Project description:During animal development, a fertilized egg is initially under the control of maternal products and only starts zygotic transcription after several cell divisions. In animals such as Xenopus, zebrafish and Drosophila, a massive increase in zygotic transcription occurs during the mid-blastula transition (MBT), when cells shift from rapid, synchronous cell divisions without gap phases to prolonged asynchronous divisions. Before MBT, only a few so-called pre-MBT genes are expressed. How transcription is set up during these early stages is poorly understood. For example, paused RNA Polymerase (Pol II) is frequently found at developmental control genes in mammalian embryonic stem cells and Drosophila embryos but when Pol II pausing is first established in the embryo is unknown. We have analyzed the genome-wide Pol II occupancy during the maternal-to-zygotic transition in hand-staged Drosophila embryos. The results show that massive Pol II recruitment and pausing is established during MBT. The ~100 genes that are transcribed before MBT are particularly short, consistent with a need for rapid transcription during these early cell divisions. Remarkably, most of these genes are transcribed without Pol II pausing and this correlates with a TATA-enriched promoter type. This suggests that distinct strategies are used for activation in the early Drosophila embryo and this may reflect general dynamic properties of promoters used throughout development. Mnase-seq in staged Drosophila embryos
Project description:Promoter-proximal pausing of RNA polymerase II (Pol II) is a widespread in higher eukaryotes. Previous studies have shown that GAF is enriched at paused genes, but the role of GAF in pausing has not been well characterized on a genome-wide level. To investigate the role of GAF in pausing, we RNAi-depleted GAF from Drosophila S2 cells, and examined the effects on promoter-proximal polymerase. We confirmed the importance of GAF for pausing on the classic pause model gene Hsp70. To determine the dependence of pausing on GAF genome-wide, we assayed the levels of transcriptionally-engaged polymerase genome-wide using GRO-seq in control and GAF-RNAi cells. We found that promoter-proximal polymerase was significantly reduced on a subset of paused genes with GAF-bound promoters. There is a dramatic change in nucleosome distribution at genes with reduction in pausing upon GAF depletion and intergenic GAF binding sites in GAF knock-down, suggesting that GAF allows the establishment of pausing at these genes by directing nucleosome displacement off of the promoter. In addition, the insulator factor BEAF, BEAF-interacting protein Chriz, and transcription M1BP enrichment on unaffected genes suggests that redundant transcription factors or insulators protect other GAF-bound paused genes from GAF knock-down effects. Three biological replicates of MNase digested chromatin from LacZ-RNAi and GAGA factor-RNAi cells.
Project description:Promoter-proximal RNA polymerase II (Pol II) pausing is implicated in the regulation of gene transcription. However, the mechanisms of pausing including its dynamics during transcriptional responses remain to be fully understood. We performed global analysis of short capped RNAs and Pol II Chromatin Immunoprecipitation sequencing in MCF-7 breast cancer cells to map Pol II pausing across the genome, and used permanganate footprinting to specifically follow pausing during transcriptional activation of several genes involved in the Epithelial to Mesenchymal Transition (EMT). We find that the gene for EMT master regulator Snail (SNAI1), but not Slug (SNAI2), shows evidence of Pol II pausing before activation. Transcriptional activation of the paused SNAI1 gene is accompanied by a further increase in Pol II pausing signal whereas activation of non-paused SNAI2 gene results in the acquisition of a typical pausing signature. The increase in pausing signal reflects increased transcription initiation without changes in Pol II pausing. Activation of the heat shock HSP70 gene involves pausing release that speeds up Pol II turnover, but does not change pausing location. We suggest that Pol II pausing is retained during transcriptional activation and can further undergo regulated release in a signal-specific manner. Untreated MCF-7 cells were analyzed for the distribution of Pol II using ChIP-sequencing with Anti-Pol II N-20 antibody (two independent biological replicates, A, B), and for the distribution of paused RNA polymerase II by sequencing of short capped RNAs (scRNAs) prepared from nuclei (three independent biological replicates, 1-3). All samples were sequenced on a MiSeq instrument in paired-end format
Project description:Promoter-proximal RNA polymerase II (Pol II) pausing is implicated in the regulation of gene transcription. However, the mechanisms of pausing including its dynamics during transcriptional responses remain to be fully understood. We performed global analysis of short capped RNAs and Pol II Chromatin Immunoprecipitation sequencing in MCF-7 breast cancer cells to map Pol II pausing across the genome, and used permanganate footprinting to specifically follow pausing during transcriptional activation of several genes involved in the Epithelial to Mesenchymal Transition (EMT). We find that the gene for EMT master regulator Snail (SNAI1), but not Slug (SNAI2), shows evidence of Pol II pausing before activation. Transcriptional activation of the paused SNAI1 gene is accompanied by a further increase in Pol II pausing signal whereas activation of non-paused SNAI2 gene results in the acquisition of a typical pausing signature. The increase in pausing signal reflects increased transcription initiation without changes in Pol II pausing. Activation of the heat shock HSP70 gene involves pausing release that speeds up Pol II turnover, but does not change pausing location. We suggest that Pol II pausing is retained during transcriptional activation and can further undergo regulated release in a signal-specific manner.
Project description:During animal development, a fertilized egg is initially under the control of maternal products and only starts zygotic transcription after several cell divisions. In animals such as Xenopus, zebrafish and Drosophila, a massive increase in zygotic transcription occurs during the mid-blastula transition (MBT), when cells shift from rapid, synchronous cell divisions without gap phases to prolonged asynchronous divisions. Before MBT, only a few so-called pre-MBT genes are expressed. How transcription is set up during these early stages is poorly understood. For example, paused RNA Polymerase (Pol II) is frequently found at developmental control genes in mammalian embryonic stem cells and Drosophila embryos but when Pol II pausing is first established in the embryo is unknown. We have analyzed the genome-wide Pol II occupancy during the maternal-to-zygotic transition in hand-staged Drosophila embryos. The results show that massive Pol II recruitment and pausing is established during MBT. The ~100 genes that are transcribed before MBT are particularly short, consistent with a need for rapid transcription during these early cell divisions. Remarkably, most of these genes are transcribed without Pol II pausing and this correlates with a TATA-enriched promoter type. This suggests that distinct strategies are used for activation in the early Drosophila embryo and this may reflect general dynamic properties of promoters used throughout development. ChIP-seq for Pol II, TBP, H3K4me3, H3K27me3 and H3Ac in Drosophila embryos
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: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. ChIP-seq data set for Pol II (rpb3) (2 replicates).