151
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Cheung S, Manhas S, Measday V. Retrotransposon targeting to RNA polymerase III-transcribed genes. Mob DNA 2018; 9:14. [PMID: 29713390 PMCID: PMC5911963 DOI: 10.1186/s13100-018-0119-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 04/16/2018] [Indexed: 12/20/2022] Open
Abstract
Retrotransposons are genetic elements that are similar in structure and life cycle to retroviruses by replicating via an RNA intermediate and inserting into a host genome. The Saccharomyces cerevisiae (S. cerevisiae) Ty1-5 elements are long terminal repeat (LTR) retrotransposons that are members of the Ty1-copia (Pseudoviridae) or Ty3-gypsy (Metaviridae) families. Four of the five S. cerevisiae Ty elements are inserted into the genome upstream of RNA Polymerase (Pol) III-transcribed genes such as transfer RNA (tRNA) genes. This particular genomic locus provides a safe environment for Ty element insertion without disruption of the host genome and is a targeting strategy used by retrotransposons that insert into compact genomes of hosts such as S. cerevisiae and the social amoeba Dictyostelium. The mechanism by which Ty1 targeting is achieved has been recently solved due to the discovery of an interaction between Ty1 Integrase (IN) and RNA Pol III subunits. We describe the methods used to identify the Ty1-IN interaction with Pol III and the Ty1 targeting consequences if the interaction is perturbed. The details of Ty1 targeting are just beginning to emerge and many unexplored areas remain including consideration of the 3-dimensional shape of genome. We present a variety of other retrotransposon families that insert adjacent to Pol III-transcribed genes and the mechanism by which the host machinery has been hijacked to accomplish this targeting strategy. Finally, we discuss why retrotransposons selected Pol III-transcribed genes as a target during evolution and how retrotransposons have shaped genome architecture.
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Affiliation(s)
- Stephanie Cheung
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
| | - Savrina Manhas
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
| | - Vivien Measday
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
- Department of Food Science, Wine Research Centre, Faculty of Land and Food Systems, University of British Columbia, Room 325-2205 East Mall, Vancouver, British Columbia V6T 1Z4 Canada
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152
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Viral proteins as a potential driver of histone depletion in dinoflagellates. Nat Commun 2018; 9:1535. [PMID: 29670105 PMCID: PMC5906630 DOI: 10.1038/s41467-018-03993-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 03/26/2018] [Indexed: 12/22/2022] Open
Abstract
Within canonical eukaryotic nuclei, DNA is packaged with highly conserved histone proteins into nucleosomes, which facilitate DNA condensation and contribute to genomic regulation. Yet the dinoflagellates, a group of unicellular algae, are a striking exception to this otherwise universal feature as they have largely abandoned histones and acquired apparently viral-derived substitutes termed DVNPs (dinoflagellate-viral-nucleoproteins). Despite the magnitude of this transition, its evolutionary drivers remain unknown. Here, using Saccharomyces cerevisiae as a model, we show that DVNP impairs growth and antagonizes chromatin by localizing to histone binding sites, displacing nucleosomes, and impairing transcription. Furthermore, DVNP toxicity can be relieved through histone depletion and cells diminish their histones in response to DVNP expression suggesting that histone reduction could have been an adaptive response to these viral proteins. These findings provide insights into eukaryotic chromatin evolution and highlight the potential for horizontal gene transfer to drive the divergence of cellular systems.
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153
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Chereji RV, Clark DJ. Major Determinants of Nucleosome Positioning. Biophys J 2018; 114:2279-2289. [PMID: 29628211 DOI: 10.1016/j.bpj.2018.03.015] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Revised: 02/27/2018] [Accepted: 03/08/2018] [Indexed: 12/21/2022] Open
Abstract
The compact structure of the nucleosome limits DNA accessibility and inhibits the binding of most sequence-specific proteins. Nucleosomes are not randomly located on the DNA but positioned with respect to the DNA sequence, suggesting models in which critical binding sites are either exposed in the linker, resulting in activation, or buried inside a nucleosome, resulting in repression. The mechanisms determining nucleosome positioning are therefore of paramount importance for understanding gene regulation and other events that occur in chromatin, such as transcription, replication, and repair. Here, we review our current understanding of the major determinants of nucleosome positioning: DNA sequence, nonhistone DNA-binding proteins, chromatin-remodeling enzymes, and transcription. We outline the major challenges for the future: elucidating the precise mechanisms of chromatin opening and promoter activation, identifying the complexes that occupy promoters, and understanding the multiscale problem of chromatin fiber organization.
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Affiliation(s)
- Răzvan V Chereji
- Division of Developmental Biology, Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.
| | - David J Clark
- Division of Developmental Biology, Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.
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154
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Grigoryev SA. Chromatin Higher-Order Folding: A Perspective with Linker DNA Angles. Biophys J 2018; 114:2290-2297. [PMID: 29628212 DOI: 10.1016/j.bpj.2018.03.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 03/03/2018] [Accepted: 03/09/2018] [Indexed: 01/24/2023] Open
Abstract
The mechanism by which the "beads-on-a-string" nucleosome chain folds into various higher-order chromatin structures in eukaryotic cell nuclei is still poorly understood. The various models depicting higher-order chromatin as regular helical fibers and the very opposite "polymer melt" theory imply that interactions between nucleosome "beads" make the main contribution to the chromatin compaction. Other models in which the geometry of linker DNA "strings" entering and exiting the nucleosome define the three-dimensional structure predict that small changes in the linker DNA configuration may strongly affect nucleosome chain folding and chromatin higher-order structure. Among those studies, the cross-disciplinary approach pioneered by Jörg Langowski that combines computational modeling with biophysical and biochemical experiments was most instrumental for understanding chromatin higher-order structure in vitro. Strikingly, many recent studies, including genome-wide nucleosome interaction mapping and chromatin imaging, show an excellent agreement with the results of three-dimensional computational modeling based on the primary role of linker DNA geometry in chromatin compaction. This perspective relates nucleosome array models with experimental studies of nucleosome array folding in vitro and in situ. I argue that linker DNA configuration plays a key role in determining nucleosome chain flexibility, topology, and propensity for self-association, thus providing new implications for regulation of chromatin accessibility to DNA binding factors and RNA transcription machinery as well as long-range communications between distant genomic sites.
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Affiliation(s)
- Sergei A Grigoryev
- Department of Biochemistry & Molecular Biology, H171, Milton S. Hershey Medical Center, Penn State University College of Medicine, Hershey, Pennsylvania.
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155
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156
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Xin B, Rohs R. Relationship between histone modifications and transcription factor binding is protein family specific. Genome Res 2018; 28:321-333. [PMID: 29326300 PMCID: PMC5848611 DOI: 10.1101/gr.220079.116] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Accepted: 01/10/2018] [Indexed: 12/20/2022]
Abstract
The very small fraction of putative binding sites (BSs) that are occupied by transcription factors (TFs) in vivo can be highly variable across different cell types. This observation has been partly attributed to changes in chromatin accessibility and histone modification (HM) patterns surrounding BSs. Previous studies focusing on BSs within DNA regulatory regions found correlations between HM patterns and TF binding specificities. However, a mechanistic understanding of TF-DNA binding specificity determinants is still not available. The ability to predict in vivo TF binding on a genome-wide scale requires the identification of features that determine TF binding based on evolutionary relationships of DNA binding proteins. To reveal protein family-dependent mechanisms of TF binding, we conducted comprehensive comparisons of HM patterns surrounding BSs and non-BSs with exactly matched core motifs for TFs in three cell lines: 33 TFs in GM12878, 37 TFs in K562, and 18 TFs in H1-hESC. These TFs displayed protein family-specific preferences for HM patterns surrounding BSs, with high agreement among cell lines. Moreover, compared to models based on DNA sequence and shape at flanking regions of BSs, HM-augmented quantitative machine-learning methods resulted in increased performance in a TF family-specific manner. Analysis of the relative importance of features in these models indicated that TFs, displaying larger HM pattern differences between BSs and non-BSs, bound DNA in an HM-specific manner on a protein family-specific basis. We propose that TF family-specific HM preferences reveal distinct mechanisms that assist in guiding TFs to their cognate BSs by altering chromatin structure and accessibility.
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Affiliation(s)
- Beibei Xin
- Computational Biology and Bioinformatics Program, Departments of Biological Sciences, Chemistry, Physics & Astronomy, and Computer Science, University of Southern California, Los Angeles, California 90089, USA
| | - Remo Rohs
- Computational Biology and Bioinformatics Program, Departments of Biological Sciences, Chemistry, Physics & Astronomy, and Computer Science, University of Southern California, Los Angeles, California 90089, USA
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157
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Chereji RV, Ramachandran S, Bryson TD, Henikoff S. Precise genome-wide mapping of single nucleosomes and linkers in vivo. Genome Biol 2018; 19:19. [PMID: 29426353 PMCID: PMC5807854 DOI: 10.1186/s13059-018-1398-0] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2017] [Accepted: 01/24/2018] [Indexed: 11/10/2022] Open
Abstract
We developed a chemical cleavage method that releases single nucleosome dyad-containing fragments, allowing us to precisely map both single nucleosomes and linkers with high accuracy genome-wide in yeast. Our single nucleosome positioning data reveal that nucleosomes occupy preferred positions that differ by integral multiples of the DNA helical repeat. By comparing nucleosome dyad positioning maps to existing genomic and transcriptomic data, we evaluated the contributions of sequence, transcription, and histones H1 and H2A.Z in defining the chromatin landscape. We present a biophysical model that neglects DNA sequence and shows that steric occlusion suffices to explain the salient features of nucleosome positioning.
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Affiliation(s)
- Răzvan V Chereji
- Division of Developmental Biology, Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Srinivas Ramachandran
- Howard Hughes Medical Institute and Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA, 98109, USA
| | - Terri D Bryson
- Howard Hughes Medical Institute and Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA, 98109, USA
| | - Steven Henikoff
- Howard Hughes Medical Institute and Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA, 98109, USA.
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158
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Catarino RR, Stark A. Assessing sufficiency and necessity of enhancer activities for gene expression and the mechanisms of transcription activation. Genes Dev 2018; 32:202-223. [PMID: 29491135 PMCID: PMC5859963 DOI: 10.1101/gad.310367.117] [Citation(s) in RCA: 124] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Enhancers are important genomic regulatory elements directing cell type-specific transcription. They assume a key role during development and disease, and their identification and functional characterization have long been the focus of scientific interest. The advent of next-generation sequencing and clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9-based genome editing has revolutionized the means by which we study enhancer biology. In this review, we cover recent developments in the prediction of enhancers based on chromatin characteristics and their identification by functional reporter assays and endogenous DNA perturbations. We discuss that the two latter approaches provide different and complementary insights, especially in assessing enhancer sufficiency and necessity for transcription activation. Furthermore, we discuss recent insights into mechanistic aspects of enhancer function, including findings about cofactor requirements and the role of post-translational histone modifications such as monomethylation of histone H3 Lys4 (H3K4me1). Finally, we survey how these approaches advance our understanding of transcription regulation with respect to promoter specificity and transcriptional bursting and provide an outlook covering open questions and promising developments.
