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Duardo RC, Guerra F, Pepe S, Capranico G. Non-B DNA structures as a booster of genome instability. Biochimie 2023; 214:176-192. [PMID: 37429410 DOI: 10.1016/j.biochi.2023.07.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Revised: 07/04/2023] [Accepted: 07/06/2023] [Indexed: 07/12/2023]
Abstract
Non-canonical secondary structures (NCSs) are alternative nucleic acid structures that differ from the canonical B-DNA conformation. NCSs often occur in repetitive DNA sequences and can adopt different conformations depending on the sequence. The majority of these structures form in the context of physiological processes, such as transcription-associated R-loops, G4s, as well as hairpins and slipped-strand DNA, whose formation can be dependent on DNA replication. It is therefore not surprising that NCSs play important roles in the regulation of key biological processes. In the last years, increasing published data have supported their biological role thanks to genome-wide studies and the development of bioinformatic prediction tools. Data have also highlighted the pathological role of these secondary structures. Indeed, the alteration or stabilization of NCSs can cause the impairment of transcription and DNA replication, modification in chromatin structure and DNA damage. These events lead to a wide range of recombination events, deletions, mutations and chromosomal aberrations, well-known hallmarks of genome instability which are strongly associated with human diseases. In this review, we summarize molecular processes through which NCSs trigger genome instability, with a focus on G-quadruplex, i-motif, R-loop, Z-DNA, hairpin, cruciform and multi-stranded structures known as triplexes.
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Affiliation(s)
- Renée C Duardo
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126, Bologna, Italy
| | - Federico Guerra
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126, Bologna, Italy
| | - Simona Pepe
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126, Bologna, Italy
| | - Giovanni Capranico
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, via Selmi 3, 40126, Bologna, Italy.
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2
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Sun M, Moquet J, Lloyd D, Barnard S, Anbalagan S, Steel H, Sommer A, Gothard L, Somaiah N, Ainsbury E. Applicability of Scoring Calyculin A-Induced Premature Chromosome Condensation Objects for Dose Assessment Including for Radiotherapy Patients. Cytogenet Genome Res 2023; 163:143-153. [PMID: 37879308 PMCID: PMC10946622 DOI: 10.1159/000534656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Accepted: 10/16/2023] [Indexed: 10/27/2023] Open
Abstract
As an extension to a previous study, a linear calibration curve covering doses from 0 to 10 Gy was constructed and evaluated in the present study using calyculin A-induced premature chromosome condensation (PCC) by scoring excess PCC objects. The main aim of this study was to assess the applicability of this PCC assay for doses below 2 Gy that are critical for triage categorization. Two separate blind tests involving a total of 6 doses were carried out; 4 out of 6 dose estimates were within the 95% confidence limits (95% CL) with the other 2 just outside. In addition, blood samples from five cancer patients undergoing external beam radiotherapy (RT) were also analyzed, and the results showed whole-body dose estimates statistically comparable to the dicentric chromosome assay (DCA) results. This is the first time that calyculin A-induced PCC was used to analyze clinical samples by scoring excess objects. Although dose estimates for the pre-RT patient samples were found to be significantly higher than the mean value for the healthy donors and were also significantly higher than those obtained using DCA, all these pre-treatment patients fell into the same category as those who may have received a low dose (<1 Gy) and do not require immediate medical care during emergency triage. Additionally, for radiological accidents with unknown exposure scenario, PCC objects and rings can be scored in parallel for the assessment of both low- and high-dose exposures. In conclusion, scoring excess objects using calyculin A-induced PCC is confirmed to be another potential biodosimetry tool in radiological emergency particularly in mass casualty scenarios, even though the data need to be interpreted with caution when cancer patients are among the casualties.
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Affiliation(s)
- Mingzhu Sun
- UK Health Security Agency (UKHSA), Department of Radiation Effects, Cytogenetics and Pathology Group, RCEHD, Didcot, UK
| | - Jayne Moquet
- UK Health Security Agency (UKHSA), Department of Radiation Effects, Cytogenetics and Pathology Group, RCEHD, Didcot, UK
| | - David Lloyd
- UK Health Security Agency (UKHSA), Department of Radiation Effects, Cytogenetics and Pathology Group, RCEHD, Didcot, UK
| | - Stephen Barnard
- UK Health Security Agency (UKHSA), Department of Radiation Effects, Cytogenetics and Pathology Group, RCEHD, Didcot, UK
| | - Selvakumar Anbalagan
- Division of Radiotherapy and Imaging, The Institute of Cancer Research (ICR), Sutton, UK
| | - Harriet Steel
- Division of Radiotherapy and Imaging, The Institute of Cancer Research (ICR), Sutton, UK
| | - Aurore Sommer
- Division of Radiotherapy and Imaging, The Institute of Cancer Research (ICR), Sutton, UK
| | - Lone Gothard
- Division of Radiotherapy and Imaging, The Institute of Cancer Research (ICR), Sutton, UK
| | - Navita Somaiah
- Division of Radiotherapy and Imaging, The Institute of Cancer Research (ICR), Sutton, UK
- The Royal Marsden NHS Foundation Trust, Downs Road, Sutton, UK
| | - Elizabeth Ainsbury
- UK Health Security Agency (UKHSA), Department of Radiation Effects, Cytogenetics and Pathology Group, RCEHD, Didcot, UK
- Environmental Research Group Within The School of Public Health, Faculty of Medicine at Imperial College of Science, Technology and Medicine, London, UK
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3
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Hill HJ, Bonser D, Golic KG. Dicentric chromosome breakage in Drosophila melanogaster is influenced by pericentric heterochromatin and occurs in nonconserved hotspots. Genetics 2023; 224:iyad052. [PMID: 37010100 PMCID: PMC10213500 DOI: 10.1093/genetics/iyad052] [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: 10/18/2022] [Revised: 10/18/2022] [Accepted: 03/13/2023] [Indexed: 04/04/2023] Open
Abstract
Chromosome breakage plays an important role in the evolution of karyotypes and can produce deleterious effects within a single individual, such as aneuploidy or cancer. Forces that influence how and where chromosomes break are not fully understood. In humans, breakage tends to occur in conserved hotspots called common fragile sites (CFS), especially during replication stress. By following the fate of dicentric chromosomes in Drosophila melanogaster, we find that breakage under tension also tends to occur in specific hotspots. Our experimental approach was to induce sister chromatid exchange in a ring chromosome to generate a dicentric chromosome with a double chromatid bridge. In the following cell division, the dicentric bridges may break. We analyzed the breakage patterns of 3 different ring-X chromosomes. These chromosomes differ by the amount and quality of heterochromatin they carry as well as their genealogical history. For all 3 chromosomes, breakage occurs preferentially in several hotspots. Surprisingly, we found that the hotspot locations are not conserved between the 3 chromosomes: each displays a unique array of breakage hotspots. The lack of hotspot conservation, along with a lack of response to aphidicolin, suggests that these breakage sites are not entirely analogous to CFS and may reveal new mechanisms of chromosome fragility. Additionally, the frequency of dicentric breakage and the durability of each chromosome's spindle attachment vary significantly between the 3 chromosomes and are correlated with the origin of the centromere and the amount of pericentric heterochromatin. We suggest that different centromere strengths could account for this.
