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Pires GP, Fioresi VS, Canal D, Canal DC, Fernandes M, Brustolini OJB, de Avelar Carpinetti P, Ferreira A, da Silva Ferreira MF. Effects of trimer repeats on Psidium guajava L. gene expression and prospection of functional microsatellite markers. Sci Rep 2024; 14:9811. [PMID: 38684872 PMCID: PMC11059378 DOI: 10.1038/s41598-024-60417-8] [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: 11/19/2023] [Accepted: 04/23/2024] [Indexed: 05/02/2024] Open
Abstract
Most research on trinucleotide repeats (TRs) focuses on human diseases, with few on the impact of TR expansions on plant gene expression. This work investigates TRs' effect on global gene expression in Psidium guajava L., a plant species with widespread distribution and significant relevance in the food, pharmacology, and economics sectors. We analyzed TR-containing coding sequences in 1,107 transcripts from 2,256 genes across root, shoot, young leaf, old leaf, and flower bud tissues of the Brazilian guava cultivars Cortibel RM and Paluma. Structural analysis revealed TR sequences with small repeat numbers (5-9) starting with cytosine or guanine or containing these bases. Functional annotation indicated TR-containing genes' involvement in cellular structures and processes (especially cell membranes and signal recognition), stress response, and resistance. Gene expression analysis showed significant variation, with a subset of highly expressed genes in both cultivars. Differential expression highlighted numerous down-regulated genes in Cortibel RM tissues, but not in Paluma, suggesting interplay between tissues and cultivars. Among 72 differentially expressed genes with TRs, 24 form miRNAs, 13 encode transcription factors, and 11 are associated with transposable elements. In addition, a set of 20 SSR-annotated, transcribed, and differentially expressed genes with TRs was selected as phenotypic markers for Psidium guajava and, potentially for closely related species as well.
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Affiliation(s)
- Giovanna Pinto Pires
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Vinicius Sartori Fioresi
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Drielli Canal
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Dener Cezati Canal
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Miquéias Fernandes
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Otávio José Bernardes Brustolini
- Laboratório Nacional de Computação Científica (LNCC). Av. Getulio Vargas, 333, Petrópolis, Rio de Janeiro, Quitandinha, 25651-076, Brazil
| | - Paola de Avelar Carpinetti
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Adésio Ferreira
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil
| | - Marcia Flores da Silva Ferreira
- Centro de Ciências Agrárias e Engenharias, Departamento de Agronomia, Universidade Federal Do Espírito Santo, Alto Universitário, s/n, Alegre, ES, 29500-000, Brazil.
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Völker J, Breslauer KJ. How sequence alterations enhance the stability and delay expansion of DNA triplet repeat domains. QRB DISCOVERY 2023; 4:e8. [PMID: 37965436 PMCID: PMC10641665 DOI: 10.1017/qrd.2023.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Revised: 08/14/2023] [Accepted: 08/17/2023] [Indexed: 11/16/2023] Open
Abstract
DNA sequence alterations within DNA repeat domains inexplicably enhance the stability and delay the expansion of interrupted repeat domains. Here we propose mechanisms that rationalise such unanticipated outcomes. Specifically, we describe how interruption of a DNA repeat domain restricts the ensemble space available to dynamic, slip out, repeat bulge loops by introducing energetic barriers to loop migration. We explain how such barriers arise because some possible loop isomers result in energetically costly mismatches in the duplex portion of the repeat domain. We propose that the reduced ensemble space is the causative feature for the observed delay in repeat DNA expansion. We further posit that the observed loss of the interrupting repeat in some expanded DNAs reflects the transient occupation of loop isomer positions that result in a mismatch in the duplex stem due to 'leakiness' in the energy barrier. We propose that if the lifetime of such a low probability event allows for recognition by the mismatch repair system, then 'repair' of the repeat interruption can occur; thereby rationalising the absence of the interruption in the final expanded DNA 'product.' Our proposed mechanistic pathways provide reasoned explanations for what have been described as 'puzzling' observations, while also yielding insights into a biomedically important set of coupled genotypic phenomena that map the linkage between DNA origami thermodynamics and phenotypic disease states.
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Affiliation(s)
- Jens Völker
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ, USA
| | - Kenneth J. Breslauer
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ, USA
- The Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, USA
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3
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Yi J, Wan L, Liu Y, Lam SL, Chan HYE, Han D, Guo P. NMR solution structures of d(GGCCTG)n repeats associated with spinocerebellar ataxia type 36. Int J Biol Macromol 2022; 201:607-615. [DOI: 10.1016/j.ijbiomac.2022.01.097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 01/11/2022] [Accepted: 01/13/2022] [Indexed: 01/03/2023]
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5
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Poggi L, Emmenegger L, Descorps-Declère S, Dumas B, Richard GF. Differential efficacies of Cas nucleases on microsatellites involved in human disorders and associated off-target mutations. Nucleic Acids Res 2021; 49:8120-8134. [PMID: 34233005 PMCID: PMC8373144 DOI: 10.1093/nar/gkab569] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 06/11/2021] [Accepted: 07/06/2021] [Indexed: 11/13/2022] Open
Abstract
Microsatellite expansions are the cause of >20 neurological or developmental human disorders. Shortening expanded repeats using specific DNA endonucleases may be envisioned as a gene editing approach. Here, we measured the efficacy of several CRISPR-Cas nucleases to induce recombination within disease-related microsatellites, in Saccharomyces cerevisiae. Broad variations in nuclease performances were detected on all repeat tracts. Wild-type Streptococcus pyogenes Cas9 (SpCas9) was more efficient than Staphylococcus aureus Cas9 on all repeats tested, except (CAG)33. Cas12a (Cpf1) was the most efficient on GAA trinucleotide repeats, whereas GC-rich repeats were more efficiently cut by SpCas9. The main genetic factor underlying Cas efficacy was the propensity of the recognition part of the sgRNA to form a stable secondary structure, independently of its structural part. This suggests that such structures form in vivo and interfere with sgRNA metabolism. The yeast genome contains 221 natural CAG/CTG and GAA/CTT trinucleotide repeats. Deep sequencing after nuclease induction identified three of them as carrying statistically significant low frequency mutations, corresponding to SpCas9 off-target double-strand breaks.
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Affiliation(s)
- Lucie Poggi
- Institut Pasteur, CNRS, UMR3525, 25 rue du Dr Roux, F-75015 Paris, France.,Sorbonne Université, Collège Doctoral, 4 Place Jussieu, F-75005 Paris, France.,Biologics Research, Sanofi R&D, 13 Quai Jules Guesde, 94403 Vitry sur Seine, France
| | - Lisa Emmenegger
- Institut Pasteur, CNRS, UMR3525, 25 rue du Dr Roux, F-75015 Paris, France
| | - Stéphane Descorps-Declère
- Institut Pasteur, CNRS, UMR3525, 25 rue du Dr Roux, F-75015 Paris, France.,Institut Pasteur, Bioinformatics and Biostatistics Hub, Department of Computational Biology, USR3756 CNRS, F-75015 Paris, France
| | - Bruno Dumas
- Biologics Research, Sanofi R&D, 13 Quai Jules Guesde, 94403 Vitry sur Seine, France
| | - Guy-Franck Richard
- Institut Pasteur, CNRS, UMR3525, 25 rue du Dr Roux, F-75015 Paris, France.,Sorbonne Université, Collège Doctoral, 4 Place Jussieu, F-75005 Paris, France
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6
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Richard GF. The Startling Role of Mismatch Repair in Trinucleotide Repeat Expansions. Cells 2021; 10:cells10051019. [PMID: 33925919 PMCID: PMC8145212 DOI: 10.3390/cells10051019] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/20/2021] [Accepted: 04/21/2021] [Indexed: 12/26/2022] Open
Abstract
Trinucleotide repeats are a peculiar class of microsatellites whose expansions are responsible for approximately 30 human neurological or developmental disorders. The molecular mechanisms responsible for these expansions in humans are not totally understood, but experiments in model systems such as yeast, transgenic mice, and human cells have brought evidence that the mismatch repair machinery is involved in generating these expansions. The present review summarizes, in the first part, the role of mismatch repair in detecting and fixing the DNA strand slippage occurring during microsatellite replication. In the second part, key molecular differences between normal microsatellites and those that show a bias toward expansions are extensively presented. The effect of mismatch repair mutants on microsatellite expansions is detailed in model systems, and in vitro experiments on mismatched DNA substrates are described. Finally, a model presenting the possible roles of the mismatch repair machinery in microsatellite expansions is proposed.