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Affiliation(s)
- Rui R Catarino
- Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), 1030 Vienna, Austria
| | - Alexander Stark
- Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), 1030 Vienna, Austria
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159
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Alexander WG. A history of genome editing in Saccharomyces cerevisiae. Yeast 2018; 35:355-360. [PMID: 29247562 DOI: 10.1002/yea.3300] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 11/29/2017] [Accepted: 12/01/2017] [Indexed: 12/14/2022] Open
Abstract
Genome editing is a form of highly precise genetic engineering which produces alterations to an organism's genome as small as a single base pair with no incidental or auxiliary modifications; this technique is crucial to the field of synthetic biology, which requires such precision in the installation of novel genetic circuits into host genomes. While a new methodology for most organisms, genome editing capabilities have been used in the budding yeast Saccharomyces cerevisiae for decades. In this review, I will present a brief history of genome editing in S. cerevisiae, discuss the current gold standard method of Cas9-mediated genome editing, and speculate on future directions of the field.
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160
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Blossey R, Schiessel H. The Latest Twists in Chromatin Remodeling. Biophys J 2018; 114:2255-2261. [PMID: 29310890 DOI: 10.1016/j.bpj.2017.12.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 12/09/2017] [Accepted: 12/12/2017] [Indexed: 02/03/2023] Open
Abstract
In its most restrictive interpretation, the notion of chromatin remodeling refers to the action of chromatin-remodeling enzymes on nucleosomes with the aim of displacing and removing them from the chromatin fiber (the effective polymer formed by a DNA molecule and proteins). This local modification of the fiber structure can have consequences for the initiation and repression of the transcription process, and when the remodeling process spreads along the fiber, it also results in long-range effects essential for fiber condensation. There are three regulatory levels of relevance that can be distinguished for this process: the intrinsic sequence preference of the histone octamer, which rules the positioning of the nucleosome along the DNA, notably in relation to the genetic information coded in DNA; the recognition or selection of nucleosomal substrates by remodeling complexes; and, finally, the motor action on the nucleosome exerted by the chromatin remodeler. Recent work has been able to provide crucial insights at each of these three levels that add new twists to this exciting and unfinished story, which we highlight in this perspective.
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Affiliation(s)
- Ralf Blossey
- University of Lille 1, Unité de Glycobiologie Structurale et Fonctionnelle, CNRS UMR8576, Lille, France.
| | - Helmut Schiessel
- Institute Lorentz for Theoretical Physics, Leiden University, Leiden, the Netherlands
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161
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Lorzadeh A, Lopez Gutierrez R, Jackson L, Moksa M, Hirst M. Generation of Native Chromatin Immunoprecipitation Sequencing Libraries for Nucleosome Density Analysis. J Vis Exp 2017. [PMID: 29286469 PMCID: PMC5755553 DOI: 10.3791/56085] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
We present a modified native chromatin immunoprecipitation sequencing (ChIP-seq) experimental protocol compatible with a Gaussian mixture distribution based analysis methodology (nucleosome density ChIP-seq; ndChIP-seq) that enables the generation of combined measurements of micrococcal nuclease (MNase) accessibility with histone modification genome-wide. Nucleosome position and local density, and the posttranslational modification of their histone subunits, act in concert to regulate local transcription states. Combinatorial measurements of nucleosome accessibility with histone modification generated by ndChIP-seq allows for the simultaneous interrogation of these features. The ndChIP-seq methodology is applicable to small numbers of primary cells inaccessible to cross-linking based ChIP-seq protocols. Taken together, ndChIP-seq enables the measurement of histone modification in combination with local nucleosome density to obtain new insights into shared mechanisms that regulate RNA transcription within rare primary cell populations.
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Affiliation(s)
- Alireza Lorzadeh
- Department of Microbiology and Immunology, Michael Smith Laboratories Centre for High-Throughput Biology, University of British Columbia
| | - Rodrigo Lopez Gutierrez
- Department of Microbiology and Immunology, Michael Smith Laboratories Centre for High-Throughput Biology, University of British Columbia
| | - Linda Jackson
- Department of Microbiology and Immunology, Michael Smith Laboratories Centre for High-Throughput Biology, University of British Columbia
| | - Michelle Moksa
- Department of Microbiology and Immunology, Michael Smith Laboratories Centre for High-Throughput Biology, University of British Columbia
| | - Martin Hirst
- Department of Microbiology and Immunology, Michael Smith Laboratories Centre for High-Throughput Biology, University of British Columbia; Canada's Michael Smith Genome Science Center, BC Cancer Agency;
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162
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Gutiérrez G, Millán-Zambrano G, Medina DA, Jordán-Pla A, Pérez-Ortín JE, Peñate X, Chávez S. Subtracting the sequence bias from partially digested MNase-seq data reveals a general contribution of TFIIS to nucleosome positioning. Epigenetics Chromatin 2017; 10:58. [PMID: 29212533 PMCID: PMC5719526 DOI: 10.1186/s13072-017-0165-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Accepted: 11/29/2017] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND TFIIS stimulates RNA cleavage by RNA polymerase II and promotes the resolution of backtracking events. TFIIS acts in the chromatin context, but its contribution to the chromatin landscape has not yet been investigated. Co-transcriptional chromatin alterations include subtle changes in nucleosome positioning, like those expected to be elicited by TFIIS, which are elusive to detect. The most popular method to map nucleosomes involves intensive chromatin digestion by micrococcal nuclease (MNase). Maps based on these exhaustively digested samples miss any MNase-sensitive nucleosomes caused by transcription. In contrast, partial digestion approaches preserve such nucleosomes, but introduce noise due to MNase sequence preferences. A systematic way of correcting this bias for massively parallel sequencing experiments is still missing. RESULTS To investigate the contribution of TFIIS to the chromatin landscape, we developed a refined nucleosome-mapping method in Saccharomyces cerevisiae. Based on partial MNase digestion and a sequence-bias correction derived from naked DNA cleavage, the refined method efficiently mapped nucleosomes in promoter regions rich in MNase-sensitive structures. The naked DNA correction was also important for mapping gene body nucleosomes, particularly in those genes whose core promoters contain a canonical TATA element. With this improved method, we analyzed the global nucleosomal changes caused by lack of TFIIS. We detected a general increase in nucleosomal fuzziness and more restricted changes in nucleosome occupancy, which concentrated in some gene categories. The TATA-containing genes were preferentially associated with decreased occupancy in gene bodies, whereas the TATA-like genes did so with increased fuzziness. The detected chromatin alterations correlated with functional defects in nascent transcription, as revealed by genomic run-on experiments. CONCLUSIONS The combination of partial MNase digestion and naked DNA correction of the sequence bias is a precise nucleosomal mapping method that does not exclude MNase-sensitive nucleosomes. This method is useful for detecting subtle alterations in nucleosome positioning produced by lack of TFIIS. Their analysis revealed that TFIIS generally contributed to nucleosome positioning in both gene promoters and bodies. The independent effect of lack of TFIIS on nucleosome occupancy and fuzziness supports the existence of alternative chromatin dynamics during transcription elongation.
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Affiliation(s)
| | - Gonzalo Millán-Zambrano
- Departamento de Genética, Universidad de Sevilla, Seville, Spain.,Instituto de Biomedicina de Sevilla, Universidad de Sevilla-CSIC-Hospital Universitario V. del Rocío, Seville, Spain.,The Gurdon Institute, University of Cambridge, Cambridge, UK
| | - Daniel A Medina
- Departamento de Bioquímica y Biología Molecular, Universitat de València, Burjassot, Valencia, Spain.,Department of Chemical and Bioprocess Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Antonio Jordán-Pla
- Departamento de Bioquímica y Biología Molecular, Universitat de València, Burjassot, Valencia, Spain.,Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - José E Pérez-Ortín
- Departamento de Bioquímica y Biología Molecular, Universitat de València, Burjassot, Valencia, Spain
| | - Xenia Peñate
- Departamento de Genética, Universidad de Sevilla, Seville, Spain. .,Instituto de Biomedicina de Sevilla, Universidad de Sevilla-CSIC-Hospital Universitario V. del Rocío, Seville, Spain.
| | - Sebastián Chávez
- Departamento de Genética, Universidad de Sevilla, Seville, Spain. .,Instituto de Biomedicina de Sevilla, Universidad de Sevilla-CSIC-Hospital Universitario V. del Rocío, Seville, Spain.
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163
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Shukla A, Bhargava P. Regulation of tRNA gene transcription by the chromatin structure and nucleosome dynamics. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2017; 1861:295-309. [PMID: 29313808 DOI: 10.1016/j.bbagrm.2017.11.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Revised: 11/27/2017] [Accepted: 11/27/2017] [Indexed: 01/19/2023]
Abstract
The short, non-coding genes transcribed by the RNA polymerase (pol) III, necessary for survival of a cell, need to be repressed under the stress conditions in vivo. The pol III-transcribed genes have adopted several novel chromatin-based regulatory mechanisms to their advantage. In the budding yeast, the sub-nucleosomal size tRNA genes are found in the nucleosome-free regions, flanked by positioned nucleosomes at both the ends. With their chromosomes-wide distribution, all tRNA genes have a different chromatin context. A single nucleosome dynamics controls the accessibility of the genes for transcription. This dynamics operates under the influence of several chromatin modifiers in a gene-specific manner, giving the scope for differential regulation of even the isogenes within a tRNA gene family. The chromatin structure around the pol III-transcribed genes provides a context conducive for steady-state transcription as well as gene-specific transcriptional regulation upon signaling from the environmental cues. This article is part of a Special Issue entitled: SI: Regulation of tRNA synthesis and modification in physiological conditions and disease edited by Dr. Boguta Magdalena.
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Affiliation(s)
- Ashutosh Shukla
- Centre for Cellular and Molecular Biology (Council of Scientific and Industrial Research), Uppal Road, Hyderabad 500007, India
| | - Purnima Bhargava
- Centre for Cellular and Molecular Biology (Council of Scientific and Industrial Research), Uppal Road, Hyderabad 500007, India.