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Affiliation(s)
- Hunter J Hill
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Danielle Bonser
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Kent G Golic
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
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4
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Brison O, Gnan S, Azar D, Koundrioukoff S, Melendez-Garcia R, Kim SJ, Schmidt M, El-Hilali S, Jaszczyszyn Y, Lachages AM, Thermes C, Chen CL, Debatisse M. Mistimed origin licensing and activation stabilize common fragile sites under tight DNA-replication checkpoint activation. Nat Struct Mol Biol 2023; 30:539-550. [PMID: 37024657 DOI: 10.1038/s41594-023-00949-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Accepted: 02/28/2023] [Indexed: 04/08/2023]
Abstract
Genome integrity requires replication to be completed before chromosome segregation. The DNA-replication checkpoint (DRC) contributes to this coordination by inhibiting CDK1, which delays mitotic onset. Under-replication of common fragile sites (CFSs), however, escapes surveillance, resulting in mitotic chromosome breaks. Here we asked whether loose DRC activation induced by modest stresses commonly used to destabilize CFSs could explain this leakage. We found that tightening DRC activation or CDK1 inhibition stabilizes CFSs in human cells. Repli-Seq and molecular combing analyses showed a burst of replication initiations implemented in mid S-phase across a subset of late-replicating sequences, including CFSs, while the bulk genome was unaffected. CFS rescue and extra-initiations required CDC6 and CDT1 availability in S-phase, implying that CDK1 inhibition permits mistimed origin licensing and firing. In addition to delaying mitotic onset, tight DRC activation therefore supports replication completion of late origin-poor domains at risk of under-replication, two complementary roles preserving genome stability.
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Affiliation(s)
- Olivier Brison
- CNRS UMR 9019, Gustave Roussy Institute, Villejuif, France
- Paris-Saclay University, Gif-sur-Yvette, France
| | - Stefano Gnan
- Curie Institute, PSL Research University, CNRS UMR 3244, Paris, France
- Sorbonne University, Paris, France
| | - Dana Azar
- Curie Institute, PSL Research University, CNRS UMR 3244, Paris, France
- Sorbonne University, Paris, France
- Laboratoire Biodiversité et Génomique Fonctionnelle, Faculté des Sciences, Université Saint-Joseph, Beirut, Lebanon
| | - Stéphane Koundrioukoff
- CNRS UMR 9019, Gustave Roussy Institute, Villejuif, France
- Sorbonne University, Paris, France
| | - Rodrigo Melendez-Garcia
- CNRS UMR 9019, Gustave Roussy Institute, Villejuif, France
- Paris-Saclay University, Gif-sur-Yvette, France
| | - Su-Jung Kim
- CNRS UMR 9019, Gustave Roussy Institute, Villejuif, France
- Paris-Saclay University, Gif-sur-Yvette, France
| | - Mélanie Schmidt
- CNRS UMR 9019, Gustave Roussy Institute, Villejuif, France
- Paris-Saclay University, Gif-sur-Yvette, France
| | - Sami El-Hilali
- Curie Institute, PSL Research University, CNRS UMR 3244, Paris, France
- Sorbonne University, Paris, France
- Villefranche sur mer Developmental Biology Laboratory, CNRS UMR7009, Villefranche-sur-Mer, France
| | - Yan Jaszczyszyn
- Paris-Saclay University, Gif-sur-Yvette, France
- Institute for Integrative Biology of the Cell (I2BC), UMR 9198CNRS, CEA, Paris-Sud University, Gif-sur-Yvette, France
| | - Anne-Marie Lachages
- Curie Institute, PSL Research University, CNRS UMR 3244, Paris, France
- UTCBS, CNRS UMR 8258/ INSERM U 1267, Sorbonne-Paris-Cité University, Paris, France
| | - Claude Thermes
- Paris-Saclay University, Gif-sur-Yvette, France
- Institute for Integrative Biology of the Cell (I2BC), UMR 9198CNRS, CEA, Paris-Sud University, Gif-sur-Yvette, France
| | - Chun-Long Chen
- Curie Institute, PSL Research University, CNRS UMR 3244, Paris, France
- Sorbonne University, Paris, France
| | - Michelle Debatisse
- CNRS UMR 9019, Gustave Roussy Institute, Villejuif, France.
- Sorbonne University, Paris, France.
