1
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Lichauco C, Foss EJ, Gatbonton-Schwager T, Athow NF, Lofts BR, Acob R, Taylor E, Lao U, Miles S, Bedalov A. Sir2 and Fun30 regulate ribosomal DNA replication timing via Mcm helicase positioning and nucleosome occupancy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.21.586113. [PMID: 38585982 PMCID: PMC10996493 DOI: 10.1101/2024.03.21.586113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
The association between late replication timing and low transcription rates in eukaryotic heterochromatin is well-known, yet the specific mechanisms underlying this link remain uncertain. In Saccharomyces cerevisiae, the histone deacetylase Sir2 is required for both transcriptional silencing and late replication at the repetitive ribosomal DNA arrays (rDNA). We have previously reported that in the absence of SIR2, a derepressed RNA PolII repositions MCM replicative helicases from their loading site at the ribosomal origin, where they abut well-positioned, high-occupancy nucleosomes, to an adjacent region with lower nucleosome occupancy. By developing a method that can distinguish activation of closely spaced MCM complexes, here we show that the displaced MCMs at rDNA origins have increased firing propensity compared to the non-displaced MCMs. Furthermore, we found that both, activation of the repositioned MCMs and low occupancy of the adjacent nucleosomes critically depend on the chromatin remodeling activity of FUN30. Our study elucidates the mechanism by which Sir2 delays replication timing, and it demonstrates, for the first time, that activation of a specific replication origin in vivo relies on the nucleosome context shaped by a single chromatin remodeler.
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Affiliation(s)
- Carmina Lichauco
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Eric J. Foss
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Tonibelle Gatbonton-Schwager
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Nelson F. Athow
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Brandon R. Lofts
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Robin Acob
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Erin Taylor
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Uyen Lao
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Shawna Miles
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
| | - Antonio Bedalov
- Translational Sciences and Therapeutics Division, Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA
- Department of Biochemistry and Department of Medicine, University of Washington, Seattle, WA
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2
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Mei Q, Yu Q, Li X, Chen J, Yu X. Regulation of telomere silencing by the core histones-autophagy-Sir2 axis. Life Sci Alliance 2023; 6:6/3/e202201614. [PMID: 36585257 PMCID: PMC9806677 DOI: 10.26508/lsa.202201614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 12/18/2022] [Accepted: 12/19/2022] [Indexed: 12/31/2022] Open
Abstract
Telomeres contain compacted heterochromatin, and genes adjacent to telomeres are subjected to transcription silencing. Maintaining telomere structure integrity and transcription silencing is important to prevent the occurrence of premature aging and aging-related diseases. How telomere silencing is regulated during aging is not well understood. Here, we find that the four core histones are reduced during yeast chronological aging, leading to compromised telomere silencing. Mechanistically, histone loss promotes the nuclear export of Sir2 and its degradation by autophagy. Meanwhile, reducing core histones enhances the autophagy pathway, which further accelerates autophagy-mediated Sir2 degradation. By screening the histone mutant library, we identify eight histone mutants and one histone modification (histone methyltransferase Set1-catalyzed H3K4 trimethylation) that regulate telomere silencing by modulating the core histones-autophagy-Sir2 axis. Overall, our findings reveal core histones and autophagy as causes of aging-coupled loss of telomere silencing and shed light on dynamic regulation of telomere structure during aging.
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Affiliation(s)
- Qianyun Mei
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, China
| | - Qi Yu
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, China
| | - Xin Li
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, China
| | - Jianguo Chen
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, China
| | - Xilan Yu
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, China
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3
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He F, Yu Q, Wang M, Wang R, Gong X, Ge F, Yu X, Li S. SESAME-catalyzed H3T11 phosphorylation inhibits Dot1-catalyzed H3K79me3 to regulate autophagy and telomere silencing. Nat Commun 2022; 13:7526. [PMID: 36473858 PMCID: PMC9726891 DOI: 10.1038/s41467-022-35182-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Accepted: 11/21/2022] [Indexed: 12/12/2022] Open
Abstract
The glycolytic enzyme, pyruvate kinase Pyk1 maintains telomere heterochromatin by phosphorylating histone H3T11 (H3pT11), which promotes SIR (silent information regulator) complex binding at telomeres and prevents autophagy-mediated Sir2 degradation. However, the exact mechanism of action for H3pT11 is poorly understood. Here, we report that H3pT11 directly inhibits Dot1-catalyzed H3K79 tri-methylation (H3K79me3) and uncover how this histone crosstalk regulates autophagy and telomere silencing. Mechanistically, Pyk1-catalyzed H3pT11 directly reduces the binding of Dot1 to chromatin and inhibits Dot1-catalyzed H3K79me3, which leads to transcriptional repression of autophagy genes and reduced autophagy. Despite the antagonism between H3pT11 and H3K79me3, they work together to promote the binding of SIR complex at telomeres to maintain telomere silencing. Furthermore, we identify Reb1 as a telomere-associated factor that recruits Pyk1-containing SESAME (Serine-responsive SAM-containing Metabolic Enzyme) complex to telomere regions to phosphorylate H3T11 and prevent the invasion of H3K79me3 from euchromatin into heterochromatin to maintain telomere silencing. Together, these results uncover a histone crosstalk and provide insights into dynamic regulation of silent heterochromatin and autophagy in response to cell metabolism.
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Affiliation(s)
- Fei He
- grid.34418.3a0000 0001 0727 9022State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, Hubei 430062 China
| | - Qi Yu
- grid.34418.3a0000 0001 0727 9022State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, Hubei 430062 China
| | - Min Wang
- grid.9227.e0000000119573309Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072 China
| | - Rongsha Wang
- grid.34418.3a0000 0001 0727 9022State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, Hubei 430062 China
| | - Xuanyunjing Gong
- grid.34418.3a0000 0001 0727 9022State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, Hubei 430062 China
| | - Feng Ge
- grid.9227.e0000000119573309Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072 China
| | - Xilan Yu
- grid.34418.3a0000 0001 0727 9022State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, Hubei 430062 China
| | - Shanshan Li
- grid.34418.3a0000 0001 0727 9022State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, Hubei 430062 China
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4
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Mansisidor AR, Risca VI. Chromatin accessibility: methods, mechanisms, and biological insights. Nucleus 2022; 13:236-276. [PMID: 36404679 PMCID: PMC9683059 DOI: 10.1080/19491034.2022.2143106] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 10/23/2022] [Accepted: 10/30/2022] [Indexed: 11/22/2022] Open
Abstract
Access to DNA is a prerequisite to the execution of essential cellular processes that include transcription, replication, chromosomal segregation, and DNA repair. How the proteins that regulate these processes function in the context of chromatin and its dynamic architectures is an intensive field of study. Over the past decade, genome-wide assays and new imaging approaches have enabled a greater understanding of how access to the genome is regulated by nucleosomes and associated proteins. Additional mechanisms that may control DNA accessibility in vivo include chromatin compaction and phase separation - processes that are beginning to be understood. Here, we review the ongoing development of accessibility measurements, we summarize the different molecular and structural mechanisms that shape the accessibility landscape, and we detail the many important biological functions that are linked to chromatin accessibility.
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Affiliation(s)
- Andrés R. Mansisidor
- Laboratory of Genome Architecture and Dynamics, The Rockefeller University, New York, NY
| | - Viviana I. Risca
- Laboratory of Genome Architecture and Dynamics, The Rockefeller University, New York, NY
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5
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Janssens DH, Otto DJ, Meers MP, Setty M, Ahmad K, Henikoff S. CUT&Tag2for1: a modified method for simultaneous profiling of the accessible and silenced regulome in single cells. Genome Biol 2022; 23:81. [PMID: 35300717 PMCID: PMC8928696 DOI: 10.1186/s13059-022-02642-w] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2021] [Accepted: 02/23/2022] [Indexed: 12/15/2022] Open
Abstract
Cleavage Under Targets and Tagmentation (CUT&Tag) is an antibody-directed transposase tethering strategy for in situ chromatin profiling in small samples and single cells. We describe a modified CUT&Tag protocol using a mixture of an antibody to the initiation form of RNA polymerase II (Pol2 Serine-5 phosphate) and an antibody to repressive Polycomb domains (H3K27me3) followed by computational signal deconvolution to produce high-resolution maps of both the active and repressive regulomes in single cells. The ability to seamlessly map active promoters, enhancers, and repressive regulatory elements using a single workflow provides a complete regulome profiling strategy suitable for high-throughput single-cell platforms.
