1
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Zhao T, Fan J, Abu-Zaid A, Burley SK, Zheng XS. Nuclear mTOR Signaling Orchestrates Transcriptional Programs Underlying Cellular Growth and Metabolism. Cells 2024; 13:781. [PMID: 38727317 PMCID: PMC11083943 DOI: 10.3390/cells13090781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2024] [Revised: 04/26/2024] [Accepted: 05/01/2024] [Indexed: 05/13/2024] Open
Abstract
mTOR is a central regulator of cell growth and metabolism in response to mitogenic and nutrient signals. Notably, mTOR is not only found in the cytoplasm but also in the nucleus. This review highlights direct involvement of nuclear mTOR in regulating transcription factors, orchestrating epigenetic modifications, and facilitating chromatin remodeling. These effects intricately modulate gene expression programs associated with growth and metabolic processes. Furthermore, the review underscores the importance of nuclear mTOR in mediating the interplay between metabolism and epigenetic modifications. By integrating its functions in nutrient signaling and gene expression related to growth and metabolism, nuclear mTOR emerges as a central hub governing cellular homeostasis, malignant transformation, and cancer progression. Better understanding of nuclear mTOR signaling has the potential to lead to novel therapies against cancer and other growth-related diseases.
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Affiliation(s)
- Tinghan Zhao
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
| | - Jialin Fan
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
| | - Ahmed Abu-Zaid
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
| | - Stephen K. Burley
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
- RCSB Protein Data Bank and Institute for Quantitative Biomedicine, Rutgers, The State University of New Jersey, 174 Frelinghuysen Road, Piscataway, NJ 08854, USA
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 174 Frelinghuysen Road, Piscataway, NJ 08854, USA
| | - X.F. Steven Zheng
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
- Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
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2
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Sharp NP, Smith DR, Driscoll G, Sun K, Vickerman CM, Martin SCT. Contribution of Spontaneous Mutations to Quantitative and Molecular Variation at the Highly Repetitive rDNA Locus in Yeast. Genome Biol Evol 2023; 15:evad179. [PMID: 37847861 PMCID: PMC10581546 DOI: 10.1093/gbe/evad179] [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] [Accepted: 09/26/2023] [Indexed: 10/19/2023] Open
Abstract
The ribosomal DNA array in Saccharomyces cerevisiae consists of many tandem repeats whose copy number is believed to be functionally important but highly labile. Regulatory mechanisms have evolved to maintain copy number by directed mutation, but how spontaneous variation at this locus is generated and selected has not been well characterized. We applied a mutation accumulation approach to quantify the impacts of mutation and selection on this unique genomic feature across hundreds of mutant strains. We find that mutational variance for this trait is relatively high, and that unselected mutations elsewhere in the genome can disrupt copy number maintenance. In consequence, copy number generally declines gradually, consistent with a previously proposed model of rDNA maintenance where a downward mutational bias is normally compensated by mechanisms that increase copy number when it is low. This pattern holds across ploidy levels and strains in the standard lab environment but differs under some stressful conditions. We identify several alleles, gene categories, and genomic features that likely affect copy number, including aneuploidy for chromosome XII. Copy number change is associated with reduced growth in diploids, consistent with stabilizing selection. Levels of standing variation in copy number are well predicted by a balance between mutation and stabilizing selection, suggesting this trait is not subject to strong diversifying selection in the wild. The rate and spectrum of point mutations within the rDNA locus itself are distinct from the rest of the genome and predictive of polymorphism locations. Our findings help differentiate the roles of mutation and selection and indicate that spontaneous mutation patterns shape several aspects of ribosomal DNA evolution.
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Affiliation(s)
- Nathaniel P Sharp
- Department of Genetics, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Denise R Smith
- Department of Genetics, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Gregory Driscoll
- Department of Genetics, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Kexin Sun
- Present address: Department of Biostatistics, University of North Carolina, Chapel Hill, North Carolina, USA
| | | | - Sterling C T Martin
- Present address: Department of Biology, Washington University, St. Louis, Missouri, USA
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3
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Bâcle J, Groizard L, Kumanski S, Moriel-Carretero M. Nuclear envelope-remodeling events as models to assess the potential role of membranes on genome stability. FEBS Lett 2023; 597:1946-1956. [PMID: 37339935 DOI: 10.1002/1873-3468.14688] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 05/31/2023] [Accepted: 05/31/2023] [Indexed: 06/22/2023]
Abstract
The nuclear envelope (NE) encloses the genetic material and functions in chromatin organization and stability. In Saccharomyces cerevisiae, the NE is bound to the ribosomal DNA (rDNA), highly repeated and transcribed, thus prone to genetic instability. While tethering limits instability, it simultaneously triggers notable NE remodeling. We posit here that NE remodeling may contribute to genome integrity maintenance. The NE importance in genome expression, structure, and integrity is well recognized, yet studies mostly focus on peripheral proteins and nuclear pores, not on the membrane itself. We recently characterized a NE invagination drastically obliterating the rDNA, which we propose here as a model to probe if and how membranes play an active role in genome stability preservation.
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Affiliation(s)
- Janélie Bâcle
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Centre National de la Recherche Scientifique, Université de Montpellier, France
| | - Léa Groizard
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Centre National de la Recherche Scientifique, Université de Montpellier, France
| | - Sylvain Kumanski
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Centre National de la Recherche Scientifique, Université de Montpellier, France
| | - María Moriel-Carretero
- Centre de Recherche en Biologie cellulaire de Montpellier (CRBM), Centre National de la Recherche Scientifique, Université de Montpellier, France
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4
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Takuma T, Ushimaru T. Vacuolar fragmentation promotes fluxes of microautophagy and micronucleophagy but not of macroautophagy. Biochem Biophys Res Commun 2022; 614:161-168. [PMID: 35597153 DOI: 10.1016/j.bbrc.2022.05.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 05/07/2022] [Indexed: 11/17/2022]
Abstract
Vacuoles and lysosomes are organelles involved in the degradation of cytoplasmic proteins and organelles. Vacuolar morphology is dynamically regulated by fission and fusion in budding yeast. Vacuolar fusion is elicited in nutrient-depleted conditions and mediated by inactivation of target of rapamycin complex 1 (TORC1) protein kinase. However, it is unknown whether and how vacuolar morphology affects macroautophagy and microautophagy, which are induced by nutrient starvation and TORC1 inactivation. Here, we developed a system to control vacuolar fission in budding yeast. Vacuolar fragmentation promoted microautophagy but not macroautophagy. Vacuolar fragmentation caused multiple nucleus-vacuole junctions. Multiple vacuoles caused by vacuolar fragmentation also improved micronucleophagy (microautophagic degradation of a portion of the nucleus). However, vacuolar morphology did not impact nucleolar remodeling, condensation of the rDNA (rRNA gene) region, or separation of ribosomal DNA from nucleolar proteins, which is evoked by TORC1 inactivation. Thus, this study provides insights into the impacts of vacuolar/lysosomal morphology on macroautophagy and microautophagy.
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Affiliation(s)
- Tsuneyuki Takuma
- Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8021, Japan
| | - Takashi Ushimaru
- Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8021, Japan; Research Institute of Green Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8021, Japan.
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5
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Interphase chromosome condensation in nutrient-starved conditions requires Cdc14 and Hmo1, but not condensin, in yeast. Biochem Biophys Res Commun 2022; 611:46-52. [PMID: 35477092 DOI: 10.1016/j.bbrc.2022.04.078] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 04/17/2022] [Indexed: 12/21/2022]
Abstract
When asynchronously growing cells suffer from nutrient depletion and inactivation of target of rapamycin complex 1 (TORC1) protein kinase, the rDNA (rRNA gene) region is condensed in budding yeast Saccharomyces cerevisiae, which is executed by condensin and Cdc14 protein phosphatase. However, it is unknown whether these mitotic factors can condense the rDNA region in nutrient-starved interphase cells. Here, we show that condensin is not involved in TORC1 inactivation-induced rDNA condensation in G1 cells. Instead, the high-mobility group protein Hmo1 drove this process. The histone deacetylase Rpd3 and Cdc14, which repress rRNA transcription, were both required for the interphase rDNA condensation. Furthermore, interphase rDNA condensation necessitated CLIP and cohibin that tether rDNA to inner nuclear membranes. Finally, we showed that Hmo1, CLIP, Rpd3, and Cdc14 were required for survival in nutrient-starved G1 cells. Thus, this study disclosed novel features of interphase chromosome condensation.
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6
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Lawrimore J, Kolbin D, Stanton J, Khan M, de Larminat SC, Lawrimore C, Yeh E, Bloom K. The rDNA is biomolecular condensate formed by polymer-polymer phase separation and is sequestered in the nucleolus by transcription and R-loops. Nucleic Acids Res 2021; 49:4586-4598. [PMID: 33836082 PMCID: PMC8096216 DOI: 10.1093/nar/gkab229] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Revised: 03/16/2021] [Accepted: 03/22/2021] [Indexed: 12/28/2022] Open
Abstract
The nucleolus is the site of ribosome biosynthesis encompassing the ribosomal DNA (rDNA) locus in a phase separated state within the nucleus. In budding yeast, we find the rDNA locus and Cdc14, a protein phosphatase that co-localizes with the rDNA, behave like a condensate formed by polymer-polymer phase separation, while ribonucleoproteins behave like a condensate formed by liquid-liquid phase separation. The compaction of the rDNA and Cdc14's nucleolar distribution are dependent on the concentration of DNA cross-linkers. In contrast, ribonucleoprotein nucleolar distribution is independent of the concentration of DNA cross-linkers and resembles droplets in vivo upon replacement of the endogenous rDNA locus with high-copy plasmids. When ribosomal RNA is transcribed from the plasmids by Pol II, the rDNA-binding proteins and ribonucleoprotein signals are weakly correlated, but upon repression of transcription, ribonucleoproteins form a single, stable droplet that excludes rDNA-binding proteins from its center. Degradation of RNA-DNA hybrid structures, known as R-loops, by overexpression of RNase H1 results in the physical exclusion of the rDNA locus from the nucleolar center. Thus, the rDNA locus is a polymer-polymer phase separated condensate that relies on transcription and physical contact with RNA transcripts to remain encapsulated within the nucleolus.