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5
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Yu Y, Xu W, Wen C, Zhao S, Li G, Liu R, Chen ZJ, Qin Y, Ma J, Yang Y, Zhao S. UBE2T resolves transcription-replication conflicts and protects common fragile sites in primordial germ cells. Cell Mol Life Sci 2023; 80:92. [PMID: 36928776 PMCID: PMC11072727 DOI: 10.1007/s00018-023-04733-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 02/04/2023] [Accepted: 02/22/2023] [Indexed: 03/18/2023]
Abstract
The proper development of primordial germ cells (PGCs) is an essential prerequisite for gametogenesis and mammalian fertility. The Fanconi anemia (FA) pathway functions in maintaining the development of PGCs. FANCT/UBE2T serves as an E2 ubiquitin-conjugating enzyme that ubiquitylates the FANCD2-FANCI complex to activate the FA pathway, but its role in the development of PGCs is not clear. In this study, we found that Ube2t knockout mice showed defects in PGC proliferation, leading to severe loss of germ cells after birth. Deletion of UBE2T exacerbated DNA damage and triggered the activation of the p53 pathway. We further demonstrated that UBE2T counteracted transcription-replication conflicts by resolving R-loops and stabilizing replication forks, and also protected common fragile sites by resolving R-loops in large genes and promoting mitotic DNA synthesis to maintain the genome stability of PGCs. Overall, these results provide new insights into the function and regulatory mechanisms of the FA pathway ensuring normal development of PGCs.
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Affiliation(s)
- Yongze Yu
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Weiwei Xu
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Canxin Wen
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Simin Zhao
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Guangyu Li
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Ran Liu
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Zi-Jiang Chen
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
- Research Unit of Gametogenesis and Health of ART-Offspring, Chinese Academy of Medical Sciences, Jinan, 250021, Shandong, China
- Shanghai Key Laboratory for Assisted Reproduction and Reproductive Genetics, Shanghai, 200135, China
- Center for Reproductive Medicine, School of Medicine, Ren Ji Hospital, Shanghai Jiao Tong University, Shanghai, 200135, China
| | - Yingying Qin
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China
| | - Jinlong Ma
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China.
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China.
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China.
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China.
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China.
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China.
| | - Yajuan Yang
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China.
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China.
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China.
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China.
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China.
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China.
| | - Shidou Zhao
- Center for Reproductive Medicine, Shandong University, Jinan, 250012, Shandong, China.
- Key Laboratory of Reproductive Endocrinology of Ministry of Education, Shandong University, Jinan, 250012, Shandong, China.
- Shandong Key Laboratory of Reproductive Medicine, Jinan, 250012, Shandong, China.
- Shandong Provincial Clinical Research Center for Reproductive Health, Jinan, 250012, Shandong, China.
- Shandong Technology Innovation Center for Reproductive Health, Jinan, 250012, Shandong, China.
- National Research Center for Assisted Reproductive Technology and Reproductive Genetics, Shandong University, Jinan, 250012, Shandong, China.
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Mitotic DNA synthesis in response to replication stress requires the sequential action of DNA polymerases zeta and delta in human cells. Nat Commun 2023; 14:706. [PMID: 36759509 PMCID: PMC9911744 DOI: 10.1038/s41467-023-35992-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 01/11/2023] [Indexed: 02/11/2023] Open
Abstract
Oncogene activation creates DNA replication stress (RS) in cancer cells, which can generate under-replicated DNA regions (UDRs) that persist until cells enter mitosis. UDRs also have the potential to generate DNA bridges in anaphase cells or micronuclei in the daughter cells, which could promote genomic instability. To suppress such damaging changes to the genome, human cells have developed a strategy to conduct 'unscheduled' DNA synthesis in mitosis (termed MiDAS) that serves to rescue under-replicated loci. Previous studies have shown that MiDAS proceeds via a POLD3-dependent pathway that shows some features of break-induced replication. Here, we define how human cells utilize both DNA gap filling (REV1 and Pol ζ) and replicative (Pol δ) DNA polymerases to complete genome duplication following a perturbed S-phase. We present evidence for the existence of a polymerase-switch during MiDAS that is required for new DNA synthesis at UDRs. Moreover, we reveal that, upon oncogene activation, cancer cell survival is significantly compromised when REV1 is depleted, suggesting that REV1 inhibition might be a feasible approach for the treatment of some human cancers.
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7
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Gotoh E. Chemical-Induced Premature Chromosome Condensation Protocol. Methods Mol Biol 2023; 2519:41-51. [PMID: 36066708 DOI: 10.1007/978-1-0716-2433-3_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Chromosome analysis is one of most fundamental techniques for cytogenetic studies. Chromosomes are conventionally prepared from mitotic cells arrested by colcemid block protocol. Premature chromosome condensation (PCC) technique is an alternative to obtain chromosomes. It was more than half century ago that the first observation of PCC phenomena reported. Since then, cell-fusion-mediated PCC method has been developed and introduced in many fields of chromosome analysis. More than quarter century ago, novel PCC technique using chemical drug has been developed. Afterwards, this simple and efficient drug-induced PCC technique becomes a standard protocol for preparing chromosomes. Thus, it seems to be the good time to introduce PCC technique protocol for the artisans in the field of cytogenetic studies.
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Affiliation(s)
- Eisuke Gotoh
- Division of Diagnostic Imaging, Department of Radiology, Japan Labour Health and Safety Organization, Tokyo Rosai Hospital, Ohta-ku, Tokyo, Japan.
