers on sites lacking nucleosome eviction by passage of RNA polymerase II. Unexpectedly, both polycomb EED and HDACs augmented HT rate in bufferring poised enhancer activition without alteration of nucleosome occupancy. Thus, our results suggest replication-indenpendent HT as an additional layer of chromatin-based regulation of functional homeostasis. Overall design: GFP-tagged H2B occupancy profile in isolated adult cardiomyocytes from Wildtype (WT) at 6 time points and in cardiac conditional EED Knockout (CKO) at 2 time points as well as nucleosome profile in CKO and WT.