Project description:Cohesin and Polycomb proteins functionally interact to control transcription at silenced, restrained, and active genes [tiling array data]
Project description:Cohesin is a well-known mediator of sister chromatid cohesion, but it also influences gene expression and development. These non-canonical roles of cohesin are not well understood, but are vital: gene expression and development are altered by modest changes in cohesin function that do not disrupt chromatid cohesion. To clarify cohesin’s roles in transcription, we measured how cohesin controls RNA polymerase II (Pol II) activity by genome-wide chromatin immunoprecipitation and precision global run-on sequencing. On average, cohesin-binding genes have more transcriptionally active Pol II and promoter-proximal Pol II pausing than non-binding genes, and are more efficient, producing higher steady state levels of mRNA per transcribing Pol II complex. Cohesin depletion frequently increases pausing at cohesin-binding genes, indicating that cohesin often facilitates transition of paused Pol II to elongation. In many cases this likely reflects a role for cohesin in transcriptional enhancer function. Strikingly, more than 95% of predicted extragenic enhancers bind cohesin, and cohesin depletion can reduce their association with Pol II, indicating that cohesin facilitates enhancer-promoter contact. Cohesin directly promotes transcription of the myc gene, and cohesin depletion reduces Pol II activity at most Myc target genes. The multiple transcriptional roles of cohesin revealed by these studies likely underlie the growth and developmental deficits caused by minor changes in cohesin activity. The PRO-seq method was used to measure transcriptionally engaged Pol II genome-wide in two replicates each of mock RNAi-treated, Nipped-B RNAi-treated, and Rad21 RNAi-treated ML-DmBG3-c2 cells.
Project description:Control of RNA transcription is critical for the development and homeostasis of all organisms, and can occur at multiple steps of the transcription cycle, including RNA polymerase II (Pol II) recruitment, initiation, promoter-proximal pausing, and elongation. That Pol II accumulates on many promoters in metazoans implies that steps other than Pol II recruitment are rate-limiting and regulated 1-6. By integrating genome-wide Pol II chromatin immunoprecipition (ChIP) and Global Run-On (GRO) genomic data sets from Drosophila cells, we examined critical features of Pol II near promoters. The accumulation of promoter-proximal polymerase is widespread, occurring on 70% of active genes; and unlike elongating Pol II within the body of genes, promoter Pol II are held paused by factors like NELF, unable to transcribe unless nuclei are treated with strong detergent. Notably, we find that the vast majority of promoter-proximal Pol II detected by ChIP are paused, thereby identifying the biochemical nature of this rate-limiting step in transcription. Finally, we demonstrate that Drosophila promoters do not have the upstream divergent Pol II that is seen so broadly and prominently on mammalian promoters. We postulate this is a consequence of Drosophila’s extensive use of directional core promoter sequence elements, which contrasts with mammals’ lack of directional elements and prevalence of CpG island core promoters. In support of this idea, we show that the fraction of mammalian promoters containing a TATA box core element is dramatically depleted of upstream divergent transcription.
Project description:Cohesin is a well-known mediator of sister chromatid cohesion, but it also influences gene expression and development. These non-canonical roles of cohesin are not well understood, but are vital: gene expression and development are altered by modest changes in cohesin function that do not disrupt chromatid cohesion. To clarify cohesinM-bM-^@M-^Ys roles in transcription, we measured how cohesin controls RNA polymerase II (Pol II) activity by genome-wide chromatin immunoprecipitation and precision global run-on sequencing. On average, cohesin-binding genes have more transcriptionally active Pol II and promoter-proximal Pol II pausing than non-binding genes, and are more efficient, producing higher steady state levels of mRNA per transcribing Pol II complex. Cohesin depletion frequently increases pausing at cohesin-binding genes, indicating that cohesin often facilitates transition of paused Pol II to elongation. In many cases this likely reflects a role for cohesin in transcriptional enhancer function. Strikingly, more than 95% of predicted extragenic enhancers bind cohesin, and cohesin depletion can reduce their association with Pol II, indicating that cohesin facilitates enhancer-promoter contact. Cohesin directly promotes transcription of the myc gene, and cohesin depletion reduces Pol II activity at most Myc target genes. The multiple transcriptional roles of cohesin revealed by these studies likely underlie the growth and developmental deficits caused by minor changes in cohesin activity. We performed ChIP-chip of Rpb3 (representing total Pol II), Ser2P-Pol II (representing elongating Pol II), and Cdk12 and CycT Pol II kinase components in Mock RNAi-treated and cohesin subunit Rad21 RNAi-treated ML-DmBG3-c2 cells, which revealed that cohesin depletion has a variety of effects on Pol II occupancy and modification, as well as on occupancy of Pol II kinases.