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D'Alfonso A, Micheli G, Camilloni G. rDNA transcription, replication and stability in Saccharomyces cerevisiae. Semin Cell Dev Biol 2024; 159-160:1-9. [PMID: 38244478 DOI: 10.1016/j.semcdb.2024.01.004] [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: 05/01/2023] [Revised: 12/20/2023] [Accepted: 01/10/2024] [Indexed: 01/22/2024]
Abstract
The ribosomal DNA locus (rDNA) is central for the functioning of cells because it encodes ribosomal RNAs, key components of ribosomes, and also because of its links to fundamental metabolic processes, with significant impact on genome integrity and aging. The repetitive nature of the rDNA gene units forces the locus to maintain sequence homogeneity through recombination processes that are closely related to genomic stability. The co-presence of basic DNA transactions, such as replication, transcription by major RNA polymerases, and recombination, in a defined and restricted area of the genome is of particular relevance as it affects the stability of the rDNA locus by both direct and indirect mechanisms. This condition is well exemplified by the rDNA of Saccharomyces cerevisiae. In this review we summarize essential knowledge on how the complexity and overlap of different processes contribute to the control of rDNA and genomic stability in this model organism.
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Affiliation(s)
- Anna D'Alfonso
- Dipartimento di Biologia e Biotecnologie C. Darwin, Università degli studi di Roma, Sapienza, Rome, Italy
| | - Gioacchino Micheli
- Istituto di Biologia e Patologia Molecolari, Consiglio Nazionale delle Ricerche, Rome, Italy
| | - Giorgio Camilloni
- Dipartimento di Biologia e Biotecnologie C. Darwin, Università degli studi di Roma, Sapienza, Rome, Italy.
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2
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Thakur BL, Kusi NA, Mosavarpour S, Zhu R, Redon CE, Fu H, Dhall A, Pongor LS, Sebastian R, Indig FE, Aladjem MI. SIRT1 Prevents R-Loops during Chronological Aging by Modulating DNA Replication at rDNA Loci. Cells 2023; 12:2630. [PMID: 37998365 PMCID: PMC10669956 DOI: 10.3390/cells12222630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 11/08/2023] [Accepted: 11/09/2023] [Indexed: 11/25/2023] Open
Abstract
In metazoans, the largest sirtuin, SIRT1, is a nuclear protein implicated in epigenetic modifications, circadian signaling, DNA recombination, replication, and repair. Our previous studies have demonstrated that SIRT1 binds replication origins and inhibits replication initiation from a group of potential initiation sites (dormant origins). We studied the effects of aging and SIRT1 activity on replication origin usage and the incidence of transcription-replication collisions (creating R-loop structures) in adult human cells obtained at different time points during chronological aging and in cancer cells. In primary, untransformed cells, SIRT1 activity declined and the prevalence of R-loops rose with chronological aging. Both the reduction in SIRT1 activity and the increased abundance of R-loops were also observed during the passage of primary cells in culture. All cells, regardless of donor age or transformation status, reacted to the short-term, acute chemical inhibition of SIRT1 with the activation of excessive replication initiation events coincident with an increased prevalence of R-loops. However, cancer cells activated dormant replication origins, genome-wide, during long-term proliferation with mutated or depleted SIRT1, whereas, in primary cells, the aging-associated SIRT1-mediated activation of dormant origins was restricted to rDNA loci. These observations suggest that chronological aging and the associated decline in SIRT1 activity relax the regulatory networks that protect cells against excess replication and that the mechanisms protecting from replication-transcription collisions at the rDNA loci manifest as differentially enhanced sensitivities to SIRT1 decline and chronological aging.
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Affiliation(s)
- Bhushan L. Thakur
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Nana A. Kusi
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Sara Mosavarpour
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Roger Zhu
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Christophe E. Redon
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Haiqing Fu
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Anjali Dhall
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Lorinc S. Pongor
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Robin Sebastian
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
| | - Fred E. Indig
- Confocal Imaging Facility, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA;
| | - Mirit I. Aladjem
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; (B.L.T.); (N.A.K.); (S.M.); (R.Z.); (C.E.R.); (H.F.); (A.D.); (L.S.P.); (R.S.)