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Affiliation(s)
- Derek H. Janssens
- grid.270240.30000 0001 2180 1622Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA
| | - Dominik J. Otto
- grid.270240.30000 0001 2180 1622Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA ,grid.270240.30000 0001 2180 1622Translational Data Science IRC, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA
| | - Michael P. Meers
- grid.270240.30000 0001 2180 1622Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA
| | - Manu Setty
- grid.270240.30000 0001 2180 1622Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA ,grid.270240.30000 0001 2180 1622Translational Data Science IRC, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA
| | - Kami Ahmad
- grid.270240.30000 0001 2180 1622Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA
| | - Steven Henikoff
- grid.270240.30000 0001 2180 1622Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 N. Fairview Ave, Seattle, WA 98109 USA ,grid.413575.10000 0001 2167 1581Howard Hughes Medical Institute, Chevy Chase, MD USA
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6
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Brothers M, Rine J. Distinguishing between recruitment and spread of silent chromatin structures in Saccharomyces cerevisiae. eLife 2022; 11:75653. [PMID: 35073254 PMCID: PMC8830885 DOI: 10.7554/elife.75653] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Accepted: 01/21/2022] [Indexed: 11/13/2022] Open
Abstract
The formation of heterochromatin at HML, HMR, and telomeres in Saccharomyces cerevisiae involves two main steps: Recruitment of Sir proteins to silencers and their spread throughout the silenced domain. We developed a method to study these two processes at single base-pair resolution. Using a fusion protein between the heterochromatin protein Sir3 and the non-site-specific bacterial adenine methyltransferase M.EcoGII, we mapped sites of Sir3-chromatin interactions genome-wide using long-read Nanopore sequencing to detect adenines methylated by the fusion protein and by ChIP-seq to map the distribution of Sir3-M.EcoGII. A silencing-deficient mutant of Sir3 lacking its Bromo-Adjacent Homology (BAH) domain, sir3-bah∆, was still recruited to HML, HMR, and telomeres. However, in the absence of the BAH domain, it was unable to spread away from those recruitment sites. Overexpression of Sir3 did not lead to further spreading at HML, HMR, and most telomeres. A few exceptional telomeres, like 6R, exhibited a small amount of Sir3 spreading, suggesting that boundaries at telomeres responded variably to Sir3 overexpression. Finally, by using a temperature-sensitive allele of SIR3 fused to M.ECOGII, we tracked the positions first methylated after induction and found that repression of genes at HML and HMR began before Sir3 occupied the entire locus.
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Affiliation(s)
- Molly Brothers
- Department of Molecular and Cell Biology, University of California, Berkeley
| | - Jasper Rine
- Department of Molecular and Cell Biology, University of California, Berkeley
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7
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Henikoff S, Henikoff JG, Ahmad K. Simplified Epigenome Profiling Using Antibody-tethered Tagmentation. Bio Protoc 2021; 11:e4043. [PMID: 34250209 PMCID: PMC8250384 DOI: 10.21769/bioprotoc.4043] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 03/24/2021] [Accepted: 04/29/2021] [Indexed: 12/02/2022] Open
Abstract
We previously introduced Cleavage Under Targets & Tagmentation (CUT&Tag), an epigenomic profiling method in which antibody tethering of the Tn5 transposase to a chromatin epitope of interest maps specific chromatin features in small samples and single cells. With CUT&Tag, intact cells or nuclei are permeabilized, followed by successive addition of a primary antibody, a secondary antibody, and a chimeric Protein A-Transposase fusion protein that binds to the antibody. Addition of Mg++ activates the transposase and inserts sequencing adapters into adjacent DNA in situ. We have since adapted CUT&Tag to also map chromatin accessibility by simply modifying the transposase activation conditions when using histone H3K4me2, H3K4me3, or Serine-5-phosphorylated RNA Polymerase II antibodies. Using these antibodies, we redirect the tagmentation of accessible DNA sites to produce chromatin accessibility maps with exceptionally high signal-to-noise and resolution. All steps from nuclei to amplified sequencing-ready libraries are performed in single PCR tubes using non-toxic reagents and inexpensive equipment, making our simplified strategy for simultaneous chromatin profiling and accessibility mapping suitable for the lab, home workbench, or classroom.
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Affiliation(s)
- Steven Henikoff
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, Washington 98109, USA.,Howard Hughes Medical Institute, Seattle WA, USA
| | - Jorja G Henikoff
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, Washington 98109, USA
| | - Kami Ahmad
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, Washington 98109, USA
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8
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Liu W, Gallego-Bartolomé J, Zhou Y, Zhong Z, Wang M, Wongpalee SP, Gardiner J, Feng S, Kuo PH, Jacobsen SE. Ectopic targeting of CG DNA methylation in Arabidopsis with the bacterial SssI methyltransferase. Nat Commun 2021; 12:3130. [PMID: 34035251 PMCID: PMC8149686 DOI: 10.1038/s41467-021-23346-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2019] [Accepted: 03/30/2021] [Indexed: 01/03/2023] Open
Abstract
The ability to target epigenetic marks like DNA methylation to specific loci is important in both basic research and in crop plant engineering. However, heritability of targeted DNA methylation, how it impacts gene expression, and which epigenetic features are required for proper establishment are mostly unknown. Here, we show that targeting the CG-specific methyltransferase M.SssI with an artificial zinc finger protein can establish heritable CG methylation and silencing of a targeted locus in Arabidopsis. In addition, we observe highly heritable widespread ectopic CG methylation mainly over euchromatic regions. This hypermethylation shows little effect on transcription while it triggers a mild but significant reduction in the accumulation of H2A.Z and H3K27me3. Moreover, ectopic methylation occurs preferentially at less open chromatin that lacks positive histone marks. These results outline general principles of the heritability and interaction of CG methylation with other epigenomic features that should help guide future efforts to engineer epigenomes. The ability to target DNA methylation to specific loci is important for both basic and applied research. Here, the authors fuse CG-specific methyltransferase SssI with an artificial zinc finger protein for DNA methylation targeting and show the chromatin features favorable for efficient gain of methylation.
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Affiliation(s)
- Wanlu Liu
- Department of Orthopedic of the Second Affiliated Hospital of Zhejiang University School of Medicine, Zhejiang University, Hangzhou, China. .,Zhejiang University-University of Edinburgh Institute (ZJU-UoE Institute), Zhejiang University School of Medicine, International Campus, Zhejiang University, Haining, China. .,Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA.
| | - Javier Gallego-Bartolomé
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA.,Instituto de Biología Molecular y Celular de Plantas (IBMCP), CSIC-Universidad Politécnica de Valencia, Valencia, Spain
| | - Yuxing Zhou
- Zhejiang University-University of Edinburgh Institute (ZJU-UoE Institute), Zhejiang University School of Medicine, International Campus, Zhejiang University, Haining, China
| | - Zhenhui Zhong
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA
| | - Ming Wang
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA
| | - Somsakul Pop Wongpalee
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA.,Department of Microbiology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
| | - Jason Gardiner
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA
| | - Suhua Feng
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA.,Eli & Edythe Broad Center of Regenerative Medicine & Stem Cell Research, University of California at Los Angeles, Los Angeles, CA, USA
| | - Peggy Hsuanyu Kuo
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA
| | - Steven E Jacobsen
- Department of Molecular, Cell and Developmental Biology, University of California at Los Angeles, Los Angeles, CA, USA. .,Eli & Edythe Broad Center of Regenerative Medicine & Stem Cell Research, University of California at Los Angeles, Los Angeles, CA, USA. .,Howard Hughes Medical Institute, University of California at Los Angeles, Los Angeles, CA, USA.
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9
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Zhang S, Yu X, Zhang Y, Xue X, Yu Q, Zha Z, Gogol M, Workman JL, Li S. Metabolic regulation of telomere silencing by SESAME complex-catalyzed H3T11 phosphorylation. Nat Commun 2021; 12:594. [PMID: 33500413 PMCID: PMC7838282 DOI: 10.1038/s41467-020-20711-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Accepted: 12/11/2020] [Indexed: 02/07/2023] Open
Abstract
Telomeres are organized into a heterochromatin structure and maintenance of silent heterochromatin is required for chromosome stability. How telomere heterochromatin is dynamically regulated in response to stimuli remains unknown. Pyruvate kinase Pyk1 forms a complex named SESAME (Serine-responsive SAM-containing Metabolic Enzyme complex) to regulate gene expression by phosphorylating histone H3T11 (H3pT11). Here, we identify a function of SESAME in regulating telomere heterochromatin structure. SESAME phosphorylates H3T11 at telomeres, which maintains SIR (silent information regulator) complex occupancy at telomeres and protects Sir2 from degradation by autophagy. Moreover, SESAME-catalyzed H3pT11 directly represses autophagy-related gene expression to further prevent autophagy-mediated Sir2 degradation. By promoting H3pT11, serine increases Sir2 protein levels and enhances telomere silencing. Loss of H3pT11 leads to reduced Sir2 and compromised telomere silencing during chronological aging. Together, our study provides insights into dynamic regulation of silent heterochromatin by histone modifications and autophagy in response to cell metabolism and aging.
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Affiliation(s)
- Shihao Zhang
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, Hubei, 430062, China
| | - Xilan Yu
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, Hubei, 430062, China
| | - Yuan Zhang
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, Hubei, 430062, China
| | - Xiangyan Xue
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, Hubei, 430062, China
| | - Qi Yu
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, Hubei, 430062, China
| | - Zitong Zha
- Human Aging Research Institute (HARI), School of Life Science, Nanchang University, Nanchang, Jiangxi, 330031, China
| | - Madelaine Gogol
- Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO, 64110, USA
| | - Jerry L Workman
- Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO, 64110, USA
| | - Shanshan Li
- State Key Laboratory of Biocatalysis and Enzyme Engineering, College of Life Sciences, Hubei University, Wuhan, Hubei, 430062, China.