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Affiliation(s)
- Josh Lawrimore
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Daniel Kolbin
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - John Stanton
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Muznah Khan
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Solenn C de Larminat
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Colleen Lawrimore
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Elaine Yeh
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Kerry Bloom
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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7
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Wang X, Zhang H, Sapio R, Yang J, Wong J, Zhang X, Guo JY, Pine S, Van Remmen H, Li H, White E, Liu C, Kiledjian M, Pestov DG, Steven Zheng XF. SOD1 regulates ribosome biogenesis in KRAS mutant non-small cell lung cancer. Nat Commun 2021; 12:2259. [PMID: 33859191 PMCID: PMC8050259 DOI: 10.1038/s41467-021-22480-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 03/16/2021] [Indexed: 12/30/2022] Open
Abstract
SOD1 is known as the major cytoplasmic superoxide dismutase and an anticancer target. However, the role of SOD1 in cancer is not fully understood. Herein we describe the generation of an inducible Sod1 knockout in KRAS-driven NSCLC mouse model. Sod1 knockout markedly reduces tumor burden in vivo and blocks growth of KRAS mutant NSCLC cells in vitro. Intriguingly, SOD1 is enriched in the nucleus and notably in the nucleolus of NSCLC cells. The nuclear and nucleolar, not cytoplasmic, form of SOD1 is essential for lung cancer cell proliferation. Moreover, SOD1 interacts with PeBoW complex and controls its assembly necessary for pre-60S ribosomal subunit maturation. Mechanistically, SOD1 regulates co-localization of PeBoW with and processing of pre-rRNA, and maturation of cytoplasmic 60S ribosomal subunits in KRAS mutant lung cancer cells. Collectively, our study unravels a nuclear SOD1 function essential for ribosome biogenesis and proliferation in KRAS-driven lung cancer.
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Affiliation(s)
- Xiaowen Wang
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
- Graduate Program in Cellular and Molecular Pharmacology, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Hong Zhang
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Russell Sapio
- Department of Cell Biology and Neuroscience, School of Osteopathic Medicine, Rowan University, Stratford, NJ, USA
| | - Jun Yang
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Justin Wong
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
| | - Xin Zhang
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Jessie Y Guo
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Medicine, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
| | - Sharon Pine
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Holly Van Remmen
- Aging and Metabolism Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Hong Li
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Center for Advanced Proteomics Research and Department of Microbiology, Biochemistry and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Eileen White
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Chen Liu
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Pathology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
| | - Megerditch Kiledjian
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Dimitri G Pestov
- Department of Cell Biology and Neuroscience, School of Osteopathic Medicine, Rowan University, Stratford, NJ, USA.
| | - X F Steven Zheng
- Rutgers Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA.
- Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, NJ, USA.
- Graduate Program in Cellular and Molecular Pharmacology, Rutgers, The State University of New Jersey, Piscataway, NJ, USA.
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8
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Mostofa MG, Morshed S, Mase S, Hosoyamada S, Kobayashi T, Ushimaru T. Cdc14 protein phosphatase and topoisomerase II mediate rDNA dynamics and nucleophagic degradation of nucleolar proteins after TORC1 inactivation. Cell Signal 2020; 79:109884. [PMID: 33321182 DOI: 10.1016/j.cellsig.2020.109884] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Revised: 12/11/2020] [Accepted: 12/11/2020] [Indexed: 10/22/2022]
Abstract
Nutrient starvation and inactivation of target of rapamycin complex 1 (TORC1) protein kinase elicits nucleophagy degrading nucleolar proteins in budding yeast. After TORC1 inactivation, nucleolar proteins are relocated to sites proximal to the nucleus-vacuole junction (NVJ), where micronucleophagy occurs, whereas ribosomal DNA (rDNA encoding rRNA) escapes from the NVJ. Condensin-mediated rDNA condensation promotes the repositioning and nucleophagic degradation of nucleolar proteins. However, the molecular mechanism of TORC1 inactivation-induced chromosome condensation is still unknown. Here, we show that Cdc14 protein phosphatase and topoisomerase II (Topo II), which are engaged in rDNA condensation in mitosis, facilitate rDNA condensation after TORC1 inactivation. rDNA condensation after rapamycin treatment was compromised in cdc14-1 and top2-4 mutants. In addition, the repositioning of rDNA and nucleolar proteins and nucleophagic degradation of nucleolar proteins were impeded in these mutants. Furthermore, Cdc14 and Topo II were required for the survival of quiescent cells in prolonged nutrient-starved conditions. This study reveals that these factors are critical for starvation responses.
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Affiliation(s)
- Md Golam Mostofa
- Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan
| | - Shamsul Morshed
- Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan
| | - Satoru Mase
- Department of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan
| | - Shun Hosoyamada
- Laboratory of Genome Regeneration, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Takehiko Kobayashi
- Laboratory of Genome Regeneration, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Takashi Ushimaru
- Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan; Department of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan.
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9
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Bo Otto F, Thumm M. Nucleophagy-Implications for Microautophagy and Health. Int J Mol Sci 2020; 21:ijms21124506. [PMID: 32599961 PMCID: PMC7352367 DOI: 10.3390/ijms21124506] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Revised: 06/18/2020] [Accepted: 06/22/2020] [Indexed: 12/12/2022] Open
Abstract
Nucleophagy, the selective subtype of autophagy that targets nuclear material for autophagic degradation, was not only shown to be a model system for the study of selective macroautophagy, but also for elucidating the role of the core autophagic machinery within microautophagy. Nucleophagy also emerged as a system associated with a variety of disease conditions including cancer, neurodegeneration and ageing. Nucleophagic processes are part of natural cell development, but also act as a response to various stress conditions. Upon releasing small portions of nuclear material, micronuclei, the autophagic machinery transfers these micronuclei to the vacuole for subsequent degradation. Despite sharing many cargos and requiring the core autophagic machinery, recent investigations revealed the aspects that set macro- and micronucleophagy apart. Central to the discrepancies found between macro- and micronucleophagy is the nucleus vacuole junction, a large membrane contact site formed between nucleus and vacuole. Exclusion of nuclear pore complexes from the junction and its exclusive degradation by micronucleophagy reveal compositional differences in cargo. Regarding their shared reliance on the core autophagic machinery, micronucleophagy does not involve normal autophagosome biogenesis observed for macronucleophagy, but instead maintains a unique role in overall microautophagy, with the autophagic machinery accumulating at the neck of budding vesicles.
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10
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Shen D, Skibbens RV. Promotion of Hyperthermic-Induced rDNA Hypercondensation in Saccharomyces cerevisiae. Genetics 2020; 214:589-604. [PMID: 31980450 PMCID: PMC7054013 DOI: 10.1534/genetics.119.302994] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Accepted: 12/29/2019] [Indexed: 12/11/2022] Open
Abstract
Ribosome biogenesis is tightly regulated through stress-sensing pathways that impact genome stability, aging and senescence. In Saccharomyces cerevisiae, ribosomal RNAs are transcribed from rDNA located on the right arm of chromosome XII. Numerous studies reveal that rDNA decondenses into a puff-like structure during interphase, and condenses into a tight loop-like structure during mitosis. Intriguingly, a novel and additional mechanism of increased mitotic rDNA compaction (termed hypercondensation) was recently discovered that occurs in response to temperature stress (hyperthermic-induced) and is rapidly reversible. Here, we report that neither changes in condensin binding or release of DNA during mitosis, nor mutation of factors that regulate cohesin binding and release, appear to play a critical role in hyperthermic-induced rDNA hypercondensation. A candidate genetic approach revealed that deletion of either HSP82 or HSC82 (Hsp90 encoding heat shock paralogs) result in significantly reduced hyperthermic-induced rDNA hypercondensation. Intriguingly, Hsp inhibitors do not impact rDNA hypercondensation. In combination, these findings suggest that Hsp90 either stabilizes client proteins, which are sensitive to very transient thermic challenges, or directly promotes rDNA hypercondensation during preanaphase. Our findings further reveal that the high mobility group protein Hmo1 is a negative regulator of mitotic rDNA condensation, distinct from its role in promoting premature condensation of rDNA during interphase upon nutrient starvation.
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Affiliation(s)
- Donglai Shen
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015
| | - Robert V Skibbens
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015
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11
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The Multiple Roles of the Cdc14 Phosphatase in Cell Cycle Control. Int J Mol Sci 2020; 21:ijms21030709. [PMID: 31973188 PMCID: PMC7038166 DOI: 10.3390/ijms21030709] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Revised: 01/17/2020] [Accepted: 01/20/2020] [Indexed: 12/20/2022] Open
Abstract
The Cdc14 phosphatase is a key regulator of mitosis in the budding yeast Saccharomyces cerevisiae. Cdc14 was initially described as playing an essential role in the control of cell cycle progression by promoting mitotic exit on the basis of its capacity to counteract the activity of the cyclin-dependent kinase Cdc28/Cdk1. A compiling body of evidence, however, has later demonstrated that this phosphatase plays other multiple roles in the regulation of mitosis at different cell cycle stages. Here, we summarize our current knowledge about the pivotal role of Cdc14 in cell cycle control, with a special focus in the most recently uncovered functions of the phosphatase.
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12
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rDNA Condensation Promotes rDNA Separation from Nucleolar Proteins Degraded for Nucleophagy after TORC1 Inactivation. Cell Rep 2019; 28:3423-3434.e2. [DOI: 10.1016/j.celrep.2019.08.059] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 06/12/2019] [Accepted: 08/20/2019] [Indexed: 12/20/2022] Open
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13
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14
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Matos-Perdomo E, Machín F. Nucleolar and Ribosomal DNA Structure under Stress: Yeast Lessons for Aging and Cancer. Cells 2019; 8:cells8080779. [PMID: 31357498 PMCID: PMC6721496 DOI: 10.3390/cells8080779] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 07/15/2019] [Accepted: 07/24/2019] [Indexed: 02/06/2023] Open
Abstract
Once thought a mere ribosome factory, the nucleolus has been viewed in recent years as an extremely sensitive gauge of diverse cellular stresses. Emerging concepts in nucleolar biology include the nucleolar stress response (NSR), whereby a series of cell insults have a special impact on the nucleolus. These insults include, among others, ultra-violet radiation (UV), nutrient deprivation, hypoxia and thermal stress. While these stresses might influence nucleolar biology directly or indirectly, other perturbances whose origin resides in the nucleolar biology also trigger nucleolar and systemic stress responses. Among the latter, we find mutations in nucleolar and ribosomal proteins, ribosomal RNA (rRNA) processing inhibitors and ribosomal DNA (rDNA) transcription inhibition. The p53 protein also mediates NSR, leading ultimately to cell cycle arrest, apoptosis, senescence or differentiation. Hence, NSR is gaining importance in cancer biology. The nucleolar size and ribosome biogenesis, and how they connect with the Target of Rapamycin (TOR) signalling pathway, are also becoming important in the biology of aging and cancer. Simple model organisms like the budding yeast Saccharomyces cerevisiae, easy to manipulate genetically, are useful in order to study nucleolar and rDNA structure and their relationship with stress. In this review, we summarize the most important findings related to this topic.