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164
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Henikoff S, Thakur J, Kasinathan S, Talbert PB. Remarkable Evolutionary Plasticity of Centromeric Chromatin. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2017; 82:71-82. [PMID: 29196559 DOI: 10.1101/sqb.2017.82.033605] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Centromeres were familiar to cell biologists in the late 19th century, but for most eukaryotes the basis for centromere specification has remained enigmatic. Much attention has been focused on the cenH3 (CENP-A) histone variant, which forms the foundation of the centromere. To investigate the DNA sequence requirements for centromere specification, we applied a variety of epigenomic approaches, which have revealed surprising diversity in centromeric chromatin properties. Whereas each point centromere of budding yeast is occupied by a single precisely positioned tetrameric nucleosome with one cenH3 molecule, the "regional" centromeres of fission yeast contain unphased presumably octameric nucleosomes with two cenH3s. In Caenorhabditis elegans, kinetochores assemble all along the chromosome at sites of cenH3 nucleosomes that resemble budding yeast point centromeres, whereas holocentric insects lack cenH3 entirely. The "satellite" centromeres of most animals and plants consist of cenH3-containing particles that are precisely positioned over homogeneous tandem repeats, but in humans, different α-satellite subfamilies are occupied by CENP-A nucleosomes with very different conformations. We suggest that this extraordinary evolutionary diversity of centromeric chromatin architectures can be understood in terms of the simplicity of the task of equal chromosome segregation that is continually subverted by selfish DNA sequences.
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Affiliation(s)
- Steven Henikoff
- Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.,Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
| | - Jitendra Thakur
- Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.,Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
| | - Sivakanthan Kasinathan
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.,Medical Scientist Training Program, University of Washington School of Medicine, Seattle, Washington 98195
| | - Paul B Talbert
- Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109.,Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
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165
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Resetting the Yeast Epigenome with Human Nucleosomes. Cell 2017; 171:1508-1519.e13. [PMID: 29198523 DOI: 10.1016/j.cell.2017.10.043] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Revised: 09/11/2017] [Accepted: 10/24/2017] [Indexed: 01/23/2023]
Abstract
Humans and yeast are separated by a billion years of evolution, yet their conserved histones retain central roles in gene regulation. Here, we "reset" yeast to use core human nucleosomes in lieu of their own (a rare event taking 20 days), which initially only worked with variant H3.1. The cells adapt by acquiring suppressor mutations in cell-division genes or by acquiring certain aneuploid states. Converting five histone residues to their yeast counterparts restored robust growth. We reveal that humanized nucleosomes are positioned according to endogenous yeast DNA sequence and chromatin-remodeling network, as judged by a yeast-like nucleosome repeat length. However, human nucleosomes have higher DNA occupancy, globally reduce RNA content, and slow adaptation to new conditions by delaying chromatin remodeling. These humanized yeasts (including H3.3) pose fundamental new questions about how chromatin is linked to many cell processes and provide a platform to study histone variants via yeast epigenome reprogramming.
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166
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Abstract
The two major steps of gene expression are transcription and translation. While hundreds of studies regarding the effect of sequence features on the translation elongation process have been published, very few connect sequence features to the transcription elongation rate. We suggest, for the first time, that short transcript sub-sequences have a typical effect on RNA polymerase (RNAP) speed: we show that nucleotide 5-mers tend to have typical RNAP speed (or transcription rate), which is consistent along different parts of genes and among different groups of genes with high correlation. We also demonstrate that relative RNAP speed correlates with mRNA levels of endogenous and heterologous genes. Furthermore, we show that the estimated transcription and translation elongation rates correlate in endogenous genes. Finally, we demonstrate that our results are consistent for different high resolution experimental measurements of RNAP densities. These results suggest for the first time that transcription elongation is partly encoded in the transcript, affected by the codon-usage, and optimized by evolution with a significant effect on gene expression and organismal fitness.
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Affiliation(s)
- Eyal Cohen
- a Balavatnick School of Computer Science , Tel Aviv University , Tel Aviv , Israel
| | - Zohar Zafrir
- b Department of Biomedical Engineering , Tel Aviv University , Tel Aviv , Israel
| | - Tamir Tuller
- b Department of Biomedical Engineering , Tel Aviv University , Tel Aviv , Israel.,c Sagol School of Neuroscience , Tel Aviv University , Tel Aviv , Israel
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167
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Kato D, Osakabe A, Arimura Y, Mizukami Y, Horikoshi N, Saikusa K, Akashi S, Nishimura Y, Park SY, Nogami J, Maehara K, Ohkawa Y, Matsumoto A, Kono H, Inoue R, Sugiyama M, Kurumizaka H. Crystal structure of the overlapping dinucleosome composed of hexasome and octasome. Science 2017; 356:205-208. [PMID: 28408607 DOI: 10.1126/science.aak9867] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2016] [Accepted: 03/17/2017] [Indexed: 12/19/2022]
Abstract
Nucleosomes are dynamic entities that are repositioned along DNA by chromatin remodeling processes. A nucleosome repositioned by the switch-sucrose nonfermentable (SWI/SNF) remodeler collides with a neighbor and forms the intermediate "overlapping dinucleosome." Here, we report the crystal structure of the overlapping dinucleosome, in which two nucleosomes are associated, at 3.14-angstrom resolution. In the overlapping dinucleosome structure, the unusual "hexasome" nucleosome, composed of the histone hexamer lacking one H2A-H2B dimer from the conventional histone octamer, contacts the canonical "octasome" nucleosome, and they intimately associate. Consequently, about 250 base pairs of DNA are left-handedly wrapped in three turns, without a linker DNA segment between the hexasome and octasome moieties. The overlapping dinucleosome structure may provide important information to understand how nucleosome repositioning occurs during the chromatin remodeling process.
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Affiliation(s)
- Daiki Kato
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
| | - Akihisa Osakabe
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
| | - Yasuhiro Arimura
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
| | - Yuka Mizukami
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
| | - Naoki Horikoshi
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
| | - Kazumi Saikusa
- Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.,Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
| | - Satoko Akashi
- Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
| | - Yoshifumi Nishimura
- Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
| | - Sam-Yong Park
- Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
| | - Jumpei Nogami
- Division of Transcriptomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Kazumitsu Maehara
- Division of Transcriptomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Yasuyuki Ohkawa
- Division of Transcriptomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Atsushi Matsumoto
- National Institutes for Quantum and Radiological Science and Technology, Kizugawa, Kyoto 619-0215, Japan
| | - Hidetoshi Kono
- National Institutes for Quantum and Radiological Science and Technology, Kizugawa, Kyoto 619-0215, Japan
| | - Rintaro Inoue
- Research Reactor Institute, Kyoto University, Osaka 590-0494, Japan
| | - Masaaki Sugiyama
- Research Reactor Institute, Kyoto University, Osaka 590-0494, Japan
| | - Hitoshi Kurumizaka
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan. .,Institute for Medical-Oriented Structural Biology, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
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168
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Koyama M, Kurumizaka H. Structural diversity of the nucleosome. J Biochem 2017; 163:85-95. [DOI: 10.1093/jb/mvx081] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Accepted: 10/31/2017] [Indexed: 02/06/2023] Open
Affiliation(s)
- Masako Koyama
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
- Research Institute for Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
- Institute for Medical-Oriented Structural Biology, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
| | - Hitoshi Kurumizaka
- Laboratory of Structural Biology, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
- Research Institute for Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
- Institute for Medical-Oriented Structural Biology, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
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169
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Wondergem JAJ, Schiessel H, Tompitak M. Performing SELEX experimentsin silico. J Chem Phys 2017; 147:174101. [DOI: 10.1063/1.5001394] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Affiliation(s)
- J. A. J. Wondergem
- Institute Lorentz for Theoretical Physics, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - H. Schiessel
- Institute Lorentz for Theoretical Physics, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | - M. Tompitak
- Institute Lorentz for Theoretical Physics, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
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170
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Frouws TD, Barth PD, Richmond TJ. Site-Specific Disulfide Crosslinked Nucleosomes with Enhanced Stability. J Mol Biol 2017; 430:45-57. [PMID: 29113904 PMCID: PMC5757783 DOI: 10.1016/j.jmb.2017.10.029] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Revised: 10/24/2017] [Accepted: 10/25/2017] [Indexed: 12/04/2022]
Abstract
We engineered nucleosome core particles (NCPs) with two site-specific cysteine crosslinks that increase the stability of the particle. The first disulfide was introduced between the two copies of H2A via an H2A-N38C point mutation, effectively crosslinking the two H2A/H2B heterodimers together to stabilize the histone octamer against H2A/H2B dimer dissociation. The second crosslink was engineered between an R40C point mutation on the N-terminal tail of H3 and the NCP DNA ends by the introduction of a convertible nucleotide. This crosslink maintains the nucleosome DNA in a fixed translational setting relative to the histone octamer and prevents dilution-driven dissociation. The X-ray crystal structures of NCPs containing the disulfides in isolation and in combination were determined. Both disulfides stabilize the structure of the NCP without disturbing the overall structure. Nucleosomes containing these modifications will be advantageous for biochemical and structural studies as a consequence of their greater resistance to dissociation during high dilution in purification, elevated salt for crystallization and vitrification for cryogenic electron microscopy. Crosslinked nucleosome core particles have increased stability against H2A/H2B dimer loss and DNA dissociation. A site-specific disulfide crosslink was introduced between the two copies of H2A in the histone octamer to stabilize its quaternary structure. Site-specific disulfide crosslinks were introduced between histone H3 and DNA within the nucleosome core particle. Three X-ray crystal structures of crosslinked nucleosome core particles were determined at high resolution.
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Affiliation(s)
- Timothy D Frouws
- ETH Zürich, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, 8093 Zürich, Switzerland
| | - Philip D Barth
- ETH Zürich, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, 8093 Zürich, Switzerland
| | - Timothy J Richmond
- ETH Zürich, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, 8093 Zürich, Switzerland.
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171
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Finnegan A, Song JS. Maximum entropy methods for extracting the learned features of deep neural networks. PLoS Comput Biol 2017; 13:e1005836. [PMID: 29084280 PMCID: PMC5679649 DOI: 10.1371/journal.pcbi.1005836] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 11/09/2017] [Accepted: 10/23/2017] [Indexed: 11/19/2022] Open
Abstract
New architectures of multilayer artificial neural networks and new methods for training them are rapidly revolutionizing the application of machine learning in diverse fields, including business, social science, physical sciences, and biology. Interpreting deep neural networks, however, currently remains elusive, and a critical challenge lies in understanding which meaningful features a network is actually learning. We present a general method for interpreting deep neural networks and extracting network-learned features from input data. We describe our algorithm in the context of biological sequence analysis. Our approach, based on ideas from statistical physics, samples from the maximum entropy distribution over possible sequences, anchored at an input sequence and subject to constraints implied by the empirical function learned by a network. Using our framework, we demonstrate that local transcription factor binding motifs can be identified from a network trained on ChIP-seq data and that nucleosome positioning signals are indeed learned by a network trained on chemical cleavage nucleosome maps. Imposing a further constraint on the maximum entropy distribution also allows us to probe whether a network is learning global sequence features, such as the high GC content in nucleosome-rich regions. This work thus provides valuable mathematical tools for interpreting and extracting learned features from feed-forward neural networks. Deep learning is a state-of-the-art reformulation of artificial neural networks that have a long history of development. It can perform superbly well in diverse automated classification and prediction problems, including handwriting recognition, image identification, and biological pattern recognition. Its modern success can be attributed to improved training algorithms, clever network architecture, rapid explosion of available data, and advanced computing power–all of which have allowed the great expansion in the number of unknown parameters to be estimated by the model. These parameters, however, are so intricately connected through highly nonlinear functions that interpreting which essential features of given data are actually used by a deep neural network for its excellent performance has been difficult. We address this problem by using ideas from statistical physics to sample new unseen data that are likely to behave similarly to original data points when passed through the trained network. This synthetic data cloud around each original data point retains informative features while averaging out nonessential ones, ultimately allowing us to extract important network-learned features from the original data set and thus improving the human interpretability of deep learning methods. We demonstrate how our method can be applied to biological sequence analysis.