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Affiliation(s)
- Guy-Franck Richard
- Institut Pasteur, CNRS UMR3525, 25 rue du Docteur Roux, 75015 Paris, France
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Zhu L, Wu H, Li H, Tang H, Zhang L, Xu H, Jiao F, Wang N, Yang L. Short Tandem Repeats in plants: Genomic distribution and function prediction. ELECTRON J BIOTECHN 2021. [DOI: 10.1016/j.ejbt.2020.12.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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8
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Tomioka I, Nagai Y, Seki K. Generation of Common Marmoset Model Lines of Spinocerebellar Ataxia Type 3. Front Neurosci 2020; 14:548002. [PMID: 33071733 PMCID: PMC7542094 DOI: 10.3389/fnins.2020.548002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Accepted: 09/07/2020] [Indexed: 01/10/2023] Open
Abstract
Animal models are indispensable tools in the development of innovative treatments for rare and incurable diseases. To date, there is almost no effective treatment for neurodegenerative diseases, and animal models that properly simulate human disease pathologies are eagerly anticipated to identify disease biomarkers and develop therapeutic methods and agents. Among experimental animals, non-human primates are the most suitable animal models for the study of neurodegenerative diseases with human-specific higher brain dysfunction and late-onset and slowly progressing symptoms. With the rapid development of novel therapies such as oligonucleotide therapeutics and genome editing technologies, non-human primate models for neurodegenerative diseases will be essential for preclinical studies and active interventional trials. In a previous publication, we reported the generation of the first transgenic marmoset model of spinocerebellar ataxia type 3 and successful obtainment of subsequent generations with stable disease onset. Moreover, we generated transgenic marmosets in which the transgene was controlled by the tetracycline-inducible gene expression system. In this mini-review, we summarize the research on our marmoset model of spinocerebellar ataxia type 3.
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Affiliation(s)
- Ikuo Tomioka
- Department of Biomedical Engineering, Shinshu University, Nagano, Japan.,Department of Neurophysiology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| | - Yoshitaka Nagai
- Department of Neurotherapeutics, Osaka University, Graduate School of Medicine, Osaka, Japan.,Department of Degenerative Neurological Diseases, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| | - Kazuhiko Seki
- Department of Neurophysiology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
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9
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Palomino‐Hernandez O, Margreiter MA, Rossetti G. Challenges in RNA Regulation in Huntington's Disease: Insights from Computational Studies. Isr J Chem 2020. [DOI: 10.1002/ijch.202000021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Oscar Palomino‐Hernandez
- Computational Biomedicine, Institute of Neuroscience and Medicine (INM-9)/Instute for advanced simulations (IAS-5)Forschungszentrum Juelich 52425 Jülich Germany
- Faculty 1RWTH Aachen 52425 Aachen Germany
- Computation-based Science and Technology Research CenterThe Cyprus Institute Nicosia 2121 Cyprus
- Institute of Life ScienceThe Hebrew University of Jerusalem Jerusalem 91904 Israel
| | - Michael A. Margreiter
- Computational Biomedicine, Institute of Neuroscience and Medicine (INM-9)/Instute for advanced simulations (IAS-5)Forschungszentrum Juelich 52425 Jülich Germany
- Faculty 1RWTH Aachen 52425 Aachen Germany
| | - Giulia Rossetti
- Computational Biomedicine, Institute of Neuroscience and Medicine (INM-9)/Instute for advanced simulations (IAS-5)Forschungszentrum Juelich 52425 Jülich Germany
- Jülich Supercomputing Centre (JSC)Forschungszentrum Jülich 52425 Jülich Germany
- Department of Hematology, Oncology, Hemostaseology and Stem Cell Transplantation University Hospital AachenRWTH Aachen University Pauwelsstraße 30 52074 Aachen Germany
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10
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Khristich AN, Mirkin SM. On the wrong DNA track: Molecular mechanisms of repeat-mediated genome instability. J Biol Chem 2020; 295:4134-4170. [PMID: 32060097 PMCID: PMC7105313 DOI: 10.1074/jbc.rev119.007678] [Citation(s) in RCA: 148] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Expansions of simple tandem repeats are responsible for almost 50 human diseases, the majority of which are severe, degenerative, and not currently treatable or preventable. In this review, we first describe the molecular mechanisms of repeat-induced toxicity, which is the connecting link between repeat expansions and pathology. We then survey alternative DNA structures that are formed by expandable repeats and review the evidence that formation of these structures is at the core of repeat instability. Next, we describe the consequences of the presence of long structure-forming repeats at the molecular level: somatic and intergenerational instability, fragility, and repeat-induced mutagenesis. We discuss the reasons for gender bias in intergenerational repeat instability and the tissue specificity of somatic repeat instability. We also review the known pathways in which DNA replication, transcription, DNA repair, and chromatin state interact and thereby promote repeat instability. We then discuss possible reasons for the persistence of disease-causing DNA repeats in the genome. We describe evidence suggesting that these repeats are a payoff for the advantages of having abundant simple-sequence repeats for eukaryotic genome function and evolvability. Finally, we discuss two unresolved fundamental questions: (i) why does repeat behavior differ between model systems and human pedigrees, and (ii) can we use current knowledge on repeat instability mechanisms to cure repeat expansion diseases?
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Affiliation(s)
| | - Sergei M Mirkin
- Department of Biology, Tufts University, Medford, Massachusetts 02155.
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11
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Defects in the GINS complex increase the instability of repetitive sequences via a recombination-dependent mechanism. PLoS Genet 2019; 15:e1008494. [PMID: 31815930 PMCID: PMC6922473 DOI: 10.1371/journal.pgen.1008494] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 12/19/2019] [Accepted: 10/25/2019] [Indexed: 12/16/2022] Open
Abstract
Faithful replication and repair of DNA lesions ensure genome maintenance. During replication in eukaryotic cells, DNA is unwound by the CMG helicase complex, which is composed of three major components: the Cdc45 protein, Mcm2-7, and the GINS complex. The CMG in complex with DNA polymerase epsilon (CMG-E) participates in the establishment and progression of the replisome. Impaired functioning of the CMG-E was shown to induce genomic instability and promote the development of various diseases. Therefore, CMG-E components play important roles as caretakers of the genome. In Saccharomyces cerevisiae, the GINS complex is composed of the Psf1, Psf2, Psf3, and Sld5 essential subunits. The Psf1-1 mutant form fails to interact with Psf3, resulting in impaired replisome assembly and chromosome replication. Here, we show increased instability of repeat tracts (mononucleotide, dinucleotide, trinucleotide and longer) in yeast psf1-1 mutants. To identify the mechanisms underlying this effect, we analyzed repeated sequence instability using derivatives of psf1-1 strains lacking genes involved in translesion synthesis, recombination, or mismatch repair. Among these derivatives, deletion of RAD52, RAD51, MMS2, POL32, or PIF1 significantly decreased DNA repeat instability. These results, together with the observed increased amounts of single-stranded DNA regions and Rfa1 foci suggest that recombinational mechanisms make important contributions to repeat tract instability in psf1-1 cells. We propose that defective functioning of the CMG-E complex in psf1-1 cells impairs the progression of DNA replication what increases the contribution of repair mechanisms such as template switch and break-induced replication. These processes require sequence homology search which in case of a repeated DNA tract may result in misalignment leading to its expansion or contraction. Processes that ensure genome stability are crucial for all organisms to avoid mutations and decrease the risk of diseases. The coordinated activity of mechanisms underlying the maintenance of high-fidelity DNA duplication and repair is critical to deal with the malfunction of replication forks or DNA damage. Repeated sequences in DNA are particularly prone to instability; these sequences undergo expansions or contractions, leading in humans to various neurological, neurodegenerative, and neuromuscular disorders. A mutant form of one of the noncatalytic subunits of active DNA helicase complex impairs DNA replication. Here, we show that this form also significantly increases the instability of mononucleotide, dinucleotide, trinucleotide and longer repeat tracts. Our results suggest that in cells that harbor a mutated variant of the helicase complex, continuation of DNA replication is facilitated by recombination processes, and this mechanism can be highly mutagenic during repair synthesis through repetitive regions, especially regions that form secondary structures. Our results indicate that proper functioning of the DNA helicase complex is crucial for maintenance of the stability of repeated DNA sequences, especially in the context of recently described disorders in which mutations or deregulation of the human homologs of genes encoding DNA helicase subunits were observed.
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12
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Dynamic DNA Energy Landscapes and Substrate Complexity in Triplet Repeat Expansion and DNA Repair. Biomolecules 2019; 9:biom9110709. [PMID: 31698848 PMCID: PMC6920812 DOI: 10.3390/biom9110709] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Revised: 10/29/2019] [Accepted: 10/31/2019] [Indexed: 12/14/2022] Open
Abstract
DNA repeat domains implicated in DNA expansion diseases exhibit complex conformational and energy landscapes that impact biological outcomes. These landscapes include ensembles of entropically driven positional interchanges between isoenergetic, isomeric looped states referred to as rollamers. Here, we present evidence for the position-dependent impact on repeat DNA energy landscapes of an oxidative lesion (8oxodG) and of an abasic site analogue (tetrahydrofuran, F), the universal intermediate in base excision repair (BER). We demonstrate that these lesions modulate repeat bulge loop distributions within the wider dynamic rollamer triplet repeat landscapes. We showed that the presence of a lesion disrupts the energy degeneracy of the rollameric positional isomers. This lesion-induced disruption leads to the redistribution of loop isomers within the repeat loop rollamer ensemble, favoring those rollameric isomers where the lesion is positioned to be energetically least disruptive. These dynamic ensembles create a highly complex energy/conformational landscape of potential BER enzyme substrates to select for processing or to inhibit processing. We discuss the implications of such lesion-induced alterations in repeat DNA energy landscapes in the context of potential BER repair outcomes, thereby providing a biophysical basis for the intriguing in vivo observation of a linkage between pathogenic triplet repeat expansion and DNA repair.