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Affiliation(s)
- Emiliano Matos-Perdomo
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, 38010 Santa Cruz de Tenerife, Spain
- Escuela de Doctorado y Estudios de Postgrado, Universidad de La Laguna, 38200 Tenerife, Spain
| | - Félix Machín
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, 38010 Santa Cruz de Tenerife, Spain.
- Instituto de Tecnologías Biomédicas, Universidad de La Laguna, 38200 Tenerife, Spain.
- Facultad de Ciencias de la Salud, Universidad Fernando Pessoa Canarias, 35450 Santa María de Guía, Gran Canaria, Spain.
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15
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Potapova TA, Gerton JL. Ribosomal DNA and the nucleolus in the context of genome organization. Chromosome Res 2019; 27:109-127. [PMID: 30656516 DOI: 10.1007/s10577-018-9600-5] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 12/13/2018] [Accepted: 12/17/2018] [Indexed: 12/12/2022]
Abstract
The nucleolus constitutes a prominent nuclear compartment, a membraneless organelle that was first documented in the 1830s. The fact that specific chromosomal regions were present in the nucleolus was recognized by Barbara McClintock in the 1930s, and these regions were termed nucleolar organizing regions, or NORs. The primary function of ribosomal DNA (rDNA) is to produce RNA components of ribosomes. Yet, ribosomal DNA also plays a pivotal role in nuclear organization by assembling the nucleolus. This review is focused on the rDNA and associated proteins in the context of genome organization. Recent advances in understanding chromatin organization suggest that chromosomes are organized into topological domains by a DNA loop extrusion process. We discuss the perspective that rDNA may also be organized in topological domains constrained by structural maintenance of chromosome protein complexes such as cohesin and condensin. Moreover, biophysical studies indicate that the nucleolar compartment may be formed by active processes as well as phase separation, a perspective that lends further insight into nucleolar organization. The application of the latest perspectives and technologies to this organelle help further elucidate its role in nuclear structure and function.
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Affiliation(s)
| | - Jennifer L Gerton
- Stowers Institute for Medical Research, Kansas City, MO, USA
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, USA
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16
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Sakamoto T, Tsujimoto-Inui Y, Sotta N, Hirakawa T, Matsunaga TM, Fukao Y, Matsunaga S, Fujiwara T. Proteasomal degradation of BRAHMA promotes Boron tolerance in Arabidopsis. Nat Commun 2018; 9:5285. [PMID: 30538237 PMCID: PMC6290004 DOI: 10.1038/s41467-018-07393-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 09/05/2018] [Indexed: 12/02/2022] Open
Abstract
High levels of boron (B) induce DNA double-strand breaks (DSBs) in eukaryotes, including plants. Here we show a molecular pathway of high B-induced DSBs by characterizing Arabidopsis thaliana hypersensitive to excess boron mutants. Molecular analysis of the mutants revealed that degradation of a SWItch/Sucrose Non-Fermentable subunit, BRAHMA (BRM), by a 26S proteasome (26SP) with specific subunits is a key process for ameliorating high-B-induced DSBs. We also found that high-B treatment induces histone hyperacetylation, which increases susceptibility to DSBs. BRM binds to acetylated histone residues and opens chromatin. Accordingly, we propose that the 26SP limits chromatin opening by BRM in conjunction with histone hyperacetylation to maintain chromatin stability and avoid DSB formation under high-B conditions. Interestingly, a positive correlation between the extent of histone acetylation and DSB formation is evident in human cultured cells, suggesting that the mechanism of DSB induction is also valid in animals. Boron is essential for plant survival but high levels can impair growth and cause DNA damage. Here the authors show that Arabidopsis can ameliorate Boron toxicity via proteasomal degradation of BRAHMA to minimize open chromatin and reduce the likelihood of DNA double strand breaks.
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Affiliation(s)
- Takuya Sakamoto
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan.,Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-8657, Japan
| | - Yayoi Tsujimoto-Inui
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan.,Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-8657, Japan
| | - Naoyuki Sotta
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-8657, Japan
| | - Takeshi Hirakawa
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan
| | - Tomoko M Matsunaga
- Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan
| | - Yoichiro Fukao
- Plant Global Education Project, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0101, Japan.,Department of Bioinformatics, Ritsumeikan University, 1-1-1, Nodihigashi, Kusatsu, Shiga, 525-8577, Japan
| | - Sachihiro Matsunaga
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan.
| | - Toru Fujiwara
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-8657, Japan.
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17
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Xue Y, Acar M. Mechanisms for the epigenetic inheritance of stress response in single cells. Curr Genet 2018; 64:1221-1228. [PMID: 29846762 PMCID: PMC6215725 DOI: 10.1007/s00294-018-0849-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 05/27/2018] [Accepted: 05/28/2018] [Indexed: 12/31/2022]
Abstract
Cells have evolved to dynamically respond to different types of environmental and physiological stress conditions. The information about a previous stress stimulus experience by a mother cell can be passed to its descendants, allowing them to better adapt to and survive in new environments. In recent years, live-cell imaging combined with cell-lineage tracking approaches has elucidated many important principles that guide stress inheritance at the single-cell and population level. In this review, we summarize different strategies that cells can employ to pass the 'memory' of previous stress responses to their descendants. Among these strategies, we focus on a recent discovery of how specific features of Msn2 nucleo-cytoplasmic shuttling dynamics could be inherited across cell lineages. We also discuss how stress response can be transmitted to progenies through changes in chromatin and through partitioning of anti-stress factors and/or damaged macromolecules between mother and daughter cells during cell division. Finally, we highlight how emergent technologies will help address open questions in the field.
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Affiliation(s)
- Yuan Xue
- Department of Molecular Cellular and Developmental Biology, Yale University, 219 Prospect Street, New Haven, CT, 06511, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA
| | - Murat Acar
- Department of Molecular Cellular and Developmental Biology, Yale University, 219 Prospect Street, New Haven, CT, 06511, USA.
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT, 06516, USA.
- Interdepartmental Program in Computational Biology and Bioinformatics, Yale University, 300 George Street, Suite 501, New Haven, CT, 06511, USA.
- Department of Physics, Yale University, Prospect Street, New Haven, CT, 06511, USA.
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18
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Condensin action and compaction. Curr Genet 2018; 65:407-415. [PMID: 30361853 DOI: 10.1007/s00294-018-0899-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Revised: 10/18/2018] [Accepted: 10/20/2018] [Indexed: 12/20/2022]
Abstract
Condensin is a multi-subunit protein complex that belongs to the family of structural maintenance of chromosomes (SMC) complexes. Condensins regulate chromosome structure in a wide range of processes including chromosome segregation, gene regulation, DNA repair and recombination. Recent research defined the structural features and molecular activities of condensins, but it is unclear how these activities are connected to the multitude of phenotypes and functions attributed to condensins. In this review, we briefly discuss the different molecular mechanisms by which condensins may regulate global chromosome compaction, organization of topologically associated domains, clustering of specific loci such as tRNA genes, rDNA segregation, and gene regulation.
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19
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Laribee RN. Transcriptional and Epigenetic Regulation by the Mechanistic Target of Rapamycin Complex 1 Pathway. J Mol Biol 2018; 430:4874-4890. [PMID: 30359581 DOI: 10.1016/j.jmb.2018.10.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 10/09/2018] [Accepted: 10/15/2018] [Indexed: 11/28/2022]
Abstract
Nutrient availability impacts health such that nutrient excess states can dysregulate epigenetic and transcriptional pathways to cause many diseases. Increasing evidence implicates aberrant regulation of nutrient signaling cascades as one means of communicating nutrient information to the epigenetic and transcriptional regulatory machinery. One such signaling cascade, the mechanistic target of rapamycin complex 1 (mTORC1), is conserved from yeast to man, and it is deregulated in diverse disease states. The catalytic subunit of the mTORC1 kinase complex (Tor1 or Tor2 in budding yeast and mTor in mammals) phosphorylates several downstream effectors regulating transcriptional and translational responses controlling growth and proliferation. Delineating mechanisms of cytoplasmic nutrient mTORC1 activation continues to be a major research focus. However, Tor kinases not only localize to the cytoplasm but also are found in the nucleus where they selectively bind and regulate genes controlling cellular metabolism and anabolism. The nuclear mTORC1 functions are now beginning to be defined, and they suggest that mTORC1 has a critical role in regulating the complex transcriptional activities required for ribosomal biogenesis. The mTORC1 pathway also interacts with epigenetic regulators required for modifying chromatin structure and function to control gene expression. Because altered nutrient states exert both individual and transgenerational phenotypic changes, mTORC1 signaling to chromatin effectors may have a significant role in mediating the effects of diet and nutrients on the epigenome. This article will discuss the recent inroads into the function of nuclear mTORC1 and its role in epigenetic and transcriptional regulation.
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Affiliation(s)
- R Nicholas Laribee
- Department of Pathology and Laboratory Medicine, and Center for Cancer Research, University of Tennessee Health Science Center, 19 South Manassas, Cancer Research Building Rm 318, Memphis, TN 38163, USA.