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Affiliation(s)
- Alex Finnegan
- Department of Physics, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States of America
- Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States of America
| | - Jun S. Song
- Department of Physics, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States of America
- Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States of America
- * E-mail:
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172
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Fuse T, Katsumata K, Morohoshi K, Mukai Y, Ichikawa Y, Kurumizaka H, Yanagida A, Urano T, Kato H, Shimizu M. Parallel mapping with site-directed hydroxyl radicals and micrococcal nuclease reveals structural features of positioned nucleosomes in vivo. PLoS One 2017; 12:e0186974. [PMID: 29073207 PMCID: PMC5658119 DOI: 10.1371/journal.pone.0186974] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Accepted: 10/11/2017] [Indexed: 12/17/2022] Open
Abstract
Micrococcal nuclease (MNase) has been widely used for analyses of nucleosome locations in many organisms. However, due to its sequence preference, the interpretations of the positions and occupancies of nucleosomes using MNase have remained controversial. Next-generation sequencing (NGS) has also been utilized for analyses of MNase-digests, but some technical biases are commonly present in the NGS experiments. Here, we established a gel-based method to map nucleosome positions in Saccharomyces cerevisiae, using isolated nuclei as the substrate for the histone H4 S47C-site-directed chemical cleavage in parallel with MNase digestion. The parallel mapping allowed us to compare the chemically and enzymatically cleaved sites by indirect end-labeling and primer extension mapping, and thus we could determine the nucleosome positions and the sizes of the nucleosome-free regions (or nucleosome-depleted regions) more accurately, as compared to nucleosome mapping by MNase alone. The analysis also revealed that the structural features of the nucleosomes flanked by the nucleosome-free region were different from those within regularly arrayed nucleosomes, showing that the structures and dynamics of individual nucleosomes strongly depend on their locations. Moreover, we demonstrated that the parallel mapping results were generally consistent with the previous genome-wide chemical mapping and MNase-Seq results. Thus, the gel-based parallel mapping will be useful for the analysis of a specific locus under various conditions.
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Affiliation(s)
- Tomohiro Fuse
- Department of Chemistry, Graduate School of Science and Engineering, Program in Chemistry and Life Science, School of Science and Engineering, Meisei University, Hino, Tokyo, Japan
| | - Koji Katsumata
- Department of Chemistry, Graduate School of Science and Engineering, Program in Chemistry and Life Science, School of Science and Engineering, Meisei University, Hino, Tokyo, Japan
| | - Koya Morohoshi
- Department of Chemistry, Graduate School of Science and Engineering, Program in Chemistry and Life Science, School of Science and Engineering, Meisei University, Hino, Tokyo, Japan
| | - Yukio Mukai
- Department of Bioscience, Faculty of Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga, Japan
| | - Yuichi Ichikawa
- Graduate School of Advanced Science and Engineering/RISE/IMSB, Waseda University, Shinjuku-ku, Tokyo, Japan
| | - Hitoshi Kurumizaka
- Graduate School of Advanced Science and Engineering/RISE/IMSB, Waseda University, Shinjuku-ku, Tokyo, Japan
| | - Akio Yanagida
- School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo, Japan
| | - Takeshi Urano
- Department of Biochemistry, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Hiroaki Kato
- Department of Biochemistry, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Mitsuhiro Shimizu
- Department of Chemistry, Graduate School of Science and Engineering, Program in Chemistry and Life Science, School of Science and Engineering, Meisei University, Hino, Tokyo, Japan
- * E-mail:
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173
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Kubik S, Bruzzone MJ, Albert B, Shore D. A Reply to "MNase-Sensitive Complexes in Yeast: Nucleosomes and Non-histone Barriers," by Chereji et al. Mol Cell 2017; 65:578-580. [PMID: 28157510 DOI: 10.1016/j.molcel.2017.01.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 01/05/2017] [Accepted: 01/06/2017] [Indexed: 11/25/2022]
Abstract
In this issue of Molecular Cell, Chereji et al. (2017) present new data on MNase-sensitive particles previously identified upstream of transcription start sites at many promoters in budding yeast, and they argue, based upon negative histone-ChIP results, that they are non-nucleosomal signals generated by transcription factors (TFs). We show instead, based upon functional experiments where the relevant TFs are rapidly depleted, that this explanation does not hold, and we argue instead that histone ChIP and chemical cleavage assays have a limited capacity to capture these highly dynamic, MNase-sensitive "fragile" nucleosomes.
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Affiliation(s)
- Slawomir Kubik
- Department of Molecular Biology and Institute for Genetics and Genomics in Geneva (iGE3), 30 quai Ernest-Ansermet, Geneva 4, CH-1211 Switzerland
| | - Maria Jessica Bruzzone
- Department of Molecular Biology and Institute for Genetics and Genomics in Geneva (iGE3), 30 quai Ernest-Ansermet, Geneva 4, CH-1211 Switzerland
| | - Benjamin Albert
- Department of Molecular Biology and Institute for Genetics and Genomics in Geneva (iGE3), 30 quai Ernest-Ansermet, Geneva 4, CH-1211 Switzerland
| | - David Shore
- Department of Molecular Biology and Institute for Genetics and Genomics in Geneva (iGE3), 30 quai Ernest-Ansermet, Geneva 4, CH-1211 Switzerland.
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174
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Deaner M, Mejia J, Alper HS. Enabling Graded and Large-Scale Multiplex of Desired Genes Using a Dual-Mode dCas9 Activator in Saccharomyces cerevisiae. ACS Synth Biol 2017; 6:1931-1943. [PMID: 28700213 DOI: 10.1021/acssynbio.7b00163] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Standard approaches for dCas9-based modification of gene expression are limited in the ability to multiplex targets, establish streamlined cassettes, and utilize commonly studied Pol II promoters. In this work, we repurpose the dCas9-VPR activator to act as a dual-mode activator/repressor that can be programmed solely on the basis of target position at gene loci. Furthermore, we implement this approach using a streamlined Pol II-ribozyme system that allows expression of many sgRNAs from a single transcript. By "stepping" dCas9-VPR within the promoter region and ORF we create graded activation and repression (respectively) of target genes, allowing precise control over multiplexed gene modulation. Expression from the Pol II system increased the net amount of sgRNA production in cells by 3.88-fold relative to the Pol III SNR52 promoter, leading to a significant improvement in dCas9-VPR repression strength. Finally, we utilize our Pol II system to create galactose-inducible switching of gene expression states and multiplex constructs capable of modulating up to 4 native genes from a single vector. Our approach represents a significant step toward minimizing DNA required to assemble CRISPR systems in eukaryotes while enhancing the efficacy (greater repression strength), scale (more sgRNAs), and scope (inducibility) of dCas9-mediated gene regulation.
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Affiliation(s)
- Matthew Deaner
- McKetta
Department of Chemical Engineering, The University of Texas at Austin, 200 E Dean Keeton Street, Stop C0400, Austin, Texas 78712, United States
| | - Julio Mejia
- McKetta
Department of Chemical Engineering, The University of Texas at Austin, 200 E Dean Keeton Street, Stop C0400, Austin, Texas 78712, United States
| | - Hal S. Alper
- McKetta
Department of Chemical Engineering, The University of Texas at Austin, 200 E Dean Keeton Street, Stop C0400, Austin, Texas 78712, United States
- Institute
for Cellular and Molecular Biology, The University of Texas at Austin, 2500 Speedway Avenue, Austin, Texas 78712, United States
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175
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van den Berg AA, Depken M. Crowding-induced transcriptional bursts dictate polymerase and nucleosome density profiles along genes. Nucleic Acids Res 2017; 45:7623-7632. [PMID: 28586463 PMCID: PMC5737439 DOI: 10.1093/nar/gkx513] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 06/03/2017] [Indexed: 12/20/2022] Open
Abstract
During eukaryotic transcription, RNA polymerase (RNAP) translocates along DNA molecules covered with nucleosomes and other DNA binding proteins. Though the interactions between a single nucleosome and RNAP are by now fairly well understood, this understanding has not been synthesized into a description of transcription on crowded genes, where multiple RNAP transcribe through nucleosomes while preserving the nucleosome coverage. We here take a deductive modeling approach to establish the consequences of RNAP–nucleosome interactions for transcription in crowded environments. We show that under physiologically crowded conditions, the interactions of RNAP with nucleosomes induce a strong kinetic attraction between RNAP molecules, causing them to self-organize into stable and moving pelotons. The peloton formation quantitatively explains the observed nucleosome and RNAP depletion close to the initiation site on heavily transcribed genes. Pelotons further translate into short-timescale transcriptional bursts at termination, resulting in burst characteristics consistent with instances of bursty transcription observed in vivo. To facilitate experimental testing of our proposed mechanism, we present several analytic relations that make testable quantitative predictions.
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Affiliation(s)
- Aafke A van den Berg
- Department of Bionanoscience, Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Martin Depken
- Department of Bionanoscience, Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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176
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Klopf E, Schmidt HA, Clauder-Münster S, Steinmetz LM, Schüller C. INO80 represses osmostress induced gene expression by resetting promoter proximal nucleosomes. Nucleic Acids Res 2017; 45:3752-3766. [PMID: 28025392 PMCID: PMC5397147 DOI: 10.1093/nar/gkw1292] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 12/13/2016] [Indexed: 12/19/2022] Open
Abstract
The conserved INO80 chromatin remodeling complex is involved in regulation of DNA damage repair, replication and transcription. It is commonly recruited to the transcription start region and contributes to the establishment of promoter-proximal nucleosomes. We find a substantial influence of INO80 on nucleosome dynamics and gene expression during stress induced transcription. Transcription induced by osmotic stress leads to genome-wide remodeling of promoter proximal nucleosomes. INO80 function is required for timely return of evicted nucleosomes to the 5΄ end of induced genes. Reduced INO80 function in Arp8-deficient cells leads to correlated prolonged transcription and nucleosome eviction. INO80 and the related complex SWR1 regulate incorporation of the H2A.Z isoform at promoter proximal nucleosomes. However, H2A.Z seems not to influence osmotic stress induced gene regulation. Furthermore, we show that high rates of transcription promote INO80 recruitment to promoter regions, suggesting a connection between active transcription and promoter proximal nucleosome remodeling. In addition, we find that absence of INO80 enhances bidirectional promoter activity at highly induced genes and expression of a number of stress induced transcripts. We suggest that INO80 has a direct repressive role via promoter proximal nucleosome remodeling to limit high levels of transcription in yeast.
