1
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Skribbe M, Soneson C, Stadler MB, Schwaiger M, Suma Sreechakram VN, Iesmantavicius V, Hess D, Moreno EPF, Braun S, Seebacher J, Smallwood SA, Bühler M. A comprehensive Schizosaccharomyces pombe atlas of physical transcription factor interactions with proteins and chromatin. Mol Cell 2025; 85:1426-1444.e8. [PMID: 40015273 DOI: 10.1016/j.molcel.2025.01.032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2024] [Revised: 12/16/2024] [Accepted: 01/30/2025] [Indexed: 03/01/2025]
Abstract
Transcription factors (TFs) are key regulators of gene expression, yet many of their targets and modes of action remain unknown. In Schizosaccharomyces pombe, one-third of TFs are solely homology predicted, with few experimentally validated. We created a comprehensive library of 89 endogenously tagged S. pombe TFs, mapping their protein and chromatin interactions using immunoprecipitation-mass spectrometry and chromatin immunoprecipitation sequencing. Our study identified protein interactors for half the TFs, with over a quarter potentially forming stable complexes. We discovered DNA-binding sites for most TFs across 2,027 unique genomic regions, revealing motifs for 38 TFs and uncovering a complex network of extensive TF cross- and autoregulation. Characterization of the largest TF family revealed conserved DNA sequence preferences but diverse binding patterns and identified a repressive heterodimer, Ntu1/Ntu2, linked to perinuclear gene localization. Our TFexplorer webtool makes all data interactively accessible, offering insights into TF interactions and regulatory mechanisms with broad biological relevance.
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Affiliation(s)
- Merle Skribbe
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland; University of Basel, Petersplatz 10, Basel, Switzerland.
| | - Charlotte Soneson
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland; SIB Swiss Institute of Bioinformatics, Basel, Switzerland
| | - Michael B Stadler
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland; University of Basel, Petersplatz 10, Basel, Switzerland; SIB Swiss Institute of Bioinformatics, Basel, Switzerland
| | - Michaela Schwaiger
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland; SIB Swiss Institute of Bioinformatics, Basel, Switzerland
| | | | | | - Daniel Hess
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland
| | | | - Sigurd Braun
- Institute for Genetics, Justus-Liebig-University Giessen, Giessen, Germany
| | - Jan Seebacher
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland
| | - Sebastien A Smallwood
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland
| | - Marc Bühler
- Friedrich Miescher Institute for Biomedical Research, Fabrikstrasse 24, Basel, Switzerland; University of Basel, Petersplatz 10, Basel, Switzerland.
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2
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Sharma S, Srivastava S, Dubey RN, Mishra P, Singh J. [SNG2], a prion form of Cut4/Apc1, confers non-Mendelian inheritance of heterochromatin silencing defect in fission yeast. Nucleic Acids Res 2024; 52:13792-13811. [PMID: 39565210 DOI: 10.1093/nar/gkae1136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 10/22/2024] [Accepted: 10/31/2024] [Indexed: 11/21/2024] Open
Abstract
Prions represent epigenetic regulator proteins that can self-propagate their structure and confer their misfolded structure and function on normally folded proteins. Like the mammalian prion PrPSc, prions also occur in fungi. While a few prions, like Swi1, affect gene expression, none are shown to affect heterochromatin structure and function. In fission yeast and metazoans, histone methyltransferase Clr4/Suv39 causes H3-Lys9 methylation, which is bound by the chromodomain protein Swi6/HP1 to assemble heterochromatin. Earlier, we showed that sng2-1 mutation in the Cut4 subunit of anaphase-promoting complex abrogates heterochromatin structure due to defective binding and recruitment of Swi6. Here, we demonstrate that the Cut4p forms a non-canonical prion form, designated as [SNG2], which abrogates heterochromatin silencing. [SNG2] exhibits various prion-like properties, e.g. non-Mendelian inheritance, requirement of Hsp proteins for its propagation, de novo generation upon cut4 overexpression, reversible curing by guanidine, cytoplasmic inheritance and formation of infectious protein aggregates, which are dissolved upon overexpression of hsp genes. Interestingly, [SNG2] prion imparts an enhanced tolerance to stress conditions, supporting its role in promoting cell survival under environmental stress during evolution.
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Affiliation(s)
- Suman Sharma
- Institute of Microbial Technology, Sector 39A, Chandigarh 160036, India
| | | | | | - Poonam Mishra
- Institute of Microbial Technology, Sector 39A, Chandigarh 160036, India
| | - Jagmohan Singh
- Institute of Microbial Technology, Sector 39A, Chandigarh 160036, India
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3
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Charlton SJ, Flury V, Kanoh Y, Genzor AV, Kollenstart L, Ao W, Brøgger P, Weisser MB, Adamus M, Alcaraz N, Delvaux de Fenffe CM, Mattiroli F, Montoya G, Masai H, Groth A, Thon G. The fork protection complex promotes parental histone recycling and epigenetic memory. Cell 2024; 187:5029-5047.e21. [PMID: 39094569 PMCID: PMC11383432 DOI: 10.1016/j.cell.2024.07.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 03/16/2024] [Accepted: 07/09/2024] [Indexed: 08/04/2024]
Abstract
The inheritance of parental histones across the replication fork is thought to mediate epigenetic memory. Here, we reveal that fission yeast Mrc1 (CLASPIN in humans) binds H3-H4 tetramers and operates as a central coordinator of symmetric parental histone inheritance. Mrc1 mutants in a key connector domain disrupted segregation of parental histones to the lagging strand comparable to Mcm2 histone-binding mutants. Both mutants showed clonal and asymmetric loss of H3K9me-mediated gene silencing. AlphaFold predicted co-chaperoning of H3-H4 tetramers by Mrc1 and Mcm2, with the Mrc1 connector domain bridging histone and Mcm2 binding. Biochemical and functional analysis validated this model and revealed a duality in Mrc1 function: disabling histone binding in the connector domain disrupted lagging-strand recycling while another histone-binding mutation impaired leading strand recycling. We propose that Mrc1 toggles histones between the lagging and leading strand recycling pathways, in part by intra-replisome co-chaperoning, to ensure epigenetic transmission to both daughter cells.
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Affiliation(s)
- Sebastian Jespersen Charlton
- Department of Biology, University of Copenhagen, Copenhagen 2200, Denmark; Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Valentin Flury
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Yutaka Kanoh
- Tokyo Metropolitan Institute of Medical Science, Tokyo 156-8506, Japan
| | | | - Leonie Kollenstart
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Wantong Ao
- Department of Biology, University of Copenhagen, Copenhagen 2200, Denmark
| | - Peter Brøgger
- Department of Biology, University of Copenhagen, Copenhagen 2200, Denmark
| | - Melanie Bianca Weisser
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Marek Adamus
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Nicolas Alcaraz
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | | | - Francesca Mattiroli
- Hubrecht Institute-KNAW & University Medical Center Utrecht, Utrecht, The Netherlands
| | - Guillermo Montoya
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark
| | - Hisao Masai
- Tokyo Metropolitan Institute of Medical Science, Tokyo 156-8506, Japan
| | - Anja Groth
- Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen 2200, Denmark; Biotech Research & Innovation Centre, University of Copenhagen, Copenhagen 2200, Denmark; Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen 2200, Denmark.
| | - Geneviève Thon
- Department of Biology, University of Copenhagen, Copenhagen 2200, Denmark.
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4
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Sahu RK, Dhakshnamoorthy J, Jain S, Folco HD, Wheeler D, Grewal SIS. Nucleosome remodeler exclusion by histone deacetylation enforces heterochromatic silencing and epigenetic inheritance. Mol Cell 2024; 84:3175-3191.e8. [PMID: 39096900 PMCID: PMC11649001 DOI: 10.1016/j.molcel.2024.07.006] [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: 06/06/2024] [Revised: 07/03/2024] [Accepted: 07/09/2024] [Indexed: 08/05/2024]
Abstract
Heterochromatin enforces transcriptional gene silencing and can be epigenetically inherited, but the underlying mechanisms remain unclear. Here, we show that histone deacetylation, a conserved feature of heterochromatin domains, blocks SWI/SNF subfamily remodelers involved in chromatin unraveling, thereby stabilizing modified nucleosomes that preserve gene silencing. Histone hyperacetylation, resulting from either the loss of histone deacetylase (HDAC) activity or the direct targeting of a histone acetyltransferase to heterochromatin, permits remodeler access, leading to silencing defects. The requirement for HDAC in heterochromatin silencing can be bypassed by impeding SWI/SNF activity. Highlighting the crucial role of remodelers, merely targeting SWI/SNF to heterochromatin, even in cells with functional HDAC, increases nucleosome turnover, causing defective gene silencing and compromised epigenetic inheritance. This study elucidates a fundamental mechanism whereby histone hypoacetylation, maintained by high HDAC levels in heterochromatic regions, ensures stable gene silencing and epigenetic inheritance, providing insights into genome regulatory mechanisms relevant to human diseases.
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Affiliation(s)
- Rakesh Kumar Sahu
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jothy Dhakshnamoorthy
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Shweta Jain
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Hernan Diego Folco
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - David Wheeler
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Shiv I S Grewal
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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5
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Sun L, Liu L, Song C, Wang Y, Jin QW. Heat stress-induced activation of MAPK pathway attenuates Atf1-dependent epigenetic inheritance of heterochromatin in fission yeast. eLife 2024; 13:e90525. [PMID: 38289024 PMCID: PMC10863984 DOI: 10.7554/elife.90525] [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: 06/27/2023] [Accepted: 01/29/2024] [Indexed: 02/15/2024] Open
Abstract
Eukaryotic cells are constantly exposed to various environmental stimuli. It remains largely unexplored how environmental cues bring about epigenetic fluctuations and affect heterochromatin stability. In the fission yeast Schizosaccharomyces pombe, heterochromatic silencing is quite stable at pericentromeres but unstable at the mating-type (mat) locus under chronic heat stress, although both loci are within the major constitutive heterochromatin regions. Here, we found that the compromised gene silencing at the mat locus at elevated temperature is linked to the phosphorylation status of Atf1, a member of the ATF/CREB superfamily. Constitutive activation of mitogen-activated protein kinase (MAPK) signaling disrupts epigenetic maintenance of heterochromatin at the mat locus even under normal temperature. Mechanistically, phosphorylation of Atf1 impairs its interaction with heterochromatin protein Swi6HP1, resulting in lower site-specific Swi6HP1 enrichment. Expression of non-phosphorylatable Atf1, tethering Swi6HP1 to the mat3M-flanking site or absence of the anti-silencing factor Epe1 can largely or partially rescue heat stress-induced defective heterochromatic maintenance at the mat locus.