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20
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Abstract
The spatiotemporal organization of chromatin plays central roles in cellular function. The ribosomal DNA (rDNA) chromatin undergoes dynamic structural changes during mitosis and stress. Here, we developed a CRISPR-based imaging system and tracked the condensation dynamics of rDNA chromatin in live yeast cells under glucose starvation. We found that acute glucose starvation triggers rapid condensation of rDNA. Time-lapse microscopy revealed two stages for rDNA condensation: a “primary stage,” when relaxed rDNA chromatin forms higher order loops or rings, and a “secondary stage,” when the rDNA rings further condense into compact clusters. Twisting of rDNA rings accompanies the secondary stage. The condensin complex, but not the cohesin complex, is required for efficient rDNA condensation in response to glucose starvation. Furthermore, we found that the DNA helicase Sgs1 is essential for the survival of cells expressing rDNA-bound dCas9, suggesting a role for helicases in facilitating DNA replication at dCas9-binding sites. A CRISPR-based imaging system allows tracking of rDNA condensation in single cells Glucose starvation triggers rDNA condensation in two prominent stages Condensin contributes to efficient rDNA condensation caused by glucose starvation Sgs1 helicase is required for normal rDNA replication at dCas9-binding sites
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Affiliation(s)
- Yuan Xue
- Department of Molecular Cellular and Developmental Biology, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
| | - Murat Acar
- Department of Molecular Cellular and Developmental Biology, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
- Systems Biology Institute, Yale University, 850 West Campus Drive, West Haven, CT 06516, USA
- Department of Physics, Yale University, 217 Prospect Street, New Haven, CT 06511, USA
- Corresponding author
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21
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Matos-Perdomo E, Machín F. The ribosomal DNA metaphase loop of Saccharomyces cerevisiae gets condensed upon heat stress in a Cdc14-independent TORC1-dependent manner. Cell Cycle 2018; 17:200-215. [PMID: 29166821 PMCID: PMC5884360 DOI: 10.1080/15384101.2017.1407890] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Chromosome morphology in Saccharomyces cerevisiae is only visible at the microscopic level in the ribosomal DNA array (rDNA). The rDNA has been thus used as a model to characterize condensation and segregation of sister chromatids in mitosis. It has been established that the metaphase structure ("loop") depends, among others, on the condensin complex; whereas its segregation also depends on that complex, the Polo-like kinase Cdc5 and the cell cycle master phosphatase Cdc14. In addition, Cdc14 also drives rDNA hypercondensation in telophase. Remarkably, since all these components are essential for cell survival, their role on rDNA condensation and segregation was established by temperature-sensitive (ts) alleles. Here, we show that the heat stress (HS) used to inactivate ts alleles (25 ºC to 37 ºC shift) causes rDNA loop condensation in metaphase-arrested wild type cells, a result that can also be mimicked by other stresses that inhibit the TORC1 pathway. Because this condensation might challenge previous findings with ts alleles, we have repeated classical experiments of rDNA condensation and segregation, yet using instead auxin-driven degradation alleles (aid alleles). We have undertaken the protein degradation at lower temperatures (25 ºC) and concluded that the classical roles for condensin, Cdc5, Cdc14 and Cdc15 still prevailed. Thus, condensin degradation disrupts rDNA higher organization, Cdc14 and Cdc5 degradation precludes rDNA segregation and Cdc15 degradation still allows rDNA hypercompaction in telophase. Finally, we provide direct genetic evidence that this HS-mediated rDNA condensation is dependent on TORC1 but, unlike the one observed in anaphase, is independent of Cdc14.
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Affiliation(s)
- Emiliano Matos-Perdomo
- a Unidad de Investigación , Hospital Universitario Ntra Sra de Candelaria , Ctra del Rosario 145, 38010 , Santa Cruz de Tenerife , Spain.,b Universidad de La Laguna , Tenerife , Spain
| | - Félix Machín
- a Unidad de Investigación , Hospital Universitario Ntra Sra de Candelaria , Ctra del Rosario 145, 38010 , Santa Cruz de Tenerife , Spain
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22
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Shen D, Skibbens RV. Chl1 DNA helicase and Scc2 function in chromosome condensation through cohesin deposition. PLoS One 2017; 12:e0188739. [PMID: 29186203 PMCID: PMC5706694 DOI: 10.1371/journal.pone.0188739] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 11/13/2017] [Indexed: 02/02/2023] Open
Abstract
Chl1 DNA helicase promotes sister chromatid cohesion and associates with both the cohesion establishment acetyltransferase Eco1/Ctf7 and the DNA polymerase processivity factor PCNA that supports Eco1/Ctf7 function. Mutation in CHL1 results in precocious sister chromatid separation and cell aneuploidy, defects that arise through reduced levels of chromatin-bound cohesins which normally tether together sister chromatids (trans tethering). Mutation of Chl1 family members (BACH1/BRIP/FANCJ and DDX11/ChlR1) also exhibit genotoxic sensitivities, consistent with a role for Chl1 in trans tethering which is required for efficient DNA repair. Chl1 promotes the recruitment of Scc2 to DNA which is required for cohesin deposition onto DNA. There is limited evidence, however, that Scc2 also directs the deposition onto DNA of condensins which promote tethering in cis (intramolecular DNA links). Here, we test the ability of Chl1 to promote cis tethering and the role of both Chl1 and Scc2 to promote condensin recruitment to DNA. The results reveal that chl1 mutant cells exhibit significant condensation defects both within the rDNA locus and genome-wide. Importantly, chl1 mutant cell condensation defects do not result from reduced chromatin binding of condensin, but instead through reduced chromatin binding of cohesin. We tested scc2-4 mutant cells and similarly found no evidence of reduced condensin recruitment to chromatin. Consistent with a role for Scc2 specifically in cohesin deposition, scc2-4 mutant cell condensation defects are irreversible. We thus term Chl1 a novel regulator of both chromatin condensation and sister chromatid cohesion through cohesin-based mechanisms. These results reveal an exciting interface between DNA structure and the highly conserved cohesin complex.
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Affiliation(s)
- Donglai Shen
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania, United States of America
| | - Robert V. Skibbens
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania, United States of America
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23
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de Los Santos-Velázquez AI, de Oya IG, Manzano-López J, Monje-Casas F. Late rDNA Condensation Ensures Timely Cdc14 Release and Coordination of Mitotic Exit Signaling with Nucleolar Segregation. Curr Biol 2017; 27:3248-3263.e5. [PMID: 29056450 DOI: 10.1016/j.cub.2017.09.028] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 08/16/2017] [Accepted: 09/13/2017] [Indexed: 12/28/2022]
Abstract
The nucleolus plays a pivotal role in multiple key cellular processes. An illustrative example is the regulation of mitotic exit in Saccharomyces cerevisiae through the nucleolar sequestration of the Cdc14 phosphatase. The peculiar structure of the nucleolus, however, has also its drawbacks. The repetitive nature of the rDNA gives rise to cohesion-independent linkages whose resolution in budding yeast requires the Cdc14-dependent inhibition of rRNA transcription, which facilitates condensin accessibility to this locus. Thus, the rDNA condenses and segregates later than most other yeast genomic regions. Here, we show that defective function of a small nucleolar ribonucleoprotein particle (snoRNP) assembly factor facilitates condensin accessibility to the rDNA and induces nucleolar hyper-condensation. Interestingly, this increased compaction of the nucleolus interferes with the proper release of Cdc14 from this organelle. This observation provides an explanation for the delayed rDNA condensation in budding yeast, which is necessary to efficiently coordinate timely Cdc14 release and mitotic exit with nucleolar compaction and segregation.
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Affiliation(s)
- Ana Isabel de Los Santos-Velázquez
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Spanish National Research Council (CSIC), University of Seville, and University Pablo de Olavide, Avda. Américo Vespucio 24, 41092 Sevilla, Spain
| | - Inés G de Oya
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Spanish National Research Council (CSIC), University of Seville, and University Pablo de Olavide, Avda. Américo Vespucio 24, 41092 Sevilla, Spain
| | - Javier Manzano-López
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Spanish National Research Council (CSIC), University of Seville, and University Pablo de Olavide, Avda. Américo Vespucio 24, 41092 Sevilla, Spain
| | - Fernando Monje-Casas
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Spanish National Research Council (CSIC), University of Seville, and University Pablo de Olavide, Avda. Américo Vespucio 24, 41092 Sevilla, Spain.
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24
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Abstract
Chromatin condensation during mitosis produces detangled and discrete DNA entities required for high fidelity sister chromatid segregation during mitosis and positions DNA away from the cleavage furrow during cytokinesis. Regional condensation during G1 also establishes a nuclear architecture through which gene transcription is regulated but remains plastic so that cells can respond to changes in nutrient levels, temperature and signaling molecules. To date, however, the potential impact of this plasticity on mitotic chromosome condensation remains unknown. Here, we report results obtained from a new condensation assay that wildtype budding yeast cells exhibit dramatic changes in rDNA conformation in response to temperature. rDNA hypercondenses in wildtype cells maintained at 37°C, compared with cells maintained at 23°C. This hypercondensation machinery can be activated during preanaphase but readily inactivated upon exposure to lower temperatures. Extended mitotic arrest at 23°C does not result in hypercondensation, negating a kinetic-based argument in which condensation that typically proceeds slowly is accelerated when cells are placed at 37°C. Neither elevated recombination nor reduced transcription appear to promote this hypercondensation. This heretofore undetected temperature-dependent hypercondensation pathway impacts current views of chromatin structure based on conditional mutant gene analyses and significantly extends our understanding of physiologic changes in chromatin architecture in response to hypothermia.