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Affiliation(s)
- Eva Klopf
- Department of Applied Genetics and Cell Biology (DAGZ), University of Natural Resources and Life Sciences, Vienna (BOKU), UFT-Campus Tulln, Konrad Lorenz Strasse 24, 3430 Tulln, Austria
| | - Heiko A Schmidt
- Center for Integrative Bioinformatics Vienna (CIBIV), Max F. Perutz Laboratories, Medical University of Vienna, University of Vienna, Campus Vienna Biocenter 5 (VBC5), 1030 Vienna, Austria
| | - Sandra Clauder-Münster
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Lars M Steinmetz
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Christoph Schüller
- Department of Applied Genetics and Cell Biology (DAGZ), University of Natural Resources and Life Sciences, Vienna (BOKU), UFT-Campus Tulln, Konrad Lorenz Strasse 24, 3430 Tulln, Austria
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177
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Nikitina T, Norouzi D, Grigoryev SA, Zhurkin VB. DNA topology in chromatin is defined by nucleosome spacing. SCIENCE ADVANCES 2017; 3:e1700957. [PMID: 29098179 PMCID: PMC5659657 DOI: 10.1126/sciadv.1700957] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 09/27/2017] [Indexed: 06/07/2023]
Abstract
In eukaryotic nucleosomes, DNA makes ~1.7 superhelical turns around histone octamer. However, there is a long-standing discrepancy between the nucleosome core structure determined by x-ray crystallography and measurements of DNA topology in circular minichromosomes, indicating that there is only ~1.0 superhelical turn per nucleosome. Although several theoretical assumptions were put forward to explain this paradox by conformational variability of the nucleosome linker, none was tested experimentally. We analyzed topological properties of DNA in circular nucleosome arrays with precisely positioned nucleosomes. Using topological electrophoretic assays and electron microscopy, we demonstrate that the DNA linking number per nucleosome strongly depends on the nucleosome spacing and varies from -1.4 to -0.9. For the predominant {10n + 5} class of nucleosome repeats found in native chromatin, our results are consistent with the DNA topology observed earlier. Thus, we reconcile the topological properties of nucleosome arrays with nucleosome core structure and provide a simple explanation for the DNA topology in native chromatin with variable DNA linker length. Topological polymorphism of the chromatin fibers described here may reflect a more general tendency of chromosomal domains containing active or repressed genes to acquire different nucleosome spacing to retain topologically distinct higher-order structures.
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Affiliation(s)
- Tatiana Nikitina
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Davood Norouzi
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Sergei A. Grigoryev
- Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Victor B. Zhurkin
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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178
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Meng H, Li H, Zheng Y, Yang Z, Jia Y, Bo S. Evolutionary analysis of nucleosome positioning sequences based on New Symmetric Relative Entropy. Genomics 2017; 110:154-161. [PMID: 28917635 DOI: 10.1016/j.ygeno.2017.09.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 09/06/2017] [Accepted: 09/12/2017] [Indexed: 10/18/2022]
Abstract
New Symmetric Relative Entropy (NSRE) was applied innovatively to analyze the nucleosome sequences in S. cerevisiae, S. pombe and Drosophila. NSRE distributions could well reflect the characteristic differences of nucleosome sequences among three organisms, and the differences indicate a concerted evolution in the sequence usage of nucleosome. Further analysis about the nucleosomes around TSS shows that the constitutive property of +1/-1 nucleosomes in S. cerevisiae is different from that in S. pombe and Drosophila, which indicates that S. cerevisiae has a different transcription regulation mechanism based on nucleosome. However, in either case, the nucleosome dyad region is conserved and always has a higher NSRE. Base composition analysis shows that this conservative property in nucleosome dyad region is mainly determined by base A and T, and the dependence degrees on base A and T are consistent in three organisms.
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Affiliation(s)
- Hu Meng
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
| | - Hong Li
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China.
| | - Yan Zheng
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
| | - Zhenhua Yang
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
| | - Yun Jia
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
| | - Suling Bo
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
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179
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Mao P, Brown AJ, Malc EP, Mieczkowski PA, Smerdon MJ, Roberts SA, Wyrick JJ. Genome-wide maps of alkylation damage, repair, and mutagenesis in yeast reveal mechanisms of mutational heterogeneity. Genome Res 2017; 27:1674-1684. [PMID: 28912372 PMCID: PMC5630031 DOI: 10.1101/gr.225771.117] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Accepted: 08/21/2017] [Indexed: 12/11/2022]
Abstract
DNA base damage is an important contributor to genome instability, but how the formation and repair of these lesions is affected by the genomic landscape and contributes to mutagenesis is unknown. Here, we describe genome-wide maps of DNA base damage, repair, and mutagenesis at single nucleotide resolution in yeast treated with the alkylating agent methyl methanesulfonate (MMS). Analysis of these maps revealed that base excision repair (BER) of alkylation damage is significantly modulated by chromatin, with faster repair in nucleosome-depleted regions, and slower repair and higher mutation density within strongly positioned nucleosomes. Both the translational and rotational settings of lesions within nucleosomes significantly influence BER efficiency; moreover, this effect is asymmetric relative to the nucleosome dyad axis and is regulated by histone modifications. Our data also indicate that MMS-induced mutations at adenine nucleotides are significantly enriched on the nontranscribed strand (NTS) of yeast genes, particularly in BER-deficient strains, due to higher damage formation on the NTS and transcription-coupled repair of the transcribed strand (TS). These findings reveal the influence of chromatin on repair and mutagenesis of base lesions on a genome-wide scale and suggest a novel mechanism for transcription-associated mutation asymmetry, which is frequently observed in human cancers.
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Affiliation(s)
- Peng Mao
- School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA
| | - Alexander J Brown
- School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA
| | - Ewa P Malc
- Department of Genetics, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | - Piotr A Mieczkowski
- Department of Genetics, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | - Michael J Smerdon
- School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA
| | - Steven A Roberts
- School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA.,Center for Reproductive Biology, Washington State University, Pullman, Washington 99164, USA
| | - John J Wyrick
- School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA.,Center for Reproductive Biology, Washington State University, Pullman, Washington 99164, USA
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180
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MNase-Sensitive Complexes in Yeast: Nucleosomes and Non-histone Barriers. Mol Cell 2017; 65:565-577.e3. [PMID: 28157509 DOI: 10.1016/j.molcel.2016.12.009] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 09/15/2016] [Accepted: 12/13/2016] [Indexed: 11/24/2022]
Abstract
Micrococcal nuclease (MNase) is commonly used to map nucleosomes genome-wide, but nucleosome maps are affected by the degree of digestion. It has been proposed that many yeast promoters are not nucleosome-free but instead occupied by easily digested, unstable, "fragile" nucleosomes. We analyzed the histone content of all MNase-sensitive complexes by MNase-ChIP-seq and sonication-ChIP-seq. We find that yeast promoters are predominantly bound by non-histone protein complexes, with little evidence for fragile nucleosomes. We do detect MNase-sensitive nucleosomes elsewhere in the genome, including at transcription termination sites. However, they have high A/T content, suggesting that MNase sensitivity does not indicate instability, but rather the preference of MNase for A/T-rich DNA, such that A/T-rich nucleosomes are digested faster than G/C-rich nucleosomes. We confirm our observations by analyzing ChIP-exo, chemical mapping, and ATAC-seq data from other laboratories. Thus, histone ChIP-seq experiments are essential to distinguish nucleosomes from other DNA-binding proteins that protect against MNase.
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181
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Nizovtseva EV, Todolli S, Olson WK, Studitsky VM. Towards quantitative analysis of gene regulation by enhancers. Epigenomics 2017; 9:1219-1231. [PMID: 28799793 DOI: 10.2217/epi-2017-0061] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Enhancers are regulatory DNA sequences that can activate transcription over large distances. Recent studies have revealed the widespread role of distant activation in eukaryotic gene regulation and in the development of various human diseases, including cancer. Here we review recent progress in the field, focusing on new experimental and computational approaches that quantify the role of chromatin structure and dynamics during enhancer-promoter interactions in vitro and in vivo.
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Affiliation(s)
- Ekaterina V Nizovtseva
- Cancer Epigenetics Program, Fox Chase Cancer Center, 333 Cottman Ave., Philadelphia, PA 19422, USA
| | - Stefjord Todolli
- Department of Chemistry & Chemical Biology, Center for Quantitative Biology, Rutgers, the State University of New Jersey, 610 Taylor Rd., Piscataway, NJ 08854, USA
| | - Wilma K Olson
- Department of Chemistry & Chemical Biology, Center for Quantitative Biology, Rutgers, the State University of New Jersey, 610 Taylor Rd., Piscataway, NJ 08854, USA
| | - Vasily M Studitsky
- Cancer Epigenetics Program, Fox Chase Cancer Center, 333 Cottman Ave., Philadelphia, PA 19422, USA.,Biology Faculty, Moscow State University, Moscow 119991, Russia.,Laboratory of Epigenetics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
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182
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Histone Acetylation, Not Stoichiometry, Regulates Linker Histone Binding in Saccharomyces cerevisiae. Genetics 2017; 207:347-355. [PMID: 28739661 DOI: 10.1534/genetics.117.1132] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 07/12/2017] [Indexed: 12/27/2022] Open
Abstract
Linker histones play a fundamental role in shaping chromatin structure, but how their interaction with chromatin is regulated is not well understood. In this study, we used a combination of genetic and genomic approaches to explore the regulation of linker histone binding in the yeast, Saccharomyces cerevisiae We found that increased expression of Hho1, the yeast linker histone, resulted in a severe growth defect, despite only subtle changes in chromatin structure. Further, this growth defect was rescued by mutations that increase histone acetylation. Consistent with this, genome-wide analysis of linker histone occupancy revealed an inverse correlation with histone tail acetylation in both yeast and mouse embryonic stem cells. Collectively, these results suggest that histone acetylation negatively regulates linker histone binding in S. cerevisiae and other organisms and provide important insight into how chromatin structure is regulated and maintained to both facilitate and repress transcription.
