151
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152
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de Boer CG, van Bakel H, Tsui K, Li J, Morris QD, Nislow C, Greenblatt JF, Hughes TR. A unified model for yeast transcript definition. Genome Res 2013; 24:154-66. [PMID: 24170600 PMCID: PMC3875857 DOI: 10.1101/gr.164327.113] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Identifying genes in the genomic context is central to a cell's ability to interpret the genome. Yet, in general, the signals used to define eukaryotic genes are poorly described. Here, we derived simple classifiers that identify where transcription will initiate and terminate using nucleic acid sequence features detectable by the yeast cell, which we integrate into a Unified Model (UM) that models transcription as a whole. The cis-elements that denote where transcription initiates function primarily through nucleosome depletion, and, using a synthetic promoter system, we show that most of these elements are sufficient to initiate transcription in vivo. Hrp1 binding sites are the major characteristic of terminators; these binding sites are often clustered in terminator regions and can terminate transcription bidirectionally. The UM predicts global transcript structure by modeling transcription of the genome using a hidden Markov model whose emissions are the outputs of the initiation and termination classifiers. We validated the novel predictions of the UM with available RNA-seq data and tested it further by directly comparing the transcript structure predicted by the model to the transcription generated by the cell for synthetic DNA segments of random design. We show that the UM identifies transcription start sites more accurately than the initiation classifier alone, indicating that the relative arrangement of promoter and terminator elements influences their function. Our model presents a concrete description of how the cell defines transcript units, explains the existence of nongenic transcripts, and provides insight into genome evolution.
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153
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Chromosomal contact permits transcription between coregulated genes. Cell 2013; 155:606-20. [PMID: 24243018 DOI: 10.1016/j.cell.2013.09.051] [Citation(s) in RCA: 137] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 07/18/2013] [Accepted: 09/23/2013] [Indexed: 12/11/2022]
Abstract
Transcription of coregulated genes occurs in the context of long-range chromosomal contacts that form multigene complexes. Such contacts and transcription are lost in knockout studies of transcription factors and structural chromatin proteins. To ask whether chromosomal contacts are required for cotranscription in multigene complexes, we devised a strategy using TALENs to cleave and disrupt gene loops in a well-characterized multigene complex. Monitoring this disruption using RNA FISH and immunofluorescence microscopy revealed that perturbing the site of contact had a direct effect on transcription of other interacting genes. Unexpectedly, this effect on cotranscription was hierarchical, with dominant and subordinate members of the multigene complex engaged in both intra- and interchromosomal contact. This observation reveals the profound influence of these chromosomal contacts on the transcription of coregulated genes in a multigene complex.
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154
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Mercer TR, Mattick JS. Understanding the regulatory and transcriptional complexity of the genome through structure. Genome Res 2013; 23:1081-8. [PMID: 23817049 PMCID: PMC3698501 DOI: 10.1101/gr.156612.113] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
An expansive functionality and complexity has been ascribed to the majority of the human genome that was unanticipated at the outset of the draft sequence and assembly a decade ago. We are now faced with the challenge of integrating and interpreting this complexity in order to achieve a coherent view of genome biology. We argue that the linear representation of the genome exacerbates this complexity and an understanding of its three-dimensional structure is central to interpreting the regulatory and transcriptional architecture of the genome. Chromatin conformation capture techniques and high-resolution microscopy have afforded an emergent global view of genome structure within the nucleus. Chromosomes fold into complex, territorialized three-dimensional domains in concert with specialized subnuclear bodies that harbor concentrations of transcription and splicing machinery. The signature of these folds is retained within the layered regulatory landscapes annotated by chromatin immunoprecipitation, and we propose that genome contacts are reflected in the organization and expression of interweaved networks of overlapping coding and noncoding transcripts. This pervasive impact of genome structure favors a preeminent role for the nucleoskeleton and RNA in regulating gene expression by organizing these folds and contacts. Accordingly, we propose that the local and global three-dimensional structure of the genome provides a consistent, integrated, and intuitive framework for interpreting and understanding the regulatory and transcriptional complexity of the human genome.
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Affiliation(s)
- Tim R Mercer
- Garvan Institute of Medical Research, Sydney, New South Wales, Australia
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155
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Abstract
Gene looping, defined as the physical interaction between the promoter and terminator regions of a RNA polymerase II-transcribed gene, is widespread in yeast and mammalian cells. Gene looping has been shown to play important roles in transcription. Gene-loop formation is dependent on regulatory proteins localized at the 5' and 3' ends of genes, such as TFIIB. However, whether other factors contribute to gene looping remains to be elucidated. Here, we investigated the contribution of intrinsic DNA and chromatin structures to gene looping. We found that Saccharomyces cerevisiae looped genes show high DNA bendability around middle and 3/4 regions in open reading frames (ORFs). This bendability pattern is conserved between yeast species, whereas the position of bendability peak varies substantially among species. Looped genes in human cells also show high DNA bendability. Nucleosome positioning around looped ORF middle regions is unstable. We also present evidence indicating that this unstable nucleosome positioning is involved in gene looping. These results suggest a mechanism by which DNA bendability and unstable nucleosome positioning could assist in the formation of gene loops.
