Pol II docking and pausing at growth and stress genes in C. elegans
ABSTRACT: Fluctuations in nutrient availability profoundly impact gene expression. Previous work revealed post-recruitment regulation of RNA Polymerase II (Pol II) during starvation and recovery in Caenorhabitis elegans, suggesting promoter-proximal pausing promotes rapid response to feeding. To test this hypothesis, we measured Pol II elongation genome-wide by two complementary approaches and analyzed elongation in conjunction with Pol II binding and expression. We confirmed bona fide pausing during starvation and also discovered Pol II docking. Pausing occurs at active stress-response genes that become down-regulated in response to feeding. In contrast “docked” Pol II accumulates without initiating upstream of inactive growth genes that become rapidly up-regulated upon feeding. Beyond differences in function and expression, these two sets of genes have different core promoter motifs, suggesting alternative transcriptional machinery. Our work suggests that growth and stress genes are both regulated post-recruitment during starvation, but at initiation and elongation, respectively, coordinating gene expression with nutrient availability. We sequenced short, capped RNA (scRNA-seq) from N2 starved L1 C. elegans as well as a TFIIS mutant (RB2083). We also prepared scRNA-seq libraries from L1 larvae using one, two, or three of the enymes used to prepare the scRNA sequencing libraries as well as scRNA-seq libraries from Drosophila S2 cells using one or two of the enzymes. We further sequenced the 5' end of mRNA in starved C. elegans L1 larvae using the same enzymes as scRNA-seq.
Project description:Our understanding of transcription by RNA polymerase II (Pol II) is limited by our knowledge of the factors that mediate this critically important process. Here we describe the identification of NDF, a nucleosome destabilizing factor that facilitates Pol II transcription in chromatin. NDF has a PWWP motif, interacts with nucleosomes near the dyad, partially disassembles nucleosomes in an ATP-independent manner, and enhances transcription by Pol II through nucleosomes in vitro and in cell nuclei. NDF affects gene expression and co-localizes with H3K36me3 over transcribed regions of a subset of active genes with a preference for longer genes relative to shorter genes. Moreover, induction of transcription leads to the recruitment of NDF over gene bodies. In humans, NDF is present in all tested tissue types, is essential in stem cells, and is frequently overexpressed in breast cancer. Thus, NDF is a factor of primary importance for Pol II transcription in chromatin.
Project description:While a role of promoter-proximal RNA Polymerase II (Pol II) pausing in regulation of eukaryotic gene expression is implied, the mechanisms and dynamics of this process are poorly understood. We performed genome-wide analysis of short capped RNAs (scRNAs) and Pol II chromatin immunoprecipitation sequencing (ChIP-seq) in human breast cancer MCF-7 cells to better understand Pol II pausing (Samarakkody, A., Abbas, A., Scheidegger, A., Warns, J., Nnoli, O., Jokinen, B., Zarns, K., Kubat, B., Dhasarathy, A. and Nechaev, S. (2015) RNA polymerase II pausing can be retained or acquired during activation of genes involved in the epithelial to mesenchymal transition. Nucleic Acids Res43, 3938-3949). The data are available at the NCBI Gene Expression Omnibus under accession number GSE67041. For both ChIP and scRNA samples, we used paired end sequencing on the Illumina MiSeq instrument. For ChIP-seq, the use of paired end sequencing allowed us to avoid ambiguities in center-read definition. For scRNA seq, this allowed us to identify both the 5'-end and the 3'-end in the same run that represent, respectively, the transcription start sites and the locations of Pol II pausing. The sharpening of Pol II ChIP-seqmetagene profiles when aligned against 5'-ends of scRNAs indicates that these RNAs can be used to define the start sites for the majority of mRNA transcription events.
Project description:Pancreatic cancer is a complex disease with a desmoplastic stroma, extreme hypoxia, and inherent resistance to therapy. Understanding the signaling and adaptive response of such an aggressive cancer is key to making advances in therapeutic efficacy and understanding disease progression. Redox factor-1 (Ref-1), a redox signaling protein, regulates the DNA binding activity of several transcription factors, including HIF-1. The conversion of HIF-1 from an oxidized to reduced state leads to enhancement of its DNA binding. In our previously published work, knockdown of Ref-1 under normoxia resulted in altered gene expression patterns on pathways including EIF2, protein kinase A, and mTOR. In this study, single cell RNA sequencing (scRNA-seq) and proteomics were used to explore the effects of Ref-1 on metabolic pathways under hypoxia.Results: We also integrated the scRNA data analysis with the proteomic analysis and found that the differentially expressed genes and pathways identified from the scRNA-seq data are highly consistent to the significant proteins observed in the proteomics data, especially for the upregulated cell cycle and transcription pathways and downregulated metabolic, apoptosis and signaling pathways under hypoxia. Conclusion: The scRNA-seq and proteomics data consistently demonstrated down-regulated central metabolism pathways in APE1/Ref-1 knockdown vs scrambled control under both normoxia and hypoxia conditions. Experimental Methods: scRNA-seq comparing pancreatic cancer cells expressing less than 20% of the Ref-1 protein was analyzed using left truncated mixture Gaussian model. Matched samples were also collected for bulk proteomic analysis of the four conditions. scRNA-seq data was validated using proteomics and qRT-PCR. Ref-1’s role in mitochondrial function was confirmed using mitochondrial function assays and qRT-PCR. Results: We also integrated the scRNA data analysis with the proteomic analysis and found that the differentially expressed genes and pathways identified from the scRNA-seq data are highly consistent to the significant proteins observed in the proteomics data, especially for the upregulated cell cycle and transcription pathways and downregulated metabolic, apoptosis and signaling pathways under hypoxia. Conclusion: The scRNA-seq and proteomics data consistently demonstrated down-regulated central metabolism pathways in APE1/Ref-1 knockdown vs scrambled control under both normoxia and hypoxia conditions.
