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Sandholtz SH, Kannan D, Beltran BG, Spakowitz AJ. Chromosome Structural Mechanics Dictates the Local Spreading of Epigenetic Marks. Biophys J 2020; 119:1630-1639. [PMID: 33010237 DOI: 10.1016/j.bpj.2020.08.039] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 08/07/2020] [Accepted: 08/17/2020] [Indexed: 10/23/2022] Open
Abstract
We present a theoretical model that demonstrates the integral role chromosome organization and structural mechanics play in the spreading of histone modifications involved in epigenetic regulation. Our model shows that heterogeneous nucleosome positioning, and the resulting position-dependent mechanical properties, must be included to reproduce several qualitative features of experimental data of histone methylation spreading around an artificially induced "nucleation site." We show that our model recreates both the extent of spreading and the presence of a subdominant peak upstream of the transcription start site. Our model indicates that the spreading of epigenetic modifications is sensitive to heterogeneity in chromatin organization and the resulting variability in the chromatin's mechanical properties, suggesting that nucleosome spacing can directly control the conferral of epigenetic marks by modifying the structural mechanics of the chromosome. It further illustrates how the physical organization of the DNA polymer may play a significant role in re-establishing the epigenetic code upon cell division.
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Affiliation(s)
| | - Deepti Kannan
- Department of Physics, University of Cambridge, Cambridge, United Kingdom
| | - Bruno G Beltran
- Biophysics Program, Stanford University, Stanford, California
| | - Andrew J Spakowitz
- Biophysics Program, Stanford University, Stanford, California; Chemical Engineering Department, Stanford University, Stanford, California; Department of Materials Science and Engineering, Stanford University, Stanford, California; Department of Applied Physics, Stanford University, Stanford, California.
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Buckle A, Nozawa RS, Kleinjan DA, Gilbert N. Functional characteristics of novel pancreatic Pax6 regulatory elements. Hum Mol Genet 2019; 27:3434-3448. [PMID: 30007277 PMCID: PMC6140780 DOI: 10.1093/hmg/ddy255] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Accepted: 07/02/2018] [Indexed: 12/28/2022] Open
Abstract
Complex diseases, such as diabetes, are influenced by comprehensive transcriptional networks. Genome-wide association studies have revealed that variants located in regulatory elements for pancreatic transcription factors are linked to diabetes, including those functionally linked to the paired box transcription factor Pax6. Pax6 deletions in adult mice cause rapid onset of classic diabetes, but the full spectrum of pancreatic Pax6 regulators is unknown. Using a regulatory element discovery approach, we identified two novel Pax6 pancreatic cis-regulatory elements in a poorly characterized regulatory desert. Both new elements, Pax6 pancreas cis-regulatory element 3 (PE3) and PE4, are located 50 and 100 kb upstream and interact with different parts of the Pax6 promoter and nearby non-coding RNAs. They drive expression in the developing pancreas and brain and code for multiple pancreas-related transcription factor-binding sites. PE3 binds CCCTC-binding factor (CTCF) and is marked by stem cell identity markers in embryonic stem cells, whilst a common variant located in the PE4 element affects binding of Pax4, a known pancreatic regulator, altering Pax6 gene expression. To determine the ability of these elements to regulate gene expression, synthetic transcriptional activators and repressors were targeted to PE3 and PE4, modulating Pax6 gene expression, as well as influencing neighbouring genes and long non-coding RNAs, implicating the Pax6 locus in pancreas function and diabetes.