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Affiliation(s)
- Li Sun
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Faculty of Medicine and Life Sciences, Xiamen UniversityXiamenChina
| | - Libo Liu
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Faculty of Medicine and Life Sciences, Xiamen UniversityXiamenChina
| | - Chunlin Song
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Faculty of Medicine and Life Sciences, Xiamen UniversityXiamenChina
| | - Yamei Wang
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Faculty of Medicine and Life Sciences, Xiamen UniversityXiamenChina
| | - Quan-wen Jin
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Faculty of Medicine and Life Sciences, Xiamen UniversityXiamenChina
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6
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Challal D, Menant A, Goksal C, Leroy E, Al-Sady B, Rougemaille M. A dual, catalytic role for the fission yeast Ccr4-Not complex in gene silencing and heterochromatin spreading. Genetics 2023; 224:iyad108. [PMID: 37279920 PMCID: PMC10411572 DOI: 10.1093/genetics/iyad108] [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: 04/11/2023] [Revised: 04/11/2023] [Accepted: 05/31/2023] [Indexed: 06/08/2023] Open
Abstract
Heterochromatic gene silencing relies on combinatorial control by specific histone modifications, the occurrence of transcription, and/or RNA degradation. Once nucleated, heterochromatin propagates within defined chromosomal regions and is maintained throughout cell divisions to warrant proper genome expression and integrity. In the fission yeast Schizosaccharomyces pombe, the Ccr4-Not complex partakes in gene silencing, but its relative contribution to distinct heterochromatin domains and its role in nucleation versus spreading have remained elusive. Here, we unveil major functions for Ccr4-Not in silencing and heterochromatin spreading at the mating type locus and subtelomeres. Mutations of the catalytic subunits Caf1 or Mot2, involved in RNA deadenylation and protein ubiquitinylation, respectively, result in impaired propagation of H3K9me3 and massive accumulation of nucleation-distal heterochromatic transcripts. Both silencing and spreading defects are suppressed upon disruption of the heterochromatin antagonizing factor Epe1. Overall, our results position the Ccr4-Not complex as a critical, dual regulator of heterochromatic gene silencing and spreading.
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Affiliation(s)
- Drice Challal
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette 91198, France
| | - Alexandra Menant
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette 91198, France
| | - Can Goksal
- Department of Microbiology & Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, CA 94143, USA
| | - Estelle Leroy
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette 91198, France
| | - Bassem Al-Sady
- Department of Microbiology & Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, CA 94143, USA
| | - Mathieu Rougemaille
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette 91198, France
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7
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Jia GS, Zhang WC, Liang Y, Liu XH, Rhind N, Pidoux A, Brysch-Herzberg M, Du LL. A high-quality reference genome for the fission yeast Schizosaccharomyces osmophilus. G3 (BETHESDA, MD.) 2023; 13:jkad028. [PMID: 36748990 PMCID: PMC10085805 DOI: 10.1093/g3journal/jkad028] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/23/2023] [Accepted: 01/23/2023] [Indexed: 02/08/2023]
Abstract
Fission yeasts are an ancient group of fungal species that diverged from each other from tens to hundreds of million years ago. Among them is the preeminent model organism Schizosaccharomyces pombe, which has significantly contributed to our understandings of molecular mechanisms underlying fundamental cellular processes. The availability of the genomes of S. pombe and 3 other fission yeast species S. japonicus, S. octosporus, and S. cryophilus has enabled cross-species comparisons that provide insights into the evolution of genes, pathways, and genomes. Here, we performed genome sequencing on the type strain of the recently identified fission yeast species S. osmophilus and obtained a complete mitochondrial genome and a nuclear genome assembly with gaps only at rRNA gene arrays. A total of 5,098 protein-coding nuclear genes were annotated and orthologs for more than 95% of them were identified. Genome-based phylogenetic analysis showed that S. osmophilus is most closely related to S. octosporus and these 2 species diverged around 16 million years ago. To demonstrate the utility of this S. osmophilus reference genome, we conducted cross-species comparative analyses of centromeres, telomeres, transposons, the mating-type region, Cbp1 family proteins, and mitochondrial genomes. These analyses revealed conservation of repeat arrangements and sequence motifs in centromere cores, identified telomeric sequences composed of 2 types of repeats, delineated relationships among Tf1/sushi group retrotransposons, characterized the evolutionary origins and trajectories of Cbp1 family domesticated transposases, and discovered signs of interspecific transfer of 2 types of mitochondrial selfish elements.
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Affiliation(s)
- Guo-Song Jia
- National Institute of Biological Sciences, Beijing 102206, China
| | - Wen-Cai Zhang
- National Institute of Biological Sciences, Beijing 102206, China
| | - Yue Liang
- National Institute of Biological Sciences, Beijing 102206, China
| | - Xi-Han Liu
- National Institute of Biological Sciences, Beijing 102206, China
| | - Nicholas Rhind
- Department of Biochemistry and Molecular Biotechnology, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Alison Pidoux
- Wellcome Centre for Cell Biology, Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, Edinburgh EH9 3BF, Scotland, UK
| | - Michael Brysch-Herzberg
- Laboratory for Wine Microbiology, Department International Business, Heilbronn University, Heilbronn 74081, Germany
| | - Li-Lin Du
- National Institute of Biological Sciences, Beijing 102206, China
- Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing 102206, China
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8
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Arcangioli B, Gangloff S. The Fission Yeast Mating-Type Switching Motto: "One-for-Two" and "Two-for-One". Microbiol Mol Biol Rev 2023; 87:e0000821. [PMID: 36629411 PMCID: PMC10029342 DOI: 10.1128/mmbr.00008-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Schizosaccharomyces pombe is an ascomycete fungus that divides by medial fission; it is thus commonly referred to as fission yeast, as opposed to the distantly related budding yeast Saccharomyces cerevisiae. The reproductive lifestyle of S. pombe relies on an efficient genetic sex determination system generating a 1:1 sex ratio and using alternating haploid/diploid phases in response to environmental conditions. In this review, we address how one haploid cell manages to generate two sister cells with opposite mating types, a prerequisite to conjugation and meiosis. This mating-type switching process depends on two highly efficient consecutive asymmetric cell divisions that rely on DNA replication, repair, and recombination as well as the structure and components of heterochromatin. We pay special attention to the intimate interplay between the genetic and epigenetic partners involved in this process to underscore the importance of basic research and its profound implication for a better understanding of chromatin biology.
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Affiliation(s)
- Benoît Arcangioli
- Genome Dynamics Unit, Genomes and Genetics Department, Pasteur Institute, Paris, France
| | - Serge Gangloff
- Genome Dynamics Unit, Genomes and Genetics Department, Pasteur Institute, Paris, France
- UMR3525, Genetics of Genomes, CNRS-Pasteur Institute, Paris, France
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9
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Esquivel-Chávez A, Maki T, Tsubouchi H, Handa T, Kimura H, Haber JE, Thon G, Iwasaki H. Euchromatin factors HULC and Set1C affect heterochromatin organization and mating-type switching in fission yeast Schizosaccharomyces pombe. Genes Genet Syst 2022; 97:123-138. [PMID: 35908934 DOI: 10.1266/ggs.22-00012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Mating-type (P or M) of fission yeast Schizosaccharomyces pombe is determined by the transcriptionally active mat1 cassette and is switched by gene conversion using a donor, either mat2 or mat3, located in an adjacent heterochromatin region (mating-type switching; MTS). In the switching process, heterochromatic donors of genetic information are selected based on the P or M cell type and on the action of two recombination enhancers, SRE2 promoting the use of mat2-P and SRE3 promoting the use of mat3-M, leading to replacement of the content of the expressed mat1 cassette. Recently, we found that the histone H3K4 methyltransferase complex Set1C participates in donor selection, raising the question of how a complex best known for its effects in euchromatin controls recombination in heterochromatin. Here, we report that the histone H2BK119 ubiquitin ligase complex HULC functions with Set1C in MTS, as mutants in the shf1, brl1, brl2 and rad6 genes showed defects similar to Set1C mutants and belonged to the same epistasis group as set1Δ. Moreover, using H3K4R and H2BK119R histone mutants and a Set1-Y897A catalytic mutant, we found that ubiquitylation of histone H2BK119 by HULC and methylation of histone H3K4 by Set1C are functionally coupled in MTS. Cell-type biases in MTS in these mutants suggested that HULC and Set1C inhibit the use of the SRE3 recombination enhancer in M cells, thus favoring SRE2 and mat2-P. Consistent with this, imbalanced switching in the mutants was traced to compromised association of the directionality factor Swi6 with the recombination enhancers in M cells. Based on their known effects at other chromosomal locations, we speculate that HULC and Set1C control nucleosome mobility and strand invasion near the SRE elements. In addition, we uncovered distinct effects of HULC and Set1C on histone H3K9 methylation and gene silencing, consistent with additional functions in the heterochromatic domain.
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Affiliation(s)
- Alfredo Esquivel-Chávez
- Department of Life Science and Technology, School of Life Science and Technology, Tokyo Institute of Technology
- Institute of Innovative Research, Tokyo Institute of Technology
| | - Takahisa Maki
- Institute of Innovative Research, Tokyo Institute of Technology
| | - Hideo Tsubouchi
- Department of Life Science and Technology, School of Life Science and Technology, Tokyo Institute of Technology
- Institute of Innovative Research, Tokyo Institute of Technology
| | - Testuya Handa
- Institute of Innovative Research, Tokyo Institute of Technology
| | - Hiroshi Kimura
- Department of Life Science and Technology, School of Life Science and Technology, Tokyo Institute of Technology
- Institute of Innovative Research, Tokyo Institute of Technology
| | - James E Haber
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University
| | | | - Hiroshi Iwasaki
- Department of Life Science and Technology, School of Life Science and Technology, Tokyo Institute of Technology
- Institute of Innovative Research, Tokyo Institute of Technology
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10
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Greenstein RA, Ng H, Barrales RR, Tan C, Braun S, Al-Sady B. Local chromatin context regulates the genetic requirements of the heterochromatin spreading reaction. PLoS Genet 2022; 18:e1010201. [PMID: 35584134 PMCID: PMC9154106 DOI: 10.1371/journal.pgen.1010201] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 05/31/2022] [Accepted: 04/13/2022] [Indexed: 11/18/2022] Open
Abstract
Heterochromatin spreading, the expansion of repressive chromatin structure from sequence-specific nucleation sites, is critical for stable gene silencing. Spreading re-establishes gene-poor constitutive heterochromatin across cell cycles but can also invade gene-rich euchromatin de novo to steer cell fate decisions. How chromatin context (i.e. euchromatic, heterochromatic) or different nucleation pathways influence heterochromatin spreading remains poorly understood. Previously, we developed a single-cell sensor in fission yeast that can separately record heterochromatic gene silencing at nucleation sequences and distal sites. Here we couple our quantitative assay to a genetic screen to identify genes encoding nuclear factors linked to the regulation of heterochromatin nucleation and the distal spreading of gene silencing. We find that mechanisms underlying gene silencing distal to a nucleation site differ by chromatin context. For example, Clr6 histone deacetylase complexes containing the Fkh2 transcription factor are specifically required for heterochromatin spreading at constitutive sites. Fkh2 recruits Clr6 to nucleation-distal chromatin sites in such contexts. In addition, we find that a number of chromatin remodeling complexes antagonize nucleation-distal gene silencing. Our results separate the regulation of heterochromatic gene silencing at nucleation versus distal sites and show that it is controlled by context-dependent mechanisms. The results of our genetic analysis constitute a broad community resource that will support further analysis of the mechanisms underlying the spread of epigenetic silencing along chromatin. Repressive structures, or heterochromatin, are seeded at specific genome sequences and then “spread” to silence nearby chromosomal regions. While much is known about the factors that seed heterochromatin, the genetic requirements for spreading are less clear. We devised a fission yeast single-cell method to examine how gene silencing is propagated by the heterochromatin spreading process specifically. Here we use this platform to ask if specific genes are required for the spreading process and whether the same or different genes direct spreading from different chromosomal seeding sites. We find a significant number of genes that specifically promote or antagonize the heterochromatin spreading process. However, different genes are required to enact spreading from different seeding sites. These results have potential implications for cell fate specification, where genes are newly silenced by heterochromatin spreading from diverse chromosomal sites. In a central finding, we show that the Clr6 protein complex, which removes chromatin marks linked to active genes, associates with the Forkhead 2 transcription factor to promote spreading of silencing structures from seeding sites at numerous chromosomal loci. In contrast, we show that proteins that remodel chromatin antagonize the spreading of gene silencing.