Project description:RNA Polymerase II (Pol II) transcriptional recycling is an underappreciated mechanism for which the required factors and contributions to overall gene expression levels are poorly understood. We describe an in vitro methodology facilitating unbiased identification of putative RNA Pol II transcriptional recycling factors and quantitative measurement of transcriptional output from recycled transcriptional components. By combing our in vitro transcription assays with other experiments (e.g. in vivo dynamic ChIP-seq assays), we identified PAF1 complex components as drivers for transcription recycling, revealing a new layer in controlling Pol II-dependent transcription. Our findings also point to RNA Pol II transcription recycling as a mechanism that functions aberrantly in disease states such as cancer, and indicate the potential to target factors such as PAF1 that drive RNA Pol II recycling in cancer.
Project description:Metazoan gene expression is often regulated after the recruitment of RNA polymerase II (Pol II) to promoters, through the controlled release of promoter-proximally paused Pol II into productive RNA synthesis. Despite the prevalence of paused Pol II, very little is known about the dynamics of these early elongation complexes or the fate of short transcription start site-associated (tss) RNAs they produce. Here, we demonstrate that paused elongation complexes can be remarkably stable, with half-lives exceeding 15 minutes at genes with inefficient pause release. Promoter-proximal termination by Pol II is infrequent and released tssRNAs are targeted for rapid degradation. Further, we provide evidence that the predominant tssRNA species observed are nascent RNAs held within early elongation complexes. We propose that stable pausing of polymerase provides a temporal window of opportunity for recruitment of factors to modulate gene expression and that the nascent tssRNA represents an appealing target for these interactions. This submission includes 13 raw data files. Four samples (chromatin, soluble, mock-treated, and Rrp40-depleted) are represented by two biological replicate raw data files, while five samples (cells, DMSO, FP, mock-treated + FP, and Rrp-40depleted + FP) are represented by single raw data files.
Project description:Poised RNA polymerase II is predominantly found at developmental control genes and is thought to allow their rapid and synchronous induction in response to extracellular signals. How the recruitment of poised RNA Pol II is regulated during development is not known. By isolating muscle tissue from Drosophila embryos at five stages of differentiation, we show that the recruitment of poised Pol II occurs at many genes de novo and this makes them permissive for future gene expression. When compared to other tissues, these changes are stage-specific and not tissue-specific. In contrast, Polycomb group repression is tissue-specific and in combination with Pol II (the balanced state) marks genes with highly dynamic expression. This suggests that poised Pol II is temporally regulated and is held in check in a tissue-specific fashion. We compare our data to mammalian embryonic stem cells and discuss a framework for predicting developmental programs based on chromatin state. mRNA-seq of Drosophila tissues during development
Project description:We report scRNA-seq data captured from 9,410 cells obtained from the skin of K14E7 transgenic and wildtype C57/BL6 mice. The K14E7 mouse model harbors the HPV16 E7 oncogene driven from a Keratin 14 promoter for keratinocyte-specific expression. We used scRNA-seq to detect and measure E7 transcription with unprecedented accuracy and resolution. With these data, we uncovered transcriptional differences between the individual cells; demonstrated that increased HPV16 E7 copy number is associated with increased expression of E7-induced genes; and showed that E7 expression is predominantly associated with basal keratinocytes.
Project description:We have employed short-capped RNA sequencing (sc-RNA-seq) in order to identify genes whose expression is regulated by promoter proximal pausing of RNA Polymerase II (RNAPI) in response to stress stimulation. We used serum-deprived mouse Swiss 3T3 fibroblasts, either untreated (control) or treated with anisomycin to induce the p38/MAP kinase pathway. Serum starved (72 h 0.2% FCS) mouse 3T3 cells were treated with anisomycin (188.5 nM) for 1 h (in duplicates). Untreated, serum-starved cells were used as a control. We isolated nuclear RNA, performed size fractionation followed by isolation of short-capped RNAs (scRNA). scRNAs were subsequently converted into DNA library and sequenced.
Project description:Non-lymphoid tissues (NLTs) harbour a pool of adaptive immune cells distinct from their counterparts in lymphoid tissues, and their development and phenotype remains largely unexplored. We used scRNA-seq to survey CD4+ T regulatory (Treg) and memory T (Tmem) cells in spleen, lymph nodes, skin and colon in an unbiased way, in mouse. This cross-tissues comparison allows us to obtain marker genes for immune populations in specific locations, as well as examine each population's heterogeneity. Additionally, a continuous phenotype of Treg migration can be modelled from the mouse data, unravelling the transcriptional stages through which these cells transition between tissues.
Project description:Detailed transcriptomic analyses of differentiated cell populations derived from human pluripotent stem cells is routinely used to assess the identity and utility of the differentiated cells. In particular, single cell RNA-sequencing (scRNA-seq) can provide insights into both the cellular and transcriptional heterogeneity of differentiated cell populations. Here we provide scRNA-seq data obtained from ROR1-expressing lens epithelial cells (ROR1e LECs) obtained via directed differentiation of CA1 human embryonic stem cells. Through the use of principal component analysis, heat maps and gene ontology assessments, we demonstrate that ROR1e LECs represent a highly purified and large-scale population of lens cells. These data provide a resource for future characterisation of both normal and cataractous human lens biology.