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10
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Henikoff S, Henikoff JG, Kaya-Okur HS, Ahmad K. Efficient chromatin accessibility mapping in situ by nucleosome-tethered tagmentation. eLife 2020; 9:e63274. [PMID: 33191916 PMCID: PMC7721439 DOI: 10.7554/elife.63274] [Citation(s) in RCA: 65] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2020] [Accepted: 11/13/2020] [Indexed: 12/27/2022] Open
Abstract
Chromatin accessibility mapping is a powerful approach to identify potential regulatory elements. A popular example is ATAC-seq, whereby Tn5 transposase inserts sequencing adapters into accessible DNA ('tagmentation'). CUT&Tag is a tagmentation-based epigenomic profiling method in which antibody tethering of Tn5 to a chromatin epitope of interest profiles specific chromatin features in small samples and single cells. Here, we show that by simply modifying the tagmentation conditions for histone H3K4me2 or H3K4me3 CUT&Tag, antibody-tethered tagmentation of accessible DNA sites is redirected to produce chromatin accessibility maps that are indistinguishable from the best ATAC-seq maps. Thus, chromatin accessibility maps can be produced in parallel with CUT&Tag maps of other epitopes with all steps from nuclei to amplified sequencing-ready libraries performed in single PCR tubes in the laboratory or on a home workbench. As H3K4 methylation is produced by transcription at promoters and enhancers, our method identifies transcription-coupled accessible regulatory sites.
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Affiliation(s)
- Steven Henikoff
- Basic Sciences Division Fred Hutchinson Cancer Research CenterSeattleUnited States
- Howard Hughes Medical InstituteSeattleUnited States
| | - Jorja G Henikoff
- Basic Sciences Division Fred Hutchinson Cancer Research CenterSeattleUnited States
| | - Hatice S Kaya-Okur
- Basic Sciences Division Fred Hutchinson Cancer Research CenterSeattleUnited States
| | - Kami Ahmad
- Basic Sciences Division Fred Hutchinson Cancer Research CenterSeattleUnited States
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11
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Stergachis AB, Debo BM, Haugen E, Churchman LS, Stamatoyannopoulos JA. Single-molecule regulatory architectures captured by chromatin fiber sequencing. Science 2020; 368:1449-1454. [PMID: 32587015 DOI: 10.1126/science.aaz1646] [Citation(s) in RCA: 83] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2019] [Revised: 01/12/2020] [Accepted: 04/24/2020] [Indexed: 12/14/2022]
Abstract
Gene regulation is chiefly determined at the level of individual linear chromatin molecules, yet our current understanding of cis-regulatory architectures derives from fragmented sampling of large numbers of disparate molecules. We developed an approach for precisely stenciling the structure of individual chromatin fibers onto their composite DNA templates using nonspecific DNA N6-adenine methyltransferases. Single-molecule long-read sequencing of chromatin stencils enabled nucleotide-resolution readout of the primary architecture of multikilobase chromatin fibers (Fiber-seq). Fiber-seq exposed widespread plasticity in the linear organization of individual chromatin fibers and illuminated principles guiding regulatory DNA actuation, the coordinated actuation of neighboring regulatory elements, single-molecule nucleosome positioning, and single-molecule transcription factor occupancy. Our approach and results open new vistas on the primary architecture of gene regulation.
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Affiliation(s)
- Andrew B Stergachis
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
| | - Brian M Debo
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.,Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
| | - Eric Haugen
- Altius Institute for Biomedical Sciences, Seattle, WA, USA
| | - L Stirling Churchman
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA, USA
| | - John A Stamatoyannopoulos
- Altius Institute for Biomedical Sciences, Seattle, WA, USA. .,Departments of Genome Sciences and Medicine, University of Washington, Seattle, WA, USA
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12
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X-rays Activate Telomeric Homologous Recombination Mediated Repair in Primary Cells. Cells 2019; 8:cells8070708. [PMID: 31336873 PMCID: PMC6678842 DOI: 10.3390/cells8070708] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 06/27/2019] [Accepted: 07/06/2019] [Indexed: 12/31/2022] Open
Abstract
Cancer cells need to acquire telomere maintenance mechanisms in order to counteract progressive telomere shortening due to multiple rounds of replication. Most human tumors maintain their telomeres expressing telomerase whereas the remaining 15%–20% utilize the alternative lengthening of telomeres (ALT) pathway. Previous studies have demonstrated that ionizing radiations (IR) are able to modulate telomere lengths and to transiently induce some of the ALT-pathway hallmarks in normal primary fibroblasts. In the present study, we investigated the telomere length modulation kinetics, telomeric DNA damage induction, and the principal hallmarks of ALT over a period of 13 days in X-ray-exposed primary cells. Our results show that X-ray-treated cells primarily display telomere shortening and telomeric damage caused by persistent IR-induced oxidative stress. After initial telomere erosion, we observed a telomere elongation that was associated to the transient activation of a homologous recombination (HR) based mechanism, sharing several features with the ALT pathway observed in cancer cells. Data indicate that telomeric damage activates telomeric HR-mediated repair in primary cells. The characterization of HR-mediated telomere repair in normal cells may contribute to the understanding of the ALT pathway and to the identification of novel strategies in the treatment of ALT-positive cancers.
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13
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Kothiwal D, Laloraya S. A SIR-independent role for cohesin in subtelomeric silencing and organization. Proc Natl Acad Sci U S A 2019; 116:5659-5664. [PMID: 30842278 PMCID: PMC6431164 DOI: 10.1073/pnas.1816582116] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Cohesin is a key determinant of chromosome architecture due to its DNA binding and tethering ability. Cohesin binds near centromeres and chromosome arms and also close to telomeres, but its role near telomeres remains elusive. In budding yeast, transcription within 20 kb of telomeres is repressed, in part by the histone-modifying silent information regulator (SIR) complex. However, extensive subtelomeric repressed domains lie outside the SIR-binding region, but the mechanism of silencing in these regions remains poorly understood. Here, we report a role for cohesin in subtelomeric silencing that extends even beyond the zone of SIR binding. Clusters of subtelomeric genes were preferentially derepressed in a cohesin mutant, whereas SIR binding was unaltered. Genetic interactions with known telomere silencing factors indicate that cohesin operates independent of the SIR-mediated pathway for telomeric silencing. Mutant cells exhibited Mpk1-dependent Sir3 hyperphosphorylation that contributes to subtelomeric derepression to a limited extent. Compaction of subtelomeric domains and tethering to the nuclear envelope were impaired in mutant cells. Our findings provide evidence for a unique SIR-independent mechanism of subtelomeric repression mediated by cohesin.
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Affiliation(s)
- Deepash Kothiwal
- Department of Biochemistry, Indian Institute of Science, 560012 Bangalore, India
| | - Shikha Laloraya
- Department of Biochemistry, Indian Institute of Science, 560012 Bangalore, India
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14
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Zhang Z, Zhang T, Ge Y, Tang M, Ma W, Zhang Q, Gong S, Wright WE, Shay J, Liu H, Zhao Y. 2D gel electrophoresis reveals dynamics of t-loop formation during the cell cycle and t-loop in maintenance regulated by heterochromatin state. J Biol Chem 2019; 294:6645-6656. [PMID: 30819801 DOI: 10.1074/jbc.ra119.007677] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 02/20/2019] [Indexed: 12/15/2022] Open
Abstract
Linear chromosome ends are capped by telomeres that have been previously reported to adopt a t-loop structure. The lack of simple methods for detecting t-loops has hindered progress in understanding the dynamics of t-loop formation and its function in protecting chromosome ends. Here, we employed a classical two-dimensional agarose gel method (2D gel method) to innovatively apply to t-loop detection. Briefly, restriction fragments of genomic DNA were separated in a 2D gel, and the telomere sequence was detected by in-gel hybridization with telomeric probe. Using this method, we found that t-loops are present throughout the cell cycle, and t-loop formation tightly couples to telomere replication. We also observed that t-loop abundance positively correlates with chromatin condensation, i.e. cells with less compact telomeric chromatin (ALT cells and trichostatin A (TSA)-treated HeLa cells) exhibited fewer t-loops. Moreover, we observed that telomere dysfunction-induced foci, ALT-associated promyelocytic leukemia bodies, and telomere sister chromatid exchanges are activated upon TSA-induced loss of t-loops. These findings confirm the importance of the t-loop in protecting linear chromosomes from damage or illegitimate recombination.
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Affiliation(s)
- Zepeng Zhang
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Tianpeng Zhang
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Yuanlong Ge
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Mengfan Tang
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Wenbin Ma
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Qinfen Zhang
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Shengzhao Gong
- Department of Chemical Engineering, Guangdong Industry Technical College, Guangzhou 510006, China
| | - Woodring E Wright
- the Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, and
| | - Jerry Shay
- the Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, and
| | - Haiying Liu
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China,
| | - Yong Zhao
- From the MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China,
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15
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Sieverman KJ, Rine J. Impact of Homologous Recombination on Silent Chromatin in Saccharomyces cerevisiae. Genetics 2018; 208:1099-1113. [PMID: 29339409 PMCID: PMC5844325 DOI: 10.1534/genetics.118.300704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 01/08/2018] [Indexed: 11/18/2022] Open
Abstract
Specialized chromatin domains repress transcription of genes within them and present a barrier to many DNA-protein interactions. Silent chromatin in the budding yeast Saccharomyces cerevisiae, akin to heterochromatin of metazoans and plants, inhibits transcription of PolII- and PolIII-transcribed genes, yet somehow grants access to proteins necessary for DNA transactions like replication and homologous recombination. In this study, we adapted a novel assay to detect even transient changes in the dynamics of transcriptional silencing at HML after it served as a template for homologous recombination. Homologous recombination specifically targeted to HML via double-strand-break formation at a homologous locus often led to transient loss of transcriptional silencing at HML Interestingly, many cells could template homology-directed repair at HML without an obligate loss of silencing, even in recombination events with extensive gene conversion tracts. In a population of cells that experienced silencing loss following recombination, transcription persisted for 2-3 hr after all double-strand breaks were repaired. mRNA levels from cells that experienced recombination-induced silencing loss did not approach the amount of mRNA seen in cells lacking transcriptional silencing. Thus, silencing loss at HML after homologous recombination was short-lived and limited.