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Affiliation(s)
- R. A. Greenstein
- Department of Microbiology &Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, California, United States of America
- TETRAD graduate program, University of California San Francisco, San Francisco, California, United States of America
| | - Henry Ng
- Department of Microbiology &Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, California, United States of America
- TETRAD graduate program, University of California San Francisco, San Francisco, California, United States of America
| | - Ramon R. Barrales
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität of Munich, Planegg-Martinsried, Germany
| | - Catherine Tan
- Department of Cell and Tissue Biology, University of California San Francisco, San Francisco, California, United States of America
- Biomedical Sciences graduate program, University of California San Francisco, San Francisco, California, United States of America
| | - Sigurd Braun
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität of Munich, Planegg-Martinsried, Germany
- Institute for Genetics, Justus-Liebig University Giessen, Giessen, Germany
| | - Bassem Al-Sady
- Department of Microbiology &Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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11
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The transcription factor Atf1 lowers the transition barrier for nucleosome-mediated establishment of heterochromatin. Cell Rep 2022; 39:110828. [PMID: 35584672 DOI: 10.1016/j.celrep.2022.110828] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Revised: 03/09/2022] [Accepted: 04/26/2022] [Indexed: 11/22/2022] Open
Abstract
Transcription factors can exert opposite effects depending on the chromosomal context. The fission yeast transcription factor Atf1 both activates numerous genes in response to stresses and mediates heterochromatic gene silencing in the mating-type region. Investigating this context dependency, we report here that the establishment of silent heterochromatin in the mating-type region occurs at a reduced rate in the absence of Atf1 binding. Quantitative modeling accounts for the observed establishment profiles by a combinatorial recruitment of histone-modifying enzymes: locally by Atf1 at two binding sites and over the whole region by dynamically appearing heterochromatic nucleosomes, a source of which is the RNAi-dependent cenH element. In the absence of Atf1 binding, the synergy is lost, resulting in a slow rate of heterochromatin formation. The system shows how DNA-binding proteins can influence local nucleosome states and thereby potentiate long-range positive feedback on histone-modification reactions to enable heterochromatin formation over large regions in a context-dependent manner.
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12
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Brown S, Mitarai N, Sneppen K. Protection of bacteriophage-sensitive Escherichia coli by lysogens. Proc Natl Acad Sci U S A 2022; 119:e2106005119. [PMID: 35344423 PMCID: PMC9168506 DOI: 10.1073/pnas.2106005119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 02/16/2022] [Indexed: 11/18/2022] Open
Abstract
SignificanceSome viruses that infect bacteria, temperate bacteriophages, can confer immunity to infection by the same virus. Here we report λ-immune bacteria could protect λ-sensitive bacteria from killing by phage λ in mixed culture. The protection depended on the extent to which the immune bacteria were able to adsorb the phage. Reconciling modeling with experiment led to identifying a decline in protection as bacteria stopped growing. Adsorption of λ was compromised by inhibition of bacterial energy metabolism, explaining the loss of protection as bacterial growth ceased.
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Affiliation(s)
- Stanley Brown
- Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Namiko Mitarai
- Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Kim Sneppen
- Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
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13
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Wang X, Paulo JA, Li X, Zhou H, Yu J, Gygi SP, Moazed D. A composite DNA element that functions as a maintainer required for epigenetic inheritance of heterochromatin. Mol Cell 2021; 81:3979-3991.e4. [PMID: 34375584 DOI: 10.1016/j.molcel.2021.07.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 04/27/2021] [Accepted: 07/14/2021] [Indexed: 11/16/2022]
Abstract
Epigenetic inheritance of heterochromatin requires DNA-sequence-independent propagation mechanisms, coupling to RNAi, or input from DNA sequence, but how DNA contributes to inheritance is not understood. Here, we identify a DNA element (termed "maintainer") that is sufficient for epigenetic inheritance of pre-existing histone H3 lysine 9 methylation (H3K9me) and heterochromatin in Schizosaccharomyces pombe but cannot establish de novo gene silencing in wild-type cells. This maintainer is a composite DNA element with binding sites for the Atf1/Pcr1 and Deb1 transcription factors and the origin recognition complex (ORC), located within a 130-bp region, and can be converted to a silencer in cells with lower rates of H3K9me turnover, suggesting that it participates in recruiting the H3K9 methyltransferase Clr4/Suv39h. These results suggest that, in the absence of RNAi, histone H3K9me is only heritable when it can collaborate with maintainer-associated DNA-binding proteins that help recruit the enzyme responsible for its epigenetic deposition.
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Affiliation(s)
- Xiaoyi Wang
- Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Joao A Paulo
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Xue Li
- Bioinformatics and Integrative Biology Program, University of Massachusetts Medical School, Worcester, MA, USA
| | - Haining Zhou
- Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Juntao Yu
- Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Steven P Gygi
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Danesh Moazed
- Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, MA, USA.
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14
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Abstract
Methylation of histone H3K9 is a hallmark of epigenetic silencing in eukaryotes. Nucleosome modifications often rely on positive feedback where enzymes are recruited by modified nucleosomes. A combination of local and global feedbacks has been proposed to account for some dynamic properties of heterochromatin, but the range at which the global feedbacks operate and the exact mode of heterochromatin propagation are not known. We investigated these questions in fission yeast. Guided by mathematical modeling, we incrementally increased the size of the mating-type region and profiled heterochromatin establishment over time. We observed exponential decays in the proportion of cells with active reporters, with rates that decreased with domain size. Establishment periods varied from a few generations in wild type to >200 generations in the longest region examined, and highly correlated silencing of two reporters located outside the nucleation center was observed. On a chromatin level, this indicates that individual regions are silenced in sudden bursts. Mathematical modeling accounts for these bursts if heterochromatic nucleosomes facilitate a deacetylation or methylation reaction at long range, in a distance-independent manner. A likely effector of three-dimensional interactions is the evolutionarily conserved Swi6HP1 H3K9me reader, indicating the bursting behavior might be a general mode of heterochromatin propagation.
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15
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Weigt M, Gao Q, Ban H, He H, Mastrobuoni G, Kempa S, Chen W, Li F. Rbm10 facilitates heterochromatin assembly via the Clr6 HDAC complex. Epigenetics Chromatin 2021; 14:8. [PMID: 33468217 PMCID: PMC7816512 DOI: 10.1186/s13072-021-00382-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2020] [Accepted: 01/08/2021] [Indexed: 01/13/2023] Open
Abstract
Splicing factors have recently been shown to be involved in heterochromatin formation, but their role in controlling heterochromatin structure and function remains poorly understood. In this study, we identified a fission yeast homologue of human splicing factor RBM10, which has been linked to TARP syndrome. Overexpression of Rbm10 in fission yeast leads to strong global intron retention. Rbm10 also interacts with splicing factors in a pattern resembling that of human RBM10, suggesting that the function of Rbm10 as a splicing regulator is conserved. Surprisingly, our deep-sequencing data showed that deletion of Rbm10 caused only minor effect on genome-wide gene expression and splicing. However, the mutant displays severe heterochromatin defects. Further analyses indicated that the heterochromatin defects in the mutant did not result from mis-splicing of heterochromatin factors. Our proteomic data revealed that Rbm10 associates with the histone deacetylase Clr6 complex and chromatin remodelers known to be important for heterochromatin silencing. Deletion of Rbm10 results in significant reduction of Clr6 in heterochromatin. Our work together with previous findings further suggests that different splicing subunits may play distinct roles in heterochromatin regulation.
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Affiliation(s)
- Martina Weigt
- Laboratory for Functional Genomics and Systems Biology, Berlin Institute for Medical Systems Biology, Max-Delbrück-Center for Molecular Medicine, 13125, Berlin, Germany
| | - Qingsong Gao
- Laboratory for Functional Genomics and Systems Biology, Berlin Institute for Medical Systems Biology, Max-Delbrück-Center for Molecular Medicine, 13125, Berlin, Germany
| | - Hyoju Ban
- Department of Biology, New York University, New York, NY, 10003-6688, USA
| | - Haijin He
- Department of Biology, New York University, New York, NY, 10003-6688, USA
| | - Guido Mastrobuoni
- Integrative Metabolomics and Proteomics, Berlin Institute of Medical Systems Biology, Max-Delbrueck Center for Molecular Medicine, 13125, Berlin, Germany
| | - Stefan Kempa
- Integrative Metabolomics and Proteomics, Berlin Institute of Medical Systems Biology, Max-Delbrueck Center for Molecular Medicine, 13125, Berlin, Germany
| | - Wei Chen
- Laboratory for Functional Genomics and Systems Biology, Berlin Institute for Medical Systems Biology, Max-Delbrück-Center for Molecular Medicine, 13125, Berlin, Germany. .,Department of Biology, Southern University of Science and Technology, Shenzhen, Guangdong, China. .,Medi-X Institute, SUSTech Academy for Advanced Interdisciplinary Studies, Southern University of Science and Technology, Shenzhen, Guangdong, China.
| | - Fei Li
- Department of Biology, New York University, New York, NY, 10003-6688, USA.
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16
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Abstract
The fission yeast silent mating-type region provides an excellent system to ask how chromatic domains with opposite effects on gene expression coexist side by side along chromosomes and to investigate roles played by DNA elements and architectural proteins in the phenomenon. By showing that the IR-L and IR-R chromatin boundaries favor heterochromatin formation in the domain that separates them, dependent on each other and on binding sites for the architectural factor TFIIIC, our work brings to light an important function of these elements and supports the notion that similar types of interactions between boundaries might in other organisms as well stimulate heterochromatin formation in intervening chromosomal loops to actively shape gene expression landscapes. In fission yeast, the inverted repeats IR-L and IR-R function as boundary elements at the edges of a 20-kb silent heterochromatic domain where nucleosomes are methylated at histone H3K9. Each repeat contains a series of B-box motifs physically associated with the architectural TFIIIC complex and with other factors including the replication regulator Sap1 and the Rix1 complex (RIXC). We demonstrate here the activity of these repeats in heterochromatin formation and maintenance. Deletion of the entire IR-R repeat or, to a lesser degree, deletion of just the B boxes impaired the de novo establishment of the heterochromatic domain. Nucleation proceeded normally at the RNA interference (RNAi)-dependent element cenH but subsequent propagation to the rest of the region occurred at reduced rates in the mutants. Once established, heterochromatin was unstable in the mutants. These defects resulted in bistable populations of cells occupying alternate “on” and “off” epigenetic states. Deleting IR-L in combination with IR-R synergistically tipped the balance toward the derepressed state, revealing a concerted action of the two boundaries at a distance. The nuclear rim protein Amo1 has been proposed to tether the mating-type region and its boundaries to the nuclear envelope, where Amo1 mutants displayed milder phenotypes than boundary mutants. Thus, the boundaries might facilitate heterochromatin propagation and maintenance in ways other than just through Amo1, perhaps by constraining a looped domain through pairing.