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8
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Gotoh E. Visualizing Active Replication Regions in S-Phase Chromosomes. Methods Mol Biol 2023; 2519:117-126. [PMID: 36066717 DOI: 10.1007/978-1-0716-2433-3_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
A basic question of cell biology is how DNA folds to chromosome. A number of recently accumulated evidences have suggested that folding of chromosome proceeds tightly coupled with DNA replication progresses. Drug-induced PCC is a useful tool for visualization of the interphase nuclei, in particular, S-phase, as S-phase prematurely condensed chromosomes (S-phase PCC). Active replicating DNA is labeled directly with Cy3-dUTP by bead loading method, and then S-phase nuclei is immediately condensed prematurely by calyculin A to obtain S-phase PCC. Active replicating regions on S-PCC are observed under a scanning confocal microscope. Cy3-dUTP-labeled S-phase PCCs clearly reveal the drastic transitional change of chromosome formation through S-phase, starting from a "cloudy nebula" to numerous numbers of "beads on a string" and finally to "striped arrays of banding structured chromosome" known as G- or R-banding pattern. The number, distribution, and shape of replication foci were also measured in individual subphase of S-phase; maximally ~1400 foci of 0.35 μm average radius size were scored at the beginning of S-phase, and the number is reduced to ~100 at the end of S-phase. Drug-induced PCC clearly provided the new insight that eukaryote DNA replication is tightly coupled with the chromosome condensation/compaction for construction of eukaryote higher-ordered chromosome structure.
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Affiliation(s)
- Eisuke Gotoh
- Division of Diagnostic Imaging, Department of Radiology, Japan Labour Health and Safety Organization, Tokyo Rosai Hospital, Ohta-ku, Tokyo, Japan.
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9
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Mirceta M, Shum N, Schmidt MHM, Pearson CE. Fragile sites, chromosomal lesions, tandem repeats, and disease. Front Genet 2022; 13:985975. [PMID: 36468036 PMCID: PMC9714581 DOI: 10.3389/fgene.2022.985975] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 09/02/2022] [Indexed: 09/16/2023] Open
Abstract
Expanded tandem repeat DNAs are associated with various unusual chromosomal lesions, despiralizations, multi-branched inter-chromosomal associations, and fragile sites. Fragile sites cytogenetically manifest as localized gaps or discontinuities in chromosome structure and are an important genetic, biological, and health-related phenomena. Common fragile sites (∼230), present in most individuals, are induced by aphidicolin and can be associated with cancer; of the 27 molecularly-mapped common sites, none are associated with a particular DNA sequence motif. Rare fragile sites ( ≳ 40 known), ≤ 5% of the population (may be as few as a single individual), can be associated with neurodevelopmental disease. All 10 molecularly-mapped folate-sensitive fragile sites, the largest category of rare fragile sites, are caused by gene-specific CGG/CCG tandem repeat expansions that are aberrantly CpG methylated and include FRAXA, FRAXE, FRAXF, FRA2A, FRA7A, FRA10A, FRA11A, FRA11B, FRA12A, and FRA16A. The minisatellite-associated rare fragile sites, FRA10B, FRA16B, can be induced by AT-rich DNA-ligands or nucleotide analogs. Despiralized lesions and multi-branched inter-chromosomal associations at the heterochromatic satellite repeats of chromosomes 1, 9, 16 are inducible by de-methylating agents like 5-azadeoxycytidine and can spontaneously arise in patients with ICF syndrome (Immunodeficiency Centromeric instability and Facial anomalies) with mutations in genes regulating DNA methylation. ICF individuals have hypomethylated satellites I-III, alpha-satellites, and subtelomeric repeats. Ribosomal repeats and subtelomeric D4Z4 megasatellites/macrosatellites, are associated with chromosome location, fragility, and disease. Telomere repeats can also assume fragile sites. Dietary deficiencies of folate or vitamin B12, or drug insults are associated with megaloblastic and/or pernicious anemia, that display chromosomes with fragile sites. The recent discovery of many new tandem repeat expansion loci, with varied repeat motifs, where motif lengths can range from mono-nucleotides to megabase units, could be the molecular cause of new fragile sites, or other chromosomal lesions. This review focuses on repeat-associated fragility, covering their induction, cytogenetics, epigenetics, cell type specificity, genetic instability (repeat instability, micronuclei, deletions/rearrangements, and sister chromatid exchange), unusual heritability, disease association, and penetrance. Understanding tandem repeat-associated chromosomal fragile sites provides insight to chromosome structure, genome packaging, genetic instability, and disease.
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Affiliation(s)
- Mila Mirceta
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Natalie Shum
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Monika H. M. Schmidt
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Christopher E. Pearson
- Program of Genetics and Genome Biology, The Hospital for Sick Children, The Peter Gilgan Centre for Research and Learning, Toronto, ON, Canada
- Program of Molecular Genetics, University of Toronto, Toronto, ON, Canada
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10
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Bukhari AB, Chan GK, Gamper AM. Targeting the DNA Damage Response for Cancer Therapy by Inhibiting the Kinase Wee1. Front Oncol 2022; 12:828684. [PMID: 35251998 PMCID: PMC8891215 DOI: 10.3389/fonc.2022.828684] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 01/21/2022] [Indexed: 12/15/2022] Open
Abstract
Cancer cells typically heavily rely on the G2/M checkpoint to survive endogenous and exogenous DNA damage, such as genotoxic stress due to genome instability or radiation and chemotherapy. The key regulator of the G2/M checkpoint, the cyclin-dependent kinase 1 (CDK1), is tightly controlled, including by its phosphorylation state. This posttranslational modification, which is determined by the opposing activities of the phosphatase cdc25 and the kinase Wee1, allows for a more rapid response to cellular stress than via the synthesis or degradation of modulatory interacting proteins, such as p21 or cyclin B. Reducing Wee1 activity results in ectopic activation of CDK1 activity and drives premature entry into mitosis with unrepaired or under-replicated DNA and causing mitotic catastrophe. Here, we review efforts to use small molecule inhibitors of Wee1 for therapeutic purposes, including strategies to combine Wee1 inhibition with genotoxic agents, such as radiation therapy or drugs inducing replication stress, or inhibitors of pathways that show synthetic lethality with Wee1. Furthermore, it become increasingly clear that Wee1 inhibition can also modulate therapeutic immune responses. We will discuss the mechanisms underlying combination treatments identifying both cell intrinsic and systemic anti-tumor activities.
