Abstract
Histone acetylation is a dynamic modification regulated by the opposing actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Deacetylation of histone tails results in chromatin tightening, and therefore, HDACs are generally regarded as transcriptional repressors. Counterintuitively, simultaneous deletion of Hdac1 and Hdac2 in embryonic stem cells (ESCs) reduces expression of the pluripotency-associated transcription factors Pou5f1, Sox2, and Nanog (PSN). By shaping global histone acetylation patterns, HDACs indirectly regulate the activity of acetyl-lysine readers, such as the transcriptional activator BRD4. Here, we use inhibitors of HDACs and BRD4 (LBH589 and JQ1, respectively) in combination with precision nuclear run-on and sequencing (PRO-seq) to examine their roles in defining the ESC transcriptome. Both LBH589 and JQ1 cause a marked reduction in the pluripotent gene network. However, although JQ1 treatment induces widespread transcriptional pausing, HDAC inhibition causes a reduction in both paused and elongating polymerase, suggesting an overall reduction in polymerase recruitment. Using enhancer RNA (eRNA) expression to measure enhancer activity, we find that LBH589-sensitive eRNAs are preferentially associated with superenhancers and PSN binding sites. These findings suggest that HDAC activity is required to maintain pluripotency by regulating the PSN enhancer network via the recruitment of RNA polymerase II.