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Kompella P, Vasquez KM. Obesity and cancer: A mechanistic overview of metabolic changes in obesity that impact genetic instability. Mol Carcinog 2019; 58:1531-1550. [PMID: 31168912 PMCID: PMC6692207 DOI: 10.1002/mc.23048] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 05/08/2019] [Accepted: 05/10/2019] [Indexed: 12/16/2022]
Abstract
Obesity, defined as a state of positive energy balance with a body mass index exceeding 30 kg/m2 in adults and 95th percentile in children, is an increasing global concern. Approximately one-third of the world's population is overweight or obese, and in the United States alone, obesity affects one in six children. Meta-analysis studies suggest that obesity increases the likelihood of developing several types of cancer, and with poorer outcomes, especially in children. The contribution of obesity to cancer risk requires a better understanding of the association between obesity-induced metabolic changes and its impact on genomic instability, which is a major driving force of tumorigenesis. In this review, we discuss how molecular changes during adipose tissue dysregulation can result in oxidative stress and subsequent DNA damage. This represents one of the many critical steps connecting obesity and cancer since oxidative DNA lesions can result in cancer-associated genetic instability. In addition, the by-products of the oxidative degradation of lipids (e.g., malondialdehyde, 4-hydroxynonenal, and acrolein), and gut microbiota-mediated secondary bile acid metabolites (e.g., deoxycholic acid and lithocholic acid), can function as genotoxic agents and tumor promoters. We also discuss how obesity can impact DNA repair efficiency, potentially contributing to cancer initiation and progression. Finally, we outline obesity-related epigenetic changes and identify the gaps in knowledge to be addressed for the development of better therapeutic strategies for the prevention and treatment of obesity-related cancers.
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Affiliation(s)
- Pallavi Kompella
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, 1400 Barbara Jordan Boulevard, Austin, TX 78723, USA
| | - Karen M. Vasquez
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, 1400 Barbara Jordan Boulevard, Austin, TX 78723, USA
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14
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Transgenic Monkey Model of the Polyglutamine Diseases Recapitulating Progressive Neurological Symptoms. eNeuro 2017; 4:eN-NWR-0250-16. [PMID: 28374014 PMCID: PMC5368386 DOI: 10.1523/eneuro.0250-16.2017] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 03/06/2017] [Accepted: 03/07/2017] [Indexed: 01/11/2023] Open
Abstract
Age-associated neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and the polyglutamine (polyQ) diseases, are becoming prevalent as a consequence of elongation of the human lifespan. Although various rodent models have been developed to study and overcome these diseases, they have limitations in their translational research utility owing to differences from humans in brain structure and function and in drug metabolism. Here, we generated a transgenic marmoset model of the polyQ diseases, showing progressive neurological symptoms including motor impairment. Seven transgenic marmosets were produced by lentiviral introduction of the human ataxin 3 gene with 120 CAG repeats encoding an expanded polyQ stretch. Although all offspring showed no neurological symptoms at birth, three marmosets with higher transgene expression developed neurological symptoms of varying degrees at 3-4 months after birth, followed by gradual decreases in body weight gain, spontaneous activity, and grip strength, indicating time-dependent disease progression. Pathological examinations revealed neurodegeneration and intranuclear polyQ protein inclusions accompanied by gliosis, which recapitulate the neuropathological features of polyQ disease patients. Consistent with neuronal loss in the cerebellum, brain MRI analyses in one living symptomatic marmoset detected enlargement of the fourth ventricle, which suggests cerebellar atrophy. Notably, successful germline transgene transmission was confirmed in the second-generation offspring derived from the symptomatic transgenic marmoset gamete. Because the accumulation of abnormal proteins is a shared pathomechanism among various neurodegenerative diseases, we suggest that this new marmoset model will contribute toward elucidating the pathomechanisms of and developing clinically applicable therapies for neurodegenerative diseases.
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Viterbo D, Michoud G, Mosbach V, Dujon B, Richard GF. Replication stalling and heteroduplex formation within CAG/CTG trinucleotide repeats by mismatch repair. DNA Repair (Amst) 2016; 42:94-106. [DOI: 10.1016/j.dnarep.2016.03.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Revised: 02/01/2016] [Accepted: 03/11/2016] [Indexed: 10/22/2022]
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16
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Richard GF. Shortening trinucleotide repeats using highly specific endonucleases: a possible approach to gene therapy? Trends Genet 2015; 31:177-86. [PMID: 25743488 DOI: 10.1016/j.tig.2015.02.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Revised: 02/04/2015] [Accepted: 02/05/2015] [Indexed: 12/31/2022]
Abstract
Trinucleotide repeat expansions are involved in more than two dozen neurological and developmental disorders. Conventional therapeutic approaches aimed at regulating the expression level of affected genes, which rely on drugs, oligonucleotides, and/or transgenes, have met with only limited success so far. An alternative approach is to shorten repeats to non-pathological lengths using highly specific nucleases. Here, I review early experiments using meganucleases, zinc-finger nucleases (ZFN), and transcription-activator like effector nucleases (TALENs) to contract trinucleotide repeats, and discuss the possibility of using CRISPR-Cas nucleases to the same end. Although this is a nascent field, I explore the possibility of designing nucleases and effectively delivering them in the context of gene therapy.
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Affiliation(s)
- Guy-Franck Richard
- Institut Pasteur, Department Genomes and Genetics, Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche (UMR) 3525, 25 Rue du Dr Roux, 75015 Paris, France
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17
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Dion V. Tissue specificity in DNA repair: lessons from trinucleotide repeat instability. Trends Genet 2014; 30:220-9. [PMID: 24842550 DOI: 10.1016/j.tig.2014.04.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Revised: 04/14/2014] [Accepted: 04/16/2014] [Indexed: 12/13/2022]
Abstract
DNA must constantly be repaired to maintain genome stability. Although it is clear that DNA repair reactions depend on cell type and developmental stage, we know surprisingly little about the mechanisms that underlie this tissue specificity. This is due, in part, to the lack of adequate study systems. This review discusses recent progress toward understanding the mechanism leading to varying rates of instability at expanded trinucleotide repeats (TNRs) in different tissues. Although they are not DNA lesions, TNRs are hotspots for genome instability because normal DNA repair activities cause changes in repeat length. The rates of expansions and contractions are readily detectable and depend on cell identity, making TNR instability a particularly convenient model system. A better understanding of this type of genome instability will provide a foundation for studying tissue-specific DNA repair more generally, which has implications in cancer and other diseases caused by mutations in the caretakers of the genome.
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Affiliation(s)
- Vincent Dion
- University of Lausanne, Center for Integrative Genomics, Bâtiment Génopode, 1015 Lausanne, Switzerland.
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Richard GF, Viterbo D, Khanna V, Mosbach V, Castelain L, Dujon B. Highly specific contractions of a single CAG/CTG trinucleotide repeat by TALEN in yeast. PLoS One 2014; 9:e95611. [PMID: 24748175 PMCID: PMC3991675 DOI: 10.1371/journal.pone.0095611] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 03/28/2014] [Indexed: 12/22/2022] Open
Abstract
Trinucleotide repeat expansions are responsible for more than two dozens severe neurological disorders in humans. A double-strand break between two short CAG/CTG trinucleotide repeats was formerly shown to induce a high frequency of repeat contractions in yeast. Here, using a dedicated TALEN, we show that induction of a double-strand break into a CAG/CTG trinucleotide repeat in heterozygous yeast diploid cells results in gene conversion of the repeat tract with near 100% efficacy, deleting the repeat tract. Induction of the same TALEN in homozygous yeast diploids leads to contractions of both repeats to a final length of 3–13 triplets, with 100% efficacy in cells that survived the double-strand breaks. Whole-genome sequencing of surviving yeast cells shows that the TALEN does not increase mutation rate. No other CAG/CTG repeat of the yeast genome showed any length alteration or mutation. No large genomic rearrangement such as aneuploidy, segmental duplication or translocation was detected. It is the first demonstration that induction of a TALEN in an eukaryotic cell leads to shortening of trinucleotide repeat tracts to lengths below pathological thresholds in humans, with 100% efficacy and very high specificity.