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11
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Kodali S, Meyer-Nava S, Landry S, Chakraborty A, Rivera-Mulia JC, Feng W. Epigenomic signatures associated with spontaneous and replication stress-induced DNA double strand breaks. Front Genet 2022; 13:907547. [PMID: 36506300 PMCID: PMC9730818 DOI: 10.3389/fgene.2022.907547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Accepted: 11/07/2022] [Indexed: 11/25/2022] Open
Abstract
Common fragile sites (CFSs) are specific regions of all individuals' genome that are predisposed to DNA double strand breaks (DSBs) and undergo subsequent rearrangements. CFS formation can be induced in vitro by mild level of DNA replication stress, such as DNA polymerase inhibition or nucleotide pool disturbance. The mechanisms of CFS formation have been linked to DNA replication timing control, transcription activities, as well as chromatin organization. However, it is unclear what specific cis- or trans-factors regulate the interplay between replication and transcription that determine CFS formation. We recently reported genome-wide mapping of DNA DSBs under replication stress induced by aphidicolin in human lymphoblastoids for the first time. Here, we systematically compared these DSBs with regards to nearby epigenomic features mapped in the same cell line from published studies. We demonstrate that aphidicolin-induced DSBs are strongly correlated with histone 3 lysine 36 trimethylation, a marker for active transcription. We further demonstrate that this DSB signature is a composite effect by the dual treatment of aphidicolin and its solvent, dimethylsulfoxide, the latter of which potently induces transcription on its own. We also present complementing evidence for the association between DSBs and 3D chromosome architectural domains with high density gene cluster and active transcription. Additionally, we show that while DSBs were detected at all but one of the fourteen finely mapped CFSs, they were not enriched in the CFS core sequences and rather demarcated the CFS core region. Related to this point, DSB density was not higher in large genes of greater than 300 kb, contrary to reported enrichment of CFS sites at these large genes. Finally, replication timing analyses demonstrate that the CFS core region contain initiation events, suggesting that altered replication dynamics are responsible for CFS formation in relatively higher level of replication stress.
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Affiliation(s)
- Sravan Kodali
- Department of Biochemistry and Molecular Biology, Upstate Medical University, Syracuse, NY, United States
| | - Silvia Meyer-Nava
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, United States
| | - Stephen Landry
- Department of Biochemistry and Molecular Biology, Upstate Medical University, Syracuse, NY, United States
| | - Arijita Chakraborty
- Department of Biochemistry and Molecular Biology, Upstate Medical University, Syracuse, NY, United States
| | - Juan Carlos Rivera-Mulia
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, United States
| | - Wenyi Feng
- Department of Biochemistry and Molecular Biology, Upstate Medical University, Syracuse, NY, United States
- *Correspondence: Wenyi Feng,
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12
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Trejo-Santillan I, Mendoza-Guevara CC, Ramos-Godinez MDP, Ramon-Gallegos E. Biosecurity test of conjugated nanoparticles of chitosanprotoporphyrin IX-vitamin B9 for their use in photodynamic therapy. IEEE Trans Nanobioscience 2021; 21:149-156. [PMID: 34606461 DOI: 10.1109/tnb.2021.3117747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Nanotechnology proposes new applications for the development of nanotransporters and active targeting molecules with the use of biodegradable polymeric nanoparticles to improve the specificity towards target cells. However, these products must comply with safety tests to be endorsed as therapeutic alternatives by regulatory organizations. The goal of this work was to evaluate the biosafety (cytotoxicity and genotoxicity) of chitosan polymeric nanoparticles conjugate with protoporphyrin IX and vitamin B9 (CNPs-PpIX-B9) that were previously optimized from the established protocol by our laboratory and tested in CHO-K1 cells by bioassay following the recommendations of the chromosomal aberrations test by OECD 473 (2016) guideline. The conjugate did not show evidence of genotoxicity (clastogenicity). Surprisingly, the significant differences between the treatments performed and the negative control do not represent increases in chromosomal aberrations, whereby the safe concentrations to use the conjugate without inducing cytotoxic or genotoxic effects are less than 0.25 mg / mL. Since it induced a significant decrease of structural chromosomal aberrations, generating a positive effect on the genomic stability of CHO-K1 cells cultured in this test system.
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13
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Munk SHN, Voutsinos V, Oestergaard VH. Large Intronic Deletion of the Fragile Site Gene PRKN Dramatically Lowers Its Fragility Without Impacting Gene Expression. Front Genet 2021; 12:695172. [PMID: 34354738 PMCID: PMC8329550 DOI: 10.3389/fgene.2021.695172] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 06/28/2021] [Indexed: 11/13/2022] Open
Abstract
Common chromosomal fragile sites (CFSs) are genomic regions prone to form breaks and gaps on metaphase chromosomes during conditions of replication stress. Moreover, CFSs are hotspots for deletions and amplifications in cancer genomes. Fragility at CFSs is caused by transcription of extremely large genes, which contributes to replication problems. These extremely large genes do not encode large proteins, but the extreme sizes of the genes originate from vast introns. Intriguingly, the intron sizes of extremely large genes are conserved between mammals and birds. Here, we have used reverse genetics to address the function and significance of the largest intron in the extremely large gene PRKN, which is highly fragile in our model system. Specifically, we have introduced an 80-kilobase deletion in intron 7 of PRKN. We find that gene expression of PRKN is largely unaffected by this intronic deletion. Strikingly, the intronic deletion, which leads to a 12% reduction of the overall size of the PRKN gene body, results in an almost twofold reduction of the PRKN fragility. Our results stress that while the large intron clearly contributes to the fragility of PRKN, it does not play an important role for PRKN expression. Taken together, our findings further add to the mystery concerning conservation of the seemingly non-functional but troublesome large introns in PRKN.