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183
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Voong LN, Xi L, Wang JP, Wang X. Genome-wide Mapping of the Nucleosome Landscape by Micrococcal Nuclease and Chemical Mapping. Trends Genet 2017; 33:495-507. [PMID: 28693826 DOI: 10.1016/j.tig.2017.05.007] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2017] [Revised: 05/10/2017] [Accepted: 05/30/2017] [Indexed: 12/30/2022]
Abstract
Nucleosomes regulate the transcription output of the genome by occluding the underlying DNA sequences from DNA-binding proteins that must act on it. Knowledge of the precise locations of nucleosomes in the genome is thus essential towards understanding how transcription is regulated. Current nucleosome-mapping strategies involve digesting chromatin with nucleases or chemical cleavage followed by high-throughput sequencing. In this review, we compare the traditional micrococcal nuclease (MNase)-based approach with a chemical cleavage strategy, with discussion on the important insights each has uncovered about the role of nucleosomes in shaping transcriptional processes.
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Affiliation(s)
- Lilien N Voong
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA
| | - Liqun Xi
- Department of Statistics, Northwestern University, Evanston, IL 60208, USA
| | - Ji-Ping Wang
- Department of Statistics, Northwestern University, Evanston, IL 60208, USA.
| | - Xiaozhong Wang
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
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184
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Chen J, Li E, Zhang X, Dong X, Lei L, Song W, Zhao H, Lai J. Genome-wide Nucleosome Occupancy and Organization Modulates the Plasticity of Gene Transcriptional Status in Maize. MOLECULAR PLANT 2017; 10:962-974. [PMID: 28487258 DOI: 10.1016/j.molp.2017.05.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 04/28/2017] [Accepted: 05/01/2017] [Indexed: 05/16/2023]
Abstract
Nucleosomes are fundamental units of chromatin that play critical roles in gene regulation by modulating DNA accessibility. However, their roles in regulating tissue-specific gene transcription are poorly understood. Here, we present genome-wide nucleosome maps of maize shoot and endosperm generated by sequencing the micrococcal nuclease digested nucleosomal DNA. The changes of gene transcriptional status between shoot and endosperm were accompanied by preferential nucleosome loss from the promoters and shifts in the first nucleosome downstream of the transcriptional start sites (+1 nucleosome) and upstream of transcriptional termination sites (-1 nucleosome). Intrinsically DNA-encoded nucleosome organization was largely associated with the capacity of a gene to alter its transcriptional status among different tissues. Compared with tissue-specific genes, constitutively expressed genes showed more pronounced 5' and 3' nucleosome-depleted regions as well as further +1 nucleosome to transcriptional start sites and -1 nucleosome to transcriptional termination sites. Moreover, nucleosome organization was more highly correlated with the plasticity of gene transcriptional status than with its expression level when examined using in vivo and predicted nucleosome data. In addition, the translational efficiencies of tissue-specific genes appeared to be greater than those of constitutively expressed genes. Taken together, our results indicate that intrinsically DNA-encoded nucleosome organization is important, beyond its role in regulating gene expression levels, in determining the plasticity of gene transcriptional status.
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Affiliation(s)
- Jian Chen
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - En Li
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - Xiangbo Zhang
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - Xiaomei Dong
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - Lei Lei
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - Weibin Song
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - Haiming Zhao
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China
| | - Jinsheng Lai
- State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding, China Agricultural University, Beijing 100193, P. R. China.
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185
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A comparison of nucleosome organization in Drosophila cell lines. PLoS One 2017; 12:e0178590. [PMID: 28570602 PMCID: PMC5453549 DOI: 10.1371/journal.pone.0178590] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 05/16/2017] [Indexed: 01/25/2023] Open
Abstract
Changes in the distribution of nucleosomes along the genome influence chromatin structure and impact gene expression by modulating the accessibility of DNA to transcriptional machinery. However, the role of genome-wide nucleosome positioning in gene expression and in maintaining differentiated cell states remains poorly understood. Drosophila melanogaster cell lines represent distinct tissue types and exhibit cell-type specific gene expression profiles. They thus could provide a useful tool for investigating cell-type specific nucleosome organization of an organism's genome. To evaluate this possibility, we compared genome-wide nucleosome positioning and occupancy in five different Drosophila tissue-specific cell lines, and in reconstituted chromatin, and then tested for correlations between nucleosome positioning, transcription factor binding motifs, and gene expression. Nucleosomes in all cell lines were positioned in accordance with previously known DNA-nucleosome interactions, with helically repeating A/T di-nucleotide pairs arranged within nucleosomal DNAs and AT-rich pentamers generally excluded from nucleosomal DNA. Nucleosome organization in all cell lines differed markedly from in vitro reconstituted chromatin, with highly expressed genes showing strong nucleosome organization around transcriptional start sites. Importantly, comparative analysis identified genomic regions that exhibited cell line-specific nucleosome enrichment or depletion. Further analysis of these regions identified 91 out of 16,384 possible heptamer sequences that showed differential nucleosomal occupation between cell lines, and 49 of the heptamers matched one or more known transcription factor binding sites. These results demonstrate that there is differential nucleosome positioning between these Drosophila cell lines and therefore identify a system that could be used to investigate the functional significance of differential nucleosomal positioning in cell type specification.
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186
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Understanding nucleosome dynamics and their links to gene expression and DNA replication. Nat Rev Mol Cell Biol 2017; 18:548-562. [PMID: 28537572 DOI: 10.1038/nrm.2017.47] [Citation(s) in RCA: 298] [Impact Index Per Article: 42.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Advances in genomics technology have provided the means to probe myriad chromatin interactions at unprecedented spatial and temporal resolution. This has led to a profound understanding of nucleosome organization within the genome, revealing that nucleosomes are highly dynamic. Nucleosome dynamics are governed by a complex interplay of histone composition, histone post-translational modifications, nucleosome occupancy and positioning within chromatin, which are influenced by numerous regulatory factors, including general regulatory factors, chromatin remodellers, chaperones and polymerases. It is now known that these dynamics regulate diverse cellular processes ranging from gene transcription to DNA replication and repair.
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187
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Abstract
Eukaryotic DNA is packaged into regularly spaced nucleosomes, resembling beads on a string. Each bead contains ∼147 bp wrapped around a core histone octamer. Linker histone (H1) binds to the linker DNA to drive chromatin folding. Micrococcal nuclease (MNase) digestion studies reveal 2 mono-nucleosomal intermediates: the core particle (∼147 bp) and the chromatosome (∼160 bp; a core particle with additional DNA protected by H1). We have recently developed an improved method for mapping nucleosomes, using exonuclease III to remove residual linker (MNase-Exo-seq). (1) We discovered 2 new intermediate particles corresponding to core particles with ∼7 bp of linker protruding from one side (∼154 bp) or both sides (∼161 bp), which are formed in the absence of H1. We propose that these "proto-chromatosomes" are stabilized by core histone-DNA contacts in the linker, ∼7 bp from the nucleosome boundaries. These contacts may determine the topography of the H1 binding site.
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Affiliation(s)
- Josefina Ocampo
- a Division of Developmental Biology, Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Feng Cui
- b Thomas H. Gosnell School of Life Sciences, Rochester Institute of Technology , Rochester , NY , USA
| | - Victor B Zhurkin
- c National Cancer Institute, National Institutes of Health , Bethesda , MD , USA
| | - David J Clark
- a Division of Developmental Biology, Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health , Bethesda , MD , USA
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188
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Tompitak M, de Bruin L, Eslami-Mossallam B, Schiessel H. Designing nucleosomal force sensors. Phys Rev E 2017; 95:052402. [PMID: 28618598 DOI: 10.1103/physreve.95.052402] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Indexed: 11/07/2022]
Abstract
About three quarters of our DNA is wrapped into nucleosomes: DNA spools with a protein core. It is well known that the affinity of a given DNA stretch to be incorporated into a nucleosome depends on the geometry and elasticity of the basepair sequence involved, causing the positioning of nucleosomes. Here we show that DNA elasticity can have a much deeper effect on nucleosomes than just their positioning: it affects their "identities". Employing a recently developed computational algorithm, the mutation Monte Carlo method, we design nucleosomes with surprising physical characteristics. Unlike any other nucleosomes studied so far, these nucleosomes are short-lived when put under mechanical tension whereas other physical properties are largely unaffected. This suggests that the nucleosome, the most abundant DNA-protein complex in our cells, might more properly be considered a class of complexes with a wide array of physical properties, and raises the possibility that evolution has shaped various nucleosome species according to their genomic context.
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Affiliation(s)
- M Tompitak
- Instituut-Lorentz for Theoretical Physics, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands
| | - L de Bruin
- Section de Mathématiques, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - B Eslami-Mossallam
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - H Schiessel
- Instituut-Lorentz for Theoretical Physics, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands
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189
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Bascom GD, Kim T, Schlick T. Kilobase Pair Chromatin Fiber Contacts Promoted by Living-System-Like DNA Linker Length Distributions and Nucleosome Depletion. J Phys Chem B 2017; 121:3882-3894. [PMID: 28299939 DOI: 10.1021/acs.jpcb.7b00998] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Nucleosome placement, or DNA linker length patterns, are believed to yield specific spatial features in chromatin fibers, but details are unknown. Here we examine by mesoscale modeling how kilobase (kb) range contacts and fiber looping depend on linker lengths ranging from 18 to 45 bp, with values modeled after living systems, including nucleosome free regions (NFRs) and gene encoding segments. We also compare artificial constructs with alternating versus randomly distributed linker lengths in the range of 18-72 bp. We show that nonuniform distributions with NFRs enhance flexibility and encourage kb-range contacts. NFRs between neighboring gene segments diminish short-range contacts between flanking nucleosomes, while enhancing kb-range contacts via hierarchical looping. We also demonstrate that variances in linker lengths enhance such contacts. In particular, moderate sized variations in fiber linker lengths (∼27 bp) encourage long-range contacts in randomly distributed linker length fibers. Our work underscores the importance of linker length patterns, alongside bound proteins, in biological regulation. Contacts formed by kb-range chromatin folding are crucial to gene activity. Because we find that special linker length distributions in living systems promote kb contacts, our work suggests ways to manipulate these patterns for regulation of gene activity.
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Affiliation(s)
- Gavin D Bascom
- Department of Chemistry, New York University , 100 Washington Square E, New York, New York 10003, United States
| | - Taejin Kim
- Department of Chemistry, New York University , 100 Washington Square E, New York, New York 10003, United States
| | - Tamar Schlick
- Department of Chemistry, New York University , 100 Washington Square E, New York, New York 10003, United States.,Courant Institute of Mathematical Sciences, New York University , 251 Mercer St, New York, New York 10012, United States.,New York University-East China Normal University Center for Computational Chemistry at New York University Shanghai , Room 340, Geography Building, North Zhongshan Road, 3663 Shanghai, China
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190
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Kubik S, Bruzzone MJ, Shore D. Establishing nucleosome architecture and stability at promoters: Roles of pioneer transcription factors and the RSC chromatin remodeler. Bioessays 2017; 39. [PMID: 28345796 DOI: 10.1002/bies.201600237] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Improvements in deep sequencing, together with methods to rapidly deplete essential transcription factors (TFs) and chromatin remodelers, have recently led to a more detailed picture of promoter nucleosome architecture in yeast and its relationship to transcriptional regulation. These studies revealed that ∼40% of all budding yeast protein-coding genes possess a unique promoter structure, where we propose that an unusually unstable nucleosome forms immediately upstream of the transcription start site (TSS). This "fragile" nucleosome (FN) promoter architecture relies on the combined action of the essential RSC (Remodels Structure of Chromatin) nucleosome remodeler and pioneer transcription factors (PTFs). FNs are associated with genes whose expression is high, coupled to cell growth, and characterized by low cell-to-cell variability (noise), suggesting that they may promote these features. Recent studies in metazoans suggest that the presence of dynamic nucleosomes upstream of the TSS at highly expressed genes may be conserved throughout evolution.