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17
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Folco HD, McCue A, Balachandran V, Grewal SIS. Cohesin Impedes Heterochromatin Assembly in Fission Yeast Cells Lacking Pds5. Genetics 2019; 213:127-141. [PMID: 31278118 PMCID: PMC6727797 DOI: 10.1534/genetics.119.302256] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Accepted: 06/24/2019] [Indexed: 01/05/2023] Open
Abstract
The fission yeast Schizosaccharomyces pombe is a powerful genetic model system for uncovering fundamental principles of heterochromatin assembly and epigenetic inheritance of chromatin states. Heterochromatin defined by histone H3 lysine 9 methylation and HP1 proteins coats large chromosomal domains at centromeres, telomeres, and the mating-type (mat) locus. Although genetic and biochemical studies have provided valuable insights into heterochromatin assembly, many key mechanistic details remain unclear. Here, we use a sensitized reporter system at the mat locus to screen for factors affecting heterochromatic silencing. In addition to known components of heterochromatin assembly pathways, our screen identified eight new factors including the cohesin-associated protein Pds5. We find that Pds5 enriched throughout heterochromatin domains is required for proper maintenance of heterochromatin. This function of Pds5 requires its associated Eso1 acetyltransferase, which is implicated in the acetylation of cohesin. Indeed, introducing an acetylation-mimicking mutation in a cohesin subunit suppresses defects in heterochromatin assembly in pds5∆ and eso1∆ cells. Our results show that in cells lacking Pds5, cohesin interferes with heterochromatin assembly. Supporting this, eliminating cohesin from the mat locus in the pds5∆ mutant restores both heterochromatin assembly and gene silencing. These analyses highlight an unexpected requirement for Pds5 in ensuring proper coordination between cohesin and heterochromatin factors to effectively maintain gene silencing.
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Affiliation(s)
- H Diego Folco
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
| | - Andrea McCue
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
| | - Vanivilasini Balachandran
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
| | - Shiv I S Grewal
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
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18
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Greenstein RA, Jones SK, Spivey EC, Rybarski JR, Finkelstein IJ, Al-Sady B. Noncoding RNA-nucleated heterochromatin spreading is intrinsically labile and requires accessory elements for epigenetic stability. eLife 2018; 7:32948. [PMID: 30020075 PMCID: PMC6070336 DOI: 10.7554/elife.32948] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Accepted: 07/17/2018] [Indexed: 12/22/2022] Open
Abstract
The heterochromatin spreading reaction is a central contributor to the formation of gene-repressive structures, which are re-established with high positional precision, or fidelity, following replication. How the spreading reaction contributes to this fidelity is not clear. To resolve the origins of stable inheritance of repression, we probed the intrinsic character of spreading events in fission yeast using a system that quantitatively describes the spreading reaction in live single cells. We show that spreading triggered by noncoding RNA-nucleated elements is stochastic, multimodal, and fluctuates dynamically across time. This lack of stability correlates with high histone turnover. At the mating type locus, this unstable behavior is restrained by an accessory cis-acting element REIII, which represses histone turnover. Further, REIII safeguards epigenetic memory against environmental perturbations. Our results suggest that the most prevalent type of spreading, driven by noncoding RNA-nucleators, is epigenetically unstable and requires collaboration with accessory elements to achieve high fidelity.
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Affiliation(s)
- R A Greenstein
- Department of Microbiology & Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, United States.,TETRAD graduate program, University of California San Francisco, San Francisco, United States
| | - Stephen K Jones
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States
| | - Eric C Spivey
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States
| | - James R Rybarski
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States
| | - Ilya J Finkelstein
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, United States.,Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, United States
| | - Bassem Al-Sady
- Department of Microbiology & Immunology, George Williams Hooper Foundation, University of California San Francisco, San Francisco, United States
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19
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Jahn LJ, Mason B, Brøgger P, Toteva T, Nielsen DK, Thon G. Dependency of Heterochromatin Domains on Replication Factors. G3 (BETHESDA, MD.) 2018; 8:477-489. [PMID: 29187422 PMCID: PMC5919735 DOI: 10.1534/g3.117.300341] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/07/2017] [Accepted: 11/20/2017] [Indexed: 01/26/2023]
Abstract
Chromatin structure regulates both genome expression and dynamics in eukaryotes, where large heterochromatic regions are epigenetically silenced through the methylation of histone H3K9, histone deacetylation, and the assembly of repressive complexes. Previous genetic screens with the fission yeast Schizosaccharomyces pombe have led to the identification of key enzymatic activities and structural constituents of heterochromatin. We report here on additional factors discovered by screening a library of deletion mutants for silencing defects at the edge of a heterochromatic domain bound by its natural boundary-the IR-R+ element-or by ectopic boundaries. We found that several components of the DNA replication progression complex (RPC), including Mrc1/Claspin, Mcl1/Ctf4, Swi1/Timeless, Swi3/Tipin, and the FACT subunit Pob3, are essential for robust heterochromatic silencing, as are the ubiquitin ligase components Pof3 and Def1, which have been implicated in the removal of stalled DNA and RNA polymerases from chromatin. Moreover, the search identified the cohesin release factor Wpl1 and the forkhead protein Fkh2, both likely to function through genome organization, the Ssz1 chaperone, the Fkbp39 proline cis-trans isomerase, which acts on histone H3P30 and P38 in Saccharomyces cerevisiae, and the chromatin remodeler Fft3. In addition to their effects in the mating-type region, to varying extents, these factors take part in heterochromatic silencing in pericentromeric regions and telomeres, revealing for many a general effect in heterochromatin. This list of factors provides precious new clues with which to study the spatiotemporal organization and dynamics of heterochromatic regions in connection with DNA replication.
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Affiliation(s)
| | - Bethany Mason
- Department of Biology, University of Copenhagen, BioCenter, 2200, Denmark
| | - Peter Brøgger
- Department of Biology, University of Copenhagen, BioCenter, 2200, Denmark
| | - Tea Toteva
- Department of Biology, University of Copenhagen, BioCenter, 2200, Denmark
| | - Dennis Kim Nielsen
- Department of Biology, University of Copenhagen, BioCenter, 2200, Denmark
| | - Genevieve Thon
- Department of Biology, University of Copenhagen, BioCenter, 2200, Denmark
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20
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Cam HP, Whitehall S. Analysis of Heterochromatin in Schizosaccharomyces pombe. Cold Spring Harb Protoc 2016; 2016:2016/11/pdb.top079889. [PMID: 27803258 DOI: 10.1101/pdb.top079889] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
This introduction briefly describes the biology of heterochromatin in the fission yeast Schizosaccharomyces pombe We highlight some of the salient features of fission yeast that render it an excellent unicellular eukaryote for studying heterochromatin. We then discuss key aspects of heterochromatin that are of interest to those in the field, and last we introduce experimental approaches often used to investigate heterochromatin.
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Affiliation(s)
- Hugh P Cam
- Biology Department, Boston College, Chestnut Hill, Massachusetts 02467
| | - Simon Whitehall
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle NE2 4HH, United Kingdom
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21
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Stress sensitivity of a fission yeast strain lacking histidine kinases is rescued by the ectopic expression of Chk1 from Candida albicans. Curr Genet 2016; 63:343-357. [PMID: 27613427 PMCID: PMC5383687 DOI: 10.1007/s00294-016-0644-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Revised: 08/23/2016] [Accepted: 08/25/2016] [Indexed: 01/07/2023]
Abstract
The development of new drugs against the pathogenic yeast Candida albicans is compelling and the evolution of relevant bioassays is important to achieve this goal. Promising drug targets are proteins that lack human counterparts which are true for the His-to-Asp phosphorelay signal transduction systems, important for stress sensing in bacteria, fungi, and plants. In the pathogenic yeast, Candida albicans, the CaChk1 histidine kinase is a trigger of the pathway that leads to a switch from yeast to hyphal growth necessary for invasion. Intriguingly, the model yeast Schizosaccharomyces pombe has a similar phosphorelay system, with three histidine kinases named Mak1, Mak2, and Mak3, which are important for the prevention of aberrant mating and sporulation on rich media. This study uncovered distinct functions for the three histidine kinases; Mak1 alone or Mak2 and Mak3 together were sufficient for the repression of the meiotic cycle when nutrients were available. Moreover, strains lacking histidine kinase genes were sensitive to various types of stress conditions in an auxotrophic strain background, while the stress sensitivity was lost in prototrophic strains. Finally, the stress sensitivity of a S. pombe strain that lacks endogenous histidine kinases could be complemented by the ectopic expression of the CaChk1 histidine kinase from C. albicans. This finding opens up for the possibility to perform a drug screen with a biological read-out in S. pombe to find inhibitors of CaChk1.
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22
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Mitarai N, Brown S, Sneppen K. Population Dynamics of Phage and Bacteria in Spatially Structured Habitats Using Phage λ and Escherichia coli. J Bacteriol 2016; 198:1783-93. [PMID: 27068593 PMCID: PMC4886755 DOI: 10.1128/jb.00965-15] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2015] [Accepted: 04/05/2016] [Indexed: 01/21/2023] Open
Abstract
UNLABELLED Bacteria living in physically structured habitats are exposed heterogeneously to both resources and different types of phages. While there have been numerous experimental approaches to examine spatially distributed bacteria exposed to phages, there is little theory to guide the design of these experiments, interpret their results, or expand the inferences drawn to a broader ecological and evolutionary context. Plaque formation provides a window into understanding phage-bacterium interactions in physically structured populations, including surfaces, semisolids, and biofilms. We develop models to address the plaque dynamics for a temperate phage and its virulent mutants. The models are compared with phage λ-Escherichia coli system to quantify their applicability. We found that temperate phages gave an increasing number of gradually smaller colonies as the distance increased from the plaque center. For low-lysogen frequency this resulted in plaques with most of the visible colonies at an intermediate distance between the center and periphery. Using spot inoculation, where phages in excess of bacteria were inoculated in a circular area, we measured the frequency and spatial distribution of lysogens. The spot morphology of cII-negative (cII(-)) and cIII(-) mutants of phage λ displays concentric rings of high-density lysogenic colonies. The simplest of these ring morphologies was reproduced by including multiplicity of infection (MOI) sensitivity in lysis-lysogeny decisions, but its failure to explain the occasional observation of multiple rings in cIII(-) mutant phages highlights unknown features of this phage. Our findings demonstrated advantages of temperate phages over virulent phages in exploiting limited resources in spatially distributed microbial populations. IMPORTANCE Phages are the most abundant organisms on earth, and yet little is known about how phages and bacterial hosts are influencing each other in density and evolution. Phages can be either virulent or temperate, a difference that is highlighted when a spatially structured bacterial population is infected. Phage λ is a temperate phage, with a capacity for dormancy that can be modified by single gene knockouts. The stochastic bias in the lysis-lysogeny decision's probability is reflected in plaque morphologies on bacterial lawns. We present a model for plaque morphology of both virulent and temperate phages, taking into account the underlying survival of bacterial microcolonies. It reproduces known plaque morphologies and speaks to advantages of temperate phages in a spatially structured environment.
