Unknown,Transcriptomics,Genomics,Proteomics

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A Probabilistic Model of Transcription Dynamics applied to Estrogen Signalling in Breast Cancer Cells

ABSTRACT: Gene transcription mediated by RNA polymerase II (pol-II) is a key step in gene expression. The dynamics of pol-II moving along the transcribed region influences the rate and timing of gene expression. In this work we present a probabilistic model of transcription dynamics which is fitted to pol-II occupancy time course data measured using ChIP-Seq. The model can be used to estimate transcription speed and to infer the temporal pol-II activity profile at the gene promoter. Model parameters are determined using either maximum likelihood estimation or via Bayesian inference using Markov chain Monte Carlo sampling. The Bayesian approach provides confidence intervals for parameter estimates and allows the use of priors that capture domain knowledge, e.g. the expected range of transcription speeds, based on previous experiments. The model describes the movement of pol-II down the gene body and can be used to identify the time of induction for transcriptionally engaged genes. By clustering the inferred promoter activity time profiles, we are able to determine which genes respond quickly to stimuli and group genes that share activity profiles and may therefore be co-regulated. We apply our methodology to biological data obtained using ChIP-seq to measure pol-II occupancy genome-wide when MCF-7 human breast cancer cells are treated with estradiol (E2). The transcription speeds we obtain agree with those obtained previously for smaller numbers of genes with the advantage that our approach can be applied genome- wide. We validate the biological significance of the pol-II promoter activity clusters by investigating cluster-specific transcription factor binding patterns and determining canonical pathway enrichment. MCF-7 cells were mock treated or with 10nM 17b-E2 to seven time points (5', 10', 20', 40', 80', 160', 320') Genome-wide identification of RNA polymerase II (RNAPII) occupancy at different time points following E2 induction of MCF-7 cells

ORGANISM(S): Homo sapiens

SUBMITTER: H.G. Stunnenberg

PROVIDER: E-GEOD-44800 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Inference of RNA polymerase II transcription dynamics from chromatin immunoprecipitation time course data.

wa Maina Ciira C Honkela Antti A Matarese Filomena F Grote Korbinian K Stunnenberg Hendrik G HG Reid George G Lawrence Neil D ND Rattray Magnus M

PLoS computational biology 20140515 5

Gene transcription mediated by RNA polymerase II (pol-II) is a key step in gene expression. The dynamics of pol-II moving along the transcribed region influence the rate and timing of gene expression. In this work, we present a probabilistic model of transcription dynamics which is fitted to pol-II occupancy time course data measured using ChIP-Seq. The model can be used to estimate transcription speed and to infer the temporal pol-II activity profile at the gene promoter. Model parameters are e ...[more]

PMID: 24830797

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Project description:To explore the global mechanisms of estrogen-regulated transcription, we used chromatin immunoprecipitation coupled with DNA microarrays to determine the localization of RNA polymerase II (Pol II), estrogen receptor alpha (ERalpha), steroid receptor coactivator proteins (SRC), and acetylated histones H3/H4 (AcH) at estrogen-regulated promoters in MCF-7 cells with or without estradiol (E2) treatment. In addition, we correlated factor occupancy with gene expression and the presence of transcription factor binding elements. Using this integrative approach, we defined a set of 58 direct E2 target genes based on E2-regulated Pol II occupancy and classified their promoters based on factor binding, histone modification, and transcriptional output. Many of these direct E2 target genes exhibit interesting modes of regulation and biological activities, some of which may be relevant to the onset and proliferation of breast cancers. Our studies indicate that about one-third of these direct E2 target genes contain promoter-proximal ERalpha-binding sites, which is considerably more than previous estimates. Some of these genes represent possible novel targets for regulation through the ERalpha/AP-1 tethering pathway. Our studies have also revealed several previously uncharacterized global features of E2-regulated gene expression, including strong positive correlations between Pol II occupancy and AcH levels, as well as between the E2-dependent recruitment of ERalpha and SRC at the promoters of E2-stimulated genes. Furthermore, our studies have revealed new mechanistic insights into E2-regulated gene expression, including the absence of SRC binding at E2-repressed genes and the presence of constitutively bound, promoter-proximally paused Pol IIs at some E2-regulated promoters. These mechanistic insights are likely to be relevant for understanding gene regulation by a wide variety of nuclear receptors. Keywords: MCF7 cells, E2, Estrogen, RNA, ER, RNA Polymerase II, SRC, Acetylated histones, ChIP-chip

Project description:Using the estrogen receptor alpha (ERalpha) as a model ligand inducible transcription factor, we sought to explicitly define parameters that determine transcription factor binding site selection on a genomic scale in an inducible system that minimizes confounding chromatin effects by the transcription factor itself. By examining several genetic and epigenetic parameters, we find that an energetically favorable estrogen response element (ERE) motif sequence, evidence of occupancy of a "pioneering" transcription factor FOXA1, the presence of the enhancer mark, H3K4me1, and an open chromatin configuration (FAIRE) at the pre-ligand state provide specificity for ER binding. Genome-wide ChIP-sequencing was done in MCF-7 cancer cell line for the following histone H3 modifications: monomethylation H3K4me1, trimethylation H3K4me3, H3K9me3, H3K27me3, acetylation H3K9ac, H3K14ac. In addition sequencing of RNA Pol II was done at same treatment conditions (E2 and DMSO). In addition, we assessed the chromatin configuration of ERα binding sites by deeply sequencing fragments isolated by Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) (Giresi et al, 2007) which enriches for nucleosome free genomic DNA in the aqueous phase of a phenol extraction. The analysis histone modifications in MCF-7 cancer cells was done by ChIP-seq data obtained either with E2 stimulation or without stimulation using vehicle as a control. Using the ERα binding sites defined by ChIP-seq (separate submission), we analyzed the population characteristics of the chromatin configuration of the ERα binding sites. To this end, we performed ChIP-seq analysis for the occupancy configuration of each of the following marks before and after E2 exposure: RNA Pol II, the activation marks H3K4me1, H3K4me3, H3K9ac and H3K14ac, and the repression marks H3K9me3 and H3K27me3. We assessed the chromatin configuration of ERα binding sites by deeply sequencing fragments isolated by Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) (Giresi et al, 2007) which enriches for nucleosome free genomic DNA in the aqueous phase of a phenol extraction. The tag count of FAIRE fragments reflects the nucleosome depletion at any given site. RNA Pol II - Cat# ab5408, Abcam; H3K9me3 - Cat# ab8898, Abcam; H3K27me3 - Cat# 07-449, Upstate Biotechnology Inc.; H3K4me1 - Cat# ab8895, Abcam; H3K4me3 - Cat# ab8580, Abcam; H3K9ac - Cat# 07-352, Upstate Biotechnology Inc.; H3K14ac - Cat# 07-353, Upstate Biotechnology Inc.

Dataset Information

A Probabilistic Model of Transcription Dynamics applied to Estrogen Signalling in Breast Cancer Cells

Publications

Inference of RNA polymerase II transcription dynamics from chromatin immunoprecipitation time course data.

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