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Affiliation(s)
- Guy-Franck Richard
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, Département Génomes & Génétique, Paris, France
- Sorbonne Universités, UPMC Univ Paris 6, IFD, Paris, France
- CNRS, UMR3525, Paris, France
- * E-mail:
| | - David Viterbo
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, Département Génomes & Génétique, Paris, France
- Sorbonne Universités, UPMC Univ Paris 6, IFD, Paris, France
- CNRS, UMR3525, Paris, France
| | - Varun Khanna
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, Département Génomes & Génétique, Paris, France
- Sorbonne Universités, UPMC Univ Paris 6, IFD, Paris, France
- CNRS, UMR3525, Paris, France
| | - Valentine Mosbach
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, Département Génomes & Génétique, Paris, France
- Sorbonne Universités, UPMC Univ Paris 6, IFD, Paris, France
- CNRS, UMR3525, Paris, France
| | - Lauriane Castelain
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, Département Génomes & Génétique, Paris, France
- Sorbonne Universités, UPMC Univ Paris 6, IFD, Paris, France
- CNRS, UMR3525, Paris, France
| | - Bernard Dujon
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, Département Génomes & Génétique, Paris, France
- Sorbonne Universités, UPMC Univ Paris 6, IFD, Paris, France
- CNRS, UMR3525, Paris, France
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Mason AG, Tomé S, Simard JP, Libby RT, Bammler TK, Beyer RP, Morton AJ, Pearson CE, La Spada AR. Expression levels of DNA replication and repair genes predict regional somatic repeat instability in the brain but are not altered by polyglutamine disease protein expression or age. Hum Mol Genet 2013; 23:1606-18. [PMID: 24191263 DOI: 10.1093/hmg/ddt551] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Expansion of CAG/CTG trinucleotide repeats causes numerous inherited neurological disorders, including Huntington's disease (HD), several spinocerebellar ataxias and myotonic dystrophy type 1. Expanded repeats are genetically unstable with a propensity to further expand when transmitted from parents to offspring. For many alleles with expanded repeats, extensive somatic mosaicism has been documented. For CAG repeat diseases, dramatic instability has been documented in the striatum, with larger expansions noted with advancing age. In contrast, only modest instability occurs in the cerebellum. Using microarray expression analysis, we sought to identify the genetic basis of these regional instability differences by comparing gene expression in the striatum and cerebellum of aged wild-type C57BL/6J mice. We identified eight candidate genes enriched in cerebellum, and validated four--Pcna, Rpa1, Msh6 and Fen1--along with a highly associated interactor, Lig1. We also explored whether expression levels of mismatch repair (MMR) proteins are altered in a line of HD transgenic mice, R6/2, that is known to show pronounced regional repeat instability. Compared with wild-type littermates, MMR expression levels were not significantly altered in R6/2 mice regardless of age. Interestingly, expression levels of these candidates were significantly increased in the cerebellum of control and HD human samples in comparison to striatum. Together, our data suggest that elevated expression levels of DNA replication and repair proteins in cerebellum may act as a safeguard against repeat instability, and may account for the dramatically reduced somatic instability present in this brain region, compared with the marked instability observed in the striatum.
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Gao C, Ren X, Mason AS, Li J, Wang W, Xiao M, Fu D. Revisiting an important component of plant genomes: microsatellites. FUNCTIONAL PLANT BIOLOGY : FPB 2013; 40:645-661. [PMID: 32481138 DOI: 10.1071/fp12325] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Accepted: 01/16/2013] [Indexed: 06/11/2023]
Abstract
Microsatellites are some of the most highly variable repetitive DNA tracts in genomes. Few studies focus on whether the characteristic instability of microsatellites is linked to phenotypic effects in plants. We summarise recent data to investigate how microsatellite variations affect gene expression and hence phenotype. We discuss how the basic characteristics of microsatellites may contribute to phenotypic effects. In summary, microsatellites in plants are universal and highly mutable, they coexist and coevolve with transposable elements, and are under selective pressure. The number of motif nucleotides, the type of motif and transposon activity all contribute to the nonrandom generation and decay of microsatellites, and to conservation and distribution biases. Although microsatellites are generated by accident, they mature through responses to environmental change before final decay. This process is mediated by organism adjustment mechanisms, which maintain a balance between birth versus death and growth versus decay in microsatellites. Close relationships also exist between the physical structure, variation and functionality of microsatellites: in most plant species, sequences containing microsatellites are associated with catalytic activity and binding functions, are expressed in the membrane and organelles, and participate in the developmental and metabolic processes. Microsatellites contribute to genome structure and functional plasticity, and may be considered to promote species evolution in plants in response to environmental changes. In conclusion, the generation, loss, functionality and evolution of microsatellites can be related to plant gene expression and functional alterations. The effect of microsatellites on phenotypic variation may be as significant in plants as it is in animals.
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Affiliation(s)
- Caihua Gao
- Engineering Research Center of South Upland Agriculture, Ministry of Education, College of Agronomy and Biotechnology, Southwest University, Chongqing 400715, China
| | - Xiaodong Ren
- Engineering Research Center of South Upland Agriculture, Ministry of Education, College of Agronomy and Biotechnology, Southwest University, Chongqing 400715, China
| | - Annaliese S Mason
- Centre for Integrative Legume Research and School of Agriculture and Food Sciences, The University of Queensland, Brisbane 4072, Qld, Australia
| | - Jiana Li
- Engineering Research Center of South Upland Agriculture, Ministry of Education, College of Agronomy and Biotechnology, Southwest University, Chongqing 400715, China
| | - Wei Wang
- Engineering Research Center of South Upland Agriculture, Ministry of Education, College of Agronomy and Biotechnology, Southwest University, Chongqing 400715, China
| | - Meili Xiao
- Engineering Research Center of South Upland Agriculture, Ministry of Education, College of Agronomy and Biotechnology, Southwest University, Chongqing 400715, China
| | - Donghui Fu
- Key Laboratory of Crop Physiology, Ecology and Genetic Breeding, Ministry of Education, Jiangxi Agricultural University, Nanchang, Jiangxi 330045, China
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Polak U, McIvor E, Dent SY, Wells RD, Napierala M. Expanded complexity of unstable repeat diseases. Biofactors 2013; 39:164-75. [PMID: 23233240 PMCID: PMC4648362 DOI: 10.1002/biof.1060] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 09/19/2012] [Indexed: 11/05/2022]
Abstract
Unstable repeat diseases (URDs) share a common mutational phenomenon of changes in the copy number of short, tandemly repeated DNA sequences. More than 20 human neurological diseases are caused by instability, predominantly, expansion of microsatellite sequences. Changes in the repeat size initiate a cascade of pathological processes, frequently characteristic of a unique disease or a small subgroup of the URDs. Understanding of both the mechanism of repeat instability and molecular consequences of the repeat expansions is critical to developing successful therapies for these diseases. Recent technological breakthroughs in whole genome, transcriptome and proteome analyses will almost certainly lead to new discoveries regarding the mechanisms of repeat instability, the pathogenesis of URDs, and will facilitate development of novel therapeutic approaches. The aim of this review is to give a general overview of unstable repeats diseases, highlight the complexities of these diseases, and feature the emerging discoveries in the field.
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Affiliation(s)
- Urszula Polak
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
- Poznan University of Medical Sciences, Department of Cell Biology, Rokietnicka 5D, 60-806 Poznan, Poland
| | - Elizabeth McIvor
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
| | - Sharon Y.R. Dent
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
| | - Robert D. Wells
- Institute of Biosciences and Technology, assing the University Health Science Center, Center for Genome Research, 2121 West Holcombe Boulevard, Houston, TX 77030, USA
| | - Marek Napierala
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Center for Cancer Epigenetics, Science Park, Smithville, Texas 78957, USA
- Correspondence should be addressed to: Dr. Marek Napierala, University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, SRD 1.134, 1808 Park Road 1C, Smithville, TX 78957, tel. 512-237-6690,
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22
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Tang W, Dominska M, Gawel M, Greenwell PW, Petes TD. Genomic deletions and point mutations induced in Saccharomyces cerevisiae by the trinucleotide repeats (GAA·TTC) associated with Friedreich's ataxia. DNA Repair (Amst) 2012. [PMID: 23182423 DOI: 10.1016/j.dnarep.2012.10.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Expansion of certain trinucleotide repeats causes several types of human diseases, and such tracts are associated with the formation of deletions and other types of genetic rearrangements in Escherichia coli, yeast, and mammalian cells. Below, we show that long (230 repeats) tracts of the trinucleotide associated with Friedreich's ataxia (GAA·TTC) stimulate both large (>50 bp) deletions and point mutations in a reporter gene located more than 1 kb from the repetitive tract. Sequence analysis of deletion breakpoints indicates that the deletions reflect non-homologous end joining of double-stranded DNA breaks (DSBs) initiated in the tract. The tract-induced point mutations appear to reflect a different mechanism involving single-strand annealing of DNA molecules generated by DSBs within the tract, followed by filling-in of single-stranded gaps by the error-prone DNA polymerase zeta.
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Affiliation(s)
- Wei Tang
- Department of Molecular Genetics and Microbiology, Duke University, Durham, NC 27710, USA
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23
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Oligodeoxynucleotide binding to (CTG) · (CAG) microsatellite repeats inhibits replication fork stalling, hairpin formation, and genome instability. Mol Cell Biol 2012; 33:571-81. [PMID: 23166299 DOI: 10.1128/mcb.01265-12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
(CTG)(n) · (CAG)(n) trinucleotide repeat (TNR) expansion in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene causes myotonic dystrophy type 1. However, a direct link between TNR instability, the formation of noncanonical (CTG)(n) · (CAG)(n) structures, and replication stress has not been demonstrated. In a human cell model, we found that (CTG)(45) · (CAG)(45) causes local replication fork stalling, DNA hairpin formation, and TNR instability. Oligodeoxynucleotides (ODNs) complementary to the (CTG)(45) · (CAG)(45) lagging-strand template eliminated DNA hairpin formation on leading- and lagging-strand templates and relieved fork stalling. Prolonged cell culture, emetine inhibition of lagging-strand synthesis, or slowing of DNA synthesis by low-dose aphidicolin induced (CTG)(45) · (CAG)(45) expansions and contractions. ODNs targeting the lagging-strand template blocked the time-dependent or emetine-induced instability but did not eliminate aphidicolin-induced instability. These results show directly that TNR replication stalling, replication stress, hairpin formation, and instability are mechanistically linked in vivo.
