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Physicochemical models of protein-DNA binding with standard and modified base pairs. Proc Natl Acad Sci U S A 2023; 120:e2205796120. [PMID: 36656856 PMCID: PMC9942898 DOI: 10.1073/pnas.2205796120] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
DNA-binding proteins play important roles in various cellular processes, but the mechanisms by which proteins recognize genomic target sites remain incompletely understood. Functional groups at the edges of the base pairs (bp) exposed in the DNA grooves represent physicochemical signatures. As these signatures enable proteins to form specific contacts between protein residues and bp, their study can provide mechanistic insights into protein-DNA binding. Existing experimental methods, such as X-ray crystallography, can reveal such mechanisms based on physicochemical interactions between proteins and their DNA target sites. However, the low throughput of structural biology methods limits mechanistic insights for selection of many genomic sites. High-throughput binding assays enable prediction of potential target sites by determining relative binding affinities of a protein to massive numbers of DNA sequences. Many currently available computational methods are based on the sequence of standard Watson-Crick bp. They assume that the contribution of overall binding affinity is independent for each base pair, or alternatively include dinucleotides or short k-mers. These methods cannot directly expand to physicochemical contacts, and they are not suitable to apply to DNA modifications or non-Watson-Crick bp. These variations include DNA methylation, and synthetic or mismatched bp. The proposed method, DeepRec, can predict relative binding affinities as function of physicochemical signatures and the effect of DNA methylation or other chemical modifications on binding. Sequence-based modeling methods are in comparison a coarse-grain description and cannot achieve such insights. Our chemistry-based modeling framework provides a path towards understanding genome function at a mechanistic level.
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Beck MA, Fischer H, Grabner LM, Groffics T, Winter M, Tangermann S, Meischel T, Zaussinger‐Haas B, Wagner P, Fischer C, Folie C, Arand J, Schöfer C, Ramsahoye B, Lagger S, Machat G, Eisenwort G, Schneider S, Podhornik A, Kothmayer M, Reichart U, Glösmann M, Tamir I, Mildner M, Sheibani‐Tezerji R, Kenner L, Petzelbauer P, Egger G, Sibilia M, Ablasser A, Seiser C. DNA hypomethylation leads to cGAS-induced autoinflammation in the epidermis. EMBO J 2021; 40:e108234. [PMID: 34586646 PMCID: PMC8591534 DOI: 10.15252/embj.2021108234] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Revised: 08/28/2021] [Accepted: 08/31/2021] [Indexed: 12/13/2022] Open
Abstract
DNA methylation is a fundamental epigenetic modification, important across biological processes. The maintenance methyltransferase DNMT1 is essential for lineage differentiation during development, but its functions in tissue homeostasis are incompletely understood. We show that epidermis-specific DNMT1 deletion severely disrupts epidermal structure and homeostasis, initiating a massive innate immune response and infiltration of immune cells. Mechanistically, DNA hypomethylation in keratinocytes triggered transposon derepression, mitotic defects, and formation of micronuclei. DNA release into the cytosol of DNMT1-deficient keratinocytes activated signaling through cGAS and STING, thus triggering inflammation. Our findings show that disruption of a key epigenetic mark directly impacts immune and tissue homeostasis, and potentially impacts our understanding of autoinflammatory diseases and cancer immunotherapy.
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Ray S, Tillo D, Ufot A, Assad N, Durell S, Vinson C. bZIP Dimers CREB1, ATF2, Zta, ATF3|cJun, and cFos|cJun Prefer to Bind to Some Double-Stranded DNA Sequences Containing 5-Formylcytosine and 5-Carboxylcytosine. Biochemistry 2020; 59:3529-3540. [PMID: 32902247 DOI: 10.1021/acs.biochem.0c00475] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In mammalian cells, 5-methylcytosine (5mC) occurs in genomic double-stranded DNA (dsDNA) and is enzymatically oxidized to 5-hydroxymethylcytosine (5hmC), then to 5-formylcytosine (5fC), and finally to 5-carboxylcytosine (5caC). These cytosine modifications are enriched in regulatory regions of the genome. The effect of these oxidative products on five bZIP dimers (CREB1, ATF2, Zta, ATF3|cJun, and cFos|cJun) binding to five types of dsDNA was measured using protein binding microarrays. The five dsDNAs contain either cytosine in both DNA strands or cytosine in one strand and either 5mC, 5hmC, 5fC, or 5caC in the second strand. Some sequences containing the CEBP half-site GCAA are bound more strongly by all five bZIP domains when dsDNA contains 5mC, 5hmC, or 5fC. dsDNA containing 5caC in some TRE (AP-1)-like sequences, e.g., TGACTAA, is better bound by Zta, ATF3|cJun, and cFos|cJun.
