Enhancers predominantly control transcription initiation [RNA-seq]

Gene transcription occurs via a cycle of linked events including initiation, promoter proximal pausing and elongation of RNA polymerase II (Pol 2). A key question is how do transcriptional enhancers influence these events to control gene expression? Here we have used a new approach to quantify transcriptional initiation and pausing in-vivo, while simultaneously identifying transcription start sites (TSSs) and pause-sites (TPSs). When analysed in parallel with nascent RNA-seq, these data show that differential gene expression is achieved predominantly via changes in transcription initiation rather than Pol 2 pausing or elongation. Using genetically engineered mouse models deleted for specific enhancers we show that these elements control gene expression via Pol 2 recruitment and/or initiation rather than via promoter proximal pause release. Using genome-wide analysis we show that enhancers, in general, control gene expression at the stage of Pol 2 recruitment and initiation rather than via pausing. To characterise intronic RNA expression levels genome wide we performed RNA-seq on poly adenylated, globin RNA and rRNA depleted RNA from primary mouse erythroid cells.