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Affiliation(s)
- Namiko Mitarai
- Center for Models of Life, Niels Bohr Institute, University of Copenhagen, Copenhagen, DenmarkPrinceton University
| | - Stanley Brown
- Center for Models of Life, Niels Bohr Institute, University of Copenhagen, Copenhagen, DenmarkPrinceton University
| | - Kim Sneppen
- Center for Models of Life, Niels Bohr Institute, University of Copenhagen, Copenhagen, DenmarkPrinceton University
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23
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Brown S, Majikes J, Martínez A, Girón TM, Fennell H, Samano EC, LaBean TH. An easy-to-prepare mini-scaffold for DNA origami. NANOSCALE 2015; 7:16621-4. [PMID: 26413973 DOI: 10.1039/c5nr04921k] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The DNA origami strategy for assembling designed supramolecular complexes requires ssDNA as a scaffold strand. A system is described that was designed approximately one third the length of the M13 bacteriophage genome for ease of ssDNA production. Folding of the 2404-base ssDNA scaffold into a variety of origami shapes with high assembly yields is demonstrated.
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Affiliation(s)
- S Brown
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen 2100, Denmark.
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24
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Abstract
Structural DNA nanotechnology, and specifically scaffolded DNA origami, is rapidly developing as a versatile method for bottom-up fabrication of novel nanometer-scale materials and devices. However, lengths of conventional single-stranded scaffolds, for example, 7,249-nucleotide circular genomic DNA from the M13mp18 phage, limit the scales of these uniquely addressable structures. Additionally, increasing DNA origami size generates the cost burden of increased staple-strand synthesis. We addressed this 2-fold problem by developing the following methods: (1) production of the largest to-date biologically derived single-stranded scaffold using a λ/M13 hybrid virus to produce a 51 466-nucleotide DNA in a circular, single-stranded form and (2) inexpensive DNA synthesis via an inkjet-printing process on a chip embossed with functionalized micropillars made from cyclic olefin copolymer. We have experimentally demonstrated very efficient assembly of a 51-kilobasepair origami from the λ/M13 hybrid scaffold folded by chip-derived staple strands. In addition, we have demonstrated two-dimensional, asymmetric origami sheets with controlled global curvature such that they land on a substrate in predictable orientations that have been verified by atomic force microscopy.
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Affiliation(s)
- Alexandria N Marchi
- Biomedical Engineering Department, Duke University , Durham, North Carolina 27708, United States
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25
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Steinhauf D, Rodriguez A, Vlachakis D, Virgo G, Maksimov V, Kristell C, Olsson I, Linder T, Kossida S, Bongcam-Rudloff E, Bjerling P. Silencing motifs in the Clr2 protein from fission yeast, Schizosaccharomyces pombe. PLoS One 2014; 9:e86948. [PMID: 24475199 PMCID: PMC3903592 DOI: 10.1371/journal.pone.0086948] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Accepted: 12/16/2013] [Indexed: 01/01/2023] Open
Abstract
The fission yeast, Schizosaccharomyces pombe, is a well-established model for heterochromatin formation, but the exact sequence of events for initiation remains to be elucidated. The essential factors involved include RNA transcribed from repeated sequences together with the methyltransferase Clr4. In addition, histone deacetylases, like Clr3, found in the SHREC complex are also necessary for transcriptional silencing. Clr2 is another crucial factor required for heterochromatin formation found in the SHREC complex. The function of Clr2 has been difficult to establish due to the lack of conserved domains or homology to proteins of known molecular function. Using a bioinformatics approach, three conserved motifs in Clr2 were identified, which contained amino acids important for transcriptional repression. Analysis of clr2 mutant strains revealed a major role for Clr2 in mating-type and rDNA silencing, and weaker effects on centromeric silencing. The effect on mating-type silencing showed variegation in several of the strains with mutated versions of Clr2 indicating an establishment or maintenance defect. Moreover, the critical amino acids in Clr2 were also necessary for transcriptional repression in a minimal system, by the tethering of Clr4 upstream of a reporter gene, inserted into the euchromatic part of the genome. Finally, in silico modeling suggested that the mutations in Clr2 cause disruption of secondary structures in the Clr2 protein. Identification of these critical amino acids in the protein provides a useful tool to explore the molecular mechanism behind the role of Clr2 in heterochromatin formation.
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Affiliation(s)
- Daniel Steinhauf
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
| | - Alejandro Rodriguez
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
| | - Dimitrios Vlachakis
- Bioinformatics and Medical Informatics Laboratory, Biomedical Research Foundation of the Academy of Athens, Athens, Greece
| | - Gordon Virgo
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
| | - Vladimir Maksimov
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
| | - Carolina Kristell
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
| | - Ida Olsson
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
| | - Tomas Linder
- Department of Microbiology, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Sophia Kossida
- Bioinformatics and Medical Informatics Laboratory, Biomedical Research Foundation of the Academy of Athens, Athens, Greece
| | - Erik Bongcam-Rudloff
- Department of Animal Breeding and Genetics, SLU Global Bioinformatics Centre, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Pernilla Bjerling
- Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, University of Uppsala, Uppsala, Sweden
- * E-mail:
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Subnuclear relocalization and silencing of a chromosomal region by an ectopic ribosomal DNA repeat. Proc Natl Acad Sci U S A 2013; 110:E4465-73. [PMID: 24191010 DOI: 10.1073/pnas.1315581110] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Our research addresses the relationship between subnuclear localization and gene expression in fission yeast. We observed the relocalization of a heterochromatic region, the mating-type region, from its natural location at the spindle-pole body to the immediate vicinity of the nucleolus. Relocalization occurred in response to a DNA rearrangement replacing a boundary element (IR-R) with a ribosomal DNA repeat (rDNA-R). Gene expression was strongly silenced in the relocalized mating-type region through mechanisms that differ from those operating in wild type. Also different from the wild-type situation, programmed recombination events failed to take place in the rDNA-R mutant. Increased silencing and perinucleolar localization depended on Reb1, a DNA-binding protein with cognate sites in the rDNA. Reb1 was recently shown to mediate long-range interchromosomal interactions in the nucleus through dimerization, providing a mechanism for the observed relocalization. Replacing the full rDNA repeat with Reb1-binding sites, and using mutants lacking the histone H3K9 methyltransferase Clr4, indicated that the relocalized region was silenced redundantly by heterochromatin and another mechanism, plausibly antisense transcription, achieving a high degree of repression in the rDNA-R strain.
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Jakočiūnas T, Holm LR, Verhein-Hansen J, Trusina A, Thon G. Two portable recombination enhancers direct donor choice in fission yeast heterochromatin. PLoS Genet 2013; 9:e1003762. [PMID: 24204285 PMCID: PMC3812072 DOI: 10.1371/journal.pgen.1003762] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Accepted: 07/18/2013] [Indexed: 01/06/2023] Open
Abstract
Mating-type switching in fission yeast results from gene conversions of the active mat1 locus by heterochromatic donors. mat1 is preferentially converted by mat2-P in M cells and by mat3-M in P cells. Here, we report that donor choice is governed by two portable recombination enhancers capable of promoting use of their adjacent cassette even when they are transposed to an ectopic location within the mat2-mat3 heterochromatic domain. Cells whose silent cassettes are swapped to mat2-M mat3-P switch mating-type poorly due to a defect in directionality but cells whose recombination enhancers were transposed together with the cassette contents switched like wild type. Trans-acting mutations that impair directionality affected the wild-type and swapped cassettes in identical ways when the recombination enhancers were transposed together with their cognate cassette, showing essential regulatory steps occur through the recombination enhancers. Our observations lead to a model where heterochromatin biases competitions between the two recombination enhancers to achieve directionality. The state of chromatin, heterochromatin or euchromatin, affects homologous recombination in eukaryotes. We study mating-type switching in fission yeast to learn how recombination is regulated in heterochromatin. Fission yeast exists as two mating-types, P or M, determined by the allele present at the expressed mat1 locus. Genetic information for the P and M mating-types is stored in two silent heterochromatic cassettes, mat2-P and mat3-M. Cells can switch mating-type by a replication-coupled recombination event where one of the silent cassettes is used as donor to convert mat1. Mating-type switching occurs in a directional manner where mat2-P is a preferred donor in M cells and mat3-M is preferred in P cells. In this study, we investigated factors responsible for these directed recombination events. We found that two portable recombination enhancers within the heterochromatic region compete with each other and direct recombination in a cell-type specific manner. We also found that heterochromatin plays an important role in directionality by biasing competitions between the two enhancers. Our findings suggest a new model for directed recombination in a heterochromatic domain and open the field for further studies of recombination regulation in other chromatin contexts.