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Patel D, Patel M, Datta S, Singh U. CGGBP1 regulates CTCF occupancy at repeats. Epigenetics Chromatin 2019; 12:57. [PMID: 31547883 PMCID: PMC6757366 DOI: 10.1186/s13072-019-0305-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Accepted: 09/12/2019] [Indexed: 12/27/2022] Open
Abstract
Background CGGBP1 is a repeat-binding protein with diverse functions in the regulation of gene expression, cytosine methylation, repeat silencing and genomic integrity. CGGBP1 has also been identified as a cooperator of histone-modifying enzymes and as a component of CTCF-containing complexes that regulate the enhancer–promoter looping. CGGBP1–CTCF cross talk in chromatin regulation has been hitherto unknown. Results Here, we report that the occupancy of CTCF at repeats depends on CGGBP1. Using ChIP-sequencing for CTCF, we describe its occupancy at repetitive DNA. Our results show that endogenous level of CGGBP1 ensures CTCF occupancy preferentially on repeats over canonical CTCF motifs. By combining CTCF ChIP-sequencing results with ChIP sequencing for three different kinds of histone modifications (H3K4me3, H3K9me3 and H3K27me3), we show that the CGGBP1-dependent repeat-rich CTCF-binding sites regulate histone marks in flanking regions. Conclusion CGGBP1 affects the pattern of CTCF occupancy. Our results posit CGGBP1 as a regulator of CTCF and its binding sites in interspersed repeats.
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Affiliation(s)
- Divyesh Patel
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India
| | - Manthan Patel
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India
| | - Subhamoy Datta
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India
| | - Umashankar Singh
- HoMeCell Lab, Biological Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat, 382355, India.
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Dnmt3a2 in the Nucleus Accumbens Shell Mediates Cue-Induced Cocaine-Seeking Behavior. J Neurosci 2019; 39:2574-2576. [PMID: 30944234 DOI: 10.1523/jneurosci.2584-18.2019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2018] [Revised: 01/23/2019] [Accepted: 02/04/2019] [Indexed: 12/19/2022] Open
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6
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Fu Y, Li J, Tang Q, Zou C, Shen L, Jin L, Li C, Fang C, Liu R, Li M, Zhao S, Li C. Integrated analysis of methylome, transcriptome and miRNAome of three pig breeds. Epigenomics 2018; 10:597-612. [PMID: 29692202 DOI: 10.2217/epi-2017-0087] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
AIM Integrated analysis of methylome and transcriptome may help understand the molecular basis of the different breeds with different traits of commercial interest. MATERIALS & METHODS We obtained the first genome-wide methylome with single-base resolution, miRNAome and transcriptome from three swine breeds. RESULTS We displayed the landscape of the three omics in the whole-genome level. Integrated outcomes of methylome with genetic selection, miRNAome and transcriptome are also provided. Finally, we identified 11 candidate differentially methylated genes associated with phenotype variance in pigs. CONCLUSION DNA methylation not only suppresses transcriptome but also miRNAome. The different -omics data have complicated interaction in directly or indirectly and exhibited close relations with the distinct phenotypic traits of growth, disease resistance and energy metabolism.