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Affiliation(s)
- Zhiming Dai
- Department of Electronics and Communication Engineering, School of Information Science and Technology, Sun Yat-Sen University, Guangzhou, China
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156
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Dang Y, Li L, Guo W, Xue Z, Liu Y. Convergent transcription induces dynamic DNA methylation at disiRNA loci. PLoS Genet 2013; 9:e1003761. [PMID: 24039604 PMCID: PMC3764098 DOI: 10.1371/journal.pgen.1003761] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 07/15/2013] [Indexed: 11/19/2022] Open
Abstract
Cytosine methylation of DNA is an important epigenetic gene silencing mechanism in plants, fungi, and animals. In the filamentous fungus Neurospora crassa, nearly all known DNA methylations occur in transposon relics and repetitive sequences, and DNA methylation does not depend on the canonical RNAi pathway. disiRNAs are Dicer-independent small non-coding RNAs that arise from gene-rich part of the Neurospora genome. Here we describe a new type of DNA methylation that is associated with the disiRNA loci. Unlike the known DNA methylation in Neurospora, disiRNA loci DNA methylation (DLDM) is highly dynamic and is regulated by an on/off mechanism. Some disiRNA production appears to rely on pol II directed transcription. Importantly, DLDM is triggered by convergent transcription and enriched in promoter regions. Together, our results establish a new mechanism that triggers DNA methylation. DNA methylation in eukayrotes refers to the modification of cytidines at 5th position with methyl group (5mC). Though absent in some species, DNA methylation is conserved across fungi, plants and animals and plays a critical role in X chromosome inactivation, genomic imprinting, transposon silencing etc. In addition, DNA methylation also occurs at the promoter sequence to regulate gene expression. Filamentous fungus Neurospora crassa has a well-known mechanism of DNA methylation for genomic defense. During sexual stage repetitive sequences (e.g. transposons) are recognized and point mutations are introduced. During vegetative stage these mutations serve as signals for establishing static DNA methylation to silence all copies of the sequences. In this study, we report a new type of DNA methylation in Neurospora. It is tightly linked to a type of non-coding small RNA termed dicer-independent siRNA (disiRNA) and therefore was termed disiRNA loci DNA methylation (DLDM). DLDM is dynamic regulated and shows an on/off pattern, i.e. most alleles contain no 5mC but some are densely methylated. Interestingly, DLDM can be triggered by convergent transcription and is accumulated at promoter regions. In summary, our findings demonstrate a new type of dynamic DNA methylation.
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Affiliation(s)
- Yunkun Dang
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Liande Li
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Wei Guo
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Zhihong Xue
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Yi Liu
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- * E-mail:
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157
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Affiliation(s)
- Dirk Eick
- Department of Molecular Epigenetics, Helmholtz Center Munich and Center for Integrated Protein Science Munich (CIPSM), Marchioninistrasse 25, 81377 Munich,
Germany
| | - Matthias Geyer
- Center of Advanced European Studies and Research, Group Physical Biochemistry,
Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
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158
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Al Husini N, Kudla P, Ansari A. A role for CF1A 3' end processing complex in promoter-associated transcription. PLoS Genet 2013; 9:e1003722. [PMID: 23966880 PMCID: PMC3744418 DOI: 10.1371/journal.pgen.1003722] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Accepted: 06/30/2013] [Indexed: 11/18/2022] Open
Abstract
The Cleavage Factor 1A (CF1A) complex, which is required for the termination of transcription in budding yeast, occupies the 3' end of transcriptionally active genes. We recently demonstrated that CF1A subunits also crosslink to the 5' end of genes during transcription. The presence of CF1A complex at the promoter suggested its possible involvement in the initiation/reinitiation of transcription. To check this possibility, we performed transcription run-on assay, RNAP II-density ChIP and strand-specific RT-PCR analysis in a mutant of CF1A subunit Clp1. As expected, RNAP II read through the termination signal in the temperature-sensitive mutant of clp1 at elevated temperature. The transcription readthrough phenotype was accompanied by a decrease in the density of RNAP II in the vicinity of the promoter region. With the exception of TFIIB and TFIIF, the recruitment of the general transcription factors onto the promoter, however, remained unaffected in the clp1 mutant. These results suggest that the CF1A complex affects the recruitment of RNAP II onto the promoter for reinitiation of transcription. Simultaneously, an increase in synthesis of promoter-initiated divergent antisense transcript was observed in the clp1 mutant, thereby implicating CF1A complex in providing directionality to the promoter-bound polymerase. Chromosome Conformation Capture (3C) analysis revealed a physical interaction of the promoter and terminator regions of a gene in the presence of a functional CF1A complex. Gene looping was completely abolished in the clp1 mutant. On the basis of these results, we propose that the CF1A-dependent recruitment of RNAP II onto the promoter for reinitiation and the regulation of directionality of promoter-associated transcription are accomplished through gene looping.