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24
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Liu CR, Chang CR, Chern Y, Wang TH, Hsieh WC, Shen WC, Chang CY, Chu IC, Deng N, Cohen S, Cheng TH. Spt4 Is Selectively Required for Transcription of Extended Trinucleotide Repeats. Cell 2012; 148:690-701. [DOI: 10.1016/j.cell.2011.12.032] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 10/03/2011] [Accepted: 12/13/2011] [Indexed: 10/28/2022]
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25
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Affiliation(s)
- Georg W J Auburger
- Section Molecular Neurogenetics, Department of Neurology, Johann Wolfgang Goeche University Medical School, Frankfurt/Main, Germany.
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26
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Topoisomerase 1 and single-strand break repair modulate transcription-induced CAG repeat contraction in human cells. Mol Cell Biol 2011; 31:3105-12. [PMID: 21628532 DOI: 10.1128/mcb.05158-11] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Expanded trinucleotide repeats are responsible for a number of neurodegenerative diseases, such as Huntington disease and myotonic dystrophy type 1. The mechanisms that underlie repeat instability in the germ line and in the somatic tissues of human patients are undefined. Using a selection assay based on contraction of CAG repeat tracts in human cells, we screened the Prestwick chemical library in a moderately high-throughput assay and identified 18 novel inducers of repeat contraction. A subset of these compounds targeted pathways involved in the management of DNA supercoiling associated with transcription. Further analyses using both small molecule inhibitors and small interfering RNA (siRNA)-mediated knockdowns demonstrated the involvement of topoisomerase 1 (TOP1), tyrosyl-DNA phosphodiesterase 1 (TDP1), and single-strand break repair (SSBR) in modulating transcription-dependent CAG repeat contractions. The TOP1-TDP1-SSBR pathway normally functions to suppress repeat instability, since interfering with it stimulated repeat contractions. We further showed that the increase in repeat contractions when the TOP1-TDP1-SSBR pathway is compromised arises via transcription-coupled nucleotide excision repair, a previously identified contributor to transcription-induced repeat instability. These studies broaden the scope of pathways involved in transcription-induced CAG repeat instability and begin to define their interrelationships.
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27
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Abstract
Repetition of trinucleotide sequences is the molecular basis of ~30 hereditary neurological and neurodegenerative diseases, and alternate structures adopted by these sequences are implicated in the etiology of such diseases. Elucidating these structures is important for advancing mechanistic understanding and ultimately treatment. Studies of (CAG) repeats are motivated by their involvement in a number of these diseases, and the structures favored by (CAG)₈ are discussed in this contribution. Utilizing the strong effect of base stacking on fluorescence quantum yield, 2-aminopurine is used in place of adenine to determine the secondary structures adopted by such repeated sequences. Alone, (CAG)₈ folds into a hairpin comprised of a duplex stem and a single-stranded loop. Energetic studies indicate that the hairpin is anchored by the interactions in the stem and has a strained loop environment. As a model for intermediates that form during repeat expansion, (CAG)₈ was also incorporated into a duplex to form a three-way junction. In contrast to the isolated (CAG)₈, this integrated repeat adopts an open, unfolded loop. Enthalpy and entropy changes associated with denaturation indicate that the stability of the three-way junction is dominated by interactions in the duplex arms and that the repeated sequence tracks global unfolding. Because 2-aminopurine provides both structural and energetic information via fluorescence and also is an innocuous substitution for adenine, significant progress in elucidating the secondary structures of (CAG) repeats will be achieved.
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28
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Expansions, contractions, and fragility of the spinocerebellar ataxia type 10 pentanucleotide repeat in yeast. Proc Natl Acad Sci U S A 2011; 108:2843-8. [PMID: 21282659 DOI: 10.1073/pnas.1009409108] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Spinocerebellar ataxia 10 (SCA10) is an autosomal dominant disease caused by large-scale expansions of the (ATTCT)(n) repeat within an intron of the human ATXN10 gene. In contrast to other expandable repeats, this pentanucleotide repeat does not form stable intra- or interstranded DNA structures, being a DNA unwinding element instead. We analyzed the instability of the (ATTCT)(n) repeat in a yeast experimental system, where its expansions led to inactivation of the URA3 reporter gene. The inactivation was due to a dramatic decrease in the mRNA levels owing to premature transcription termination and RNA polyadenylation at the repeat. The rates of expansions strongly increased with the repeat's length, mimicking genetic anticipation in human pedigrees. A first round of genetic analysis showed that a functional TOF1 gene precludes, whereas a functional RAD5 gene promotes, expansions of the (ATTCT)(n) repeat. We hypothesize that repeat expansions could occur upon fortuitous template switching during DNA replication. The rate of repeat contractions was elevated in the Tof1 knockout strain, but it was not affected by the RAD5 gene. Supporting the notion of replication irregularities, we found that (ATTCT)(n) repeats also cause length-dependent chromosomal fragility in yeast. Repeat-mediated fragility was also affected by the Tof1 and Rad5 proteins, being reduced in their absence.
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29
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Friedreich's ataxia (GAA)n•(TTC)n repeats strongly stimulate mitotic crossovers in Saccharomyces cerevisae. PLoS Genet 2011; 7:e1001270. [PMID: 21249181 PMCID: PMC3020933 DOI: 10.1371/journal.pgen.1001270] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2010] [Accepted: 12/07/2010] [Indexed: 11/19/2022] Open
Abstract
Expansions of trinucleotide GAA•TTC tracts are associated with the human disease Friedreich's ataxia, and long GAA•TTC tracts elevate genome instability in yeast. We show that tracts of (GAA)230•(TTC)230 stimulate mitotic crossovers in yeast about 10,000-fold relative to a “normal” DNA sequence; (GAA)n•(TTC)n tracts, however, do not significantly elevate meiotic recombination. Most of the mitotic crossovers are associated with a region of non-reciprocal transfer of information (gene conversion). The major class of recombination events stimulated by (GAA)n•(TTC)n tracts is a tract-associated double-strand break (DSB) that occurs in unreplicated chromosomes, likely in G1 of the cell cycle. These findings indicate that (GAA)n•(TTC)n tracts can be a potent source of loss of heterozygosity in yeast. Although meiotic recombination has been much more studied than mitotic recombination, mitotic recombination is a universal property. Meiotic recombination rates are quite variable within the genome, with some chromosomal regions (hotspots) having much higher levels of exchange than other regions (coldspots). For mitotic recombination, although some types of DNA sequences are known to be associated with elevated recombination rates (highly-transcribed genes, inverted repeated sequences), relatively few hotspots have been described. In this report, we show that a 690 base pair region consisting of 230 copies of the (GAA)n•(TTC)n trinucleotide repeat stimulates mitotic crossovers in yeast 10,000-fold more strongly than an “average” yeast sequence. This sequence is a preferred site for chromosome breakage in stationary phase yeast cells. Our findings may be relevant to understanding the expansions of the (GAA)n•(TTC)n trinucleotide repeat tracts that are associated with the human disease Friedreich's ataxia.
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30
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Wagner JM, Kaufmann SH. Prospects for the Use of ATR Inhibitors to Treat Cancer. Pharmaceuticals (Basel) 2010; 3:1311-1334. [PMID: 27713304 PMCID: PMC4033983 DOI: 10.3390/ph3051311] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 04/12/2010] [Accepted: 04/19/2010] [Indexed: 01/08/2023] Open
Abstract
ATR is an apical kinase in one of the DNA-damage induced checkpoint pathways. Despite the development of inhibitors of kinases structurally related to ATR, as well as inhibitors of the ATR substrate Chk1, no ATR inhibitors have yet been developed. Here we review the effects of ATR downregulation in cancer cells and discuss the potential for development of ATR inhibitors for clinical use.
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Affiliation(s)
- Jill M Wagner
- Division of Oncology Research, College of Medicine, Mayo Clinic, 200 First St., S.W., Rochester, MN 55905, USA.
| | - Scott H Kaufmann
- Division of Oncology Research, College of Medicine, Mayo Clinic, 200 First St., S.W., Rochester, MN 55905, USA.
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31
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Degtyareva NN, Reddish MJ, Sengupta B, Petty JT. Structural studies of a trinucleotide repeat sequence using 2-aminopurine. Biochemistry 2010; 48:2340-6. [PMID: 19170594 DOI: 10.1021/bi802225y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The secondary structure of repeated trinucleotide sequences results in the development of several neurodegenerative diseases, and these studies consider the (CAG)(8) sequence that forms a stem-loop hairpin. The structural and thermodynamic properties of this hairpin are assessed using 2-aminopurine substitutions for adenine at six positions in this repeated sequence. Circular dichroism spectra and thermal denaturation experiments show that the secondary structure is not disturbed by the modifications. The local structure of the hairpin was monitored using the fluorescence intensities of 2-aminopurines, the changes in the intensity relative to the denatured state, and the sensitivity of the fluorescence to quenching by acrylamide. To establish the stem and loop characteristics in (CAG)(8), known reference points for stem, loop, and exposed base motifs were used. In the vicinity of the loop, the bases become more solvent exposed, which suggests that the instability associated with this repeated hairpin influences the global secondary structure. These results provide the basis to interpret the structures adopted by other repeated (CAG) structures.