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Affiliation(s)
- Yuhua Fu
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
| | - Jingxuan Li
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
| | - Qianzi Tang
- Institute of Animal Genetics & Breeding, College of Animal Science & Technology, Sichuan Agricultural University, Chengdu, 611130, PR China
| | - Cheng Zou
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
| | - Linyuan Shen
- Institute of Animal Genetics & Breeding, College of Animal Science & Technology, Sichuan Agricultural University, Chengdu, 611130, PR China
| | - Long Jin
- Institute of Animal Genetics & Breeding, College of Animal Science & Technology, Sichuan Agricultural University, Chengdu, 611130, PR China
| | - Cencen Li
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
| | - Chengchi Fang
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
| | - Rui Liu
- Institute of Animal Genetics & Breeding, College of Animal Science & Technology, Sichuan Agricultural University, Chengdu, 611130, PR China
| | - Mingzhou Li
- Institute of Animal Genetics & Breeding, College of Animal Science & Technology, Sichuan Agricultural University, Chengdu, 611130, PR China
| | - Shuhong Zhao
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
| | - Changchun Li
- Key Lab of Agriculture Animal Genetics, Breeding, & Reproduction of Ministry of Education, College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, 430070, PR China
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Yin Y, Morgunova E, Jolma A, Kaasinen E, Sahu B, Khund-Sayeed S, Das PK, Kivioja T, Dave K, Zhong F, Nitta KR, Taipale M, Popov A, Ginno PA, Domcke S, Yan J, Schübeler D, Vinson C, Taipale J. Impact of cytosine methylation on DNA binding specificities of human transcription factors. Science 2018; 356:356/6337/eaaj2239. [PMID: 28473536 DOI: 10.1126/science.aaj2239] [Citation(s) in RCA: 679] [Impact Index Per Article: 113.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 03/09/2017] [Indexed: 12/17/2022]
Abstract
The majority of CpG dinucleotides in the human genome are methylated at cytosine bases. However, active gene regulatory elements are generally hypomethylated relative to their flanking regions, and the binding of some transcription factors (TFs) is diminished by methylation of their target sequences. By analysis of 542 human TFs with methylation-sensitive SELEX (systematic evolution of ligands by exponential enrichment), we found that there are also many TFs that prefer CpG-methylated sequences. Most of these are in the extended homeodomain family. Structural analysis showed that homeodomain specificity for methylcytosine depends on direct hydrophobic interactions with the methylcytosine 5-methyl group. This study provides a systematic examination of the effect of an epigenetic DNA modification on human TF binding specificity and reveals that many developmentally important proteins display preference for mCpG-containing sequences.
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Affiliation(s)
- Yimeng Yin
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Ekaterina Morgunova
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Arttu Jolma
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Eevi Kaasinen
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Biswajyoti Sahu
- Genome-Scale Biology Program, Post Office Box 63, FI-00014 University of Helsinki, Helsinki, Finland
| | - Syed Khund-Sayeed
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Room 3128, Building 37, Bethesda, MD 20892, USA
| | - Pratyush K Das
- Genome-Scale Biology Program, Post Office Box 63, FI-00014 University of Helsinki, Helsinki, Finland
| | - Teemu Kivioja
- Genome-Scale Biology Program, Post Office Box 63, FI-00014 University of Helsinki, Helsinki, Finland
| | - Kashyap Dave
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Fan Zhong
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Kazuhiro R Nitta
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Minna Taipale
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Alexander Popov
- European Synchrotron Radiation Facility, 38043 Grenoble, France
| | - Paul A Ginno
- Friedrich-Miescher-Institute for Biomedical Research (FMI), Maulbeerstrasse 66, 4058 Basel, Switzerland
| | - Silvia Domcke
- Friedrich-Miescher-Institute for Biomedical Research (FMI), Maulbeerstrasse 66, 4058 Basel, Switzerland.,Faculty of Science, University of Basel, Petersplatz 1, 4003 Basel, Switzerland
| | - Jian Yan
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden
| | - Dirk Schübeler