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Affiliation(s)
- Kathryn J Sieverman
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California at Berkeley, California 94720
| | - Jasper Rine
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California at Berkeley, California 94720
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16
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Pivotal roles of PCNA loading and unloading in heterochromatin function. Proc Natl Acad Sci U S A 2018; 115:E2030-E2039. [PMID: 29440488 DOI: 10.1073/pnas.1721573115] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In Saccharomyces cerevisiae, heterochromatin structures required for transcriptional silencing of the HML and HMR loci are duplicated in coordination with passing DNA replication forks. Despite major reorganization of chromatin structure, the heterochromatic, transcriptionally silent states of HML and HMR are successfully maintained throughout S-phase. Mutations of specific components of the replisome diminish the capacity to maintain silencing of HML and HMR through replication. Similarly, mutations in histone chaperones involved in replication-coupled nucleosome assembly reduce gene silencing. Bridging these observations, we determined that the proliferating cell nuclear antigen (PCNA) unloading activity of Elg1 was important for coordinating DNA replication forks with the process of replication-coupled nucleosome assembly to maintain silencing of HML and HMR through S-phase. Collectively, these data identified a mechanism by which chromatin reassembly is coordinated with DNA replication to maintain silencing through S-phase.
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17
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The Nuts and Bolts of Transcriptionally Silent Chromatin in Saccharomyces cerevisiae. Genetics 2017; 203:1563-99. [PMID: 27516616 DOI: 10.1534/genetics.112.145243] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 05/30/2016] [Indexed: 12/31/2022] Open
Abstract
Transcriptional silencing in Saccharomyces cerevisiae occurs at several genomic sites including the silent mating-type loci, telomeres, and the ribosomal DNA (rDNA) tandem array. Epigenetic silencing at each of these domains is characterized by the absence of nearly all histone modifications, including most prominently the lack of histone H4 lysine 16 acetylation. In all cases, silencing requires Sir2, a highly-conserved NAD(+)-dependent histone deacetylase. At locations other than the rDNA, silencing also requires additional Sir proteins, Sir1, Sir3, and Sir4 that together form a repressive heterochromatin-like structure termed silent chromatin. The mechanisms of silent chromatin establishment, maintenance, and inheritance have been investigated extensively over the last 25 years, and these studies have revealed numerous paradigms for transcriptional repression, chromatin organization, and epigenetic gene regulation. Studies of Sir2-dependent silencing at the rDNA have also contributed to understanding the mechanisms for maintaining the stability of repetitive DNA and regulating replicative cell aging. The goal of this comprehensive review is to distill a wide array of biochemical, molecular genetic, cell biological, and genomics studies down to the "nuts and bolts" of silent chromatin and the processes that yield transcriptional silencing.
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18
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McCleary DF, Steakley DL, Rine J. Sir protein-independent repair of dicentric chromosomes in Saccharomyces cerevisiae. Mol Biol Cell 2016; 27:2879-83. [PMID: 27466318 PMCID: PMC5025274 DOI: 10.1091/mbc.e16-02-0102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 07/20/2016] [Indexed: 12/02/2022] Open
Abstract
Sir2 has been reported to be recruited to dicentric chromosomes under tension, and these chromosomes are especially vulnerable to breakage in sir2Δ mutants. Loss of viability in such mutants is an indirect effect of repression of nonhomologous end joining in Sir− mutants. Enrichment of Sir2 at chromosomes under tension is not observed. Sir2 protein has been reported to be recruited to dicentric chromosomes under tension, and such chromosomes are reported to be especially vulnerable to breakage in sir2Δ mutants. We found that the loss of viability in such mutants was an indirect effect of the repression of nonhomologous end joining in Sir− mutants and that the apparent recruitment of Sir2 protein to chromosomes under tension was likely due to methodological weakness in early chromatin immunoprecipitation studies.
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Affiliation(s)
- David F McCleary
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - David Lee Steakley
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - Jasper Rine
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
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19
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Mao P, Liu J, Zhang Z, Zhang H, Liu H, Gao S, Rong YS, Zhao Y. Homologous recombination-dependent repair of telomeric DSBs in proliferating human cells. Nat Commun 2016; 7:12154. [PMID: 27396625 PMCID: PMC4942568 DOI: 10.1038/ncomms12154] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 06/07/2016] [Indexed: 12/28/2022] Open
Abstract
Telomeres prevent chromosome ends from being recognized as double-stranded breaks (DSBs). Meanwhile, G/C-rich repetitive telomeric DNA is susceptible to attack by DNA-damaging agents. How cells balance the need to protect DNA ends and the need to repair DNA lesions in telomeres is unknown. Here we show that telomeric DSBs are efficiently repaired in proliferating cells, but are irreparable in stress-induced and replicatively senescent cells. Using the CRISPR-Cas9 technique, we specifically induce DSBs at telomeric or subtelomeric regions. We find that DSB repair (DSBR) at subtelomeres occurs in an error-prone manner resulting in small deletions, suggestive of NHEJ. However, DSBR in telomeres involves 'telomere-clustering', 3'-protruding C-rich telomeric ssDNA, and HR between sister-chromatid or interchromosomal telomeres. DSBR in telomeres is suppressed by deletion or inhibition of Rad51. These findings reveal proliferation-dependent DSBR in telomeres and suggest that telomeric HR, which is normally constitutively suppressed, is activated in the context of DSBR.
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Affiliation(s)
- Pingsu Mao
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
- Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, China
| | - Jingfan Liu
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
- Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, China
- Zhongshan Medical School, Sun Yat-sen University, Guangzhou 510006, China
| | - Zepeng Zhang
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Hong Zhang
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Haiying Liu
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
- Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, China
| | - Song Gao
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou 510060, China
| | - Yikang S. Rong
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Yong Zhao
- Key Laboratory of Gene Engineering of the Ministry of Education, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China
- Collaborative Innovation Center of High Performance Computing, National University of Defense Technology, Changsha 410073, China
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20
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Dyachenko OV, Tarlachkov SV, Marinitch DV, Shevchuk TV, Buryanov YI. Expression of exogenous DNA methyltransferases: application in molecular and cell biology. BIOCHEMISTRY (MOSCOW) 2015; 79:77-87. [PMID: 24794723 DOI: 10.1134/s0006297914020011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
DNA methyltransferases might be used as powerful tools for studies in molecular and cell biology due to their ability to recognize and modify nitrogen bases in specific sequences of the genome. Methylation of the eukaryotic genome using exogenous DNA methyltransferases appears to be a promising approach for studies on chromatin structure. Currently, the development of new methods for targeted methylation of specific genetic loci using DNA methyltransferases fused with DNA-binding proteins is especially interesting. In the present review, expression of exogenous DNA methyltransferase for purposes of in vivo analysis of the functional chromatin structure along with investigation of the functional role of DNA methylation in cell processes are discussed, as well as future prospects for application of DNA methyltransferases in epigenetic therapy and in plant selection.
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Affiliation(s)
- O V Dyachenko
- Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
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21
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Steakley DL, Rine J. On the Mechanism of Gene Silencing in Saccharomyces cerevisiae. G3 (BETHESDA, MD.) 2015; 5:1751-63. [PMID: 26082137 PMCID: PMC4528331 DOI: 10.1534/g3.115.018515] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/11/2015] [Accepted: 06/15/2015] [Indexed: 11/18/2022]
Abstract
Multiple mechanisms have been proposed for gene silencing in Saccharomyces cerevisiae, ranging from steric occlusion of DNA binding proteins from their recognition sequences in silenced chromatin to a specific block in the formation of the preinitiation complex to a block in transcriptional elongation. This study provided strong support for the steric occlusion mechanism by the discovery that RNA polymerase of bacteriophage T7 could be substantially blocked from transcribing from its cognate promoter when embedded in silenced chromatin. Moreover, unlike previous suggestions, we found no evidence for stalled RNA polymerase II within silenced chromatin. The effectiveness of the Sir protein-based silencing mechanism to block transcription activated by Gal4 at promoters in the domain of silenced chromatin was marginal, yet it improved when tested against mutant forms of the Gal4 protein, highlighting a role for specific activators in their sensitivity to gene silencing.
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Affiliation(s)
- David Lee Steakley
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, Stanley Hall, University of California Berkeley, Berkeley, California 94720
| | - Jasper Rine
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, Stanley Hall, University of California Berkeley, Berkeley, California 94720
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22
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Abstract
Silencing assays have proven to be powerful tools not only for understanding how epigenetic processes function and defining the structural components of silent chromatin, but also for a useful readout for characterizing the functions of proteins involved in chromatin biology that influence epigenetic processes directly or indirectly. This chapter describes a collection of assays for monitoring silencing in Saccharomyces cerevisiae, including qualitative and quantitative methods as well as protocols that provide either indirect or direct measurements of the transcriptional state of loci regulated by silent chromatin.