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14
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Boteva L, Nozawa RS, Naughton C, Samejima K, Earnshaw WC, Gilbert N. Common Fragile Sites Are Characterized by Faulty Condensin Loading after Replication Stress. Cell Rep 2021; 32:108177. [PMID: 32966795 PMCID: PMC7511797 DOI: 10.1016/j.celrep.2020.108177] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 07/22/2020] [Accepted: 08/31/2020] [Indexed: 12/17/2022] Open
Abstract
Cells coordinate interphase-to-mitosis transition, but recurrent cytogenetic lesions appear at common fragile sites (CFSs), termed CFS expression, in a tissue-specific manner after replication stress, marking regions of instability in cancer. Despite such a distinct defect, no model fully provides a molecular explanation for CFSs. We show that CFSs are characterized by impaired chromatin folding, manifesting as disrupted mitotic structures visible with molecular fluorescence in situ hybridization (FISH) probes in the presence and absence of replication stress. Chromosome condensation assays reveal that compaction-resistant chromatin lesions persist at CFSs throughout the cell cycle and mitosis. Cytogenetic and molecular lesions are marked by faulty condensin loading at CFSs, a defect in condensin-I-mediated compaction, and are coincident with mitotic DNA synthesis (MIDAS). This model suggests that, in conditions of exogenous replication stress, aberrant condensin loading leads to molecular defects and CFS expression, concomitantly providing an environment for MIDAS, which, if not resolved, results in chromosome instability.
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Affiliation(s)
- Lora Boteva
- MRC Human Genetics Unit, The University of Edinburgh, Crewe Rd South, Edinburgh EH4 2XU, UK
| | - Ryu-Suke Nozawa
- MRC Human Genetics Unit, The University of Edinburgh, Crewe Rd South, Edinburgh EH4 2XU, UK
| | - Catherine Naughton
- MRC Human Genetics Unit, The University of Edinburgh, Crewe Rd South, Edinburgh EH4 2XU, UK
| | - Kumiko Samejima
- Wellcome Centre for Cell Biology, The University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - William C Earnshaw
- Wellcome Centre for Cell Biology, The University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - Nick Gilbert
- MRC Human Genetics Unit, The University of Edinburgh, Crewe Rd South, Edinburgh EH4 2XU, UK.
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15
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Komar D, Juszczynski P. Rebelled epigenome: histone H3S10 phosphorylation and H3S10 kinases in cancer biology and therapy. Clin Epigenetics 2020; 12:147. [PMID: 33054831 PMCID: PMC7556946 DOI: 10.1186/s13148-020-00941-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Accepted: 09/28/2020] [Indexed: 12/15/2022] Open
Abstract
Background With the discovery that more than half of human cancers harbor mutations in chromatin proteins, deregulation of epigenetic mechanisms has been recognized a hallmark of malignant transformation. Post-translational modifications (PTMs) of histone proteins, as main components of epigenetic regulatory machinery, are also broadly accepted as therapeutic target. Current “epigenetic” therapies target predominantly writers, erasers and readers of histone acetylation and (to a lesser extent) methylation, leaving other types of PTMs largely unexplored. One of them is the phosphorylation of serine 10 on histone H3 (H3S10ph). Main body H3S10ph is emerging as an important player in the initiation and propagation of cancer, as it facilitates cellular malignant transformation and participates in fundamental cellular functions. In normal cells this histone mark dictates the hierarchy of additional histone modifications involved in the formation of protein binding scaffolds, transcriptional regulation, blocking repressive epigenetic information and shielding gene regions from heterochromatin spreading. During cell division, this mark is essential for chromosome condensation and segregation. It is also involved in the function of specific DNA–RNA hybrids, called R-loops, which modulate transcription and facilitate chromosomal instability. Increase in H3S10ph is observed in numerous cancer types and its abundance has been associated with inferior prognosis. Many H3S10-kinases, including MSK1/2, PIM1, CDK8 and AURORA kinases, have been long considered targets in cancer therapy. However, since these proteins also participate in other critical processes, including signal transduction, apoptotic signaling, metabolic fitness and transcription, their chromatin functions are often neglected. Conclusions H3S10ph and enzymes responsible for deposition of this histone modification are important for chromatin activity and oncogenesis. Epigenetic-drugs targeting this axis of modifications, potentially in combination with conventional or targeted therapy, provide a promising angle in search for knowledge-driven therapeutic strategies in oncology.
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Affiliation(s)
- Dorota Komar
- Department of Experimental Hematology, Institute of Hematology and Transfusion Medicine, Gandhi 14 Str, 02-776, Warsaw, Poland.
| | - Przemyslaw Juszczynski
- Department of Experimental Hematology, Institute of Hematology and Transfusion Medicine, Gandhi 14 Str, 02-776, Warsaw, Poland
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16
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Sun M, Moquet J, Lloyd D, Ainsbury E. A faster and easier biodosimetry method based on calyculin A-induced premature chromosome condensation (PCC) by scoring excess objects. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2020; 40:892-905. [PMID: 32590374 DOI: 10.1088/1361-6498/aba085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Dicentric analysis and the ring PCC assay as established biodosimetry methods both have limitations in the estimation of absorbed doses in suspected overexposure cases between 5 and 10 Gy. The proposed method based on calyculin A-induced PCC overcomes these limitations by scoring excess objects as the endpoint. This new scoring method can potentially serve as a faster and up-scalable approach that complements the existing methods with higher accuracy at different dose ranges. It can also potentially be performed by less skilled workers when no automated system is available in mass casualty emergency cases to assist with the triage of patients. Additionally, it offers the possibility to further reduce the sample size and PCC induction time. In this pilot study, a calibration curve for excess objects was constructed using the new scoring method for the first time and a blind validation test composed of three unknown doses was carried out. Almost all the dose estimates were within the 95% confidence limits of the actual test doses by scoring only 50-100 PCC spreads. This method was found to be more accurate than ring PCC for doses below 10 Gy.