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Affiliation(s)
- Donglai Shen
- a Department of Biological Sciences , Lehigh University , Bethlehem , PA , USA
| | - Robert V Skibbens
- a Department of Biological Sciences , Lehigh University , Bethlehem , PA , USA
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25
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Abstract
Eukaryotic genomes are packaged in chromatin. The higher-order organization of nucleosome core particles is controlled by the association of the intervening linker DNA with either the linker histone H1 or high mobility group box (HMGB) proteins. While H1 is thought to stabilize the nucleosome by preventing DNA unwrapping, the DNA bending imposed by HMGB may propagate to the nucleosome to destabilize chromatin. For metazoan H1, chromatin compaction requires its lysine-rich C-terminal domain, a domain that is buried between globular domains in the previously characterized yeast Saccharomyces cerevisiae linker histone Hho1p. Here, we discuss the functions of S. cerevisiae HMO1, an HMGB family protein unique in containing a terminal lysine-rich domain and in stabilizing genomic DNA. On ribosomal DNA (rDNA) and genes encoding ribosomal proteins, HMO1 appears to exert its role primarily by stabilizing nucleosome-free regions or "fragile" nucleosomes. During replication, HMO1 likewise appears to ensure low nucleosome density at DNA junctions associated with the DNA damage response or the need for topoisomerases to resolve catenanes. Notably, HMO1 shares with the mammalian linker histone H1 the ability to stabilize chromatin, as evidenced by the absence of HMO1 creating a more dynamic chromatin environment that is more sensitive to nuclease digestion and in which chromatin-remodeling events associated with DNA double-strand break repair occur faster; such chromatin stabilization requires the lysine-rich extension of HMO1. Thus, HMO1 appears to have evolved a unique linker histone-like function involving the ability to stabilize both conventional nucleosome arrays as well as DNA regions characterized by low nucleosome density or the presence of noncanonical nucleosomes.
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26
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Li Y, Tsang CK, Wang S, Li X, Yang Y, Fu L, Huang W, Li M, Wang H, Zheng XS. MAF1 suppresses AKT-mTOR signaling and liver cancer through activation of PTEN transcription. Hepatology 2016; 63:1928-42. [PMID: 26910647 PMCID: PMC5021206 DOI: 10.1002/hep.28507] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 02/17/2016] [Indexed: 12/12/2022]
Abstract
UNLABELLED The phosphatidylinositol 3-kinase/phosphatidylinositol 3,4,5-trisphosphate 3-phosphatase/protein kinase B/mammalian target of rapamycin (PI3K-PTEN-AKT-mTOR) pathway is a central controller of cell growth and a key driver for human cancer. MAF1 is an mTOR downstream effector and transcriptional repressor of ribosomal and transfer RNA genes. MAF1 expression is markedly reduced in hepatocellular carcinomas, which is correlated with disease progression and poor prognosis. Consistently, MAF1 displays tumor-suppressor activity toward in vitro and in vivo cancer models. Surprisingly, blocking the synthesis of ribosomal and transfer RNAs is insufficient to account for MAF1's tumor-suppressor function. Instead, MAF1 down-regulation paradoxically leads to activation of AKT-mTOR signaling, which is mediated by decreased PTEN expression. MAF1 binds to the PTEN promoter, enhancing PTEN promoter acetylation and activity. CONCLUSION In contrast to its canonical function as a transcriptional repressor, MAF1 can also act as a transcriptional activator for PTEN, which is important for MAF1's tumor-suppressor function. These results have implications in disease staging, prognostic prediction, and AKT-mTOR-targeted therapy in liver cancer. (Hepatology 2016;63:1928-1942).
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Affiliation(s)
- Yue Li
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina
| | - Chi Kwan Tsang
- Rutgers Cancer Institute of New Jersey and Department of Pharmacology, Robert Wood Johnson Medical School, Rutgersthe State University of New JerseyNew BrunswickNJ
| | - Suihai Wang
- State Key Laboratory of Organ Failure Research, Institute of Antibody Engineering, School of BiotechnologySouthern Medical UniversityGuangzhouChina
| | - Xiao‐Xing Li
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina
| | - Yang Yang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina
| | - Liwu Fu
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina
| | - Wenlin Huang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina
| | - Ming Li
- State Key Laboratory of Organ Failure Research, Institute of Antibody Engineering, School of BiotechnologySouthern Medical UniversityGuangzhouChina
| | - Hui‐Yun Wang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina,Rutgers Cancer Institute of New Jersey and Department of Pharmacology, Robert Wood Johnson Medical School, Rutgersthe State University of New JerseyNew BrunswickNJ
| | - X.F. Steven Zheng
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer MedicineSun Yat‐sen University Cancer CenterGuangzhouChina,Rutgers Cancer Institute of New Jersey and Department of Pharmacology, Robert Wood Johnson Medical School, Rutgersthe State University of New JerseyNew BrunswickNJ
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27
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Abstract
Because the genome stores all genetic information required for growth and development, it is of pivotal importance to maintain DNA integrity, especially during cell division, when the genome is prone to replication errors and damage. Although over the last two decades it has become evident that the basic cell cycle toolbox of plants shares several similarities with those of fungi and mammals, plants appear to have evolved a set of distinct checkpoint regulators in response to different types of DNA stress. This might be a consequence of plants' sessile lifestyle, which exposes them to a set of unique DNA damage-inducing conditions. In this review, we highlight the types of DNA stress that plants typically experience and describe the plant-specific molecular mechanisms that control cell division in response to these stresses.
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Affiliation(s)
- Zhubing Hu
- Department of Plant Systems Biology, VIB, B-9052 Gent, Belgium
| | - Toon Cools
- Department of Plant Systems Biology, VIB, B-9052 Gent, Belgium
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28
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Yang XZ, Li XX, Zhang YJ, Rodriguez-Rodriguez L, Xiang MQ, Wang HY, Zheng XFS. Rab1 in cell signaling, cancer and other diseases. Oncogene 2016; 35:5699-5704. [PMID: 27041585 PMCID: PMC5396462 DOI: 10.1038/onc.2016.81] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Revised: 02/23/2016] [Accepted: 02/26/2016] [Indexed: 12/17/2022]
Abstract
The endoplasmic reticulum (ER) and Golgi membrane system have major roles in cell signaling and regulation of the biosynthesis/transport of proteins and lipids in response to environmental cues such as amino acid and cholesterol levels. Rab1 is the founding member of the Rab small GTPase family, which is known to mediate dynamic membrane trafficking between ER and Golgi. Growing evidence indicate that Rab1 proteins have important functions beyond their classical vesicular transport functions, including nutrient sensing and signaling, cell migration and presentation of cell-surface receptors. Moreover, deregulation of RAB1 expression has been linked to a myriad of human diseases such as cancer, cardiomyopathy and Parkinson's disease. Further investigating these new physiological and pathological functions of Rab1 should provide new opportunities for better understanding of the disease processes and may lead to more effective therapeutic interventions.
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Affiliation(s)
- X-Z Yang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, China
| | - X-X Li
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, China
| | - Y-J Zhang
- Rutgers Cancer Institute of New Jersey, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA.,Oncology Department, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - L Rodriguez-Rodriguez
- Rutgers Cancer Institute of New Jersey, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA.,Department of Medicine, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
| | - M-Q Xiang
- Center for Advanced Biotechnology and Medicine, and Department of Pediatrics, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA.,State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - H-Y Wang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, China.,Rutgers Cancer Institute of New Jersey, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA.,Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
| | - X F S Zheng
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, China.,Rutgers Cancer Institute of New Jersey, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA.,Department of Pharmacology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
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29
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Wang D, Mansisidor A, Prabhakar G, Hochwagen A. Condensin and Hmo1 Mediate a Starvation-Induced Transcriptional Position Effect within the Ribosomal DNA Array. Cell Rep 2016; 14:1010-1017. [PMID: 26832415 DOI: 10.1016/j.celrep.2016.01.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 10/30/2015] [Accepted: 12/28/2015] [Indexed: 02/06/2023] Open
Abstract
Repetitive DNA arrays are important structural features of eukaryotic genomes that are often heterochromatinized to suppress repeat instability. It is unclear, however, whether all repeats within an array are equally subject to heterochromatin formation and gene silencing. Here, we show that in starving Saccharomyces cerevisiae, silencing of reporter genes within the ribosomal DNA (rDNA) array is less pronounced in outer repeats compared with inner repeats. This position effect is linked to the starvation-induced contraction of the nucleolus. We show that the chromatin regulators condensin and Hmo1 redistribute within the rDNA upon starvation; that Hmo1, like condensin, is required for nucleolar contraction; and that the position effect partially depends on both proteins. Starvation-induced nucleolar contraction and differential desilencing of the outer rDNA repeats may provide a mechanism to activate rDNA-encoded RNAPII transcription units without causing general rDNA instability.
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Affiliation(s)
- Danni Wang
- Department of Biology, New York University, New York, NY 10003, USA
| | | | | | - Andreas Hochwagen
- Department of Biology, New York University, New York, NY 10003, USA.
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30
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Benoist C, Guérin C, Noirot P, Dervyn E. Constitutive Stringent Response Restores Viability of Bacillus subtilis Lacking Structural Maintenance of Chromosome Protein. PLoS One 2015; 10:e0142308. [PMID: 26539825 PMCID: PMC4634966 DOI: 10.1371/journal.pone.0142308] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Accepted: 10/19/2015] [Indexed: 11/18/2022] Open
Abstract
Bacillus subtilis mutants lacking the SMC-ScpAB complex are severely impaired for chromosome condensation and partitioning, DNA repair, and cells are not viable under standard laboratory conditions. We isolated suppressor mutations that restored the capacity of a smc deletion mutant (Δsmc) to grow under standard conditions. These suppressor mutations reduced chromosome segregation defects and abrogated hypersensitivity to gyrase inhibitors of Δsmc. Three suppressor mutations were mapped in genes involved in tRNA aminoacylation and maturation pathways. A transcriptomic survey of isolated suppressor mutations pointed to a potential link between suppression of Δsmc and induction of the stringent response. This link was confirmed by (p)ppGpp quantification which indicated a constitutive induction of the stringent response in multiple suppressor strains. Furthermore, sublethal concentrations of arginine hydroxamate (RHX), a potent inducer of stringent response, restored growth of Δsmc under non permissive conditions. We showed that production of (p)ppGpp alone was sufficient to suppress the thermosensitivity exhibited by the Δsmc mutant. Our findings shed new light on the coordination between chromosome dynamics mediated by SMC-ScpAB and other cellular processes during rapid bacterial growth.