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23
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Bi X. Heterochromatin structure: lessons from the budding yeast. IUBMB Life 2014; 66:657-66. [PMID: 25355678 DOI: 10.1002/iub.1322] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 10/12/2014] [Accepted: 10/14/2014] [Indexed: 12/28/2022]
Abstract
The eukaryotic genome can be roughly divided into euchromatin and heterochromatin domains that are structurally and functionally distinct. Heterochromatin is characterized by its high compactness and its inhibitory effect on DNA transactions such as gene expression. Formation of heterochromatin involves special histone modifications and the recruitment and spread of silencing complexes and causes changes in the primary and higher order structures of chromatin. The past two decades have seen dramatic advances in dissecting the molecular aspects of heterochromatin because of the identification of the histone code for heterochromatin as well as its writers and erasers (histone-modifying enzymes) and readers (silencing factors recognizing histone modifications). How heterochromatic histone modifications and silencing factors contribute to the special primary and higher order structures of heterochromatin has begun to be understood. The budding yeast Saccharomyces cerevisiae has long been used as a model organism for heterochromatin studies. Results from these studies have contributed significantly to the elucidation of the general principles governing the formation, maintenance, and function of heterochromatin. This review is focused on investigations into the structural aspects of heterochromatin in S. cerevisiae. Current understanding of other aspects of heterochromatin including how it promotes gene silencing and its epigenetic inheritance is briefly summarized.
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Affiliation(s)
- Xin Bi
- Department of Biology, University of Rochester, Rochester, NY, USA
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24
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Kueng S, Oppikofer M, Gasser SM. SIR proteins and the assembly of silent chromatin in budding yeast. Annu Rev Genet 2013; 47:275-306. [PMID: 24016189 DOI: 10.1146/annurev-genet-021313-173730] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Saccharomyces cerevisiae provides a well-studied model system for heritable silent chromatin in which a histone-binding protein complex [the SIR (silent information regulator) complex] represses gene transcription in a sequence-independent manner by spreading along nucleosomes, much like heterochromatin in higher eukaryotes. Recent advances in the biochemistry and structural biology of the SIR-chromatin system bring us much closer to a molecular understanding of yeast silent chromatin. Simultaneously, genome-wide approaches have shed light on the biological importance of this form of epigenetic repression. Here, we integrate genetic, structural, and cell biological data into an updated overview of yeast silent chromatin assembly.
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Affiliation(s)
- Stephanie Kueng
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland
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25
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Oppikofer M, Kueng S, Gasser SM. SIR–nucleosome interactions: Structure–function relationships in yeast silent chromatin. Gene 2013; 527:10-25. [DOI: 10.1016/j.gene.2013.05.088] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2013] [Revised: 05/27/2013] [Accepted: 05/30/2013] [Indexed: 01/09/2023]
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26
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Grunstein M, Gasser SM. Epigenetics in Saccharomyces cerevisiae. Cold Spring Harb Perspect Biol 2013; 5:cshperspect.a017491. [PMID: 23818500 DOI: 10.1101/cshperspect.a017491] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Saccharomyces cerevisiae provides a well-studied model system for heritable silent chromatin, in which a nonhistone protein complex--the SIR complex--represses genes by spreading in a sequence-independent manner, much like heterochromatin in higher eukaryotes. The ability to study mutations in histones and to screen genome-wide for mutations that impair silencing has yielded an unparalleled depth of detail about this system. Recent advances in the biochemistry and structural biology of the SIR-chromatin complex bring us much closer to a molecular understanding of how Sir3 selectively recognizes the deacetylated histone H4 tail and demethylated histone H3 core. The existence of appropriate mutants has also shown how components of the silencing machinery affect physiological processes beyond transcriptional repression.
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Affiliation(s)
- Michael Grunstein
- University of California, Los Angeles, Los Angeles, California 90095, USA
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27
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Coleman BI, Ribacke U, Manary M, Bei AK, Winzeler EA, Wirth DF, Duraisingh MT. Nuclear repositioning precedes promoter accessibility and is linked to the switching frequency of a Plasmodium falciparum invasion gene. Cell Host Microbe 2013; 12:739-50. [PMID: 23245319 DOI: 10.1016/j.chom.2012.11.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Revised: 07/14/2012] [Accepted: 10/26/2012] [Indexed: 02/07/2023]
Abstract
Variation of surface adhesins, such as the Plasmodium falciparum erythrocyte invasion ligand PfRh4, is critical for virulence and immune evasion in many microbes. While phenotypic switching is linked to transcriptional changes and chromatin function, the determinants of switching frequency remain poorly defined. By expressing a prokaryotic DNA methylase in P. falciparum, we directly assayed accessibility of transcriptionally active and silent chromatin at the PfRh4 locus. Parasites selected for in vivo PfRh4 activation show a reversible increase in promoter accessibility and exhibit perinuclear repositioning of the locus from a silent to a conserved activation domain. Forced activation of a proximal gene results in a similar repositioning of the PfRh4 locus, with a concomitant increase in PfRh4 activation in a subpopulation of parasites and promoter accessibility correlating with actively transcribed loci. Thus, nuclear repositioning is associated with increased P. falciparum switching frequency, while promoter accessibility is tightly linked to clonally active PfRh4 promoters.
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Affiliation(s)
- Bradley I Coleman
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115, USA
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28
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Oppikofer M, Kueng S, Keusch JJ, Hassler M, Ladurner AG, Gut H, Gasser SM. Dimerization of Sir3 via its C-terminal winged helix domain is essential for yeast heterochromatin formation. EMBO J 2013; 32:437-49. [PMID: 23299941 DOI: 10.1038/emboj.2012.343] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Accepted: 12/04/2012] [Indexed: 12/11/2022] Open
Abstract
Gene silencing in budding yeast relies on the binding of the Silent Information Regulator (Sir) complex to chromatin, which is mediated by extensive interactions between the Sir proteins and nucleosomes. Sir3, a divergent member of the AAA+ ATPase-like family, contacts both the histone H4 tail and the nucleosome core. Here, we present the structure and function of the conserved C-terminal domain of Sir3, comprising 138 amino acids. This module adopts a variant winged helix-turn-helix (wH) architecture that exists as a stable homodimer in solution. Mutagenesis shows that the self-association mediated by this domain is essential for holo-Sir3 dimerization. Its loss impairs Sir3 loading onto nucleosomes in vitro and eliminates silencing at telomeres and HM loci in vivo. Replacing the Sir3 wH domain with an unrelated bacterial dimerization motif restores both HM and telomeric repression in sir3Δ cells. In contrast, related wH domains of archaeal and human members of the Orc1/Sir3 family are monomeric and have DNA binding activity. We speculate that a dimerization function for the wH evolved with Sir3's ability to facilitate heterochromatin formation.
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Affiliation(s)
- Mariano Oppikofer
- Friedrich Miescher Institute for Biomedical Research, Basel 4058, Switzerland
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29
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Abstract
The mechanisms that maintain the stability of chromosome ends have broad impact on genome integrity in all eukaryotes. Budding yeast is a premier organism for telomere studies. Many fundamental concepts of telomere and telomerase function were first established in yeast and then extended to other organisms. We present a comprehensive review of yeast telomere biology that covers capping, replication, recombination, and transcription. We think of it as yeast telomeres—soup to nuts.
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30
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Kueng S, Tsai-Pflugfelder M, Oppikofer M, Ferreira HC, Roberts E, Tsai C, Roloff TC, Sack R, Gasser SM. Regulating repression: roles for the sir4 N-terminus in linker DNA protection and stabilization of epigenetic states. PLoS Genet 2012; 8:e1002727. [PMID: 22654676 PMCID: PMC3359979 DOI: 10.1371/journal.pgen.1002727] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 04/11/2012] [Indexed: 01/19/2023] Open
Abstract
Silent information regulator proteins Sir2, Sir3, and Sir4 form a heterotrimeric complex that represses transcription at subtelomeric regions and homothallic mating type (HM) loci in budding yeast. We have performed a detailed biochemical and genetic analysis of the largest Sir protein, Sir4. The N-terminal half of Sir4 is dispensable for SIR–mediated repression of HM loci in vivo, except in strains that lack Yku70 or have weak silencer elements. For HM silencing in these cells, the C-terminal domain (Sir4C, residues 747–1,358) must be complemented with an N-terminal domain (Sir4N; residues 1–270), expressed either independently or as a fusion with Sir4C. Nonetheless, recombinant Sir4C can form a complex with Sir2 and Sir3 in vitro, is catalytically active, and has sedimentation properties similar to a full-length Sir4-containing SIR complex. Sir4C-containing SIR complexes bind nucleosomal arrays and protect linker DNA from nucleolytic digestion, but less effectively than wild-type SIR complexes. Consistently, full-length Sir4 is required for the complete repression of subtelomeric genes. Supporting the notion that the Sir4 N-terminus is a regulatory domain, we find it extensively phosphorylated on cyclin-dependent kinase consensus sites, some being hyperphosphorylated during mitosis. Mutation of two major phosphoacceptor sites (S63 and S84) derepresses natural subtelomeric genes when combined with a serendipitous mutation (P2A), which alone can enhance the stability of either the repressed or active state. The triple mutation confers resistance to rapamycin-induced stress and a loss of subtelomeric repression. We conclude that the Sir4 N-terminus plays two roles in SIR–mediated silencing: it contributes to epigenetic repression by stabilizing the SIR–mediated protection of linker DNA; and, as a target of phosphorylation, it can destabilize silencing in a regulated manner. Three Silent Information Regulator (SIR) proteins Sir2, Sir3, and Sir4 are involved in the epigenetic gene silencing of the homothallic mating (HM) loci and of telomere-proximal genes in budding yeast. They bind as a heterotrimeric complex to chromatin, repressing the underlying genes. Sir2 has an essential histone deacetylase activity, and Sir3 binds nucleosomes, with a high specificity for unmodified histones. We explored Sir4, whose role had largely remained a mystery. We report here that Sir4 N- and C-terminal domains have distinct functions: The Sir4 C-terminus binds all proteins essential for SIR–mediated silencing and is sufficient to repress HM loci, but surprisingly it is not sufficient to efficiently repress at telomeres. The Sir4 N-terminus binds DNA, which strengthens the SIR–chromatin interaction and helps target Sir4 to telomeric loci. In addition the Sir4 N-terminus binds sequence-specific factors that recruit Sir4 to sites of repression. We find that the Sir4 N-terminus is a target of mitotic phosphorylation. Mutation of the phosphoacceptor sites indicates that they help fine-tune subtelomeric repression. We propose therefore that phosphorylation of the Sir4 N-terminal domain modulates epigenetic repression at telomeres in response to cell cycle and/or stress situations.