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Affiliation(s)
- Tadas Jakočiūnas
- Department of Biology, University of Copenhagen, BioCenter, Copenhagen, Denmark
| | - Lærke Rebekka Holm
- Department of Biology, University of Copenhagen, BioCenter, Copenhagen, Denmark
| | | | - Ala Trusina
- Department of Biology, University of Copenhagen, BioCenter, Copenhagen, Denmark
| | - Geneviève Thon
- Department of Biology, University of Copenhagen, BioCenter, Copenhagen, Denmark
- * E-mail:
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Creamer KM, Partridge JF. RITS-connecting transcription, RNA interference, and heterochromatin assembly in fission yeast. WILEY INTERDISCIPLINARY REVIEWS-RNA 2011; 2:632-46. [PMID: 21823226 DOI: 10.1002/wrna.80] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In recent years, a bevy of evidence has been unearthed indicating that 'silent' heterochromatin is not as transcriptionally inert as once thought. In the unicellular yeast Schizosaccharomyces pombe, the processing of transcripts derived from centromeric repeats into homologous short interfering RNA (siRNA) is essential for the formation of centromeric heterochromatin. Deletion of genes required for siRNA biogenesis showed that core components of the canonical RNA interference (RNAi) pathway are essential for centromeric heterochromatin assembly as well as for centromere function. Subsequent purification of the RNA-induced initiation of transcriptional gene silencing (RITS) complex provided the critical link between siRNAs and heterochromatin assembly, with RITS acting as a physical bridge between noncoding RNA scaffolds and chromatin. Here, we review current understanding of how RITS promotes heterochromatin formation and how it participates in transcription-coupled silencing. WIREs RNA 2011 2 632-646 DOI: 10.1002/wrna.80 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Kevin M Creamer
- Integrated Program in Biomedical Sciences, University of Tennessee Health Science Center, Memphis, USA
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Hansen KR, Hazan I, Shanker S, Watt S, Verhein-Hansen J, Bähler J, Martienssen RA, Partridge JF, Cohen A, Thon G. H3K9me-independent gene silencing in fission yeast heterochromatin by Clr5 and histone deacetylases. PLoS Genet 2011; 7:e1001268. [PMID: 21253571 PMCID: PMC3017117 DOI: 10.1371/journal.pgen.1001268] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Accepted: 12/03/2010] [Indexed: 01/01/2023] Open
Abstract
Nucleosomes in heterochromatic regions bear histone modifications that distinguish them from euchromatic nucleosomes. Among those, histone H3 lysine 9 methylation (H3K9me) and hypoacetylation have been evolutionarily conserved and are found in both multicellular eukaryotes and single-cell model organisms such as fission yeast. In spite of numerous studies, the relative contributions of the various heterochromatic histone marks to the properties of heterochromatin remain largely undefined. Here, we report that silencing of the fission yeast mating-type cassettes, which are located in a well-characterized heterochromatic region, is hardly affected in cells lacking the H3K9 methyltransferase Clr4. We document the existence of a pathway parallel to H3K9me ensuring gene repression in the absence of Clr4 and identify a silencing factor central to this pathway, Clr5. We find that Clr5 controls gene expression at multiple chromosomal locations in addition to affecting the mating-type region. The histone deacetylase Clr6 acts in the same pathway as Clr5, at least for its effects in the mating-type region, and on a subset of other targets, notably a region recently found to be prone to neo-centromere formation. The genomic targets of Clr5 also include Ste11, a master regulator of sexual differentiation. Hence Clr5, like the multi-functional Atf1 transcription factor which also modulates chromatin structure in the mating-type region, controls sexual differentiation and genome integrity at several levels. Globally, our results point to histone deacetylases as prominent repressors of gene expression in fission yeast heterochromatin. These deacetylases can act in concert with, or independently of, the widely studied H3K9me mark to influence gene silencing at heterochromatic loci.
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Affiliation(s)
- Klavs R. Hansen
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
- Department of Plant Genetics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
| | - Idit Hazan
- Department of Microbiology and Molecular Genetics, Institute for Medical Research Israel – Canada (IMRIC), The Hebrew University – Hadassah Medical School, Jerusalem, Israel
| | - Sreenath Shanker
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Stephen Watt
- Department of Genetics, Evolution, and Environment, University College London, London, United Kingdom
- University College London Cancer Institute, London, United Kingdom
| | | | - Jürg Bähler
- Department of Genetics, Evolution, and Environment, University College London, London, United Kingdom
- University College London Cancer Institute, London, United Kingdom
| | - Robert A. Martienssen
- Department of Plant Genetics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
| | - Janet F. Partridge
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee, United States of America
| | - Amikam Cohen
- Department of Microbiology and Molecular Genetics, Institute for Medical Research Israel – Canada (IMRIC), The Hebrew University – Hadassah Medical School, Jerusalem, Israel
| | - Geneviève Thon
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
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30
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Brown S, Mathiasen S. Particle-dissociating peptides. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2011; 23:132-135. [PMID: 21053338 DOI: 10.1002/adma.201002130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Affiliation(s)
- Stanley Brown
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen, Denmark.
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31
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Garcia JF, Dumesic PA, Hartley PD, El-Samad H, Madhani HD. Combinatorial, site-specific requirement for heterochromatic silencing factors in the elimination of nucleosome-free regions. Genes Dev 2010; 24:1758-71. [PMID: 20675407 DOI: 10.1101/gad.1946410] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
High-resolution nucleosome occupancy maps of heterochromatic regions of wild-type and silencing-defective mutants of the fission yeast Schizosaccharomyces pombe revealed that heterochromatin induces the elimination of nucleosome-free regions (NFRs). NFRs associated with transcription initiation sites as well as those not associated with promoters are affected. We dissected the roles of the histone H3K9 methyltransferase Clr4 and the HP1 proteins Swi6 and Chp2, as well as the two catalytic activities of the SHREC histone deacetylase (HDAC)/ATPase effector complex. Strikingly, different DNA sites have distinct combinatorial requirements for these factors: Five classes of NFRs were identified that are eliminated by silencing factors through a mechanistic hierarchy governed by Clr4. The SHREC HDAC activity plays a major role in the elimination of class I-IV NFRs by antagonizing the action of RSC, a remodeling complex implicated in NFR formation. We propose that heterochromatin formation involves the deployment in several sequence-specific mechanisms to eliminate gaps between nucleosomes, thereby blocking access to the DNA.
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Affiliation(s)
- Jennifer F Garcia
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158, USA
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32
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Grewal SI. RNAi-dependent formation of heterochromatin and its diverse functions. Curr Opin Genet Dev 2010; 20:134-41. [PMID: 20207534 PMCID: PMC3005588 DOI: 10.1016/j.gde.2010.02.003] [Citation(s) in RCA: 192] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2010] [Revised: 02/02/2010] [Accepted: 02/05/2010] [Indexed: 12/23/2022]
Abstract
Expression profiling of eukaryotic genomes has revealed widespread transcription outside the confines of protein-coding genes, leading to production of antisense and non-coding RNAs (ncRNAs). Studies in Schizosaccharomyces pombe and multicellular organisms suggest that transcription and ncRNAs provide a framework for the assembly of heterochromatin, which has been linked to various chromosomal processes. In addition to gene regulation, heterochromatin is crucial for centromere function, cell fate determination as well as transcriptional and posttranscriptional silencing of repetitive DNA elements. Recently, heterochromatin factors have been shown to suppress antisense RNAs at euchromatic loci. These findings define conserved pathways that probably have major impact on the epigenetic regulation of eukaryotic genomes.
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Affiliation(s)
- Shiv Is Grewal
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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33
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Kristell C, Orzechowski Westholm J, Olsson I, Ronne H, Komorowski J, Bjerling P. Nitrogen depletion in the fission yeast Schizosaccharomyces pombe causes nucleosome loss in both promoters and coding regions of activated genes. Genome Res 2010; 20:361-71. [PMID: 20086243 DOI: 10.1101/gr.098558.109] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Gene transcription is associated with local changes in chromatin, both in nucleosome positions and in chemical modifications of the histones. Chromatin dynamics has mostly been studied on a single-gene basis. Those genome-wide studies that have been made primarily investigated steady-state transcription. However, three studies of genome-wide changes in chromatin during the transcriptional response to heat shock in the budding yeast Saccharomyces cerevisiae revealed nucleosome eviction in promoter regions but only minor effects in coding regions. Here, we describe the short-term response to nitrogen starvation in the fission yeast Schizosaccharomyces pombe. Nitrogen depletion leads to a fast induction of a large number of genes in S. pombe and is thus suitable for genome-wide studies of chromatin dynamics during gene regulation. After 20 min of nitrogen removal, 118 transcripts were up-regulated. The distribution of regulated genes throughout the genome was not random; many up-regulated genes were found in clusters, while large parts of the genome were devoid of up-regulated genes. Surprisingly, this up-regulation was associated with nucleosome eviction of equal magnitudes in the promoters and in the coding regions. The nucleosome loss was not limited to induction by nitrogen depletion but also occurred during cadmium treatment. Furthermore, the lower nucleosome density persisted for at least 60 min after induction. Two highly induced genes, urg1(+) and urg2(+), displayed a substantial nucleosome loss, with only 20% of the nucleosomes being left in the coding region. We conclude that nucleosome loss during transcriptional activation is not necessarily limited to promoter regions.
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Affiliation(s)
- Carolina Kristell
- Department of Medical Biochemistry and Microbiology (IMBIM), University of Uppsala, SE-751 23 Uppsala, Sweden
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Dubey RN, Nakwal N, Bisht KK, Saini A, Haldar S, Singh J. Interaction of APC/C-E3 ligase with Swi6/HP1 and Clr4/Suv39 in heterochromatin assembly in fission yeast. J Biol Chem 2009; 284:7165-76. [PMID: 19117951 PMCID: PMC2652303 DOI: 10.1074/jbc.m806461200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 12/22/2008] [Indexed: 11/06/2022] Open
Abstract
Heterochromatin assembly in fission yeast is initiated by binding of Swi6/HP1 to the Lys-9-dimethylated H3 followed by spreading via cooperative recruitment of Swi6/HP1. Recruitment of Cohesin by Swi6/HP1 further stabilizes the heterochromatin structure and integrity. Subsequently, polyubiquitylation of Cut2 by anaphase-promoting complex-cyclosome (APC/C)-ubiquitin-protein isopeptide ligase (E3 ligase) followed by degradation of Cut2 releases Cut1, which cleaves the Rad21 subunit of Cohesin, facilitating sister chromatid separation during mitosis. Here, we demonstrate a surprising role of APC/C in assembly of heterochromatin and silencing at mating type, centromere, and ribosomal DNA loci. Coincidentally with the loss of silencing, recruitment of Swi6, H3-Lys-9-Me2, and Clr4 at dg-dh repeats at cen1 and the K region of mat locus is abrogated in mutants cut4, cut9, and nuc2. Surprisingly, both Cut4 and Cut9 are also highly enriched at these regions in wild type and depleted in swi6Delta mutant. Cut4 and Cut9 interact directly with Swi6/HP1 and Clr4, whereas the mutant Cut4 does not, suggesting that a direct physical interaction of APC subunits Cut4 and Cut9 with Swi6 and Clr4 is instrumental in heterochromatin assembly. The silencing defect in APC mutants is causally related to ubiquitylation activity of APC-E3 ligase. Like swi6 mutant, APC mutants are also defective in Cohesin recruitment and exhibit defects like lagging chromosomes, chromosome loss, and aberrant recombination in the mat region. In addition, APC mutants exhibit a bidirectional expression of dh repeats, suggesting a role in the RNA interference pathway. Thus, APC and heterochromatin proteins Swi6 and Clr4 play a mutually cooperative role in heterochromatin assembly, thereby ensuring chromosomal integrity, inheritance, and segregation during mitosis and meiosis.
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35
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Reorganization of chromatin is an early response to nitrogen starvation in Schizosaccharomyces pombe. Chromosoma 2008; 118:99-112. [PMID: 18936951 DOI: 10.1007/s00412-008-0180-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Revised: 09/10/2008] [Accepted: 09/11/2008] [Indexed: 01/09/2023]
Abstract
There are several documented events of changes in subnuclear localization during gene activation. However, there are conflicting data on whether the nuclear periphery is a compartment for gene repression or activation and whether genes are moved to the pores at the nuclear membrane (NM) or not during gene activation. Nitrogen starvation of fission yeast serves as a good model system for studying gene induction, as it causes fast regulation of hundreds of genes. In this study, the subnuclear localization of two gene clusters repressed by nitrogen was investigated. During normal growth conditions, the gene clusters localized to the nuclear periphery at the opposite side of the nucleus as compared to the spindle pole body. This constrained localization was dependent on the histone deacetylase Clr3, known to transcriptionally repress genes in these clusters. Already 20 min after nitrogen depletion, drastic changes in subnuclear localization of the two loci were observed, away from the NM toward the nuclear interior. At least for one of the clusters, the movement was clearly transcription dependent. Data presented in this paper illustrates how interconnected events of gene activation and nuclear reorganization are as well as provides a suggestion of how nuclear organization might be maintained.