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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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Yokoyama M, Sasaki M, Kobayashi T. Spt4 promotes cellular senescence by activating non-coding RNA transcription in ribosomal RNA gene clusters. Cell Rep 2023; 42:111944. [PMID: 36640349 DOI: 10.1016/j.celrep.2022.111944] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 07/06/2022] [Accepted: 12/19/2022] [Indexed: 01/11/2023] Open
Abstract
Genome instability can drive aging in many organisms. The ribosomal RNA gene (rDNA) cluster is one of the most unstable regions in the genome and the stability of this region impacts replicative lifespan in budding yeast. To understand the underlying mechanism, we search for yeast mutants with stabler rDNA and longer lifespans than wild-type cells. We show that absence of a transcription elongation factor, Spt4, results in increased rDNA stability, reduced levels of non-coding RNA transcripts from the regulatory E-pro promoter in the rDNA, and extended replicative lifespan in a SIR2-dependent manner. Spt4-dependent lifespan restriction is abolished in the absence of non-coding RNA transcription at the E-pro locus. The amount of Spt4 increases and its function becomes more important as cells age. These findings suggest that Spt4 is a promising aging factor that accelerates cellular senescence through rDNA instability driven by non-coding RNA transcription.
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Affiliation(s)
- Masaaki Yokoyama
- Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan; Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Mariko Sasaki
- Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan; Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
| | - Takehiko Kobayashi
- Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan; Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
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5
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Zhao G, Rusche LN. Sirtuins in Epigenetic Silencing and Control of Gene Expression in Model and Pathogenic Fungi. Annu Rev Microbiol 2022; 76:157-178. [PMID: 35609947 DOI: 10.1146/annurev-micro-041020-100926] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Fungi, including yeasts, molds, and mushrooms, proliferate on decaying matter and then adopt quiescent forms once nutrients are depleted. This review explores how fungi use sirtuin deacetylases to sense and respond appropriately to changing nutrients. Because sirtuins are NAD+-dependent deacetylases, their activity is sensitive to intracellular NAD+ availability. This allows them to transmit information about a cell's metabolic state on to the biological processes they influence. Fungal sirtuins are primarily known to deacetylate histones, repressing transcription and modulating genome stability. Their target genes include those involved in NAD+ homeostasis, metabolism, sporulation, secondary metabolite production, and virulence traits of pathogenic fungi. By targeting different genes over evolutionary time, sirtuins serve as rewiring points that allow organisms to evolve novel responses to low NAD+ stress by bringing relevant biological processes under the control of sirtuins. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Guolei Zhao
- Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, USA; ,
| | - Laura N Rusche
- Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, USA; ,
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Sanchez JC, Ollodart A, Large CRL, Clough C, Alvino GM, Tsuchiya M, Crane M, Kwan EX, Kaeberlein M, Dunham MJ, Raghuraman MK, Brewer BJ. Phenotypic and Genotypic Consequences of CRISPR/Cas9 Editing of the Replication Origins in the rDNA of Saccharomyces cerevisiae. Genetics 2019; 213:229-249. [PMID: 31292210 PMCID: PMC6727806 DOI: 10.1534/genetics.119.302351] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Accepted: 06/28/2019] [Indexed: 12/15/2022] Open
Abstract
The complex structure and repetitive nature of eukaryotic ribosomal DNA (rDNA) is a challenge for genome assembly, thus the consequences of sequence variation in rDNA remain unexplored. However, renewed interest in the role that rDNA variation may play in diverse cellular functions, aside from ribosome production, highlights the need for a method that would permit genetic manipulation of the rDNA. Here, we describe a clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based strategy to edit the rDNA locus in the budding yeast Saccharomyces cerevisiae, developed independently but similar to one developed by others. Using this approach, we modified the endogenous rDNA origin of replication in each repeat by deleting or replacing its consensus sequence. We characterized the transformants that have successfully modified their rDNA locus and propose a mechanism for how CRISPR/Cas9-mediated editing of the rDNA occurs. In addition, we carried out extended growth and life span experiments to investigate the long-term consequences that altering the rDNA origin of replication have on cellular health. We find that long-term growth of the edited clones results in faster-growing suppressors that have acquired segmental aneusomy of the rDNA-containing region of chromosome XII or aneuploidy of chromosomes XII, II, or IV. Furthermore, we find that all edited isolates suffer a reduced life span, irrespective of their levels of extrachromosomal rDNA circles. Our work demonstrates that it is possible to quickly, efficiently, and homogeneously edit the rDNA origin via CRISPR/Cas9.
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Affiliation(s)
- Joseph C Sanchez
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
- Bioscience Division, Los Alamos National Laboratory, Los Alamos New Mexico 87544
| | - Anja Ollodart
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
| | - Christopher R L Large
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
| | - Courtnee Clough
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
| | - Gina M Alvino
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
| | - Mitsuhiro Tsuchiya
- Department of Pathology, University of Washington, Seattle, Washington 98195
| | - Matthew Crane
- Department of Pathology, University of Washington, Seattle, Washington 98195
| | - Elizabeth X Kwan
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
| | - Matt Kaeberlein
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
- Department of Pathology, University of Washington, Seattle, Washington 98195
| | - Maitreya J Dunham
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
| | - M K Raghuraman
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
| | - Bonita J Brewer
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195
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