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Affiliation(s)
- Nadra Al Husini
- Department of Biological Sciences, Wayne State University, Detroit, Michigan, United States of America
| | - Paul Kudla
- Department of Biological Sciences, Wayne State University, Detroit, Michigan, United States of America
| | - Athar Ansari
- Department of Biological Sciences, Wayne State University, Detroit, Michigan, United States of America
- * E-mail:
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159
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Salem T, Gomard T, Court F, Moquet-Torcy G, Brockly F, Forné T, Piechaczyk M. Chromatin loop organization of the junb locus in mouse dendritic cells. Nucleic Acids Res 2013; 41:8908-25. [PMID: 23921639 PMCID: PMC3799436 DOI: 10.1093/nar/gkt669] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The junb gene behaves as an immediate early gene in bacterial lipopolysaccharide (LPS)-stimulated dendritic cells (DCs), where its transient transcriptional activation is necessary for the induction of inflammatory cytokines. junb is a short gene and its transcriptional activation by LPS depends on the binding of NF-κB to an enhancer located just downstream of its 3′ UTR. Here, we have addressed the mechanisms underlying the transcriptional hyper-reactivity of junb. Using transfection and pharmacological assays to complement chromatin immunoprecipitation analyses addressing the localization of histones, polymerase II, negative elongation factor (NELF)-, DRB sensitivity-inducing factor (DSIF)- and Positive Transcription Factor b complexes, we demonstrate that junb is a RNA Pol II-paused gene where Pol II is loaded in the transcription start site domain but poorly active. Moreover, High salt-Recovered Sequence, chromosome conformation capture (3C)- and gene transfer experiments show that (i) junb is organized in a nuclear chromatin loop bringing into close spatial proximity the upstream promoter region and the downstream enhancer and (ii) this configuration permits immediate Pol II release on the junb body on binding of LPS-activated NF-κB to the enhancer. Thus, our work unveils a novel topological framework underlying fast junb transcriptional response in DCs. Moreover, it also points to a novel layer of complexity in the modes of action of NF-κB.
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Affiliation(s)
- Tamara Salem
- Equipe labellisée par la Ligue Nationale contre le Cancer, Institut de Génétique Moléculaire de Montpellier UMR 5535 CNRS, 1919 route de Mende, 34293 Montpellier cedex 5, France, Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier cedex 5, France and Université Montpellier 1, 5 Bd Henry IV, 34967 Montpellier cedex 2, France
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160
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Abstract
How cells ensure that productive transcription from divergent promoters is limited to the downstream protein-coding region is an important question in the transcription field. A recent study in Nature proposed an answer by revealing that the upstream antisense transcripts undergo early termination through the polyadenylation signal-dependent pathway, and the downstream sense transcripts are protected from premature cleavage by U1 small nuclear ribonucleoprotein (snRNP).
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161
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Transcriptional directionality of the human insulin-degrading enzyme promoter. Mol Cell Biochem 2013; 382:237-42. [DOI: 10.1007/s11010-013-1739-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 06/14/2013] [Indexed: 11/30/2022]
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162
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Venkatesh S, Workman JL, Smolle M. UpSETing chromatin during non-coding RNA production. Epigenetics Chromatin 2013; 6:16. [PMID: 23738864 PMCID: PMC3680234 DOI: 10.1186/1756-8935-6-16] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Accepted: 05/10/2013] [Indexed: 01/01/2023] Open
Abstract
The packaging of eukaryotic DNA into nucleosomal arrays permits cells to tightly regulate and fine-tune gene expression. The ordered disassembly and reassembly of these nucleosomes allows RNA polymerase II (RNAPII) conditional access to the underlying DNA sequences. Disruption of nucleosome reassembly following RNAPII passage results in spurious transcription initiation events, leading to the production of non-coding RNA (ncRNA). We review the molecular mechanisms involved in the suppression of these cryptic initiation events and discuss the role played by ncRNAs in regulating gene expression.
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Affiliation(s)
- Swaminathan Venkatesh
- Stowers Institute for Medical Research, 1000 E 50th Street, Kansas City, MO 64110, USA.