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Affiliation(s)
- Natalya N Degtyareva
- Department of Chemistry, Furman University, Greenville, South Carolina 29613, USA
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32
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Yang JH, Freudenreich CH. The Rtt109 histone acetyltransferase facilitates error-free replication to prevent CAG/CTG repeat contractions. DNA Repair (Amst) 2010; 9:414-20. [PMID: 20083442 DOI: 10.1016/j.dnarep.2009.12.022] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Revised: 12/23/2009] [Accepted: 12/29/2009] [Indexed: 10/20/2022]
Abstract
Lysine 56 is acetylated on newly synthesized histone H3 in yeast, Drosophila and mammalian cells. All of the proteins involved in histone H3 lysine 56 (H3K56) acetylation are important for maintaining genome integrity. These include Rtt109, a histone acetyltransferase, responsible for acetylating H3K56, Asf1, a histone H3/H4 chaperone, and Hst3 and Hst4, histone deacetylases which remove the acetyl group from H3K56. Here we demonstrate a new role for Rtt109 and H3K56 acetylation in maintaining repetitive DNA sequences in Saccharomyces cerevisiae. We found that cells lacking RTT109 had a high level of CAG/CTG repeat contractions and a twofold increase in breakage at CAG/CTG repeats. In addition, repeat contractions were significantly increased in cells lacking ASF1 and in an hst3Deltahst4Delta double mutant. Because the Rtt107/Rtt101 complex was previously shown to be recruited to stalled replication forks in an Rtt109-dependent manner, we tested whether this complex was involved. However, contractions in rtt109Delta cells were not due to an inability to recruit the Rtt107/Rtt101 complex to repeats, as absence of these proteins had no effect on repeat stability. On the other hand, Dnl4 and Rad51-dependent pathways did play a role in creating some of the repeat contractions in rtt109Delta cells. Our results show that H3K56 acetylation by Rtt109 is important for stabilizing DNA repeats, likely by facilitating proper nucleosome assembly at the replication fork to prevent DNA structure formation and subsequent slippage events or fork breakage.
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Affiliation(s)
- Jiahui H Yang
- Department of Biology, Tufts University, Medford, MA 02155, USA
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33
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Mueller CM, Hilbert JE, Martens W, Thornton CA, Moxley RT, Greene MH. Hypothesis: neoplasms in myotonic dystrophy. Cancer Causes Control 2009; 20:2009-20. [PMID: 19642006 PMCID: PMC3110730 DOI: 10.1007/s10552-009-9395-y] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Accepted: 06/22/2009] [Indexed: 01/20/2023]
Abstract
Tumorigenesis is a multi-step process due to an accumulation of genetic mutations in multiple genes in diverse pathways which ultimately lead to loss of control over cell growth. It is well known that inheritance of rare germline mutations in genes involved in tumorigenesis pathways confer high lifetime risk of neoplasia in affected individuals. Furthermore, a substantial number of multiple malformation syndromes include cancer susceptibility in their phenotype. Studies of the mechanisms underlying these inherited syndromes have added to the understanding of both normal development and the pathophysiology of carcinogenesis. Myotonic dystrophy (DM) represents a group of autosomal dominant, multisystemic diseases that share the clinical features of myotonia, muscle weakness, and early-onset cataracts. Myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2) result from unstable nucleotide repeat expansions in their respective genes. There have been multiple reports of tumors in individuals with DM, most commonly benign calcifying cutaneous tumors known as pilomatricomas. We provide a summary of the tumors reported in DM and a hypothesis for a possible mechanism of tumorigenesis. We hope to stimulate further study into the potential role of DM genes in tumorigenesis, and help define DM pathogenesis, and facilitate developing novel treatment modalities.
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Affiliation(s)
- Christine M Mueller
- Clinical Genetics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health/DHHS, 6120 Executive Boulevard, EPS 7101, Rockville, MD 20852-7231, USA.
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Double-strand break repair pathways protect against CAG/CTG repeat expansions, contractions and repeat-mediated chromosomal fragility in Saccharomyces cerevisiae. Genetics 2009; 184:65-77. [PMID: 19901069 DOI: 10.1534/genetics.109.111039] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Trinucleotide repeats can form secondary structures, whose inappropriate repair or replication can lead to repeat expansions. There are multiple loci within the human genome where expansion of trinucleotide repeats leads to disease. Although it is known that expanded repeats accumulate double-strand breaks (DSBs), it is not known which DSB repair pathways act on such lesions and whether inaccurate DSB repair pathways contribute to repeat expansions. Using Saccharomyces cerevisiae, we found that CAG/CTG tracts of 70 or 155 repeats exhibited significantly elevated levels of breakage and expansions in strains lacking MRE11, implicating the Mre11/Rad50/Xrs2 complex in repairing lesions at structure-forming repeats. About two-thirds of the expansions that occurred in the absence of MRE11 were dependent on RAD52, implicating aberrant homologous recombination as a mechanism for generating expansions. Expansions were also elevated in a sae2 deletion background and these were not dependent on RAD52, supporting an additional role for Mre11 in facilitating Sae2-dependent hairpin processing at the repeat. Mre11 nuclease activity and Tel1-dependent checkpoint functions were largely dispensable for repeat maintenance. In addition, we found that intact homologous recombination and nonhomologous end-joining pathways of DSB repair are needed to prevent repeat fragility and that both pathways also protect against repeat instability. We conclude that failure of principal DSB repair pathways to repair breaks that occur within the repeats can result in the accumulation of atypical intermediates, whose aberrant resolution will then lead to CAG expansions, contractions, and repeat-mediated chromosomal fragility.
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Ludwig AL, Raske C, Tassone F, Garcia-Arocena D, Hershey JW, Hagerman PJ. Translation of the FMR1 mRNA is not influenced by AGG interruptions. Nucleic Acids Res 2009; 37:6896-904. [PMID: 19752155 PMCID: PMC2777427 DOI: 10.1093/nar/gkp713] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The fragile X mental retardation 1 (FMR1) gene contains a CGG-repeat element within its 5′ untranslated region (5′UTR) which, for alleles with more than ∼40 repeats, increasingly affects both transcription (up-regulation) and translation (inhibition) of the repeat-containing RNA with increasing CGG-repeat length. Translational inhibition is thought to be due to impaired ribosomal scanning through the CGG-repeat region, which is postulated to form highly stable secondary/tertiary structure. One striking difference between alleles in the premutation range (55–200 CGG repeats) and those in the normal range (<∼40 repeats) is the reduced number/absence of ‘expansion stabilizing’ AGG interruptions in the larger alleles. Such interruptions, which generally occur every 9–11 repeats in normal alleles, are thought to disrupt the extended CGG-repeat hairpin structure, thus facilitating translational initiation. To test this hypothesis, we have measured the translational efficiency of CGG-repeat mRNAs with 0–2 AGG interruptions, both in vitro (rabbit reticulocyte lysates) and in cell culture (HEK-293 cells). We demonstrate that the AGG interruptions have no detectable influence on translational efficiency in either a cell-free system or cell culture, indicating that any AGG-repeat-induced alterations in secondary/tertiary structure, if present, do not involve the rate-limiting step(s) in translational initiation.
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Affiliation(s)
- Anna L Ludwig
- Department of Biochemistry and Molecular Medicine, School of Medicine, University of California Davis, 4303 Tupper Hall, Davis, CA 95616, USA
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36
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Daude N, Wohlgemuth S, Rogaeva E, Farid AH, Heaton M, Westaway D. Frequent missense and insertion/deletion polymorphisms in the ovine Shadoo gene parallel species-specific variation in PrP. PLoS One 2009; 4:e6538. [PMID: 19657386 PMCID: PMC2716538 DOI: 10.1371/journal.pone.0006538] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Accepted: 07/15/2009] [Indexed: 11/18/2022] Open
Abstract
Background The cellular prion protein PrPC is encoded by the Prnp gene. This protein is expressed in the central nervous system (CNS) and serves as a precursor to the misfolded PrPSc isoform in prion diseases. The prototype prion disease is scrapie in sheep, and whereas Prnp exhibits common missense polymorphisms for V136A, R154H and Q171R in ovine populations, genetic variation in mouse Prnp is limited. Recently the CNS glycoprotein Shadoo (Sho) has been shown to resemble PrPC both in a central hydrophobic domain and in activity in a toxicity assay performed in cerebellar neurons. Sho protein levels are reduced in prion infections in rodents. Prompted by these properties of the Sho protein we investigated the extent of natural variation in SPRN. Principal Findings Paralleling the case for ovine versus human and murine PRNP, we failed to detect significant coding polymorphisms that alter the mature Sho protein in a sample of neurologically normal humans, or in diverse strains of mice. However, ovine SPRN exhibited 4 missense mutations and expansion/contraction in a series of 5 tandem Ala/Gly-containing repeats R1-R5 encoding Sho's hydrophobic domain. A Val71Ala polymorphism and polymorphic expansion of wt 67(Ala)3Gly70 to 67(Ala)5Gly72 reached frequencies of 20%, with other alleles including Δ67–70 and a 67(Ala)6Gly73 expansion. Sheep V71, A71, Δ67–70 and 67(Ala)6Gly73 SPRN alleles encoded proteins with similar stability and posttranslational processing in transfected neuroblastoma cells. Significance Frequent coding polymorphisms are a hallmark of the sheep PRNP gene and our data indicate a similar situation applies to ovine SPRN. Whether a common selection pressure balances diversity at both loci remains to be established.