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Affiliation(s)
- Camille Benoist
- INRA, UMR1319 Micalis, 78350, Jouy-en-Josas, France
- AgroParisTech, UMR Micalis 1319, 78350, Jouy-en-Josas, France
| | - Cyprien Guérin
- Mathématiques et Informatique Appliquées du Génome à l’Environnement, UR1404, INRA, Domaine de Vilvert, 78350, Jouy-en-Josas, France
| | - Philippe Noirot
- INRA, UMR1319 Micalis, 78350, Jouy-en-Josas, France
- AgroParisTech, UMR Micalis 1319, 78350, Jouy-en-Josas, France
| | - Etienne Dervyn
- INRA, UMR1319 Micalis, 78350, Jouy-en-Josas, France
- AgroParisTech, UMR Micalis 1319, 78350, Jouy-en-Josas, France
- * E-mail:
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31
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Rutledge MT, Russo M, Belton JM, Dekker J, Broach JR. The yeast genome undergoes significant topological reorganization in quiescence. Nucleic Acids Res 2015. [PMID: 26202961 PMCID: PMC4787801 DOI: 10.1093/nar/gkv723] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
We have examined the three-dimensional organization of the yeast genome during quiescence by a chromosome capture technique as a means of understanding how genome organization changes during development. For exponentially growing cells we observe high levels of inter-centromeric interaction but otherwise a predominance of intrachromosomal interactions over interchromosomal interactions, consistent with aggregation of centromeres at the spindle pole body and compartmentalization of individual chromosomes within the nucleoplasm. Three major changes occur in the organization of the quiescent cell genome. First, intrachromosomal associations increase at longer distances in quiescence as compared to growing cells. This suggests that chromosomes undergo condensation in quiescence, which we confirmed by microscopy by measurement of the intrachromosomal distances between two sites on one chromosome. This compaction in quiescence requires the condensin complex. Second, inter-centromeric interactions decrease, consistent with prior data indicating that centromeres disperse along an array of microtubules during quiescence. Third, inter-telomeric interactions significantly increase in quiescence, an observation also confirmed by direct measurement. Thus, survival during quiescence is associated with substantial topological reorganization of the genome.
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Affiliation(s)
- Mark T Rutledge
- Department of Biochemistry and Molecular Biology, Penn State College of Medicine, Hershey, PA 17033, USA Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Mariano Russo
- Department of Biochemistry and Molecular Biology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Jon-Matthew Belton
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Job Dekker
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - James R Broach
- Department of Biochemistry and Molecular Biology, Penn State College of Medicine, Hershey, PA 17033, USA
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32
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Rio1 promotes rDNA stability and downregulates RNA polymerase I to ensure rDNA segregation. Nat Commun 2015; 6:6643. [PMID: 25851096 DOI: 10.1038/ncomms7643] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Accepted: 02/13/2015] [Indexed: 01/30/2023] Open
Abstract
The conserved protein kinase Rio1 localizes to the cytoplasm and nucleus of eukaryotic cells. While the roles of Rio1 in the cytoplasm are well characterized, its nuclear function remains unknown. Here we show that nuclear Rio1 promotes rDNA array stability and segregation in Saccharomyces cerevisiae. During rDNA replication in S phase, Rio1 downregulates RNA polymerase I (PolI) and recruits the histone deacetylase Sir2. Both interventions ensure rDNA copy-number homeostasis and prevent the formation of extrachromosomal rDNA circles, which are linked to accelerated ageing in yeast. During anaphase, Rio1 downregulates PolI by targeting its subunit Rpa43, causing PolI to dissociate from the rDNA. By stimulating the processing of PolI-generated transcripts at the rDNA, Rio1 allows for rDNA condensation and segregation in late anaphase. These events finalize the genome transmission process. We identify Rio1 as an essential nucleolar housekeeper that integrates rDNA replication and segregation with ribosome biogenesis.
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33
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Nucleolar organization, ribosomal DNA array stability, and acrocentric chromosome integrity are linked to telomere function. PLoS One 2014; 9:e92432. [PMID: 24662969 PMCID: PMC3963894 DOI: 10.1371/journal.pone.0092432] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 02/21/2014] [Indexed: 12/16/2022] Open
Abstract
The short arms of the ten acrocentric human chromosomes share several repetitive DNAs, including ribosomal RNA genes (rDNA). The rDNA arrays correspond to nucleolar organizing regions that coalesce each cell cycle to form the nucleolus. Telomere disruption by expressing a mutant version of telomere binding protein TRF2 (dnTRF2) causes non-random acrocentric fusions, as well as large-scale nucleolar defects. The mechanisms responsible for acrocentric chromosome sensitivity to dysfunctional telomeres are unclear. In this study, we show that TRF2 normally associates with the nucleolus and rDNA. However, when telomeres are crippled by dnTRF2 or RNAi knockdown of TRF2, gross nucleolar and chromosomal changes occur. We used the controllable dnTRF2 system to precisely dissect the timing and progression of nucleolar and chromosomal instability induced by telomere dysfunction, demonstrating that nucleolar changes precede the DNA damage and morphological changes that occur at acrocentric short arms. The rDNA repeat arrays on the short arms decondense, and are coated by RNA polymerase I transcription binding factor UBF, physically linking acrocentrics to one another as they become fusogenic. These results highlight the importance of telomere function in nucleolar stability and structural integrity of acrocentric chromosomes, particularly the rDNA arrays. Telomeric stress is widely accepted to cause DNA damage at chromosome ends, but our findings suggest that it also disrupts chromosome structure beyond the telomere region, specifically within the rDNA arrays located on acrocentric chromosomes. These results have relevance for Robertsonian translocation formation in humans and mechanisms by which acrocentric-acrocentric fusions are promoted by DNA damage and repair.
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34
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Abstract
Mitotic chromosome condensation is a prerequisite for the accurate segregation of chromosomes during cell division, and the conserved condensin complex a central player of this process. However, how condensin binds chromatin and shapes mitotic chromosomes remain poorly understood. Recent genome-wide binding studies showing that in most species condensin is enriched near highly expressed genes suggest a conserved link between condensin occupancy and high transcription rates. To gain insight into the mechanisms of condensin binding and mitotic chromosome condensation, we searched for factors that collaborate with condensin through a synthetic lethal genetic screen in the fission yeast Schizosaccharomyces pombe. We isolated novel mutations affecting condensin, as well as mutations in four genes not previously implicated in mitotic chromosome condensation in fission yeast. These mutations cause chromosome segregation defects similar to those provoked by defects in condensation. We also identified a suppressor of the cut3-477 condensin mutation, which largely rescued chromosome segregation during anaphase. Remarkably, of the five genes identified in this study, four encode transcription co-factors. Our results therefore provide strong additional evidence for a functional connection between chromosome condensation and transcription.
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35
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Workman JJ, Chen H, Laribee RN. Environmental signaling through the mechanistic target of rapamycin complex 1: mTORC1 goes nuclear. Cell Cycle 2014; 13:714-25. [PMID: 24526113 PMCID: PMC3979908 DOI: 10.4161/cc.28112] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Mechanistic target of rapamycin complex 1 (mTORC1) is a well-known regulator of cell growth and proliferation in response to environmental stimuli and stressors. To date, the majority of mTORC1 studies have focused on its function as a cytoplasmic effector of translation regulation. However, recent studies have identified additional, nuclear-specific roles for mTORC1 signaling related to transcription of the ribosomal DNA (rDNA) and ribosomal protein (RP) genes, mitotic cell cycle control, and the regulation of epigenetic processes. As this area of study is still in its infancy, the purpose of this review to highlight these significant findings and discuss the relevance of nuclear mTORC1 signaling dysregulation as it pertains to health and disease.
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Affiliation(s)
- Jason J Workman
- Department of Pathology and Laboratory Medicine and Center for Cancer Research; University of Tennessee Health Science Center; Memphis, TN USA
| | - Hongfeng Chen
- Department of Pathology and Laboratory Medicine and Center for Cancer Research; University of Tennessee Health Science Center; Memphis, TN USA
| | - R Nicholas Laribee
- Department of Pathology and Laboratory Medicine and Center for Cancer Research; University of Tennessee Health Science Center; Memphis, TN USA
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36
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Wierman MB, Smith JS. Yeast sirtuins and the regulation of aging. FEMS Yeast Res 2014; 14:73-88. [PMID: 24164855 PMCID: PMC4365911 DOI: 10.1111/1567-1364.12115] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 10/09/2013] [Accepted: 10/13/2013] [Indexed: 11/29/2022] Open
Abstract
The sirtuins are a phylogenetically conserved family of NAD(+) -dependent protein deacetylases that consume one molecule of NAD(+) for every deacetylated lysine side chain. Their requirement for NAD(+) potentially makes them prone to regulation by fluctuations in NAD(+) or biosynthesis intermediates, thus linking them to cellular metabolism. The Sir2 protein from Saccharomyces cerevisiae is the founding sirtuin family member and has been well characterized as a histone deacetylase that functions in transcriptional silencing of heterochromatin domains and as a pro-longevity factor for replicative life span (RLS), defined as the number of times a mother cell divides (buds) before senescing. Deleting SIR2 shortens RLS, while increased gene dosage causes extension. Furthermore, Sir2 has been implicated in mediating the beneficial effects of caloric restriction (CR) on life span, not only in yeast, but also in higher eukaryotes. While this paradigm has had its share of disagreements and debate, it has also helped rapidly drive the aging research field forward. S. cerevisiae has four additional sirtuins, Hst1, Hst2, Hst3, and Hst4. This review discusses the function of Sir2 and the Hst homologs in replicative aging and chronological aging, and also addresses how the sirtuins are regulated in response to environmental stresses such as CR.