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Affiliation(s)
- Stephanie Kueng
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | | | - Mariano Oppikofer
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
- Faculty of Natural Sciences, University of Basel, Basel, Switzerland
| | - Helder C. Ferreira
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Emma Roberts
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Chinyen Tsai
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | | | - Ragna Sack
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Susan M. Gasser
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
- Faculty of Natural Sciences, University of Basel, Basel, Switzerland
- * E-mail:
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Functions of protosilencers in the formation and maintenance of heterochromatin in Saccharomyces cerevisiae. PLoS One 2012; 7:e37092. [PMID: 22615905 PMCID: PMC3355138 DOI: 10.1371/journal.pone.0037092] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2012] [Accepted: 04/17/2012] [Indexed: 11/19/2022] Open
Abstract
In Saccharomyces cerevisiae, transcriptionally silent heterochromatin at HML and HMR loci is established by silencers that recruit SIR complex and promote its propagation along chromatin. Silencers consist of various combinations of two or three binding sites for origin recognition complex (ORC), Abf1 and Rap1. A single ORC, Abf1 or Rap1 site cannot promote silencing, but can enhance silencing by a distant silencer, and is called a protosilencer. The mechanism of protosilencer function is not known. We examine the functions of ORC, Abf1 and Rap1 sites as components of the HMR-E silencer, and as protosilencers. We find that the Rap1 site makes a larger and unique contribution to HMR-E function compared to ORC and Abf1 sites. On the other hand, Rap1 site does not act as a protosilencer to assist HML-E silencer in forming heterochromatin, whereas ORC and Abf1 sites do. Therefore, different mechanisms may be involved in the roles of Rap1 site as a component of HMR-E and as a protosilencer. Heterochromatin formed by ORC or Abf1 site in collaboration with HML-E is not as stable as that formed by HMR-E and HML-E, but increasing the copy number of Abf1 site enhances heterochromatin stability. ORC and Abf1 sites acting as protosilencers do not modulate chromatin structure in the absence of SIR complex, which argues against the hypothesis that protosilencers serve to create a chromatin structure favorable for SIR complex propagation. We also investigate the function of ARS1 containing an ORC site and an Abf1 site as a protosilencer. We find that ARS1 inserted at HML enhances heterochromatin stability, and promotes de novo formation of a chromatin structure that partially resembles heterochromatin in an S phase dependent manner. Taken together, our results indicate that protosilencers aid in the formation and maintenance of heterochromatin structure.
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Scher R, Garcia JBF, Pascoalino B, Schenkman S, Cruz AK. Characterization of anti-silencing factor 1 in Leishmania major. Mem Inst Oswaldo Cruz 2012; 107:377-86. [DOI: 10.1590/s0074-02762012000300013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 01/11/2012] [Indexed: 02/19/2023] Open
Affiliation(s)
- Ricardo Scher
- Universidade de São Paulo, Brasil; Universidade Federal de Sergipe, Brasil
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Pardo CE, Darst RP, Nabilsi NH, Delmas AL, Kladde MP. Simultaneous single-molecule mapping of protein-DNA interactions and DNA methylation by MAPit. ACTA ACUST UNITED AC 2011; Chapter 21:Unit 21.22. [PMID: 21732317 DOI: 10.1002/0471142727.mb2122s95] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Sites of protein binding to DNA are inferred from footprints or spans of protection against a probing reagent. In most protocols, sites of accessibility to a probe are detected by mapping breaks in DNA strands. As discussed in this unit, such methods obscure molecular heterogeneity by averaging cuts at a given site over all DNA strands in a sample population. The DNA methyltransferase accessibility protocol for individual templates (MAPit), an alternative method described in this unit, localizes protein-DNA interactions by probing with cytosine-modifying DNA methyltransferases followed by bisulfite sequencing. Sequencing individual DNA products after amplification of bisulfite-converted sequences permits assignment of the methylation status of every enzyme target site along a single DNA strand. Use of the GC-methylating enzyme M.CviPI allows simultaneous mapping of chromatin accessibility and endogenous CpG methylation. MAPit is therefore the only footprinting method that can detect subpopulations of molecules with distinct patterns of protein binding or chromatin architecture and correlate them directly with the occurrence of endogenous methylation. Additional advantages of MAPit methylation footprinting as well as considerations for experimental design and potential sources of error are discussed.
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Affiliation(s)
- Carolina E Pardo
- Department of Biochemistry and Molecular Biology and UF Shands Cancer Center Program in Cancer Genetics, Epigenetics and Tumor Virology, University of Florida College of Medicine, Gainesville, Florida, USA
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The C-terminus of histone H2B is involved in chromatin compaction specifically at telomeres, independently of its monoubiquitylation at lysine 123. PLoS One 2011; 6:e22209. [PMID: 21829450 PMCID: PMC3146481 DOI: 10.1371/journal.pone.0022209] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Accepted: 06/17/2011] [Indexed: 12/11/2022] Open
Abstract
Telomeric heterochromatin assembly in budding yeast propagates through the association of Silent Information Regulator (SIR) proteins with nucleosomes, and the nucleosome array has been assumed to fold into a compacted structure. It is believed that the level of compaction and gene repression within heterochromatic regions can be modulated by histone modifications, such as acetylation of H3 lysine 56 and H4 lysine 16, and monoubiquitylation of H2B lysine 123. However, it remains unclear as to whether or not gene silencing is a direct consequence of the compaction of chromatin. Here, by investigating the role of the carboxy-terminus of histone H2B in heterochromatin formation, we identify that the disorderly compaction of chromatin induced by a mutation at H2B T122 specifically hinders telomeric heterochromatin formation. H2B T122 is positioned within the highly conserved AVTKY motif of the αC helix of H2B. Heterochromatin containing the T122E substitution in H2B remains inaccessible to ectopic dam methylase with dramatically increased mobility in sucrose gradients, indicating a compacted chromatin structure. Genetic studies indicate that this unique phenotype is independent of H2B K123 ubiquitylation and Sir4. In addition, using ChIP analysis, we demonstrate that telomere structure in the mutant is further disrupted by a defect in Sir2/Sir3 binding and the resulting invasion of euchromatic histone marks. Thus, we have revealed that the compaction of chromatin per se is not sufficient for heterochromatin formation. Instead, these results suggest that an appropriately arrayed chromatin mediated by H2B C-terminus is required for SIR binding and the subsequent formation of telomeric chromatin in yeast, thereby identifying an intrinsic property of the nucleosome that is required for the establishment of telomeric heterochromatin. This requirement is also likely to exist in higher eukaryotes, as the AVTKY motif of H2B is evolutionarily conserved.
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Abstract
In eukaryotes, all DNA-templated reactions occur in the context of chromatin. Nucleosome packaging inherently restricts DNA accessibility for regulatory proteins but also provides an opportunity to regulate DNA-based processes through modulating nucleosome positions and local chromatin structure. Recent advances in genome-scale methods are yielding increasingly detailed profiles of the genomic distribution of nucleosomes, their modifications and their modifiers. The picture now emerging is one in which the dynamic control of genome accessibility is governed by contributions from DNA sequence, ATP-dependent chromatin remodelling and nucleosome modifications. Here we discuss the interplay of these processes by reviewing our current understanding of how chromatin access contributes to the regulation of transcription, replication and repair.
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A dual role of H4K16 acetylation in the establishment of yeast silent chromatin. EMBO J 2011; 30:2610-21. [PMID: 21666601 DOI: 10.1038/emboj.2011.170] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Accepted: 04/28/2011] [Indexed: 11/09/2022] Open
Abstract
Discrete regions of the eukaryotic genome assume heritable chromatin structure that is refractory to transcription. In budding yeast, silent chromatin is characterized by the binding of the Silent Information Regulatory (Sir) proteins to unmodified nucleosomes. Using an in vitro reconstitution assay, which allows us to load Sir proteins onto arrays of regularly spaced nucleosomes, we have examined the impact of specific histone modifications on Sir protein binding and linker DNA accessibility. Two typical marks for active chromatin, H3K79(me) and H4K16(ac) decrease the affinity of Sir3 for chromatin, yet only H4K16(ac) affects chromatin structure, as measured by nuclease accessibility. Surprisingly, we found that the Sir2-4 subcomplex, unlike Sir3, has higher affinity for chromatin carrying H4K16(ac). NAD-dependent deacetylation of H4K16(ac) promotes binding of the SIR holocomplex but not of the Sir2-4 heterodimer. This function of H4K16(ac) cannot be substituted by H3K56(ac). We conclude that acetylated H4K16 has a dual role in silencing: it recruits Sir2-4 and repels Sir3. Moreover, the deacetylation of H4K16(ac) by Sir2 actively promotes the high-affinity binding of the SIR holocomplex.