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Affiliation(s)
- Nathalie Daude
- Centre for Prions and Protein Folding Diseases, University of Alberta, Edmonton, Alberta, Canada
| | - Serene Wohlgemuth
- Centre for Prions and Protein Folding Diseases, University of Alberta, Edmonton, Alberta, Canada
| | - Ekaterina Rogaeva
- Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, Canada
| | - A. Hossein Farid
- Department of Animal Science, Nova Scotia Agricultural College, Truro, Nova Scotia, Canada
| | - Mike Heaton
- United States Department of Agriculture, U. S. Meat Animal Research Center, Clay Center, Nebraska, United States of America
| | - David Westaway
- Centre for Prions and Protein Folding Diseases, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
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Abstract
Yeast and mammalian genomes are replete with nearly identical copies of long dispersed repeats in the form of retrotransposons. Mechanisms clearly exist to maintain genome structure in the face of potential rearrangement between the dispersed repeats, but the nature of this machinery is poorly understood. Here we describe a series of distinct "retrotransposon overdose" (RO) lineages in which the number of Ty1 elements in the Saccharomyces cerevisiae genome has been increased by as much as 10 fold. Although these RO strains are remarkably normal in growth rate, they demonstrate an intrinsic supersensitivity to DNA-damaging agents. We describe the identification of mutants in the DNA replication pathway that enhance this RO-specific DNA damage supersensitivity by promoting ectopic recombination between Ty1 elements. Abrogation of normal DNA replication leads to rampant genome instability primarily in the form of chromosomal aberrations and confirms the central role of DNA replication accuracy in the stabilization of repetitive DNA.
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38
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Keene FR, Smith JA, Collins JG. Metal complexes as structure-selective binding agents for nucleic acids. Coord Chem Rev 2009. [DOI: 10.1016/j.ccr.2009.01.004] [Citation(s) in RCA: 167] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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39
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Voineagu I, Freudenreich CH, Mirkin SM. Checkpoint responses to unusual structures formed by DNA repeats. Mol Carcinog 2009; 48:309-18. [PMID: 19306277 DOI: 10.1002/mc.20512] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
DNA sequences that are prone to adopting non-B DNA secondary structures are associated with hotspots of genomic instability. The fine mechanisms by which alternative DNA structures induce phenomena such as repeat expansions, chromosomal fragility, or gross chromosomal rearrangements are under intensive studies. It is well established that DNA damage checkpoint responses play a crucial role in maintaining a stable genome. It is far less clear, however, whether and how the checkpoint machinery responds to alternative DNA structures. This review discusses the role of the interplay between DNA damage checkpoints and alternative DNA structures in genome maintenance.
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Affiliation(s)
- Irina Voineagu
- Department of Biology, Tufts University, 165 Packard Ave., Medford, MA 02155, USA
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40
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Abstract
Triplet repeat expansion is the molecular basis for several human diseases. Intensive studies using systems in bacteria, yeast, flies, mammalian cells, and mice have provided important insights into the molecular processes that are responsible for mediating repeat instability. The age-dependent, ongoing repeat instability in somatic tissues, especially in terminally differentiated neurons, strongly suggests a robust role for pathways that are independent of DNA replication. Several genetic studies have indicated that transcription can play a critical role in repeat instability, potentially providing a basis for the instability observed in neurons. Transcription-induced repeat instability can be modulated by several DNA repair proteins, including those involved in mismatch repair (MMR) and transcription-coupled nucleotide excision repair (TC-NER). Though the mechanism is unclear, it is likely that transcription facilitates the formation of repeat-specific secondary structures, which act as intermediates to trigger DNA repair, eventually leading to changes in the length of the repeat tract. In addition, other processes associated with transcription can also modulate repeat instability, as shown in a variety of different systems. Overall, the mechanisms underlying repeat instability in humans are unexpectedly complicated. Because repeat-disease genes are widely expressed, transcription undoubtedly contributes to the repeat instability observed in many diseases, but it may be especially important in nondividing cells. Transcription-induced instability is likely to involve an extensive interplay not only of the core transcription machinery and DNA repair proteins, but also of proteins involved in chromatin remodeling, regulation of supercoiling, and removal of stalled RNA polymerases, as well as local DNA sequence effects.
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Affiliation(s)
- Yunfu Lin
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
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41
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SRS2 and SGS1 prevent chromosomal breaks and stabilize triplet repeats by restraining recombination. Nat Struct Mol Biol 2009; 16:159-67. [PMID: 19136956 DOI: 10.1038/nsmb.1544] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Accepted: 12/04/2008] [Indexed: 01/30/2023]
Abstract
Several molecular mechanisms have been proposed to explain trinucleotide repeat expansions. Here we show that in yeast srs2Delta cells, CTG repeats undergo both expansions and contractions, and they show increased chromosomal fragility. Deletion of RAD52 or RAD51 suppresses these phenotypes, suggesting that recombination triggers trinucleotide repeat instability in srs2Delta cells. In sgs1Delta cells, CTG repeats undergo contractions and increased fragility by a mechanism partially dependent on RAD52 and RAD51. Analysis of replication intermediates revealed abundant joint molecules at the CTG repeats during S phase. These molecules migrate similarly to reversed replication forks, and their presence is dependent on SRS2 and SGS1 but not RAD51. Our results suggest that Srs2 promotes fork reversal in repetitive sequences, preventing repeat instability and fragility. In the absence of Srs2 or Sgs1, DNA damage accumulates and is processed by homologous recombination, triggering repeat rearrangements.
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42
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Richard GF, Kerrest A, Dujon B. Comparative genomics and molecular dynamics of DNA repeats in eukaryotes. Microbiol Mol Biol Rev 2008; 72:686-727. [PMID: 19052325 PMCID: PMC2593564 DOI: 10.1128/mmbr.00011-08] [Citation(s) in RCA: 323] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Repeated elements can be widely abundant in eukaryotic genomes, composing more than 50% of the human genome, for example. It is possible to classify repeated sequences into two large families, "tandem repeats" and "dispersed repeats." Each of these two families can be itself divided into subfamilies. Dispersed repeats contain transposons, tRNA genes, and gene paralogues, whereas tandem repeats contain gene tandems, ribosomal DNA repeat arrays, and satellite DNA, itself subdivided into satellites, minisatellites, and microsatellites. Remarkably, the molecular mechanisms that create and propagate dispersed and tandem repeats are specific to each class and usually do not overlap. In the present review, we have chosen in the first section to describe the nature and distribution of dispersed and tandem repeats in eukaryotic genomes in the light of complete (or nearly complete) available genome sequences. In the second part, we focus on the molecular mechanisms responsible for the fast evolution of two specific classes of tandem repeats: minisatellites and microsatellites. Given that a growing number of human neurological disorders involve the expansion of a particular class of microsatellites, called trinucleotide repeats, a large part of the recent experimental work on microsatellites has focused on these particular repeats, and thus we also review the current knowledge in this area. Finally, we propose a unified definition for mini- and microsatellites that takes into account their biological properties and try to point out new directions that should be explored in a near future on our road to understanding the genetics of repeated sequences.
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Affiliation(s)
- Guy-Franck Richard
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, CNRS, URA2171, Université Pierre et Marie Curie, UFR927, 25 rue du Dr. Roux, F-75015, Paris, France.
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43
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DNA energy landscapes via calorimetric detection of microstate ensembles of metastable macrostates and triplet repeat diseases. Proc Natl Acad Sci U S A 2008; 105:18326-30. [PMID: 19015511 DOI: 10.1073/pnas.0810376105] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Biopolymers exhibit rough energy landscapes, thereby allowing biological processes to access a broad range of kinetic and thermodynamic states. In contrast to proteins, the energy landscapes of nucleic acids have been the subject of relatively few experimental investigations. In this study, we use calorimetric and spectroscopic observables to detect, resolve, and selectively enrich energetically discrete ensembles of microstates within metastable DNA structures. Our results are consistent with metastable, "native" DNA states being composed of an ensemble of discrete and kinetically stable microstates of differential stabilities, rather than exclusively being a single, discrete thermodynamic species. This conceptual construct is important for understanding the linkage between biopolymer conformational/configurational space and biological function, such as in protein folding, allosteric control of enzyme activity, RNA and DNA folding and function, DNA structure and biological regulation, etc. For the specific DNA sequences and structures studied here, the demonstration of discrete, kinetically stable microstates potentially has biological consequences for understanding the development and onset of DNA expansion and triplet repeat diseases.
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44
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Kim HM, Narayanan V, Mieczkowski PA, Petes TD, Krasilnikova MM, Mirkin SM, Lobachev KS. Chromosome fragility at GAA tracts in yeast depends on repeat orientation and requires mismatch repair. EMBO J 2008; 27:2896-906. [PMID: 18833189 DOI: 10.1038/emboj.2008.205] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Accepted: 09/15/2008] [Indexed: 11/10/2022] Open
Abstract
Expansion of triplex-forming GAA/TTC repeats in the first intron of FXN gene results in Friedreich's ataxia. Besides FXN, there are a number of other polymorphic GAA/TTC loci in the human genome where the size variations thus far have been considered to be a neutral event. Using yeast as a model system, we demonstrate that expanded GAA/TTC repeats represent a threat to eukaryotic genome integrity by triggering double-strand breaks and gross chromosomal rearrangements. The fragility potential strongly depends on the length of the tracts and orientation of the repeats relative to the replication origin, which correlates with their propensity to adopt triplex structure and to block replication progression. We show that fragility is mediated by mismatch repair machinery and requires the MutSbeta and endonuclease activity of MutLalpha. We suggest that the mechanism of GAA/TTC-induced chromosomal aberrations defined in yeast can also operate in human carriers with expanded tracts.