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163
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Maamar H, Cabili MN, Rinn J, Raj A. linc-HOXA1 is a noncoding RNA that represses Hoxa1 transcription in cis. Genes Dev 2013; 27:1260-71. [PMID: 23723417 DOI: 10.1101/gad.217018.113] [Citation(s) in RCA: 107] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Recently, researchers have uncovered the presence of many long noncoding RNAs (lncRNAs) in embryonic stem cells and believe they are important regulators of the differentiation process. However, there are only a few examples explicitly linking lncRNA activity to transcriptional regulation. Here, we used transcript counting and spatial localization to characterize a lncRNA (dubbed linc-HOXA1) located ∼50 kb from the Hoxa gene cluster in mouse embryonic stem cells. Single-cell transcript counting revealed that linc-HOXA1 and Hoxa1 RNA are highly variable at the single-cell level and that whenever linc-HOXA1 RNA abundance was high, Hoxa1 mRNA abundance was low and vice versa. Knockdown analysis revealed that depletion of linc-HOXA1 RNA at its site of transcription increased transcription of the Hoxa1 gene cis to the chromosome and that exposure of cells to retinoic acid can disrupt this interaction. We further showed that linc-HOXA1 RNA represses Hoxa1 by recruiting the protein PURB as a transcriptional cofactor. Our results highlight the power of transcript visualization to characterize lncRNA function and also suggest that PURB can facilitate lncRNA-mediated transcriptional regulation.
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Affiliation(s)
- Hédia Maamar
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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164
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Hebenstreit D. Are gene loops the cause of transcriptional noise? Trends Genet 2013; 29:333-8. [PMID: 23663933 DOI: 10.1016/j.tig.2013.04.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 03/22/2013] [Accepted: 04/02/2013] [Indexed: 12/14/2022]
Abstract
Expression levels of the same mRNA or protein vary significantly among the cells of an otherwise identical population. Such biological noise has great functional implications and is largely due to transcriptional bursting, the episodic production of mRNAs in short, intense bursts, interspersed by periods of transcriptional inactivity. Bursting has been demonstrated in a wide range of pro- and eukaryotic species, attesting to its universal importance. However, the mechanistic origins of bursting remain elusive. A different type of phenomenon, which has also been suggested to be widespread, is the physical interaction between the promoter and 3' end of a gene. Several functional roles have been proposed for such gene loops, including the facilitation of transcriptional reinitiation. Here, I discuss the most recent findings related to these subjects and argue that gene loops are a likely cause of transcriptional bursting and, thus, biological noise.
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Affiliation(s)
- Daniel Hebenstreit
- School of Life Sciences, Gibbet Hill Campus, The University of Warwick, Coventry, CV4 7AL, UK.
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165
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Pelechano V, Wei W, Steinmetz LM. Extensive transcriptional heterogeneity revealed by isoform profiling. Nature 2013; 497:127-31. [PMID: 23615609 PMCID: PMC3705217 DOI: 10.1038/nature12121] [Citation(s) in RCA: 332] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Accepted: 03/26/2013] [Indexed: 12/20/2022]
Abstract
Transcript function is determined by sequence elements arranged on an individual RNA molecule. Variation in transcripts can affect messenger RNA stability, localization and translation, or produce truncated proteins that differ in localization or function. Given the existence of overlapping, variable transcript isoforms, determining the functional impact of the transcriptome requires identification of full-length transcripts, rather than just the genomic regions that are transcribed. Here, by jointly determining both transcript ends for millions of RNA molecules, we reveal an extensive layer of isoform diversity previously hidden among overlapping RNA molecules. Variation in transcript boundaries seems to be the rule rather than the exception, even within a single population of yeast cells. Over 26 major transcript isoforms per protein-coding gene were expressed in yeast. Hundreds of short coding RNAs and truncated versions of proteins are concomitantly encoded by alternative transcript isoforms, increasing protein diversity. In addition, approximately 70% of genes express alternative isoforms that vary in post-transcriptional regulatory elements, and tandem genes frequently produce overlapping or even bicistronic transcripts. This extensive transcript diversity is generated by a relatively simple eukaryotic genome with limited splicing, and within a genetically homogeneous population of cells. Our findings have implications for genome compaction, evolution and phenotypic diversity between single cells. These data also indicate that isoform diversity as well as RNA abundance should be considered when assessing the functional repertoire of genomes.
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Affiliation(s)
- Vicent Pelechano
- Genome Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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166
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Mukundan B, Ansari A. Srb5/Med18-mediated termination of transcription is dependent on gene looping. J Biol Chem 2013; 288:11384-94. [PMID: 23476016 PMCID: PMC3630880 DOI: 10.1074/jbc.m112.446773] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 02/21/2013] [Indexed: 11/06/2022] Open
Abstract
We have earlier demonstrated the involvement of Mediator subunit Srb5/Med18 in the termination of transcription for a subset of genes in yeast. Srb5/Med18 could affect termination either indirectly by modulating CTD-Ser(2) phosphorylation near the 3' end of a gene or directly by physically interacting with the cleavage and polyadenylation factor or cleavage factor 1 (CF1) complex and facilitating their recruitment to the terminator region. Here, we show that the CTD-Ser(2) phosphorylation pattern on Srb5/Med18-dependent genes remains unchanged in the absence of Srb5 in cells. Coimmunoprecipitation analysis revealed the physical interaction of Srb5/Med18 with the CF1 complex. No such interaction of Srb5/Med18 with the cleavage and polyadenylation factor complex, however, could be detected. The Srb5/Med18-CF1 interaction was not observed in the looping defective sua7-1 strain. Srb5/Med18 cross-linking to the 3' end of genes was also abolished in the sua7-1 strain. Chromosome conformation capture analysis revealed that the looped architecture of Srb5/Med18-dependent genes was abrogated in srb5(-) cells. Furthermore, Srb5-dependent termination of transcription was compromised in the looping defective sua7-1 cells. The overall conclusion of these results is that gene looping plays a crucial role in Srb5/Med18 facilitated termination of transcription, and the looped gene architecture may have a general role in termination of transcription in budding yeast.