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37
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Chromatin: constructing the big picture. EMBO J 2011; 30:1885-95. [PMID: 21527910 DOI: 10.1038/emboj.2011.135] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Accepted: 04/06/2011] [Indexed: 02/06/2023] Open
Abstract
Chromatin is the ensemble of genomic DNA and a large number of proteins. Various genome-wide mapping techniques have begun to reveal that, despite the tremendous complexity, chromatin organization is governed by simple principles. This review discusses the principles that drive the spatial architecture of chromatin, as well as genome-wide-binding patterns of chromatin proteins.
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Chang JS, Winston F. Spt10 and Spt21 are required for transcriptional silencing in Saccharomyces cerevisiae. EUKARYOTIC CELL 2011; 10:118-29. [PMID: 21057056 PMCID: PMC3019801 DOI: 10.1128/ec.00246-10] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2010] [Accepted: 10/26/2010] [Indexed: 11/20/2022]
Abstract
In Saccharomyces cerevisiae, transcriptional silencing occurs at three classes of genomic regions: near the telomeres, at the silent mating type loci, and within the ribosomal DNA (rDNA) repeats. In all three cases, silencing depends upon several factors, including specific types of histone modifications. In this work we have investigated the roles in silencing for Spt10 and Spt21, two proteins previously shown to control transcription of particular histone genes. Building on a recent study showing that Spt10 is required for telomeric silencing, our results show that in both spt10 and spt21 mutants, silencing is reduced near telomeres and at HMLα, while it is increased at the rDNA. Both spt10 and spt21 mutations cause modest effects on Sir protein recruitment and histone modifications at telomeric regions, and they cause significant changes in chromatin structure, as judged by its accessibility to dam methylase. These silencing and chromatin changes are not seen upon deletion of HTA2-HTB2, the primary histone locus regulated by Spt10 and Spt21. These results suggest that Spt10 and Spt21 control silencing in S. cerevisiae by altering chromatin structure through roles beyond the control of histone gene expression.
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Affiliation(s)
- Jennifer S. Chang
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115
| | - Fred Winston
- Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115
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39
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Pardo CE, Carr IM, Hoffman CJ, Darst RP, Markham AF, Bonthron DT, Kladde MP. MethylViewer: computational analysis and editing for bisulfite sequencing and methyltransferase accessibility protocol for individual templates (MAPit) projects. Nucleic Acids Res 2010; 39:e5. [PMID: 20959287 PMCID: PMC3017589 DOI: 10.1093/nar/gkq716] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Bisulfite sequencing is a widely-used technique for examining cytosine DNA methylation at nucleotide resolution along single DNA strands. Probing with cytosine DNA methyltransferases followed by bisulfite sequencing (MAPit) is an effective technique for mapping protein-DNA interactions. Here, MAPit methylation footprinting with M.CviPI, a GC methyltransferase we previously cloned and characterized, was used to probe hMLH1 chromatin in HCT116 and RKO colorectal cancer cells. Because M.CviPI-probed samples contain both CG and GC methylation, we developed a versatile, visually-intuitive program, called MethylViewer, for evaluating the bisulfite sequencing results. Uniquely, MethylViewer can simultaneously query cytosine methylation status in bisulfite-converted sequences at as many as four different user-defined motifs, e.g. CG, GC, etc., including motifs with degenerate bases. Data can also be exported for statistical analysis and as publication-quality images. Analysis of hMLH1 MAPit data with MethylViewer showed that endogenous CG methylation and accessible GC sites were both mapped on single molecules at high resolution. Disruption of positioned nucleosomes on single molecules of the PHO5 promoter was detected in budding yeast using M.CviPII, increasing the number of enzymes available for probing protein-DNA interactions. MethylViewer provides an integrated solution for primer design and rapid, accurate and detailed analysis of bisulfite sequencing or MAPit datasets from virtually any biological or biochemical system.
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Affiliation(s)
- Carolina E Pardo
- Department of Biochemistry and Molecular Biology, University of Florida Shands Cancer Center Program in Cancer Genetics, Epigenetics and Tumor Virology, Gainesville, FL 32610-3633, USA
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40
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Accessibility of the Drosophila genome discriminates PcG repression, H4K16 acetylation and replication timing. Nat Struct Mol Biol 2010; 17:894-900. [DOI: 10.1038/nsmb.1825] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2009] [Accepted: 04/02/2010] [Indexed: 01/16/2023]
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41
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van Steensel B, Braunschweig U, Filion GJ, Chen M, van Bemmel JG, Ideker T. Bayesian network analysis of targeting interactions in chromatin. Genome Res 2009; 20:190-200. [PMID: 20007327 DOI: 10.1101/gr.098822.109] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In eukaryotes, many chromatin proteins together regulate gene expression. Chromatin proteins often direct the genomic binding pattern of other chromatin proteins, for example, by recruitment or competition mechanisms. The network of such targeting interactions in chromatin is complex and still poorly understood. Based on genome-wide binding maps, we constructed a Bayesian network model of the targeting interactions among a broad set of 43 chromatin components in Drosophila cells. This model predicts many novel functional relationships. For example, we found that the homologous proteins HP1 and HP1C each target the heterochromatin protein HP3 to distinct sets of genes in a competitive manner. We also discovered a central role for the remodeling factor Brahma in the targeting of several DNA-binding factors, including GAGA factor, JRA, and SU(VAR)3-7. Our network model provides a global view of the targeting interplay among dozens of chromatin components.
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Affiliation(s)
- Bas van Steensel
- Division of Gene Regulation, Netherlands Cancer Institute, 1066 CX Amsterdam, the Netherlands.
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42
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Loney ER, Inglis PW, Sharp S, Pryde FE, Kent NA, Mellor J, Louis EJ. Repressive and non-repressive chromatin at native telomeres in Saccharomyces cerevisiae. Epigenetics Chromatin 2009; 2:18. [PMID: 19954519 PMCID: PMC3225887 DOI: 10.1186/1756-8935-2-18] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Accepted: 12/02/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In Saccharomyces cerevisiae genes that are located close to a telomere can become transcriptionally repressed by an epigenetic process known as telomere position effect. There is large variation in the level of the telomere position effect among telomeres, with many native ends exhibiting little repression. RESULTS Chromatin analysis, using microccocal nuclease and indirect end labelling, reveals distinct patterns for ends with different silencing states. Differences were observed in the promoter accessibility of a subtelomeric reporter gene and a characteristic array of phased nucleosomes was observed on the centromere proximal side of core X at a repressive end. The silent information regulator proteins 2 - 4, the yKu heterodimer and the subtelomeric core X element are all required for the maintenance of the chromatin structure of repressive ends. However, gene deletions of particular histone modification proteins can eliminate the silencing without the disruption of this chromatin structure. CONCLUSION Our data identifies chromatin features that correlate with the silencing state and indicate that an array of phased nucleosomes is not sufficient for full repression.
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Affiliation(s)
- Esther R Loney
- 1Department of Oncology, University of Western Ontario, Ontario, Canada.
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43
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Johnson A, Li G, Sikorski TW, Buratowski S, Woodcock CL, Moazed D. Reconstitution of heterochromatin-dependent transcriptional gene silencing. Mol Cell 2009; 35:769-81. [PMID: 19782027 DOI: 10.1016/j.molcel.2009.07.030] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Revised: 05/22/2009] [Accepted: 07/22/2009] [Indexed: 12/26/2022]
Abstract
Heterochromatin assembly in budding yeast requires the SIR complex, which contains the NAD-dependent deacetylase Sir2 and the Sir3 and Sir4 proteins. Sir3 binds to nucleosomes containing deacetylated histone H4 lysine 16 (H4K16) and, with Sir4, promotes spreading of Sir2 and deacetylation along the chromatin fiber. Combined action of histone modifying and binding activities is a conserved hallmark of heterochromatin, but the relative contribution of each activity to silencing has remained unclear. Here, we reconstitute SIR-chromatin complexes using purified components and show that the SIR complex efficiently deacetylates chromatin templates and promotes the assembly of altered structures that silence Gal4-VP16-activated transcription. Silencing requires all three Sir proteins, even with fully deacetylated chromatin, and involves the specific association of Sir3 with deacetylated H4K16. These results define a minimal set of components that mediate heterochromatic gene silencing and demonstrate distinct contributions for histone deacetylation and nucleosome binding in the silencing mechanism.
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Affiliation(s)
- Aaron Johnson
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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44
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Teytelman L, Özaydın B, Zill O, Lefrançois P, Snyder M, Rine J, Eisen MB. Impact of chromatin structures on DNA processing for genomic analyses. PLoS One 2009; 4:e6700. [PMID: 19693276 PMCID: PMC2725323 DOI: 10.1371/journal.pone.0006700] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Accepted: 07/31/2009] [Indexed: 11/25/2022] Open
Abstract
Chromatin has an impact on recombination, repair, replication, and evolution of DNA. Here we report that chromatin structure also affects laboratory DNA manipulation in ways that distort the results of chromatin immunoprecipitation (ChIP) experiments. We initially discovered this effect at the Saccharomyces cerevisiae HMR locus, where we found that silenced chromatin was refractory to shearing, relative to euchromatin. Using input samples from ChIP-Seq studies, we detected a similar bias throughout the heterochromatic portions of the yeast genome. We also observed significant chromatin-related effects at telomeres, protein binding sites, and genes, reflected in the variation of input-Seq coverage. Experimental tests of candidate regions showed that chromatin influenced shearing at some loci, and that chromatin could also lead to enriched or depleted DNA levels in prepared samples, independently of shearing effects. Our results suggested that assays relying on immunoprecipitation of chromatin will be biased by intrinsic differences between regions packaged into different chromatin structures - biases which have been largely ignored to date. These results established the pervasiveness of this bias genome-wide, and suggested that this bias can be used to detect differences in chromatin structures across the genome.