- Friedrich-Miescher-Institute for Biomedical Research (FMI), Maulbeerstrasse 66, 4058 Basel, Switzerland.,Faculty of Science, University of Basel, Petersplatz 1, 4003 Basel, Switzerland
| | - Charles Vinson
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Room 3128, Building 37, Bethesda, MD 20892, USA
| | - Jussi Taipale
- Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 141 83 Stockholm, Sweden. .,Genome-Scale Biology Program, Post Office Box 63, FI-00014 University of Helsinki, Helsinki, Finland
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8
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Syed KS, He X, Tillo D, Wang J, Durell SR, Vinson C. 5-Methylcytosine (5mC) and 5-Hydroxymethylcytosine (5hmC) Enhance the DNA Binding of CREB1 to the C/EBP Half-Site Tetranucleotide GCAA. Biochemistry 2016; 55:6940-6948. [PMID: 27951657 DOI: 10.1021/acs.biochem.6b00796] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In human and mouse stem cells and brain, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) can occur outside of CG dinucleotides. Using protein binding microarrays (PBMs) containing 60-mer DNA probes, we evaluated the effect of 5mC and 5hmC on one DNA strand on the double-stranded DNA binding of the mouse B-ZIP transcription factors (TFs) CREB1, ATF1, and JUND. 5mC inhibited binding of CREB1 to the canonical CRE half-site |GTCA but enhanced binding to the C/EBP half-site |GCAA. 5hmC inhibited binding of CREB1 to all 8-mers except TGAT|GCAA, where binding is enhanced. We observed similar DNA binding patterns with ATF1, a closely related B-ZIP domain. In contrast, both 5mC and 5hmC inhibited binding of JUND. These results identify new DNA sequences that are well-bound by CREB1 and ATF1 only when they contain 5mC or 5hmC. Analysis of two X-ray structures examines the consequences of 5mC and 5hmC on DNA binding by CREB and FOS|JUN.
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Affiliation(s)
- Khund Sayeed Syed
- Laboratory of Metabolism and ‡Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health , Room 3128, Building 37, Bethesda, Maryland 20892, United States
| | - Ximiao He
- Laboratory of Metabolism and ‡Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health , Room 3128, Building 37, Bethesda, Maryland 20892, United States
| | - Desiree Tillo
- Laboratory of Metabolism and ‡Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health , Room 3128, Building 37, Bethesda, Maryland 20892, United States
| | - Jun Wang
- Laboratory of Metabolism and ‡Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health , Room 3128, Building 37, Bethesda, Maryland 20892, United States
| | - Stewart R Durell
- Laboratory of Metabolism and ‡Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health , Room 3128, Building 37, Bethesda, Maryland 20892, United States
| | - Charles Vinson
- Laboratory of Metabolism and ‡Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health , Room 3128, Building 37, Bethesda, Maryland 20892, United States
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9
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Tillo D, Mukherjee S, Vinson C. Inheritance of Cytosine Methylation. J Cell Physiol 2016; 231:2346-52. [DOI: 10.1002/jcp.25350] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 02/19/2016] [Indexed: 12/12/2022]
Affiliation(s)
- Desiree Tillo
- Laboratory of Metabolism; National Cancer Institute; National Institutes of Health; Bethesda Maryland
| | - Sanjit Mukherjee
- Laboratory of Metabolism; National Cancer Institute; National Institutes of Health; Bethesda Maryland
| | - Charles Vinson
- Laboratory of Metabolism; National Cancer Institute; National Institutes of Health; Bethesda Maryland
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10
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He X, Tillo D, Vierstra J, Syed KS, Deng C, Ray GJ, Stamatoyannopoulos J, FitzGerald PC, Vinson C. Methylated Cytosines Mutate to Transcription Factor Binding Sites that Drive Tetrapod Evolution. Genome Biol Evol 2015; 7:3155-69. [PMID: 26507798 PMCID: PMC4994754 DOI: 10.1093/gbe/evv205] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
In mammals, the cytosine in CG dinucleotides is typically methylated producing
5-methylcytosine (5mC), a chemically less stable form of cytosine that can spontaneously
deaminate to thymidine resulting in a T•G mismatched base pair. Unlike other eukaryotes
that efficiently repair this mismatched base pair back to C•G, in mammals, 5mCG
deamination is mutagenic, sometimes producing TG dinucleotides, explaining the depletion
of CG dinucleotides in mammalian genomes. It was suggested that new TG dinucleotides
generate genetic diversity that may be critical for evolutionary change. We tested this