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Affiliation(s)
- Margaret B Wierman
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA, USA
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37
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Ganley ARD, Kobayashi T. Ribosomal DNA and cellular senescence: new evidence supporting the connection between rDNA and aging. FEMS Yeast Res 2014; 14:49-59. [DOI: 10.1111/1567-1364.12133] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 12/10/2013] [Accepted: 12/19/2013] [Indexed: 12/19/2022] Open
Affiliation(s)
- Austen R. D. Ganley
- Institute of Natural and Mathematical Sciences; Massey University; Auckland New Zealand
| | - Takehiko Kobayashi
- Division of Cytogenetics; National Institute of Genetics; Mishima Shizuoka Japan
- Department of Genetics; The Graduate University for Advanced Studies; SOKENDAI; Mishima Shizuoka Japan
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38
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Edwards AL, Sangurdekar DP, Jeong KS, Khodursky AB, Rybenkov VV. Transient growth arrest in Escherichia coli induced by chromosome condensation. PLoS One 2013; 8:e84027. [PMID: 24376785 PMCID: PMC3871593 DOI: 10.1371/journal.pone.0084027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 11/18/2013] [Indexed: 11/21/2022] Open
Abstract
MukB is a bacterial SMC (structural maintenance of chromosome) protein that regulates the global folding of the Escherichia coli chromosome by bringing distant DNA segments together. We report that moderate overproduction of MukB may lead, depending on strain and growth conditions, to transient growth arrest. In DH5α cells, overproduction of MukB or MukBEF using pBAD expression system triggered growth arrest 2.5 h after induction. The exit from growth arrest was accompanied by the loss of the overproducing plasmid and a decline in the abundance of MukBEF. The arrested cells showed a compound gene expression profile which can be characterized by the following features: (i) a broad and deep downregulation of ribosomal proteins (up to 80-fold); (ii) downregulation of groups of genes encoding enzymes involved in nucleotide metabolism, respiration, and central metabolism; (iii) upregulation of some of the genes responsive to general stress; and (iv) degradation of the patterns of spatial correlations in the transcriptional activity of the chromosome. The transcriptional state of the MukB induced arrest is most similar to stationary cells and cells recovered from stationary phase into a nutrient deprived medium, to amino acid starved cells and to the cells shifting from glucose to acetate. The mukB++ state is dissimilar from all examined transcriptional states generated by protein overexpression with the possible exception of RpoE and RpoH overexpression. Thus, the transcription profile of MukB-arrested cells can be described as a combination of responses typical for other growth-arrested cells and those for overproducers of DNA binding proteins with a particularly deep down-regulation of ribosomal genes.
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MESH Headings
- Chromosomal Proteins, Non-Histone/genetics
- Chromosomal Proteins, Non-Histone/metabolism
- Chromosomes, Bacterial/chemistry
- Chromosomes, Bacterial/genetics
- Chromosomes, Bacterial/metabolism
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Bacterial/metabolism
- Escherichia coli/cytology
- Escherichia coli/genetics
- Escherichia coli/growth & development
- Escherichia coli/metabolism
- Escherichia coli Proteins/genetics
- Escherichia coli Proteins/metabolism
- Gene Expression Regulation, Bacterial
- Time Factors
- Transcription, Genetic
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Affiliation(s)
- Andrea L. Edwards
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, United States of America
| | - Dipen P. Sangurdekar
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St Paul, Minnesota, United States of America
| | - Kyeong S. Jeong
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St Paul, Minnesota, United States of America
| | - Arkady B. Khodursky
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St Paul, Minnesota, United States of America
| | - Valentin V. Rybenkov
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, United States of America
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39
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The anaphase promoting complex regulates yeast lifespan and rDNA stability by targeting Fob1 for degradation. Genetics 2013; 196:693-709. [PMID: 24361936 DOI: 10.1534/genetics.113.158949] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Genomic stability, stress response, and nutrient signaling all play critical, evolutionarily conserved roles in lifespan determination. However, the molecular mechanisms coordinating these processes with longevity remain unresolved. Here we investigate the involvement of the yeast anaphase promoting complex (APC) in longevity. The APC governs passage through M and G1 via ubiquitin-dependent targeting of substrate proteins and is associated with cancer and premature aging when defective. Our two-hybrid screen utilizing Apc5 as bait recovered the lifespan determinant Fob1 as prey. Fob1 is unstable specifically in G1, cycles throughout the cell cycle in a manner similar to Clb2 (an APC target), and is stabilized in APC (apc5(CA)) and proteasome (rpn10) mutants. Deletion of FOB1 increased replicative lifespan (RLS) in wild type (WT), apc5(CA), and apc10 cells, and suppressed apc5(CA) cell cycle progression and rDNA recombination defects. Alternatively, increased FOB1 expression decreased RLS in WT cells, but did not reduce the already short apc5(CA) RLS, suggesting an epistatic interaction between apc5(CA) and fob1. Mutation to a putative L-Box (Fob1(E420V)), a Destruction Box-like motif, abolished Fob1 modifications, stabilized the protein, and increased rDNA recombination. Our work provides a mechanistic role played by the APC to promote replicative longevity and genomic stability in yeast.
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40
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Wallace HA, Bosco G. Condensins and 3D Organization of the Interphase Nucleus. CURRENT GENETIC MEDICINE REPORTS 2013; 1:219-229. [PMID: 24563825 DOI: 10.1007/s40142-013-0024-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Condensins are conserved multi-subunit protein complexes that participate in eukaryotic genome organization. Well known for their role in mitotic chromosome condensation, condensins have recently emerged as integral components of diverse interphase processes. Recent evidence shows that condensins are involved in chromatin organization, gene expression, and DNA repair and indicates similarities between the interphase and mitotic functions of condensin. Recent work has enhanced our knowledge of how chromatin architecture is dynamically regulated by condensin to impact essential cellular processes.
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Affiliation(s)
- Heather A Wallace
- Department of Genetics, Geisel School of Medicine at Dartmouth, 609 Vail, HB 7400, Hanover, NH 03755, USA
| | - Giovanni Bosco
- Department of Genetics, Geisel School of Medicine at Dartmouth, 609 Vail, HB 7400, Hanover, NH 03755, USA
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41
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Abstract
Condensins are multisubunit protein complexes that play a fundamental role in the structural and functional organization of chromosomes in the three domains of life. Most eukaryotic species have two different types of condensin complexes, known as condensins I and II, that fulfill nonoverlapping functions and are subjected to differential regulation during mitosis and meiosis. Recent studies revealed that the two complexes contribute to a wide variety of interphase chromosome functions, such as gene regulation, recombination, and repair. Also emerging are their cell type- and tissue-specific functions and relevance to human disease. Biochemical and structural analyses of eukaryotic and bacterial condensins steadily uncover the mechanisms of action of this class of highly sophisticated molecular machines. Future studies on condensins will not only enhance our understanding of chromosome architecture and dynamics, but also help address a previously underappreciated yet profound set of questions in chromosome biology.
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Affiliation(s)
- Tatsuya Hirano
- Chromosome Dynamics Laboratory, RIKEN Advanced Science Institute, Wako, Saitama, Japan.
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42
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Wu N, Yu H. The Smc complexes in DNA damage response. Cell Biosci 2012; 2:5. [PMID: 22369641 PMCID: PMC3329402 DOI: 10.1186/2045-3701-2-5] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2011] [Accepted: 02/27/2012] [Indexed: 02/03/2023] Open
Abstract
The structural maintenance of chromosomes (Smc) proteins regulate nearly all aspects of chromosome biology and are critical for genomic stability. In eukaryotes, six Smc proteins form three heterodimers--Smc1/3, Smc2/4, and Smc5/6--which together with non-Smc proteins form cohesin, condensin, and the Smc5/6 complex, respectively. Cohesin is required for proper chromosome segregation. It establishes and maintains sister-chromatid cohesion until all sister chromatids achieve bipolar attachment to the mitotic spindle. Condensin mediates chromosome condensation during mitosis. The Smc5/6 complex has multiple roles in DNA repair. In addition to their major functions in chromosome cohesion and condensation, cohesin and condensin also participate in the cellular DNA damage response. Here we review recent progress on the functions of all three Smc complexes in DNA repair and their cell cycle regulation by posttranslational modifications, such as acetylation, phosphorylation, and sumoylation. An in-depth understanding of the mechanisms by which these complexes promote DNA repair and genomic stability may help us to uncover the molecular basis of genomic instability in human cancers and devise ways that exploit this instability to treat cancers.
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Affiliation(s)
- Nan Wu
- Department of Pharmacology, Howard Hughes Medical Institute, 6001 Forest Park Road, Dallas, TX 75390, USA.
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43
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Ha CW, Sung MK, Huh WK. Nsi1 plays a significant role in the silencing of ribosomal DNA in Saccharomyces cerevisiae. Nucleic Acids Res 2012; 40:4892-903. [PMID: 22362748 PMCID: PMC3367210 DOI: 10.1093/nar/gks188] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In eukaryotic cells, ribosomal DNA (rDNA) forms the basis of the nucleolus. In Saccharomyces cerevisiae, 100-200 copies of a 9.1-kb rDNA repeat exist as a tandem array on chromosome XII. The stability of this highly repetitive array is maintained through silencing. However, the precise mechanisms that regulate rDNA silencing are poorly understood. Here, we report that S. cerevisiae Ydr026c, which we name NTS1 silencing protein 1 (Nsi1), plays a significant role in rDNA silencing. By studying the subcellular localization of 159 nucleolar proteins, we identified 11 proteins whose localization pattern is similar to that of Net1, a well-established rDNA silencing factor. Among these proteins is Nsi1, which is associated with the NTS1 region of rDNA and is required for rDNA silencing at NTS1. In addition, Nsi1 physically interacts with the known rDNA silencing factors Net1, Sir2 and Fob1. The loss of Nsi1 decreases the association of Sir2 with NTS1 and increases histone acetylation at NTS1. Furthermore, Nsi1 contributes to the longevity of yeast cells. Taken together, our findings suggest that Nsi1 is a new rDNA silencing factor that contributes to rDNA stability and lifespan extension in S. cerevisiae.
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Affiliation(s)
- Cheol Woong Ha
- School of Biological Sciences and Research Center for Functional Cellulomics, Institute of Microbiology, Seoul National University, Seoul 151-747, Republic of Korea
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44
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Rodley CDM, Pai DA, Mills TA, Engelke DR, O'Sullivan JM. tRNA gene identity affects nuclear positioning. PLoS One 2011; 6:e29267. [PMID: 22206006 PMCID: PMC3242769 DOI: 10.1371/journal.pone.0029267] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 11/23/2011] [Indexed: 12/13/2022] Open
Abstract
The three-dimensional organization of genomes is dynamic and plays a critical role in the regulation of cellular development and phenotypes. Here we use proximity-based ligation methods (i.e. chromosome conformation capture [3C] and circularized chromosome confrmation capture [4C]) to explore the spatial organization of tRNA genes and their locus-specific interactions with the ribosomal DNA. Directed replacement of one lysine and two leucine tRNA loci shows that tRNA spatial organization depends on both tRNA coding sequence identity and the surrounding chromosomal loci. These observations support a model whereby the three-dimensional, spatial organization of tRNA loci within the nucleus utilizes tRNA gene-specific signals to affect local interactions, though broader organization of chromosomal regions are determined by factors outside the tRNA genes themselves.