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Affiliation(s)
- Leonid Teytelman
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, University of California, Berkeley, California, United States of America
| | - Bilge Özaydın
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, University of California, Berkeley, California, United States of America
| | - Oliver Zill
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, University of California, Berkeley, California, United States of America
| | - Philippe Lefrançois
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, United States of America
| | - Michael Snyder
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, United States of America
| | - Jasper Rine
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, University of California, Berkeley, California, United States of America
| | - Michael B. Eisen
- Department of Molecular and Cell Biology, California Institute of Quantitative Biosciences, University of California, Berkeley, California, United States of America
- Howard Hughes Medical Institute, University of California, Berkeley, California, United States of America
- * E-mail:
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45
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Histone H3 N-terminus regulates higher order structure of yeast heterochromatin. Proc Natl Acad Sci U S A 2009; 106:13153-9. [PMID: 19666585 DOI: 10.1073/pnas.0906866106] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In budding yeast, telomeres and the mating type (HM) loci are found in a heterochromatin-like silent structure initiated by Rap1 and extended by the interaction of Silencing Information Regulator (Sir) proteins with histones. Binding data demonstrate that both the H3 and H4 N-terminal domains required for silencing in vivo interact directly with Sir3 and Sir4 in vitro. The role of H4 lysine 16 deacetylation is well established in Sir3 protein recruitment; however, that of the H3 N-terminal tail has remained unclear. To characterize the role of H3 in silent chromatin formation and compare it to H4 we have generated comprehensive high resolution genome-wide binding maps of heterochromatin proteins. We found that H4 lysine 16 deacetylation is required for the recruitment and spreading of heterochromatin proteins at all telomeres and HM loci. In contrast, the H3 N terminus is required for neither recruitment nor spreading of Sir proteins. Instead, deletion of the H3 tail leads to increased accessibility within heterochromatin of an ectopic bacterial dam methylase and the decreased mobility of an HML heterochromatic fragment in sucrose gradients. These findings indicate an altered chromatin structure. We propose that Sir proteins recruited by the H4 tail then interact with the H3 tail to form a higher order silent chromatin structure.
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46
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Silent chromatin at the middle and ends: lessons from yeasts. EMBO J 2009; 28:2149-61. [PMID: 19629038 PMCID: PMC2722250 DOI: 10.1038/emboj.2009.185] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2009] [Accepted: 06/15/2009] [Indexed: 11/09/2022] Open
Abstract
Eukaryotic centromeres and telomeres are specialized chromosomal regions that share one common characteristic: their underlying DNA sequences are assembled into heritably repressed chromatin. Silent chromatin in budding and fission yeast is composed of fundamentally divergent proteins tat assemble very different chromatin structures. However, the ultimate behaviour of silent chromatin and the pathways that assemble it seem strikingly similar among Saccharomyces cerevisiae (S. cerevisiae), Schizosaccharomyces pombe (S. pombe) and other eukaryotes. Thus, studies in both yeasts have been instrumental in dissecting the mechanisms that establish and maintain silent chromatin in eukaryotes, contributing substantially to our understanding of epigenetic processes. In this review, we discuss current models for the generation of heterochromatic domains at centromeres and telomeres in the two yeast species.
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47
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Towbin BD, Meister P, Gasser SM. The nuclear envelope--a scaffold for silencing? Curr Opin Genet Dev 2009; 19:180-6. [PMID: 19303765 DOI: 10.1016/j.gde.2009.01.006] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 01/23/2009] [Accepted: 01/27/2009] [Indexed: 01/19/2023]
Abstract
An increasing number of studies indicate that chromosomes are spatially organized in the interphase nucleus and that some genes tend to occupy characteristic zones of the nuclear volume. FISH studies in mammalian cells suggest a differential localization of active and inactive loci, with inactive heterochromatin being largely perinuclear. Recent genome-wide mapping techniques confirm that the nuclear lamina, which lies beneath the nuclear envelope, interacts preferentially with silent genes. To address the functional significance of spatial compartmentation, gain-of-function assays in which chromatin is targeted to the nuclear periphery have now been carried out. Such experiments yielded coherent models in yeast; however, conflicting results in mammalian cells leave it unclear whether these concepts apply to higher organisms. Nevertheless, the recent discovery that evolutionarily conserved inner nuclear membrane proteins support the peripheral anchoring of yeast heterochromatin suggests that certain principles of nuclear organization may hold true from yeast to man.
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Affiliation(s)
- Benjamin D Towbin
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
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Vogel MJ, Pagie L, Talhout W, Nieuwland M, Kerkhoven RM, van Steensel B. High-resolution mapping of heterochromatin redistribution in a Drosophila position-effect variegation model. Epigenetics Chromatin 2009; 2:1. [PMID: 19178722 PMCID: PMC2644302 DOI: 10.1186/1756-8935-2-1] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Accepted: 01/29/2009] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND Position-effect variegation (PEV) is the stochastic transcriptional silencing of a gene positioned adjacent to heterochromatin. white-mottled X-chromosomal inversions in Drosophila are classic PEV models that show variegation of the eye color gene white due to its relocation next to pericentric heterochromatin. It has been suggested that in these models the spreading of heterochromatin across the rearrangement breakpoint causes the silencing of white. However, the extent of this spreading and the precise pattern of heterochromatin redistribution have remained unclear. To obtain insight into the mechanism of PEV, we constructed high-resolution binding maps of Heterochromatin Protein 1 (HP1) on white-mottled chromosomes. RESULTS We find that HP1 invades euchromatin across the inversion breakpoints over approximately 175 kb and approximately 30 kb, causing de novo association of HP1 with 20 genes. However, HP1 binding levels in these regions show substantial local variation, and white is the most strongly bound gene. Remarkably, white is also the only gene that is detectably repressed by heterochromatin. Furthermore, we find that HP1 binding to the invaded region is particularly sensitive to the dosage of the histone methyltransferase Su(var)3-9, indicating that the de novo formed heterochromatin is less stable than naturally occurring constitutive heterochromatin. CONCLUSION Our molecular maps demonstrate that heterochromatin can invade a normally euchromatic region, yet the strength of HP1 binding and effects on gene expression are highly dependent on local context. Our data suggest that the white gene has an unusual intrinsic affinity for heterochromatin, which may cause this gene to be more sensitive to PEV than most other genes.
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Affiliation(s)
- Maartje J Vogel
- Division of Gene Regulation, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Ludo Pagie
- Division of Gene Regulation, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Wendy Talhout
- Division of Gene Regulation, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Marja Nieuwland
- Central Microarray Facility, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Ron M Kerkhoven
- Central Microarray Facility, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - Bas van Steensel
- Division of Gene Regulation, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
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Bisht KK, Arora S, Ahmed S, Singh J. Role of heterochromatin in suppressing subtelomeric recombination in fission yeast. Yeast 2009; 25:537-48. [PMID: 18615848 DOI: 10.1002/yea.1603] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Telomere length is regulated by a complex interplay of several factors, including telomerase, telomere-binding proteins, DNA replication machinery and recombination. In yeast, DNA polymerase alpha is required for de novo synthesis of telomeres from broken ends of DNA, and it also suppresses the elongation of normal telomeric repeats. Heterochromatin proteins Clr1-Clr4 and Swi6 and DNA polalpha organize heterochromatin structure at mating type, centromere, rDNA and telomere regions that are refractory to transcription and recombination in Schizosaccharomyces pombe. Here, we have addressed the role of heterochromatin structure in regulating the integrity and organization of telomeric regions. Here, we show that subtelomeric duplication and rearrangements occur in polalpha and heterochromatin mutants and find that some of the putative duplication events are dependent on the Rad50 pathway. Thus, our study shows a role of heterochromatin in maintaining the integrity of the subtelomeric regions by suppressing their recombination in Sz. pombe.
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50
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Hiraga SI, Botsios S, Donaldson AD. Histone H3 lysine 56 acetylation by Rtt109 is crucial for chromosome positioning. ACTA ACUST UNITED AC 2008; 183:641-51. [PMID: 19001125 PMCID: PMC2582893 DOI: 10.1083/jcb.200806065] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Correct intranuclear organization of chromosomes is crucial for many genome functions, but the mechanisms that position chromatin are not well understood. We used a layered screen to identify Saccharomyces cerevisiae mutants defective in telomere localization to the nuclear periphery. We find that events in S phase are crucial for correct telomere localization. In particular, the histone chaperone Asf1 functions in telomere peripheral positioning. Asf1 stimulates acetylation of histone H3 lysine 56 (H3K56) by the histone acetyltransferase Rtt109. Analysis of rtt109Δ and H3K56 mutants suggests that the acetylation/deacetylation cycle of the H3K56 residue is required for proper telomere localization. The function of H3K56 acetylation in localizing chromosome domains is not confined to telomeres because deletion of RTT109 also prevents the correct peripheral localization of a newly identified S. cerevisiae “chromosome-organizing clamp” locus. Because chromosome positioning is subject to epigenetic inheritance, H3K56 acetylation may mediate correct chromosome localization by facilitating accurate transmission of chromatin status during DNA replication.
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Affiliation(s)
- Shin-Ichiro Hiraga
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, Scotland, UK
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