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Affiliation(s)
- Banupriya Mukundan
- From the Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202
| | - Athar Ansari
- From the Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202
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167
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Chen RAJ, Down TA, Stempor P, Chen QB, Egelhofer TA, Hillier LW, Jeffers TE, Ahringer J. The landscape of RNA polymerase II transcription initiation in C. elegans reveals promoter and enhancer architectures. Genome Res 2013; 23:1339-47. [PMID: 23550086 PMCID: PMC3730107 DOI: 10.1101/gr.153668.112] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
RNA polymerase transcription initiation sites are largely unknown in Caenorhabditis elegans. The initial 5′ end of most protein-coding transcripts is removed by trans-splicing, and noncoding initiation sites have not been investigated. We characterized the landscape of RNA Pol II transcription initiation, identifying 73,500 distinct clusters of initiation. Bidirectional transcription is frequent, with a peak of transcriptional pairing at 120 bp. We assign transcription initiation sites to 7691 protein-coding genes and find that they display features typical of eukaryotic promoters. Strikingly, the majority of initiation events occur in regions with enhancer-like chromatin signatures. Based on the overlap of transcription initiation clusters with mapped transcription factor binding sites, we define 2361 transcribed intergenic enhancers. Remarkably, productive transcription elongation across these enhancers is predominantly in the same orientation as that of the nearest downstream gene. Directed elongation from an upstream enhancer toward a downstream gene could potentially deliver RNA polymerase II to a proximal promoter, or alternatively might function directly as a distal promoter. Our results provide a new resource to investigate transcription regulation in metazoans.
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Affiliation(s)
- Ron A-J Chen
- The Gurdon Institute, and Department of Genetics, University of Cambridge, Cambridge CB3 0DH, United Kingdom
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168
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Ghamari A, van de Corput MP, Thongjuea S, van Cappellen WA, van IJcken W, van Haren J, Soler E, Eick D, Lenhard B, Grosveld FG. In vivo live imaging of RNA polymerase II transcription factories in primary cells. Genes Dev 2013; 27:767-77. [PMID: 23592796 PMCID: PMC3639417 DOI: 10.1101/gad.216200.113] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Accepted: 03/18/2013] [Indexed: 11/24/2022]
Abstract
Transcription steps are marked by different modifications of the C-terminal domain of RNA polymerase II (RNAPII). Phosphorylation of Ser5 and Ser7 by cyclin-dependent kinase 7 (CDK7) as part of TFIIH marks initiation, whereas phosphorylation of Ser2 by CDK9 marks elongation. These processes are thought to take place in localized transcription foci in the nucleus, known as "transcription factories," but it has been argued that the observed clusters/foci are mere fixation or labeling artifacts. We show that transcription factories exist in living cells as distinct foci by live-imaging fluorescently labeled CDK9, a kinase known to associate with active RNAPII. These foci were observed in different cell types derived from CDK9-mCherry knock-in mice. We show that these foci are very stable while highly dynamic in exchanging CDK9. Chromatin immunoprecipitation (ChIP) coupled with deep sequencing (ChIP-seq) data show that the genome-wide binding sites of CDK9 and initiating RNAPII overlap on transcribed genes. Immunostaining shows that CDK9-mCherry foci colocalize with RNAPII-Ser5P, much less with RNAPII-Ser2P, and not with CDK12 (a kinase reported to be involved in the Ser2 phosphorylation) or with splicing factor SC35. In conclusion, transcription factories exist in living cells, and initiation and elongation of transcripts takes place in different nuclear compartments.