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17
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Folate stress induces SLX1- and RAD51-dependent mitotic DNA synthesis at the fragile X locus in human cells. Proc Natl Acad Sci U S A 2020; 117:16527-16536. [PMID: 32601218 PMCID: PMC7368274 DOI: 10.1073/pnas.1921219117] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Folate deficiency is associated with multiple disorders in humans. Through the analysis of the fragile X syndrome locus (FRAXA) in immortalized human lymphocytes or fibroblasts, we demonstrate that FRAXA undergoes DNA synthesis in mitosis (MiDAS). We demonstrate that this process occurs via break-induced DNA replication and requires the SLX1/SLX4 endonuclease complex, the RAD51 recombinase and POLD3, a subunit of polymerase delta. We also demonstrate that other loci undergo MiDAS upon folate stress. This study reveals a function of human SLX1 in the maintenance of FRAXA stability and provides evidence that, in addition to FRAXA, MiDAS occurs at other loci following folate deprivation. These findings provide insight into the diverse and detrimental consequences of folate deficiency in human cells. Folate deprivation drives the instability of a group of rare fragile sites (RFSs) characterized by CGG trinucleotide repeat (TNR) sequences. Pathological expansion of the TNR within the FRAXA locus perturbs DNA replication and is the major causative factor for fragile X syndrome, a sex-linked disorder associated with cognitive impairment. Although folate-sensitive RFSs share many features with common fragile sites (CFSs; which are found in all individuals), they are induced by different stresses and share no sequence similarity. It is known that a pathway (termed MiDAS) is employed to complete the replication of CFSs in early mitosis. This process requires RAD52 and is implicated in generating translocations and copy number changes at CFSs in cancers. However, it is unclear whether RFSs also utilize MiDAS and to what extent the fragility of CFSs and RFSs arises by shared or distinct mechanisms. Here, we demonstrate that MiDAS does occur at FRAXA following folate deprivation but proceeds via a pathway that shows some mechanistic differences from that at CFSs, being dependent on RAD51, SLX1, and POLD3. A failure to complete MiDAS at FRAXA leads to severe locus instability and missegregation in mitosis. We propose that break-induced DNA replication is required for the replication of FRAXA under folate stress and define a cellular function for human SLX1. These findings provide insights into how folate deprivation drives instability in the human genome.
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18
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O'Neill RJ. Seq'ing identity and function in a repeat-derived noncoding RNA world. Chromosome Res 2020; 28:111-127. [PMID: 32146545 PMCID: PMC7393779 DOI: 10.1007/s10577-020-09628-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Revised: 02/07/2020] [Accepted: 02/14/2020] [Indexed: 01/06/2023]
Abstract
Innovations in high-throughout sequencing approaches are being marshaled to both reveal the composition of the abundant and heterogeneous noncoding RNAs that populate cell nuclei and lend insight to the mechanisms by which noncoding RNAs influence chromosome biology and gene expression. This review focuses on some of the recent technological developments that have enabled the isolation of nascent transcripts and chromatin-associated and DNA-interacting RNAs. Coupled with emerging genome assembly and analytical approaches, the field is poised to achieve a comprehensive catalog of nuclear noncoding RNAs, including those derived from repetitive regions within eukaryotic genomes. Herein, particular attention is paid to the challenges and advances in the sequence analyses of repeat and transposable element-derived noncoding RNAs and in ascribing specific function(s) to such RNAs.
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Affiliation(s)
- Rachel J O'Neill
- Institute for Systems Genomics, University of Connecticut, Storrs, CT, 06269, USA.
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT, 06269, USA.
- Department of Genetics and Genome Sciences, University of Connecticut Health Center, Farmington, CT, 06030, USA.
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19
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Transcription-mediated organization of the replication initiation program across large genes sets common fragile sites genome-wide. Nat Commun 2019; 10:5693. [PMID: 31836700 PMCID: PMC6911102 DOI: 10.1038/s41467-019-13674-5] [Citation(s) in RCA: 65] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 11/15/2019] [Indexed: 12/29/2022] Open
Abstract
Common fragile sites (CFSs) are chromosome regions prone to breakage upon replication stress known to drive chromosome rearrangements during oncogenesis. Most CFSs nest in large expressed genes, suggesting that transcription could elicit their instability; however, the underlying mechanisms remain elusive. Genome-wide replication timing analyses here show that stress-induced delayed/under-replication is the hallmark of CFSs. Extensive genome-wide analyses of nascent transcripts, replication origin positioning and fork directionality reveal that 80% of CFSs nest in large transcribed domains poor in initiation events, replicated by long-travelling forks. Forks that travel long in late S phase explains CFS replication features, whereas formation of sequence-dependent fork barriers or head-on transcription–replication conflicts do not. We further show that transcription inhibition during S phase, which suppresses transcription–replication encounters and prevents origin resetting, could not rescue CFS stability. Altogether, our results show that transcription-dependent suppression of initiation events delays replication of large gene bodies, committing them to instability. Common Fragile Sites (CFSs) are chromosome regions prone to breakage upon replication stress known to drive chromosome rearrangements during oncogenesis. Here the authors use genome-wide and single cell techniques to assess how replication timing and transcriptional activity correlate with genome stability.