conjecture by examining the DNA sequence properties of regulatory sequences identified by
DNase I hypersensitive sites (DHSs) in human and mouse genomes. We hypothesized that the
new TG dinucleotides generate transcription factor binding sites (TFBS) that become
tissue-specific DHSs (TS-DHSs). We find that 8-mers containing the CG dinucleotide are
enriched in DHSs in both species. However, 8-mers containing a TG and no CG dinucleotide
are preferentially enriched in TS-DHSs when compared with 8-mers with neither a TG nor a
CG dinucleotide. The most enriched 8-mer with a TG and no CG dinucleotide in
tissue-specific regulatory regions in both genomes is the AP-1 motif
(TGAC/GTCAN), and we find evidence that
TG dinucleotides in the AP-1 motif arose from CG dinucleotides. Additional TS-DHS-enriched
TFBS containing the TG/CA dinucleotide are the E-Box motif
(GCAGCTGC), the NF-1 motif (GGCA—TGCC), and the
GR (glucocorticoid receptor) motif (G-ACA—TGT-C). Our results support the
suggestion that cytosine methylation is mutagenic in tetrapods producing TG dinucleotides
that create TFBS that drive evolution.
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Affiliation(s)
- Ximiao He
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Desiree Tillo
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Jeff Vierstra
- Department of Genome Sciences, University of Washington
| | - Khund-Sayeed Syed
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Callie Deng
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - G Jordan Ray
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | | | - Peter C FitzGerald
- Genome Analysis Unit, Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Charles Vinson
- Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
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Nucleosomes are enriched at the boundaries of hypomethylated regions (HMRs) in mouse dermal fibroblasts and keratinocytes. Epigenetics Chromatin 2014; 7:34. [PMID: 25506399 PMCID: PMC4265496 DOI: 10.1186/1756-8935-7-34] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Accepted: 11/04/2014] [Indexed: 12/21/2022] Open
Abstract
Background The interplay between epigenetic modifications and chromatin structure are integral to our understanding of genome function. Methylation of cytosine (5mC) at CG dinucleotides, traditionally associated with transcriptional repression, is the most highly studied chemical modification of DNA, occurring at over 70% of all CG dinucleotides in the genome. Hypomethylated regions (HMRs) often occur in CG islands (CGIs), however, they also occur outside of CGIs and function as cell-type specific enhancers. During the process of differentiation, reorganization of chromatin and nucleosome arrangement at regulatory regions is thought to occur in order for the establishment of cell-type specific transcriptional programs. However, the specifics regarding the organization of nucleosomes at HMRs and the potential mechanisms regulating nucleosome occupancy in these regions are unknown. Here, we have investigated nucleosome organization around hypomethylated regions (HMRs) identified in two mouse primary cells. Results Microccocal nuclease (MNase) digested mononucleosomes from primary cultures of new-born female mouse dermal fibroblasts and keratinocytes were mapped and compared to the HMRs obtained from single base-pair resolution methylomes. In both cell types, we find that nucleosomes are enriched at HMR boundaries. In contrast to the nucleosomes found at boundaries of HMRs in CGIs, HMRs outside of CGIs are calculated to be preferentially bound by nucleosomes, with phased nucleosomes propagating into the methylated region. Nucleosomes are enriched at the tissue-specific HMRs (TS-HMR) boundaries in both cell types suggesting that nucleosome organization surrounding HMR boundaries is independent of methylation status. In addition, we find potential transcription factor (TF) binding sites (E-box motifs) enriched in non-CGI TS-HMR boundaries. Conclusions Our results show that intrinsic nucleosome occupancy score (INOS) positively correlate with the nucleosome organization surrounding non-CGI TS-HMRs, suggesting that DNA sequence plays a role in the establishment of HMRs in the genome. Since nucleosomes impact all processes involving the genome, our results provide a link between epigenetic modifications, chromatin structure, and regulatory function. Electronic supplementary material The online version of this article (doi:10.1186/1756-8935-7-34) contains supplementary material, which is available to authorized users.
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