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Affiliation(s)
- Alireza Ghamari
- Department of Cell Biology, Erasmus Medical Center, 3015GE Rotterdam, the Netherlands
| | | | - Supat Thongjuea
- Computational Biology Unit-Bergen Centre for Computational Science
- Sars Centre for Marine Molecular Biology, University of Bergen, N-5008 Bergen, Norway
| | - Wiggert A. van Cappellen
- Department of Reproduction and Development, Erasmus Medical Center, 3015GE Rotterdam, the Netherlands
| | - Wilfred van IJcken
- Biomics Department, Erasmus Medical Center, 3015GE, Rotterdam, the Netherlands
| | - Jeffrey van Haren
- Department of Cell Biology, Erasmus Medical Center, 3015GE Rotterdam, the Netherlands
| | - Eric Soler
- Department of Cell Biology, Erasmus Medical Center, 3015GE Rotterdam, the Netherlands
| | - Dirk Eick
- Department of Molecular Epigenetics, Helmholtz Zentrum München, Center of Integrated Protein Science (CIPSM), D-81377 Munich, Germany
| | - Boris Lenhard
- Computational Biology Unit-Bergen Centre for Computational Science
- Sars Centre for Marine Molecular Biology, University of Bergen, N-5008 Bergen, Norway
| | - Frank G. Grosveld
- Department of Cell Biology, Erasmus Medical Center, 3015GE Rotterdam, the Netherlands
- Centre for Biomedical Genetics, 3015GE Rotterdam, the Netherlands
- Cancer Genomics Centre, 3015GE Rotterdam, the Netherlands
- Netherlands Consortium for Systems Biology, 3015GE Rotterdam, the Netherlands
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169
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Simonatto M, Barozzi I, Natoli G. Non-coding transcription at cis-regulatory elements: computational and experimental approaches. Methods 2013; 63:66-75. [PMID: 23542771 DOI: 10.1016/j.ymeth.2013.03.021] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 03/18/2013] [Accepted: 03/20/2013] [Indexed: 12/17/2022] Open
Abstract
Mammalian genomes are pervasively transcribed, generating mostly RNAs with no coding potential that display different size, structure and interspecies sequence conservation. A prominent contribution to the ncRNA pool comes from the transcription of cis-regulatory elements, namely promoters, enhancers and locus control regions. While this phenomenon has been extensively documented, possible roles of such ncRNAs in gene regulation are still unclear. Addressing this issue will require experimental strategies dealing with the low abundance of enhancer-templated ncRNAs and aimed at specifically dissecting the relative role of transcription per se vs. RNA products. In this review, we first focus on the identification and characterization of cis-regulatory elements, highlighting the differences between emerging classes of ncRNAs associated to specific chromatin signatures. We then discuss current experimental strategies to dissect the function of nc transcription and computational approaches to the analysis and classification of regulatory sequences identified in next-generation sequencing experiments.
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Affiliation(s)
- Marta Simonatto
- Department of Experimental Oncology, European Institute of Oncology (IEO), Via Adamello 16, 20139 Milan, Italy.
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170
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DNA looping facilitates targeting of a chromatin remodeling enzyme. Mol Cell 2013; 50:93-103. [PMID: 23478442 DOI: 10.1016/j.molcel.2013.02.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 01/15/2013] [Accepted: 01/30/2013] [Indexed: 12/14/2022]
Abstract
ATP-dependent chromatin remodeling enzymes are highly abundant and play pivotal roles regulating DNA-dependent processes. The mechanisms by which they are targeted to specific loci have not been well understood on a genome-wide scale. Here, we present evidence that a major targeting mechanism for the Isw2 chromatin remodeling enzyme to specific genomic loci is through sequence-specific transcription factor (TF)-dependent recruitment. Unexpectedly, Isw2 is recruited in a TF-dependent fashion to a large number of loci without TF binding sites. Using the 3C assay, we show that Isw2 can be targeted by Ume6- and TFIIB-dependent DNA looping. These results identify DNA looping as a mechanism for the recruitment of a chromatin remodeling enzyme and define a function for DNA looping. We also present evidence suggesting that Ume6-dependent DNA looping is involved in chromatin remodeling and transcriptional repression, revealing a mechanism by which the three-dimensional folding of chromatin affects DNA-dependent processes.
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171
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Cavalli G, Misteli T. Functional implications of genome topology. Nat Struct Mol Biol 2013; 20:290-9. [PMID: 23463314 PMCID: PMC6320674 DOI: 10.1038/nsmb.2474] [Citation(s) in RCA: 299] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 11/20/2012] [Indexed: 01/21/2023]
Abstract
Although genomes are defined by their sequence, the linear arrangement of nucleotides is only their most basic feature. A fundamental property of genomes is their topological organization in three-dimensional space in the intact cell nucleus. The application of imaging methods and genome-wide biochemical approaches, combined with functional data, is revealing the precise nature of genome topology and its regulatory functions in gene expression and genome maintenance. The emerging picture is one of extensive self-enforcing feedback between activity and spatial organization of the genome, suggestive of a self-organizing and self-perpetuating system that uses epigenetic dynamics to regulate genome function in response to regulatory cues and to propagate cell-fate memory.
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Affiliation(s)
- Giacomo Cavalli
- Institut de Génétique Humaine, UPR 1142, Centre National de la Recherche Scientifique, Montpellier, France.