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Affiliation(s)
- Adam Buckle
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XR, UK
| | - Ryu-Suke Nozawa
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XR, UK
| | - Dirk A Kleinjan
- Centre for Mammalian Synthetic Biology, University of Edinburgh, Edinburgh EH9 3FF, UK
| | - Nick Gilbert
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XR, UK
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Traewachiwiphak S, Yokthongwattana C, Ves-Urai P, Charoensawan V, Yokthongwattana K. Gene expression and promoter characterization of heat-shock protein 90B gene (HSP90B) in the model unicellular green alga Chlamydomonas reinhardtii. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2018; 272:107-116. [PMID: 29807581 DOI: 10.1016/j.plantsci.2018.04.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 03/11/2018] [Accepted: 04/12/2018] [Indexed: 06/08/2023]
Abstract
Molecular chaperones or heat shock proteins are a large protein family with important functions in every cellular organism. Among all types of the heat shock proteins, information on the ER-localized HSP90 protein (HSP90B) and its encoding gene is relatively scarce in the literature, especially in photosynthetic organisms. In this study, expression profiles as well as promoter sequence of the HSP90B gene were investigated in the model green alga Chlamydomonas reinhardtii. We have found that HSP90B is strongly induced by heat and ER stresses, while other short-term exposure to abiotic stresses, such as salinity, dark-to-light transition or light stress does not appear to affect the expression. Promoter truncation analysis as well as chromatin immunoprecipitation using the antibodies recognizing histone H3 and acetylated histone H3, revealed a putative core constitutive promoter sequence between -1 to -253 bp from the transcription start site. Our results also suggested that the nucleotides upstream of the core promoter may contain repressive elements such as putative repressor binding site(s).
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Affiliation(s)
- Somchoke Traewachiwiphak
- Department of Biochemistry, Faculty of Science, Mahidol University, 272 Rama 6 Rd., Bangkok 10400, Thailand; Center for Excellence in Protein and Enzyme Technology, Faculty of Science, Mahidol University, 272 Rama 6 Rd., Bangkok 10400, Thailand
| | - Chotika Yokthongwattana
- Department of Biochemistry, Faculty of Science, Kasetsart University, 50 Ngamwongwan Rd., Bangkok 10900, Thailand
| | - Parthompong Ves-Urai
- Department of Biochemistry, Faculty of Science, Mahidol University, 272 Rama 6 Rd., Bangkok 10400, Thailand
| | - Varodom Charoensawan
- Department of Biochemistry, Faculty of Science, Mahidol University, 272 Rama 6 Rd., Bangkok 10400, Thailand; Integrative Computational BioScience (ICBS) Center, Mahidol University, Nakhon Pathom, Thailand; Systems Biology of Diseases Research Unit, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Kittisak Yokthongwattana
- Department of Biochemistry, Faculty of Science, Mahidol University, 272 Rama 6 Rd., Bangkok 10400, Thailand; Center for Excellence in Protein and Enzyme Technology, Faculty of Science, Mahidol University, 272 Rama 6 Rd., Bangkok 10400, Thailand.
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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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Voong LN, Xi L, Sebeson AC, Xiong B, Wang JP, Wang X. Insights into Nucleosome Organization in Mouse Embryonic Stem Cells through Chemical Mapping. Cell 2016; 167:1555-1570.e15. [PMID: 27889238 DOI: 10.1016/j.cell.2016.10.049] [Citation(s) in RCA: 120] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 09/05/2016] [Accepted: 10/27/2016] [Indexed: 12/21/2022]
Abstract
Nucleosome organization influences gene activity by controlling DNA accessibility to transcription machinery. Here, we develop a chemical biology approach to determine mammalian nucleosome positions genome-wide. We uncovered surprising features of nucleosome organization in mouse embryonic stem cells. In contrast to the prevailing model, we observe that for nearly all mouse genes, a class of fragile nucleosomes occupies previously designated nucleosome-depleted regions around transcription start sites and transcription termination sites. We show that nucleosomes occupy DNA targets for a subset of DNA-binding proteins, including CCCTC-binding factor (CTCF) and pluripotency factors. Furthermore, we provide evidence that promoter-proximal nucleosomes, with the +1 nucleosome in particular, contribute to the pausing of RNA polymerase II. Lastly, we find a characteristic preference for nucleosomes at exon-intron junctions. Taken together, we establish an accurate method for defining the nucleosome landscape and provide a valuable resource for studying nucleosome-mediated gene regulation in mammalian cells.
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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
| | - Amy C Sebeson
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA
| | - Bin Xiong
- 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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