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Abstract
Stably maintaining specific states of gene expression during cell division is crucial for cellular differentiation. In fission yeast, such patterns result from directed gene rearrangements and chromosomally inherited epigenetic gene control mechanisms that control mating cell type. Recent advances have shown that a specific DNA strand at the mat1 locus is "differentiated" by a novel strand-specific imprint so that nonequivalent sister chromatids are produced. Therefore, cellular differentiation is a natural consequence of the fact that DNA strands are complementary and nonequivalent. Another epigenetic control that "silences" library copies of mat-information is due to heterochromatin organization. This is a clear case where Mendel's gene is composed of DNA plus the associated epigenetic moiety. Following up on initial genetic studies with more recent molecular investigations, this system has become one of the prominent models to understand mechanisms of gene regulation, genome integrity, and cellular differentiation. By applying lessons learned from these studies, such epigenetic gene control mechanisms, which must be installed in somatic cells, might explain mechanisms of cellular differentiation and development in higher eukaryotes.
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Affiliation(s)
- Amar J S Klar
- Gene Regulation and Chromosome Biology Laboratory, NIH, National Cancer Institute at Frederick, Frederick, MD 21702, USA.
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37
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Brown S, Jespersen TS, Nygård J. A genetic analysis of carbon-nanotube-binding proteins. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2008; 4:416-420. [PMID: 18348229 DOI: 10.1002/smll.200700940] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Affiliation(s)
- Stanley Brown
- Department of Biology and Nanoscience Center, University of Copenhagen Ole Maaløes Vej 5, 2200 Copenhagen, Denmark.
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38
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The fission yeast homologue of CENP-B, Abp1, regulates directionality of mating-type switching. EMBO J 2008; 27:1029-38. [PMID: 18354497 DOI: 10.1038/emboj.2008.53] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2007] [Accepted: 02/25/2008] [Indexed: 01/04/2023] Open
Abstract
In fission yeast, mating-type switching involves replacing genetic information contained at the expressed mat1 locus by that of either the mat2P or mat3M donor loci. Donor selection is nonrandom, as mat1P cells preferentially use mat3M for switching, whereas mat1M cells use mat2P. Switching directionality is determined by the cell-type-specific distribution of the Swi2-Swi5 complex that, in mat1P cells, localises to mat3M and, only in mat1M cells, spreads to mat2P in a heterochromatin-dependent manner. Mechanisms regulating spreading of Swi2-Swi5 across heterochromatin are not fully understood. Here, we show that the fission yeast homologue of CENP-B, Abp1, binds to the silent domain of the mating-type locus and regulates directionality of switching. Deletion of abp1 prevents utilisation of mat2P, as when heterochromatin is disrupted and spreading of Swi2-Swi5 is impaired. Our results show that, indeed, deletion of abp1 abolishes spreading of Swi2-Swi5 to mat2P. However, in abp1Delta cells, heterochromatin organisation at the mating-type locus is preserved, indicating that Abp1 is actually required for efficient spreading of Swi2-Swi5 through heterochromatin. Cbh1 and Cbh2, which are also homologous to CENP-B, have only a minor contribution to the regulation of directionality of switching, which is in contrast with the strong effects observed for Abp1.
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39
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Girard A, Hannon GJ. Conserved themes in small-RNA-mediated transposon control. Trends Cell Biol 2008; 18:136-48. [PMID: 18282709 PMCID: PMC2995447 DOI: 10.1016/j.tcb.2008.01.004] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Revised: 01/03/2008] [Accepted: 01/11/2008] [Indexed: 11/23/2022]
Abstract
Eukaryotes are engaged in a constant struggle against transposable elements, which have invaded and profoundly shaped their genomes. Over the past decade, a growing body of evidence has pointed to a role for small RNAs in transposon defense. Although the strategies used in different organisms vary in their details, they have strikingly similar general properties. Basically, all mechanisms consist of three components. First, transposon detection prompts the production of small RNAs, which are Piwi-interacting RNAs in some organisms and small interfering RNAs in others. Second, the population of small RNAs targeting active transposons is amplified through an RNA-dependent RNA polymerase-based or Slicer-based mechanism. Third, small RNAs are incorporated into Argonaute- or Piwi-containing effector complexes, which target transposon transcripts for post-transcriptional silencing and/or target transposon DNA for repressive chromatin modification and DNA methylation. These properties produce robust systems that limit the catastrophic consequences of transposon mobilization, which can result in the accumulation of deleterious mutations, changes in gene expression patterns, and conditions such as gonadal hypotrophy and sterility.
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Affiliation(s)
- Angélique Girard
- Watson School of Biological Sciences, Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA
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40
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Chp1-Tas3 interaction is required to recruit RITS to fission yeast centromeres and for maintenance of centromeric heterochromatin. Mol Cell Biol 2008; 28:2154-66. [PMID: 18212052 DOI: 10.1128/mcb.01637-07] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The maintenance of centromeric heterochromatin in fission yeast relies on the RNA interference-dependent complexes RITS (RNA-induced transcriptional silencing complex) and RDRC (RNA-directed RNA polymerase complex), which cooperate in a positive feedback loop to recruit high levels of histone H3 K9 methyltransferase activity to centromeres and to promote the assembly and maintenance of centromeric heterochromatin. However, it is unclear how these complexes are targeted to chromatin. RITS comprises Chp1, which binds K9-methylated histone H3; Ago1, which binds short interfering (siRNAs); the adaptor protein Tas3, which links Ago1 to Chp1; and centromeric siRNAs. We have generated mutants in RITS to determine the contribution of the two potential chromatin-targeting proteins Chp1 and Ago1 to the centromeric recruitment of RITS. Mutations in Tas3 that disrupt Ago1 binding are permissive for RITS recruitment and maintain centromeric heterochromatin, but the role of Tas3's interaction with Chp1 is unknown. Here, we define the Chp1 interaction domain of Tas3. A strain expressing a tas3 mutant that cannot bind Chp1 (Tas3(Delta)(10-24)) failed to maintain centromeric heterochromatin, with a loss of centromeric siRNAs, a failure to recruit RITS and RDRC to centromeres, and high levels of chromosome loss. These findings suggest a pivotal role for Chp1 and its association with Tas3 for the recruitment of RITS, RDRC, and histone H3 K9 methyltransferase activity to centromeres.
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41
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Dodd IB, Micheelsen MA, Sneppen K, Thon G. Theoretical analysis of epigenetic cell memory by nucleosome modification. Cell 2007; 129:813-22. [PMID: 17512413 DOI: 10.1016/j.cell.2007.02.053] [Citation(s) in RCA: 308] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Revised: 02/15/2007] [Accepted: 02/23/2007] [Indexed: 11/19/2022]
Abstract
Chromosomal regions can adopt stable and heritable alternative states resulting in bistable gene expression without changes to the DNA sequence. Such epigenetic control is often associated with alternative covalent modifications of histones. The stability and heritability of the states are thought to involve positive feedback where modified nucleosomes recruit enzymes that similarly modify nearby nucleosomes. We developed a simplified stochastic model for dynamic nucleosome modification based on the silent mating-type region of the yeast Schizosaccharomyces pombe. We show that the mechanism can give strong bistability that is resistant both to high noise due to random gain or loss of nucleosome modifications and to random partitioning upon DNA replication. However, robust bistability required: (1) cooperativity, the activity of more than one modified nucleosome, in the modification reactions and (2) that nucleosomes occasionally stimulate modification beyond their neighbor nucleosomes, arguing against a simple continuous spreading of nucleosome modification.
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Affiliation(s)
- Ian B Dodd
- Center for Models of Life, Niels Bohr Institute, Blegdamsvej 17, DK-2100, Copenhagen Ø, Denmark
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42
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Alfredsson-Timmins J, Henningson F, Bjerling P. The Clr4 methyltransferase determines the subnuclear localization of the mating-type region in fission yeast. J Cell Sci 2007; 120:1935-43. [PMID: 17504808 DOI: 10.1242/jcs.03457] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genome has a non-random spatial distribution in the cell nucleus. In Schizosaccharomyces pombe, it has been shown that the centromeres, telomeres and the mating-type region localize to the nuclear membrane (NM), the former by attaching to the spindle pole body (SPB). In addition, reporter genes inserted into these areas are transcriptionally repressed because of the formation of specialized chromatin structures. Performing live cell analysis we found that in a wild-type strain the mating-type region was positioned in the proximity of the SPB, the location where the pericentromeric heterochromatin is also found. In a strain lacking the histone methyltransferase Clr4, crucial for the formation of heterochromatin, the mating-type region had a random localization in the nucleus. Moreover, in a strain in which the two boundary elements IR-L and IR-R had been deleted, the mating-type region was displaced from its position at the proximity of the SPB, but remained in the vicinity of the NM. Moreover, in all investigated strains with silencing deficiencies the distance between the mating-type region and the SPB increased. This result indicates a correlation between transcriptional derepression and displacement of the region. Two different models of how the mating-type chromatin is organized in the nucleus are discussed.
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Affiliation(s)
- Jenny Alfredsson-Timmins
- University of Uppsala, Department of Medical Biochemistry and Microbiology (IMBIM), Box 582, SE-751 23 Uppsala, Sweden
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Li F, Goto DB, Zaratiegui M, Tang X, Martienssen R, Cande WZ. Two novel proteins, dos1 and dos2, interact with rik1 to regulate heterochromatic RNA interference and histone modification. Curr Biol 2006; 15:1448-57. [PMID: 16040243 DOI: 10.1016/j.cub.2005.07.021] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2005] [Revised: 06/30/2005] [Accepted: 07/01/2005] [Indexed: 11/20/2022]
Abstract
BACKGROUND Chromosomal behavior during mitosis and meiosis depends in part on heterochromatic modifications such as histone H3 lysine-9 methylation (H3K9me). In fission yeast, the Heterochromatin Protein 1 homolog Swi6 recognizes H3K9me, silences transcription, and retains cohesin at pericentromeric repeats. Heterochromatin formation also depends on processing of transcripts derived from centromeric repeats by the RNAi machinery. The DDB1 homolog, Rik1, and histone methyltransferase, Clr4, act in a complex to promote H3K9me. However, the mechanism underlying this interaction is poorly understood. RESULTS Using a cytological screen, we have identified two novel genes, dos1(+) and dos2(+), which are required for localization of Swi6. Deletion of either of these genes results in mitotic and meiotic chromosome missegregation, defects in mitotic centromeric cohesion and meiotic telomere clustering, and loss of heterochromatic silencing. Dos1 is predominantly located in the nucleus in a Dos2-dependent manner and directly interacts with Rik1. Each of these genes is required for the association of H3K9me with centromeric repeats, as well as for the production of small interfering RNAs. CONCLUSIONS Dos1 and Dos2 are required for the formation of heterochromatin in fission yeast. We hypothesize that the physical interaction between Dos1 and Rik1 represents a role in regulating activity of the Rik1/Clr4 complex. Dos2 contributes to this role by regulating Dos1 localization. Our findings suggest a mechanism for recruitment of Clr4 in the RNAi-dependent heterochromatin pathway, in which Dos1 and Dos2 are essential.