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172
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Abstract
Gene loops have been described in different organisms from yeast to human and form through interaction between components of the transcription pre-initiation complex and Ssu72, a member of the 3' end cleavage and polyadenylation complex. A recent study by Tan-Wong et al. reports a new role for gene loops in promoting ORF transcription directionality from otherwise bidirectional promoters.
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Affiliation(s)
- Manuele Castelnuovo
- Department of Cell Biology, NCCR Frontiers in Genetics, iGE3 and University of Geneva, Geneva, Switzerland
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173
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Andersen PK, Jensen TH, Lykke-Andersen S. Making ends meet: coordination between RNA 3'-end processing and transcription initiation. WILEY INTERDISCIPLINARY REVIEWS-RNA 2013; 4:233-46. [PMID: 23450686 DOI: 10.1002/wrna.1156] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
RNA polymerase II (RNAPII)-mediated gene transcription initiates at promoters and ends at terminators. Transcription termination is intimately connected to 3'-end processing of the produced RNA and already when loaded at the promoter, RNAPII starts to become configured for this downstream event. Conversely, RNAPII is 'reset' as part of the 3'-end processing/termination event, thus preparing the enzyme for its next round of transcription--possibly on the same gene. There is both direct and circumstantial evidence for preferential recycling of RNAPII from the gene terminator back to its own promoter, which supposedly increases the efficiency of the transcription process under conditions where RNAPII levels are rate limiting. Here, we review differences and commonalities between initiation and 3'-end processing/termination processes on various types of RNAPII transcribed genes. In doing so, we discuss the requirements for efficient 3'-end processing/termination and how these may relate to proper recycling of RNAPII.
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Affiliation(s)
- Pia K Andersen
- Centre for mRNP Biogenesis and Metabolism, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
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174
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Bidirectional promoters as important drivers for the emergence of species-specific transcripts. PLoS One 2013; 8:e57323. [PMID: 23460838 PMCID: PMC3583895 DOI: 10.1371/journal.pone.0057323] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Accepted: 01/21/2013] [Indexed: 11/23/2022] Open
Abstract
The diversification of gene functions has been largely attributed to the process of gene duplication. Novel examples of genes originating from previously untranscribed regions have been recently described without regard to a unifying functional mechanism for their emergence. Here we propose a model mechanism that could generate a large number of lineage-specific novel transcripts in vertebrates through the activation of bidirectional transcription from unidirectional promoters. We examined this model in silico using human transcriptomic and genomic data and identified evidence consistent with the emergence of more than 1,000 primate-specific transcripts. These are transcripts with low coding potential and virtually no functional annotation. They initiate at less than 1 kb upstream of an oppositely transcribed conserved protein coding gene, in agreement with the generally accepted definition of bidirectional promoters. We found that the genomic regions upstream of ancestral promoters, where the novel transcripts in our dataset reside, are characterized by preferential accumulation of transposable elements. This enhances the sequence diversity of regions located upstream of ancestral promoters, further highlighting their evolutionary importance for the emergence of transcriptional novelties. By applying a newly developed test for positive selection to transposable element-derived fragments in our set of novel transcripts, we found evidence of adaptive evolution in the human lineage in nearly 3% of the novel transcripts in our dataset. These findings indicate that at least some novel transcripts could become functionally relevant, and thus highlight the evolutionary importance of promoters, through their capacity for bidirectional transcription, for the emergence of novel genes.
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175
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Abstract
The genome is dynamically organized in the nuclear space in a manner that reflects and influences nuclear functions. Developmental processes that govern the formation and maintenance of epigenetic memories are also tightly linked to adaptive changes in the physical and functional landscape of the nuclear architecture. Biological and biophysical principles governing the three-dimensional folding of chromatin are therefore central to our understanding of epigenetic regulation during adaptive responses and in complex diseases, such as cancer. Accumulating evidence points to the direction that global alterations in nuclear architecture and chromatin folding conspire with unstable epigenetic states of the primary chromatin fiber to drive the phenotypic plasticity of cancer cells.
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Affiliation(s)
- Anita Göndör
- Microbiology, Tumor and Cell Biology, Karolinska Institutet, Nobels väg 16, KI Solna Campus, Box 280, SE-171 77 Stockholm, Sweden.
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176
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Abstract
Upon binding to a promoter, RNA polymerase II can synthesize either a coding mRNA or a divergently transcribed noncoding RNA. In a recent issue of Science, Tan-Wong et al. (2012) find that intragenic looping increases the proper orientation of RNA polymerase II, reducing the production of divergent noncoding transcripts.