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Affiliation(s)
| | - Dave A. Pai
- Department of Biological Chemistry, The University of Michigan, Ann Arbor, Michigan, United States of America
| | - Tyrone A. Mills
- Institute of Natural Sciences, Massey University, Auckland, New Zealand
| | - David R. Engelke
- Department of Biological Chemistry, The University of Michigan, Ann Arbor, Michigan, United States of America
| | - Justin M. O'Sullivan
- Institute of Natural Sciences, Massey University, Auckland, New Zealand
- * E-mail:
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45
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Ünal E, Amon A. Gamete formation resets the aging clock in yeast. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2011; 76:73-80. [PMID: 21890640 DOI: 10.1101/sqb.2011.76.011379] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Gametogenesis is a process whereby a germ cell differentiates into haploid gametes. We found that, in budding yeast, replicatively aged cells remove age-induced cellular damage during gametogenesis. Importantly, gametes of aged cells have the same replicative potential as those derived from young cells, indicating that life span resets during gametogenesis. Here, we explore the potential mechanisms responsible for gametogenesis-induced rejuvenation and discuss putative analogous mechanisms in higher eukaryotes.
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Affiliation(s)
- E Ünal
- David H. Koch Institute for Integrative Cancer Research, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
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46
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Sakamoto T, Inui YT, Uraguchi S, Yoshizumi T, Matsunaga S, Mastui M, Umeda M, Fukui K, Fujiwara T. Condensin II alleviates DNA damage and is essential for tolerance of boron overload stress in Arabidopsis. THE PLANT CELL 2011; 23:3533-46. [PMID: 21917552 PMCID: PMC3203421 DOI: 10.1105/tpc.111.086314] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Revised: 08/07/2011] [Accepted: 08/29/2011] [Indexed: 05/18/2023]
Abstract
Although excess boron (B) is known to negatively affect plant growth, its molecular mechanism of toxicity is unknown. We previously isolated two Arabidopsis thaliana mutants, hypersensitive to excess B (heb1-1 and heb2-1). In this study, we found that HEB1 and HEB2 encode the CAP-G2 and CAP-H2 subunits, respectively, of the condensin II protein complex, which functions in the maintenance of chromosome structure. Growth of Arabidopsis seedlings in medium containing excess B induced expression of condensin II subunit genes. Simultaneous treatment with zeocin, which induces DNA double-strand breaks (DSBs), and aphidicolin, which blocks DNA replication, mimicked the effect of excess B on root growth in the heb mutants. Both excess B and the heb mutations upregulated DSBs and DSB-inducible gene transcription, suggesting that DSBs are a cause of B toxicity and that condensin II reduces the incidence of DSBs. The Arabidopsis T-DNA insertion mutant atr-2, which is sensitive to replication-blocking reagents, was also sensitive to excess B. Taken together, these data suggest that the B toxicity mechanism in plants involves DSBs and possibly replication blocks and that plant condensin II plays a role in DNA damage repair or in protecting the genome from certain genotoxic stressors, particularly excess B.
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Affiliation(s)
- Takuya Sakamoto
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Yayoi Tsujimoto Inui
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Shimpei Uraguchi
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Takeshi Yoshizumi
- Plant Functional Genomics Research Team, Plant Functional Genomics Research Group, Plant Science Center RIKEN Yokohama Institute, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
| | - Sachihiro Matsunaga
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Minami Mastui
- Plant Functional Genomics Research Team, Plant Functional Genomics Research Group, Plant Science Center RIKEN Yokohama Institute, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
| | - Masaaki Umeda
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Takayama, Ikoma, Nara 630-0101, Japan
| | - Kiichi Fukui
- Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Toru Fujiwara
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
- Core Research for Evolutional Science and Technology, Japan Science and 21 Technology Agency, Chiyoda-ku, Tokyo 102-0075, Japan
- Address correspondence to
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Tsang CK, Liu H, Zheng XFS. mTOR binds to the promoters of RNA polymerase I- and III-transcribed genes. Cell Cycle 2010; 9:953-7. [PMID: 20038818 DOI: 10.4161/cc.9.5.10876] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Target of rapamycin (TOR) is a conserved regulator of gene expression from yeast to humans. In budding yeast, TOR is associated with ribosomal DNA (rDNA) promoter, which is critical for ribosome biogenesis and transfer RNA (tRNA) synthesis. Whether mTOR behaves similarly in mammalian cells is unknown. Here, we report that mTOR is detected at several different promoters in human and murine cells, including that of rDNA and tRNA genes. The association of mTOR with these promoters is regulated by growth signals and sensitive to rapamycin. Together, our observations suggest that mTOR is closely involved in gene regulation at the promoters, which is a conserved mechanism to control RNA polymerase I- and III-dependent genes that are critical for protein synthesis and cell growth.
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Affiliation(s)
- Chi Kwan Tsang
- Department of Pharmacology and Cancer Institute of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ, USA
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Pai DA, Engelke DR. Spatial organization of genes as a component of regulated expression. Chromosoma 2009; 119:13-25. [PMID: 19727792 DOI: 10.1007/s00412-009-0236-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Revised: 08/05/2009] [Accepted: 08/06/2009] [Indexed: 12/15/2022]
Abstract
The DNA of living cells is highly compacted. Inherent in this spatial constraint is the need for cells to organize individual genetic loci so as to facilitate orderly retrieval of information. Complex genetic regulatory mechanisms are crucial to all organisms, and it is becoming increasingly evident that spatial organization of genes is one very important mode of regulation for many groups of genes. In eukaryotic nuclei, it appears not only that DNA is organized in three-dimensional space but also that this organization is dynamic and interactive with the transcriptional state of the genes. Spatial organization occurs throughout evolution and with genes transcribed by all classes of RNA polymerases in all eukaryotic nuclei, from yeast to human. There is an increasing body of work examining the ways in which this organization and consequent regulation are accomplished. In this review, we discuss the diverse strategies that cells use to preferentially localize various classes of genes.
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Affiliation(s)
- Dave A Pai
- Department of Biological Chemistry, University of Michigan, 1150 W. Medical Center Dr., Ann Arbor, MI, 48109-0606, USA
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Hwang WW, Madhani HD. Nonredundant requirement for multiple histone modifications for the early anaphase release of the mitotic exit regulator Cdc14 from nucleolar chromatin. PLoS Genet 2009; 5:e1000588. [PMID: 19662160 PMCID: PMC2716543 DOI: 10.1371/journal.pgen.1000588] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2008] [Accepted: 07/07/2009] [Indexed: 12/03/2022] Open
Abstract
In Saccharomyces cerevisiae, the conserved phosphatase Cdc14 is required for the exit from mitosis. It is anchored on nucleolar chromatin by the Cfi1/Net1 protein until early anaphase, at which time it is released into the nucleoplasm. Two poorly understood, redundant pathways promote Cdc14 release, the FEAR (Cdc fourteen early release) network and the MEN (mitotic exit network). Through the analysis of genetic interactions, we report here a novel requirement for the ubiquitination of histone H2B by the Bre1 ubiquitin ligase in the cell cycle–dependent release of Cdc14 from nucleolar chromatin when the MEN is inactivated. This function for H2B ubiquitination is mediated by its activation of histone H3 methylation on lysines 4 and 79 (meH3K4 and meH3K79) but, surprisingly, is not dependent on the histone deacetylase (HDAC) Sir2, which associates with Cdc14 on nucleolar chromatin as part of the RENT complex. We also observed a defect in Cdc14 release in cells lacking H3 lysine 36 methylation (meH3K36) and in cells lacking an HDAC recruited by this modification. These histone modifications represent previously unappreciated factors required for the accessibility to and/or action on nucleolar chromatin of FEAR network components. The nonredundant role for these modifications in this context contrasts with the notion of a highly combinatorial code by which histone marks act to control biological processes. During proliferation, eukaryotic cells segregate their replicated genome to generate two identical progeny through a highly regulated process called mitosis. Inaccuracy in this process results in cell inviability or aneuploidy. In the S. cerevisiae cell cycle, the exit from the mitotic state is triggered by the release of the phosphatase Cdc14 during the anaphase stage of mitosis from nucleolar chromatin, where it is sequestered and kept inactive. The role of chromatin, if any, in the regulation of Cdc14 sequestration and/or release is unexplored. Using genetic analysis, we have discovered that multiple evolutionarily conserved histone modifications are required for the early anaphase release of Cdc14. These include monoubiquitination of histone H2B as well as two methylations of histone H3 on lysines 4 and 79 that require H2B monoubiquitination to occur efficiently. In addition, methylation of H3 on lysine 36 and a histone deacetylase recruited by this modification are also required. We suggest that these histone modifications are required on nucleolar chromatin for the accessibility and/or action of factors involved in the early anaphase release of Cdc14. The nonredundant requirement for multiple chromatin modifications stands in contrast to the popular notion of a highly combinatorial “histone code” for the action of histone modifications.
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Affiliation(s)
- William W. Hwang
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Hiten D. Madhani
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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Abstract
Since the earliest stages of evolution, organisms have faced the challenge of sensing and adapting to environmental changes for their survival under compromising conditions such as food depletion or stress. Implicit in these responses are mechanisms developed during evolution that include the targeting of chromatin to allow or prevent expression of fundamental genes and to protect genome integrity. Among the different approaches to study these mechanisms, the analysis of the response to a moderate reduction of energy intake, also known as calorie restriction (CR), has become one of the best sources of information regarding the factors and pathways involved in metabolic adaptation from lower to higher eukaryotes. Furthermore, responses to CR are involved in life span regulation-conserved from yeast to mammals-and therefore have garnered major research interest. Herein we review current knowledge of responses to CR at the molecular level and their functional link to chromatin.
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Affiliation(s)
- Alejandro Vaquero
- Chromatin Biology Laboratory, Cancer Epigenetics and Biology Program (PEBC), ICREA, and IDIBELL, L'Hospitalet de Llobregat, Barcelona, Spain.
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