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Affiliation(s)
- Fei Li
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA
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Yamada T, Fischle W, Sugiyama T, Allis CD, Grewal SIS. The nucleation and maintenance of heterochromatin by a histone deacetylase in fission yeast. Mol Cell 2006; 20:173-85. [PMID: 16246721 DOI: 10.1016/j.molcel.2005.10.002] [Citation(s) in RCA: 240] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2005] [Revised: 09/20/2005] [Accepted: 10/04/2005] [Indexed: 01/08/2023]
Abstract
Posttranslational modifications of histones play an essential role in heterochromatin assembly. Whereas the role of Clr4/Suv39h-mediated methylation of histone H3 at lysine 9 (H3K9) in heterochromatin assembly is well studied, the exact function of histone deacetylases (HDACs) in this process is unclear. We show that Clr3, a fission yeast homolog of mammalian class II HDACs, acts in a distinct pathway parallel to RNAi-directed heterochromatin nucleation to recruit Clr4 and mediate H3K9 methylation at the silent mating-type region and centromeres. At the mat locus, Clr3 is recruited at a specific site through a mechanism involving ATF/CREB family proteins. Once recruited, Clr3 spreads across the 20 kb silenced domain that requires its own HDAC activity and heterochromatin proteins including Swi6/HP1. We also demonstrate that Clr3 contributes to heterochromatin maintenance by stabilizing H3K9 trimethylation and by preventing histone modifications associated with active transcription, and that it limits RNA polymerase II accessibility to naturally silenced repeats at heterochromatin domains.
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Affiliation(s)
- Takatomi Yamada
- Laboratory of Molecular Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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45
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Hansen KR, Ibarra PT, Thon G. Evolutionary-conserved telomere-linked helicase genes of fission yeast are repressed by silencing factors, RNAi components and the telomere-binding protein Taz1. Nucleic Acids Res 2006; 34:78-88. [PMID: 16407326 PMCID: PMC1326240 DOI: 10.1093/nar/gkj415] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
In Schizosaccharomyces pombe the RNAi machinery and proteins mediating heterochromatin formation regulate the transcription of non-coding centromeric repeats. These repeats share a high sequence similarity with telomere-linked helicase (tlh) genes, implying an ancestral relationship between the two types of elements and suggesting that transcription of the tlh genes might be regulated by the same factors as centromeric repeats. Indeed, we found that mutants lacking the histone methyltransferase Clr4, the Pcu4 cullin, Clr7 or Clr8, accumulate high levels of tlh forward and reverse transcripts. Mutations and conditions perturbing histone acetylation had similar effects further demonstrating that the tlh genes are normally repressed by heterochromatin. In contrast, mutations in the RNAi factors Dcr1, Ago1 or Rdp1 led only to a modest derepression of the tlh genes indicating an alternate pathway recruits heterochromatin components to telomeres. The telomere-binding protein Taz1 might be part of such a redundant pathway, tlh transcripts being present at low levels in Deltataz1 mutants and at higher levels in Deltataz1 Deltadcr1 double mutants. Surprisingly, the chromodomain protein Chp1, a component of the Ago1-containing RITS complex, contributes more to tlh repression than Ago1, indicating the repressive effects of Chp1 are partially independent of RITS. The tlh genes are found in the subtelomeric regions of several other fungi raising the intriguing possibility of conserved regulation and function.
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Affiliation(s)
| | | | - Geneviève Thon
- To whom correspondence should be addressed at Department of Genetics, Institute of Molecular Biology and Physiology, University of Copenhagen, Øster Farimagsgade 2A, 1353 Copenhagen K, Denmark. Tel: +45 35 32 21 08; Fax: +45 35 32 21 13;
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Thon G, Hansen KR, Altes SP, Sidhu D, Singh G, Verhein-Hansen J, Bonaduce MJ, Klar AJS. The Clr7 and Clr8 directionality factors and the Pcu4 cullin mediate heterochromatin formation in the fission yeast Schizosaccharomyces pombe. Genetics 2005; 171:1583-95. [PMID: 16157682 PMCID: PMC1456086 DOI: 10.1534/genetics.105.048298] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Fission yeast heterochromatin is formed at centromeres, telomeres, and in the mating-type region where it mediates the transcriptional silencing of the mat2-P and mat3-M donor loci and the directionality of mating-type switching. We conducted a genetic screen for directionality mutants. This screen revealed the essential role of two previously uncharacterized factors, Clr7 and Clr8, in heterochromatin formation. Clr7 and Clr8 are required for localization of the Swi6 chromodomain protein and for histone H3 lysine 9 methylation, thereby influencing not only mating-type switching but also transcriptional silencing in all previously characterized heterochromatic regions, chromosome segregation, and meiotic recombination in the mating-type region. We present evidence for physical interactions between Clr7 and the mating-type region and between Clr7 and the S. pombe cullin Pcu4, indicating that a complex containing these proteins mediates an early step in heterochromatin formation and implying a role for ubiquitination at this early stage prior to the action of the Clr4 histone methyl-transferase. Like Clr7 and Clr8, Pcu4 is required for histone H3 lysine 9 methylation, and bidirectional centromeric transcripts that are normally processed into siRNA by the RNAi machinery in wild-type cells are easily detected in cells lacking Clr7, Clr8, or Pcu4. Another physical interaction, between the nucleoporin Nup189 and Clr8, suggests that Clr8 might be involved in tethering heterochromatic regions to the nuclear envelope by association with the nuclear-pore complex.
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Affiliation(s)
- Geneviève Thon
- Department of Genetics, Institute of Molecular Biology and Physiology, University of Copenhagen, Øster Farimasgade 2A, DK-1353 Copenhagen K, Denmark.
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Martienssen RA, Zaratiegui M, Goto DB. RNA interference and heterochromatin in the fission yeast Schizosaccharomyces pombe. Trends Genet 2005; 21:450-6. [PMID: 15979194 DOI: 10.1016/j.tig.2005.06.005] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2005] [Revised: 05/17/2005] [Accepted: 06/08/2005] [Indexed: 10/25/2022]
Abstract
Fission yeast is a useful model for RNA interference because it has single-copy genes for components of the RNAi pathway such as argonaute, dicer and RNA-dependent RNA polymerase (RdRP). Functions for RNAi revealed in S. pombe, such as heterochromatic silencing and chromosome segregation, are likely to be ancient because they are shared with some other eukaryotes. The underlying mechanisms are being rapidly unraveled.
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48
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Petrie VJ, Wuitschick JD, Givens CD, Kosinski AM, Partridge JF. RNA interference (RNAi)-dependent and RNAi-independent association of the Chp1 chromodomain protein with distinct heterochromatic loci in fission yeast. Mol Cell Biol 2005; 25:2331-46. [PMID: 15743828 PMCID: PMC1061622 DOI: 10.1128/mcb.25.6.2331-2346.2005] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The establishment of centromeric heterochromatin in the fission yeast Schizosaccharomyces pombe is dependent on the RNA interference (RNAi) pathway. Dicer cleaves centromeric transcripts to produce short interfering RNAs (siRNAs) that actively recruit components of heterochromatin to centromeres. Both centromeric siRNAs and the heterochromatin component Chp1 are components of the RITS (RNA-induced initiation of transcriptional gene silencing) complex, and the association of RITS with centromeres is linked to Dicer activity. In turn, centromeric binding of RITS promotes Clr4-mediated methylation of histone H3 lysine 9 (K9), recruitment of Swi6, and formation of heterochromatin. Similar to centromeres, the mating type locus (Mat) is coated in K9-methylated histone H3 and is bound by Swi6. Here we report that Chp1 associates with the mating type locus and telomeres and that Chp1 localization to heterochromatin depends on its chromodomain and the C-terminal domain of the protein. Another protein component of the RITS complex, Tas3, also binds to Mat and telomeres. Tas3 interacts with Chp1 through the C-terminal domain of Chp1, and this interaction is necessary for Tas3 stability. Interestingly, in cells lacking the Argonaute (Ago1) protein component of the RITS complex, or lacking Dicer (and hence siRNAs), Chp1 and Tas3 can still bind to noncentromeric loci, although their association with centromeres is lost. Thus, Chp1 and Tas3 exist as an Ago1-independent subcomplex that associates with noncentromeric heterochromatin independently of the RNAi pathway.
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Affiliation(s)
- Victoria J Petrie
- Department of Biochemistry, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105, USA
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Hansen KR, Burns G, Mata J, Volpe TA, Martienssen RA, Bähler J, Thon G. Global effects on gene expression in fission yeast by silencing and RNA interference machineries. Mol Cell Biol 2005; 25:590-601. [PMID: 15632061 PMCID: PMC543407 DOI: 10.1128/mcb.25.2.590-601.2005] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Histone modifications influence gene expression in complex ways. The RNA interference (RNAi) machinery can repress transcription by recruiting histone-modifying enzymes to chromatin, although it is not clear whether this is a general mechanism for gene silencing or whether it requires repeated sequences such as long terminal repeats (LTRs). We analyzed the global effects of the Clr3 and Clr6 histone deacetylases, the Clr4 methyltransferase, the zinc finger protein Clr1, and the RNAi proteins Dicer, RdRP, and Argonaute on the transcriptome of Schizosaccharomyces pombe (fission yeast). The clr mutants derepressed similar subsets of genes, many of which also became transcriptionally activated in cells that were exposed to environmental stresses such as nitrogen starvation. Many genes that were repressed by the Clr proteins clustered in extended regions close to the telomeres. Surprisingly few genes were repressed by both the silencing and RNAi machineries, with transcripts from centromeric repeats and Tf2 retrotransposons being notable exceptions. We found no correlation between repression by RNAi and proximity to LTRs, and the wtf family of repeated sequences seems to be repressed by histone deacetylation independent of RNAi. Our data indicate that the RNAi and Clr proteins show only a limited functional overlap and that the Clr proteins play more global roles in gene silencing.
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Affiliation(s)
- Klavs R Hansen
- Department of Genetics, Institute of Molecular Biology, University of Copenhagen, Øster Farimagsgade 2A, Copenhagen 1353 K, Denmark
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Abstract
Exclusive gene expression, where only one member of a gene or gene cassette family is selected for expression, plays an important role in the establishment of cell identity in several biological systems. Here, we compare four such systems: mating-type switching in fission and budding yeast, where cells choose between expressing one of the two different mating-type cassettes, and immunoglobulin and odorant receptor gene expression in mammals, where the number of gene choices is substantially higher. The underlying mechanisms that establish this selective expression pattern in each system differ in almost every detail. In all four systems, once a successful gene activation event has taken place, a feedback mechanism affects the fate of the cell. In the mammalian systems, feedback is mediated by the expressed cell surface receptor to ensure monoallelic gene expression, whereas in the yeasts, the expressed gene cassette at the mating-type locus affects donor choice during the subsequent switching event.
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