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177
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Uchiumi F, Fujikawa M, Miyazaki S, Tanuma SI. Implication of bidirectional promoters containing duplicated GGAA motifs of mitochondrial function-associated genes. AIMS MOLECULAR SCIENCE 2013. [DOI: 10.3934/molsci.2013.1.1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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178
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Castelo-Branco G, Amaral PP, Engström PG, Robson SC, Marques SC, Bertone P, Kouzarides T. The non-coding snRNA 7SK controls transcriptional termination, poising, and bidirectionality in embryonic stem cells. Genome Biol 2013; 14:R98. [PMID: 24044525 PMCID: PMC4053805 DOI: 10.1186/gb-2013-14-9-r98] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 09/10/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Pluripotency is characterized by a unique transcriptional state, in which lineage-specification genes are poised for transcription upon exposure to appropriate stimuli, via a bivalency mechanism involving the simultaneous presence of activating and repressive methylation marks at promoter-associated histones. Recent evidence suggests that other mechanisms, such as RNA polymerase II pausing, might be operational in this process, but their regulation remains poorly understood. RESULTS Here we identify the non-coding snRNA 7SK as a multifaceted regulator of transcription in embryonic stem cells. We find that 7SK represses a specific cohort of transcriptionally poised genes with bivalent or activating chromatin marks in these cells, suggesting a novel poising mechanism independent of Polycomb activity. Genome-wide analysis shows that 7SK also prevents transcription downstream of polyadenylation sites at several active genes, indicating that 7SK is required for normal transcriptional termination or control of 3′-UTR length. In addition, 7SK suppresses divergent upstream antisense transcription at more than 2,600 loci, including many that encode divergent long non-coding RNAs, a finding that implicates the 7SK snRNA in the control of transcriptional bidirectionality. CONCLUSIONS Our study indicates that a single non-coding RNA, the snRNA 7SK, is a gatekeeper of transcriptional termination and bidirectional transcription in embryonic stem cells and mediates transcriptional poising through a mechanism independent of chromatin bivalency.
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Affiliation(s)
- Gonçalo Castelo-Branco
- The Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Laboratory of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet,SE-17177 Stockholm, Sweden
| | - Paulo P Amaral
- The Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Pär G Engström
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Cambridge CB10 1SD, UK
- Present address: Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Box 1031, SE-17121 Solna, Sweden
| | - Samuel C Robson
- The Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Sueli C Marques
- Laboratory of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet,SE-17177 Stockholm, Sweden
| | - Paul Bertone
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Cambridge CB10 1SD, UK
- Genome Biology and Developmental Biology Units, European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany
- Wellcome Trust – Medical Research Council Cambridge Stem Cell Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Tony Kouzarides
- The Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
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179
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Crevillén P, Sonmez C, Wu Z, Dean C. A gene loop containing the floral repressor FLC is disrupted in the early phase of vernalization. EMBO J 2012; 32:140-8. [PMID: 23222483 DOI: 10.1038/emboj.2012.324] [Citation(s) in RCA: 123] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Accepted: 10/31/2012] [Indexed: 12/18/2022] Open
Abstract
Gene activation in eukaryotes frequently involves interactions between chromosomal regions. We have investigated whether higher-order chromatin structures are involved in the regulation of the Arabidopsis floral repressor gene FLC, a target of several chromatin regulatory pathways. Here, we identify a gene loop involving the physical interaction of the 5' and 3' flanking regions of the FLC locus using chromosome conformation capture. The FLC loop is unaffected by mutations disrupting conserved chromatin regulatory pathways leading to very different expression states. However, the loop is disrupted during vernalization, the cold-induced, Polycomb-dependent epigenetic silencing of FLC. Loop disruption parallels timing of the cold-induced FLC transcriptional shut-down and upregulation of FLC antisense transcripts, but does not need a cold-induced PHD protein required for the epigenetic silencing. We suggest that gene loop disruption is an early step in the switch from an expressed to a Polycomb-silenced state.
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Affiliation(s)
- Pedro Crevillén
- Department of Cell and Developmental Biology, John Innes Centre, Norwich, UK
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180
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Affiliation(s)
- Michael Hampsey
- Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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181
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Mischo HE, Proudfoot NJ. Disengaging polymerase: terminating RNA polymerase II transcription in budding yeast. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:174-85. [PMID: 23085255 PMCID: PMC3793857 DOI: 10.1016/j.bbagrm.2012.10.003] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Revised: 10/01/2012] [Accepted: 10/05/2012] [Indexed: 11/29/2022]
Abstract
Termination of transcription by RNA polymerase II requires two distinct processes: The formation of a defined 3′ end of the transcribed RNA, as well as the disengagement of RNA polymerase from its DNA template. Both processes are intimately connected and equally pivotal in the process of functional messenger RNA production. However, research in recent years has elaborated how both processes can additionally be employed to control gene expression in qualitative and quantitative ways. This review embraces these new findings and attempts to paint a broader picture of how this final step in the transcription cycle is of critical importance to many aspects of gene regulation. This article is part of a Special Issue entitled: RNA polymerase II Transcript Elongation.
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Affiliation(s)
- Hannah E Mischo
- Cancer Research UK London Research Institute, Blanche Lane South Mimms, Herts, UK.
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