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Affiliation(s)
- Slawomir Kubik
- Department of Molecular Biology and Institute of Genetics and Genomics in Geneva (iGE3), University of Geneva, Geneva, Switzerland
| | - Maria Jessica Bruzzone
- Department of Molecular Biology and Institute of Genetics and Genomics in Geneva (iGE3), University of Geneva, Geneva, Switzerland
| | - David Shore
- Department of Molecular Biology and Institute of Genetics and Genomics in Geneva (iGE3), University of Geneva, Geneva, Switzerland
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191
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Maree JP, Povelones ML, Clark DJ, Rudenko G, Patterton HG. Well-positioned nucleosomes punctuate polycistronic pol II transcription units and flank silent VSG gene arrays in Trypanosoma brucei. Epigenetics Chromatin 2017; 10:14. [PMID: 28344657 PMCID: PMC5359979 DOI: 10.1186/s13072-017-0121-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Accepted: 03/14/2017] [Indexed: 12/18/2022] Open
Abstract
Background The compaction of DNA in chromatin in eukaryotes allowed the expansion of genome size and coincided with significant evolutionary diversification. However, chromatin generally represses DNA function, and mechanisms coevolved to regulate chromatin structure and its impact on DNA. This included the selection of specific nucleosome positions to modulate accessibility to the DNA molecule. Trypanosoma brucei, a member of the Excavates supergroup, falls in an ancient evolutionary branch of eukaryotes and provides valuable insight into the organization of chromatin in early genomes. Results We have mapped nucleosome positions in T. brucei and identified important differences compared to other eukaryotes: The RNA polymerase II initiation regions in T. brucei do not exhibit pronounced nucleosome depletion, and show little evidence for defined −1 and +1 nucleosomes. In contrast, a well-positioned nucleosome is present directly on the splice acceptor sites within the polycistronic transcription units. The RNA polyadenylation sites were depleted of nucleosomes, with a single well-positioned nucleosome present immediately downstream of the predicted sites. The regions flanking the silent variant surface glycoprotein (VSG) gene cassettes showed extensive arrays of well-positioned nucleosomes, which may repress cryptic transcription initiation. The silent VSG genes themselves exhibited a less regular nucleosomal pattern in both bloodstream and procyclic form trypanosomes. The DNA replication origins, when present within silent VSG gene cassettes, displayed a defined nucleosomal organization compared with replication origins in other chromosomal core regions. Conclusions Our results indicate that some organizational features of chromatin are evolutionarily ancient, and may already have been present in the last eukaryotic common ancestor. Electronic supplementary material The online version of this article (doi:10.1186/s13072-017-0121-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | - Megan Lindsay Povelones
- Department of Biology, Pennsylvania State University (Brandywine Campus), Media, PA 19063 USA
| | - David Johannes Clark
- Division of Developmental Biology, Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, MD USA
| | - Gloria Rudenko
- Department of Life Sciences, Imperial College London, South Kensington, London, SW7 2AZ UK
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192
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Lukačišin M, Landon M, Jajoo R. Sequence-specific thermodynamic properties of nucleic acids influence both transcriptional pausing and backtracking in yeast. PLoS One 2017; 12:e0174066. [PMID: 28301878 PMCID: PMC5354634 DOI: 10.1371/journal.pone.0174066] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2016] [Accepted: 03/02/2017] [Indexed: 01/22/2023] Open
Abstract
RNA Polymerase II pauses and backtracks during transcription, with many consequences for gene expression and cellular physiology. Here, we show that the energy required to melt double-stranded nucleic acids in the transcription bubble predicts pausing in Saccharomyces cerevisiae far more accurately than nucleosome roadblocks do. In addition, the same energy difference also determines when the RNA polymerase backtracks instead of continuing to move forward. This data-driven model corroborates—in a genome wide and quantitative manner—previous evidence that sequence-dependent thermodynamic features of nucleic acids influence both transcriptional pausing and backtracking.
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Affiliation(s)
- Martin Lukačišin
- Department of Systems Biology, Harvard Medical School, Boston, MA, United States of America
- IST Austria, Klosterneuburg, Austria
| | - Matthieu Landon
- Department of Systems Biology, Harvard Medical School, Boston, MA, United States of America
- Department of Genetics, Harvard Medical School, Boston, MA, United States of America
- Ecole des Mines de Paris, Mines Paristech, Paris, France
| | - Rishi Jajoo
- Department of Systems Biology, Harvard Medical School, Boston, MA, United States of America
- * E-mail:
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193
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Vainshtein Y, Rippe K, Teif VB. NucTools: analysis of chromatin feature occupancy profiles from high-throughput sequencing data. BMC Genomics 2017; 18:158. [PMID: 28196481 PMCID: PMC5309995 DOI: 10.1186/s12864-017-3580-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Accepted: 02/10/2017] [Indexed: 12/21/2022] Open
Abstract
Background Biomedical applications of high-throughput sequencing methods generate a vast amount of data in which numerous chromatin features are mapped along the genome. The results are frequently analysed by creating binary data sets that link the presence/absence of a given feature to specific genomic loci. However, the nucleosome occupancy or chromatin accessibility landscape is essentially continuous. It is currently a challenge in the field to cope with continuous distributions of deep sequencing chromatin readouts and to integrate the different types of discrete chromatin features to reveal linkages between them. Results Here we introduce the NucTools suite of Perl scripts as well as MATLAB- and R-based visualization programs for a nucleosome-centred downstream analysis of deep sequencing data. NucTools accounts for the continuous distribution of nucleosome occupancy. It allows calculations of nucleosome occupancy profiles averaged over several replicates, comparisons of nucleosome occupancy landscapes between different experimental conditions, and the estimation of the changes of integral chromatin properties such as the nucleosome repeat length. Furthermore, NucTools facilitates the annotation of nucleosome occupancy with other chromatin features like binding of transcription factors or architectural proteins, and epigenetic marks like histone modifications or DNA methylation. The applications of NucTools are demonstrated for the comparison of several datasets for nucleosome occupancy in mouse embryonic stem cells (ESCs) and mouse embryonic fibroblasts (MEFs). Conclusions The typical workflows of data processing and integrative analysis with NucTools reveal information on the interplay of nucleosome positioning with other features such as for example binding of a transcription factor CTCF, regions with stable and unstable nucleosomes, and domains of large organized chromatin K9me2 modifications (LOCKs). As potential limitations and problems we discuss how inter-replicate variability of MNase-seq experiments can be addressed. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-3580-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Yevhen Vainshtein
- Functional Genomics Group, Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, Nobelstraße 12, 70569, Stuttgart, Germany.
| | - Karsten Rippe
- Research Group Genome Organization & Function, German Cancer Research Center (DKFZ) and Bioquant, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
| | - Vladimir B Teif
- School of Biological Sciences, University of Essex, Wivenhoe Park, CO4 3SQ, Colchester, UK.
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194
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Zheng Y, Li H, Wang Y, Meng H, Zhang Q, Zhao X. Evolutionary mechanism and biological functions of 8-mers containing CG dinucleotide in yeast. Chromosome Res 2017; 25:173-189. [PMID: 28181048 DOI: 10.1007/s10577-017-9554-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 12/27/2016] [Accepted: 01/27/2017] [Indexed: 01/01/2023]
Abstract
The rules of k-mer non-random usage and the biological functions are worthy of special attention. Firstly, the article studied human 8-mer spectra and found that only the spectra of cytosine-guanine (CG) dinucleotide classification formed independent unimodal distributions when the 8-mers were classified into three subsets under 16 dinucleotide classifications. Secondly, the distribution rules were reproduced by other seven species including yeast, which showed that the evolution phenomenon had species universality. It followed that we proposed two theoretical conjectures: (1) CG1 motifs (8-mers including 1 CG) are the nucleosome-binding motifs. (2) CG2 motifs (8-mers including two or more than two CG) are the modular units of CpG islands. Our conjectures were confirmed in yeast by the following results: a maximum of average area under the receiver operating characteristic (AUC) resulted from CG1 information during nucleosome core sequences, and linker sequences were distinguished by three CG subsets; there was a one-to-one relationship between abundant CG1 signal regions and histone positions; the sequence changing of squeezed nucleosomes was relevant with the strength of CG1 signals; and the AUC value of 0.986 was based on CG2 information when CpG islands and non-CpG islands were distinguished by the three CG subsets.
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Affiliation(s)
- Yan Zheng
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China
| | - Hong Li
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China. .,, No.235, West University Street, Hohhot, Inner Mongolia, China.
| | - Yue Wang
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China
| | - Hu Meng
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China
| | - Qiang Zhang
- College of Science, Inner Mongolia Agricultural University, Hohhot, 010018, China
| | - Xiaoqing Zhao
- Biotechnology research centre, Inner Mongolia Academy of Agricultural and Animal Husbandry Science, Hohhot, 010021, China
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195
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Fischl H, Howe FS, Furger A, Mellor J. Paf1 Has Distinct Roles in Transcription Elongation and Differential Transcript Fate. Mol Cell 2017; 65:685-698.e8. [PMID: 28190769 PMCID: PMC5316414 DOI: 10.1016/j.molcel.2017.01.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Revised: 09/22/2016] [Accepted: 01/05/2017] [Indexed: 12/12/2022]
Abstract
RNA polymerase II (Pol2) movement through chromatin and the co-transcriptional processing and fate of nascent transcripts is coordinated by transcription elongation factors (TEFs) such as polymerase-associated factor 1 (Paf1), but it is not known whether TEFs have gene-specific functions. Using strand-specific nucleotide resolution techniques, we show that levels of Paf1 on Pol2 vary between genes, are controlled dynamically by environmental factors via promoters, and reflect levels of processing and export factors on the encoded transcript. High levels of Paf1 on Pol2 promote transcript nuclear export, whereas low levels reflect nuclear retention. Strains lacking Paf1 show marked elongation defects, although low levels of Paf1 on Pol2 are sufficient for transcription elongation. Our findings support distinct Paf1 functions: a core general function in transcription elongation, satisfied by the lowest Paf1 levels, and a regulatory function in determining differential transcript fate by varying the level of Paf1 on Pol2.