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Affiliation(s)
- Hyun-Min Kim
- School of Biology and Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA
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45
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Cimprich KA, Cortez D. ATR: an essential regulator of genome integrity. Nat Rev Mol Cell Biol 2008; 9:616-27. [PMID: 18594563 DOI: 10.1038/nrm2450] [Citation(s) in RCA: 1284] [Impact Index Per Article: 80.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Genome maintenance is a constant concern for cells, and a coordinated response to DNA damage is required to maintain cellular viability and prevent disease. The ataxia-telangiectasia mutated (ATM) and ATM and RAD3-related (ATR) protein kinases act as master regulators of the DNA-damage response by signalling to control cell-cycle transitions, DNA replication, DNA repair and apoptosis. Recent studies have provided new insights into the mechanisms that control ATR activation, have helped to explain the overlapping but non-redundant activities of ATR and ATM in DNA-damage signalling, and have clarified the crucial functions of ATR in maintaining genome integrity.
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Affiliation(s)
- Karlene A Cimprich
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Clark Center, 318 Campus Drive, W350B, Stanford, California 94305-5441, USA.
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46
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Brandström M, Ellegren H. Genome-wide analysis of microsatellite polymorphism in chicken circumventing the ascertainment bias. Genome Res 2008; 18:881-7. [PMID: 18356314 DOI: 10.1101/gr.075242.107] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Studies of microsatellites evolution based on marker data almost inherently suffer from an ascertainment bias because there is selection for the most mutable and polymorphic loci during marker development. To circumvent this bias we took advantage of whole-genome shotgun sequence data from three unrelated chicken individuals that, when aligned to the genome reference sequence, give sequence information on two chromosomes from about one-fourth (375,000) of all microsatellite loci containing di- through pentanucleotide repeat motifs in the chicken genome. Polymorphism is seen at loci with as few as five repeat units, and the proportion of dimorphic loci then increases to 50% for sequences with approximately 10 repeat units, to reach a maximum of 75%-80% for sequences with 15 or more repeat units. For any given repeat length, polymorphism increases with decreasing GC content of repeat motifs for dinucleotides, nonhairpin-forming trinucleotides, and tetranucleotides. For trinucleotide repeats which are likely to form hairpin structures, polymorphism increases with increasing GC content, indicating that the relative stability of hairpins affects the rate of replication slippage. For any given repeat length, polymorphism is significantly lower for imperfect compared to perfect repeats and repeat interruptions occur in >15% of loci. However, interruptions are not randomly distributed within repeat arrays but are preferentially located toward the ends. There is negative correlation between microsatellite abundance and single nucleotide polymorphism (SNP) density, providing large-scale genomic support for the hypothesis that equilibrium microsatellite distributions are governed by a balance between rate of replication slippage and rate of point mutation.
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Affiliation(s)
- Mikael Brandström
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
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47
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Haberman Y, Amariglio N, Rechavi G, Eisenberg E. Trinucleotide repeats are prevalent among cancer-related genes. Trends Genet 2007; 24:14-8. [PMID: 18054813 DOI: 10.1016/j.tig.2007.09.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2007] [Revised: 09/27/2007] [Accepted: 09/28/2007] [Indexed: 10/22/2022]
Abstract
Trinucleotide repeats (TNRs) have been primarily connected to neurologic and neuromuscular diseases, with few specific TNRs linked with various tumors. Here we conduct a genome-wide analysis and show that TNRs are five times more prevalent in cancer-related human genes. Interestingly, we also find that cancer-related genes are significantly longer than other genes. Our results suggest that genes containing TNRs are more prone to mutagenesis. The database of TNR genes can be used as a list of candidate cancer-related genes.
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Affiliation(s)
- Yael Haberman
- Department of Pediatric Hemato-Oncology, the Edmond and Lily Safra Children's Hospital and Cancer Research Center, Sheba Medical Center and Sackler School of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel
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48
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Lam SL, Lai KF, Chi LM. Proton chemical shift prediction of A.A mismatches in B-DNA duplexes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 187:105-11. [PMID: 17475525 DOI: 10.1016/j.jmr.2007.04.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2007] [Revised: 03/29/2007] [Accepted: 04/04/2007] [Indexed: 05/15/2023]
Abstract
A proton chemical shift prediction method has been developed for double helical DNAs containing A.A mismatches. This method makes use of the chemical shift prediction scheme for normal B-DNA duplexes developed by Altona and co-workers and a set of A.A mismatch triplet chemical shift values and corrections factors extracted from reference sequences. The triplet values are used for predicting chemical shifts of A.A mismatches whereas the normal B-DNA chemical shifts and correction factors are used for the flanking residues of A.A mismatches. Both 5'- and 3'-correction factors have been determined from the chemical shift differences upon replacing the A.A mismatch in a duplex with an A.T base pair. Based on 560 sets of predicted and experimental chemical shifts, the overall prediction accuracy for various types of protons has been determined to be 0.07 ppm with an excellent correlation coefficient of 0.9996.
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Affiliation(s)
- Sik Lok Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
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49
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Yang J, Freudenreich CH. Haploinsufficiency of yeast FEN1 causes instability of expanded CAG/CTG tracts in a length-dependent manner. Gene 2007; 393:110-5. [PMID: 17383831 PMCID: PMC1904339 DOI: 10.1016/j.gene.2007.01.025] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Revised: 01/23/2007] [Accepted: 01/24/2007] [Indexed: 11/17/2022]
Abstract
Trinucleotide repeat diseases, such as Huntington's disease, are caused by the expansion of trinucleotide repeats above a threshold of about 35 repeats. Once expanded, the repeats are unstable and tend to expand further both in somatic cells and during transmission, resulting in a more severe disease phenotype. Flap endonuclease 1 (Fen1), has an endonuclease activity specific for 5' flap structures and is involved in Okazaki fragment processing and base excision repair. Fen1 also plays an important role in preventing instability of CAG/CTG trinucleotide repeat sequences, as the expansion frequency of CAG/CTG repeats is increased in FEN1 mutants in vitro and in yeast cells defective for the yeast homolog, RAD27. Here we have tested whether one copy of yeast FEN1 is enough to maintain CAG/CTG tract stability in diploid yeast cells. We found that CAG/CTG repeats are stable in RAD27 +/- cells if the tract is 70 repeats long and exhibit a slightly increased expansion frequency if the tract is 85 or 130 repeats long. However for CAG-155 tracts, the repeat expansion frequency in RAD27 +/- cells is significantly higher than in RAD27 +/+ cells. This data indicates that cells containing longer CAG/CTG repeats need more Fen1 protein to maintain tract stability and that maintenance of long CAG/CTG repeats is particularly sensitive to Fen1 levels. Our results may explain the relatively small effects seen in the Huntington's disease (HD) FEN1 +/- heterozygous mice and myotonic dystrophy type 1 (DM1) FEN1 +/- heterozygous mice, and suggest that inefficient flap processing by Fen1 could play a role in the continued expansions seen in humans with trinucleotide repeat expansion diseases.
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Affiliation(s)
- Jiahui Yang
- Department of Biology, Tufts University, Medford, MA 02155, USA
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50
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Kato M, Haku T, Hibino T, Fukada H, Mishima Y, Yamashita I, Minoshima S, Nagayama K, Shimizu N. Stable minihairpin structures forming at minisatellite DNA isolated from yellow fin sea bream Acanthopagrus latus. Comp Biochem Physiol B Biochem Mol Biol 2006; 146:427-37. [PMID: 17258918 DOI: 10.1016/j.cbpb.2006.11.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2006] [Revised: 11/27/2006] [Accepted: 11/28/2006] [Indexed: 12/20/2022]
Abstract
The lengths of simple repeat sequences are generally unstable or polymorphic (highly variable with respect to the numbers of tandem repeats). Previously we have isolated a family of minisatellite DNA (GenBank accession AF422186) that appears specifically and abundantly in the genome of yellow fin sea bream Acanthopagrus latus but not in closely-related red sea bream Pagrus major, and found that the numbers of tandem arrays in the homologous loci are polymorphic. This means that the minisatellite sequence has appeared and propagated in A. latus genome after speciation. In order to understand what makes the minisatellite widespread within the A. latus genome and what causes the polymorphic nature of the number of tandem repeats, the structural features of single-stranded polynucleotides were analyzed by electrophoresis, chemical modification, circular dichroism (CD), differential scanning calorimetry (DSC) and electron microscopy. The results suggest that a portion of the repeat unit forms a stable minihairpin structure, and it can cause polymerase pausing within the minisatellite DNA.
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Affiliation(s)
- Mikio Kato
- Department of Biological Science, Osaka Prefecture University Graduate School of Science, 1-1 Gakuencho, Naka-ku, Sakai 599-8531, Japan.
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