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Affiliation(s)
- Harry Fischl
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Françoise S Howe
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Andre Furger
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Jane Mellor
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
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196
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Bascom G, Schlick T. Linking Chromatin Fibers to Gene Folding by Hierarchical Looping. Biophys J 2017; 112:434-445. [PMID: 28153411 DOI: 10.1016/j.bpj.2017.01.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 01/05/2017] [Accepted: 01/06/2017] [Indexed: 12/16/2022] Open
Abstract
While much is known about DNA structure on the basepair level, this scale represents only a fraction of the structural levels involved in folding the genomic material. With recent advances in experimental and theoretical techniques, a variety of structures have been observed on the fiber, gene, and chromosome levels of genome organization. Here we view chromatin architecture from nucleosomes and fibers to genes and chromosomes, highlighting the rich structural diversity and fiber fluidity emerging from both experimental and theoretical techniques. In this context, we discuss our recently proposed folding mechanism, which we call "hierarchical looping", similar to rope flaking used in mountain climbing, where 10-nm zigzag chromatin fibers are compacted laterally into self-associating loops which then stack and fold in space. We propose that hierarchical looping may act as a bridge between fibers and genes as well as provide a mechanism to relate key features of interphase and metaphase chromosome architecture to genome structural changes. This motif emerged by analysis of ultrastructural internucleosome contact data by electron microscopy-assisted nucleosome interaction capture cross-linking experiments, in combination with mesoscale modeling. We suggest that while the local folding of chromatin can be regulated at the fiber level by adjustment of internal factors such as linker-histone binding affinities, linker DNA lengths, and divalent ion levels, hierarchical looping on the gene level can additionally be controlled by posttranslational modifications and external factors such as polycomb group proteins. From a combination of 3C data and mesoscale modeling, we suggest that hierarchical looping could also play a role in epigenetic gene silencing, as stacked loops may occlude access to transcription start sites. With advances in crystallography, single-molecule in vitro biochemistry, in vivo imaging techniques, and genome-wide contact data experiments, various modeling approaches are allowing for previously unavailable structural interpretation of these data at multiple spatial and temporal scales. An unprecedented level of productivity and opportunity is on the horizon for the chromatin structure field.
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Affiliation(s)
- Gavin Bascom
- Department of Chemistry, New York University, New York, New York
| | - Tamar Schlick
- Department of Chemistry, New York University, New York, New York; Courant Institute of Mathematical Sciences, New York University, New York, New York; New York University-East China Normal University Center for Computational Chemistry at New York University Shanghai, Shanghai, China.
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197
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Histone H3K4 and H3K36 Methylation Independently Recruit the NuA3 Histone Acetyltransferase in Saccharomyces cerevisiae. Genetics 2017; 205:1113-1123. [PMID: 28108585 DOI: 10.1534/genetics.116.199422] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Accepted: 12/23/2016] [Indexed: 11/18/2022] Open
Abstract
Histone post-translational modifications (PTMs) alter chromatin structure by promoting the interaction of chromatin-modifying complexes with nucleosomes. The majority of chromatin-modifying complexes contain multiple domains that preferentially interact with modified histones, leading to speculation that these domains function in concert to target nucleosomes with distinct combinations of histone PTMs. In Saccharomyces cerevisiae, the NuA3 histone acetyltransferase complex contains three domains, the PHD finger in Yng1, the PWWP domain in Pdp3, and the YEATS domain in Taf14; which in vitro bind to H3K4 methylation, H3K36 methylation, and acetylated and crotonylated H3K9, respectively. While the in vitro binding has been well characterized, the relative in vivo contributions of these histone PTMs in targeting NuA3 is unknown. Here, through genome-wide colocalization and by mutational interrogation, we demonstrate that the PHD finger of Yng1, and the PWWP domain of Pdp3 independently target NuA3 to H3K4 and H3K36 methylated chromatin, respectively. In contrast, we find no evidence to support the YEATS domain of Taf14 functioning in NuA3 recruitment. Collectively our results suggest that the presence of multiple histone PTM binding domains within NuA3, rather than restricting it to nucleosomes containing distinct combinations of histone PTMs, can serve to increase the range of nucleosomes bound by the complex. Interestingly, however, the simple presence of NuA3 is insufficient to ensure acetylation of the associated nucleosomes, suggesting a secondary level of acetylation regulation that does not involve control of HAT-nucleosome interactions.
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198
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Plasmodium falciparum Nucleosomes Exhibit Reduced Stability and Lost Sequence Dependent Nucleosome Positioning. PLoS Pathog 2016; 12:e1006080. [PMID: 28033404 PMCID: PMC5198986 DOI: 10.1371/journal.ppat.1006080] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 11/19/2016] [Indexed: 11/19/2022] Open
Abstract
The packaging and organization of genomic DNA into chromatin represents an additional regulatory layer of gene expression, with specific nucleosome positions that restrict the accessibility of regulatory DNA elements. The mechanisms that position nucleosomes in vivo are thought to depend on the biophysical properties of the histones, sequence patterns, like phased di-nucleotide repeats and the architecture of the histone octamer that folds DNA in 1.65 tight turns. Comparative studies of human and P. falciparum histones reveal that the latter have a strongly reduced ability to recognize internal sequence dependent nucleosome positioning signals. In contrast, the nucleosomes are positioned by AT-repeat sequences flanking nucleosomes in vivo and in vitro. Further, the strong sequence variations in the plasmodium histones, compared to other mammalian histones, do not present adaptations to its AT-rich genome. Human and parasite histones bind with higher affinity to GC-rich DNA and with lower affinity to AT-rich DNA. However, the plasmodium nucleosomes are overall less stable, with increased temperature induced mobility, decreased salt stability of the histones H2A and H2B and considerable reduced binding affinity to GC-rich DNA, as compared with the human nucleosomes. In addition, we show that plasmodium histone octamers form the shortest known nucleosome repeat length (155bp) in vitro and in vivo. Our data suggest that the biochemical properties of the parasite histones are distinct from the typical characteristics of other eukaryotic histones and these properties reflect the increased accessibility of the P. falciparum genome. Nucleosomes are not positioned randomly on DNA but on preferential sites with respect to the underlying DNA sequence. Histones belong to the most conserved eukaryotic proteins, as sequence dependent nucleosome positioning is an essential regulatory feature of nucleosomes, determining the accessibility of regulatory factors to DNA. We determined the biochemical properties of plasmodium histones and show that they are distinct from human forms, explaining the accessible chromatin structure of P. falciparum. Amino acid exchanges in the histones do not present an adaption to the AT-rich genome, but rather reduce the binding affinity to GC-rich DNA sequences, resulting in rather unstable nucleosomes with labile H2A and H2B, requiring extra-nucleosomal positioning signals to keep them on place. Plasmodium chromatin exhibits the shortest nucleosome spacing known to date potentially inhibiting the formation of higher order structures and maintaining chromatin accessible.
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199
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Todolli S, Perez PJ, Clauvelin N, Olson WK. Contributions of Sequence to the Higher-Order Structures of DNA. Biophys J 2016; 112:416-426. [PMID: 27955889 DOI: 10.1016/j.bpj.2016.11.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 11/11/2016] [Accepted: 11/15/2016] [Indexed: 11/17/2022] Open
Abstract
One of the critical unanswered questions in genome biophysics is how the primary sequence of DNA bases influences the global properties of very-long-chain molecules. The local sequence-dependent features of DNA found in high-resolution structures introduce irregularities in the disposition of adjacent residues that facilitate the specific binding of proteins and modulate the global folding and interactions of double helices with hundreds of basepairs. These features also determine the positions of nucleosomes on DNA and the lengths of the interspersed DNA linkers. Like the patterns of basepair association within DNA, the arrangements of nucleosomes in chromatin modulate the properties of longer polymers. The intrachromosomal loops detected in genomic studies contain hundreds of nucleosomes, and given that the simulated configurations of chromatin depend on the lengths of linker DNA, the formation of these loops may reflect sequence-dependent information encoded within the positioning of the nucleosomes. With knowledge of the positions of nucleosomes on a given genome, methods are now at hand to estimate the looping propensities of chromatin in terms of the spacing of nucleosomes and to make a direct connection between the DNA base sequence and larger-scale chromatin folding.
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Affiliation(s)
- Stefjord Todolli
- Center for Quantitative Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey
| | - Pamela J Perez
- Center for Quantitative Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey
| | - Nicolas Clauvelin
- Center for Quantitative Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey
| | - Wilma K Olson
- Department of Chemistry and Chemical Biology, The State University of New Jersey, Piscataway, New Jersey; Center for Quantitative Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey.
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200
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Xiong J, Gao S, Dui W, Yang W, Chen X, Taverna SD, Pearlman RE, Ashlock W, Miao W, Liu Y. Dissecting relative contributions of cis- and trans-determinants to nucleosome distribution by comparing Tetrahymena macronuclear and micronuclear chromatin. Nucleic Acids Res 2016; 44:10091-10105. [PMID: 27488188 PMCID: PMC5137421 DOI: 10.1093/nar/gkw684] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 07/21/2016] [Accepted: 07/24/2016] [Indexed: 02/06/2023] Open
Abstract
The ciliate protozoan Tetrahymena thermophila contains two types of structurally and functionally differentiated nuclei: the transcriptionally active somatic macronucleus (MAC) and the transcriptionally silent germ-line micronucleus (MIC). Here, we demonstrate that MAC features well-positioned nucleosomes downstream of transcription start sites and flanking splice sites. Transcription-associated trans-determinants promote nucleosome positioning in MAC. By contrast, nucleosomes in MIC are dramatically delocalized. Nucleosome occupancy in MAC and MIC are nonetheless highly correlated with each other, as well as with in vitro reconstitution and predictions based upon DNA sequence features, revealing unexpectedly strong contributions from cis-determinants. In particular, well-positioned nucleosomes are often matched with GC content oscillations. As many nucleosomes are coordinately accommodated by both cis- and trans-determinants, we propose that their distribution is shaped by the impact of these nucleosomes on the mutational and transcriptional landscape, and driven by evolutionary selection.
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Affiliation(s)
- Jie Xiong
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA,Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China,These authors contributed equally to this work as first authors
| | - Shan Gao
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China,Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266003, China,These authors contributed equally to this work as first authors
| | - Wen Dui
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Wentao Yang
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Xiao Chen
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
| | - Sean D. Taverna
- Department of Pharmacology and Molecular Sciences and The Center for Epigenetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ronald E. Pearlman
- Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada
| | - Wendy Ashlock
- Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada
| | - Wei Miao
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China,Correspondence may also be addressed to Wei Miao.
| | - Yifan Liu
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA,To whom correspondence should be addressed. Tel: +1 734 6154239;
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