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20
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Mladenov E, Fan X, Paul-Konietzko K, Soni A, Iliakis G. DNA-PKcs and ATM epistatically suppress DNA end resection and hyperactivation of ATR-dependent G 2-checkpoint in S-phase irradiated cells. Sci Rep 2019; 9:14597. [PMID: 31601897 PMCID: PMC6787047 DOI: 10.1038/s41598-019-51071-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 09/20/2019] [Indexed: 11/29/2022] Open
Abstract
We previously reported that cells exposed to low doses of ionizing radiation (IR) in the G2-phase of the cell cycle activate a checkpoint that is epistatically regulated by ATM and ATR operating as an integrated module. In this module, ATR interphases exclusively with the cell cycle to implement the checkpoint, mainly using CHK1. The ATM/ATR module similarly regulates DNA end-resection at low IR-doses. Strikingly, at high IR-doses, the ATM/ATR coupling relaxes and each kinase exerts independent contributions to resection and the G2-checkpoint. DNA-PKcs links to the ATM/ATR module and defects cause hyper-resection and hyperactivation of G2-checkpoint at all doses examined. Surprisingly, our present report reveals that cells irradiated in S-phase utilize a different form of wiring between DNA-PKcs/ATM/ATR: The checkpoint activated in G2-phase is regulated exclusively by ATR/CHK1; similarly at high and low IR-doses. DNA end-resection supports ATR-activation, but inhibition of ATR leaves resection unchanged. DNA-PKcs and ATM link now epistatically to resection and their inhibition causes hyper-resection and ATR-dependent G2-checkpoint hyperactivation at all IR-doses. We propose that DNA-PKcs, ATM and ATR form a modular unit to regulate DSB processing with their crosstalk distinctly organized in S- and G2- phase, with strong dependence on DSB load only in G2-phase.
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Affiliation(s)
- Emil Mladenov
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
| | - Xiaoxiang Fan
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Katja Paul-Konietzko
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - Aashish Soni
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany
| | - George Iliakis
- Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, 45122, Essen, Germany.
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21
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Pentzold C, Shah SA, Hansen NR, Le Tallec B, Seguin-Orlando A, Debatisse M, Lisby M, Oestergaard VH. FANCD2 binding identifies conserved fragile sites at large transcribed genes in avian cells. Nucleic Acids Res 2019; 46:1280-1294. [PMID: 29253234 PMCID: PMC5815096 DOI: 10.1093/nar/gkx1260] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Accepted: 12/05/2017] [Indexed: 12/14/2022] Open
Abstract
Common Chromosomal Fragile Sites (CFSs) are specific genomic regions prone to form breaks on metaphase chromosomes in response to replication stress. Moreover, CFSs are mutational hotspots in cancer genomes, showing that the mutational mechanisms that operate at CFSs are highly active in cancer cells. Orthologs of human CFSs are found in a number of other mammals, but the extent of CFS conservation beyond the mammalian lineage is unclear. Characterization of CFSs from distantly related organisms can provide new insight into the biology underlying CFSs. Here, we have mapped CFSs in an avian cell line. We find that, overall the most significant CFSs coincide with extremely large conserved genes, from which very long transcripts are produced. However, no significant correlation between any sequence characteristics and CFSs is found. Moreover, we identified putative early replicating fragile sites (ERFSs), which is a distinct class of fragile sites and we developed a fluctuation analysis revealing high mutation rates at the CFS gene PARK2, with deletions as the most prevalent mutation. Finally, we show that avian homologs of the human CFS genes despite their fragility have resisted the general intron size reduction observed in birds suggesting that CFSs have a conserved biological function.
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Affiliation(s)
- Constanze Pentzold
- Department of Biology; University of Copenhagen; Copenhagen N 2200, Denmark
| | - Shiraz Ali Shah
- Department of Biology; University of Copenhagen; Copenhagen N 2200, Denmark
| | - Niels Richard Hansen
- Department of Mathematical Sciences, University of Copenhagen, Copenhagen 2100, Denmark
| | - Benoît Le Tallec
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), CNRS-UMR8197 - Inserm U1024, Paris F-75005, France
| | - Andaine Seguin-Orlando
- Center for GeoGenetics, Natural History Museum of Denmark; University of Copenhagen; Copenhagen 1350, Denmark.,Danish National High-throughput DNA Sequencing Centre, University of Copenhagen, Øster Farimagsgade 2D, Copenhagen K 1353, Denmark
| | | | - Michael Lisby
- Department of Biology; University of Copenhagen; Copenhagen N 2200, Denmark.,Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Blegdamsvej 3b, DK-2200 Copenhagen N, Denmark
| | - Vibe H Oestergaard
- Department of Biology; University of Copenhagen; Copenhagen N 2200, Denmark
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22
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Deng L, Wu RA, Sonneville R, Kochenova OV, Labib K, Pellman D, Walter JC. Mitotic CDK Promotes Replisome Disassembly, Fork Breakage, and Complex DNA Rearrangements. Mol Cell 2019; 73:915-929.e6. [PMID: 30849395 PMCID: PMC6410736 DOI: 10.1016/j.molcel.2018.12.021] [Citation(s) in RCA: 92] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Revised: 10/03/2018] [Accepted: 12/21/2018] [Indexed: 12/27/2022]
Abstract
DNA replication errors generate complex chromosomal rearrangements and thereby contribute to tumorigenesis and other human diseases. One mechanism that triggers these errors is mitotic entry before the completion of DNA replication. To address how mitosis might affect DNA replication, we used Xenopus egg extracts. When mitotic CDK (Cyclin B1-CDK1) is used to drive interphase egg extracts into a mitotic state, the replicative CMG (CDC45/MCM2-7/GINS) helicase undergoes ubiquitylation on its MCM7 subunit, dependent on the E3 ubiquitin ligase TRAIP. Whether replisomes have stalled or undergone termination, CMG ubiquitylation is followed by its extraction from chromatin by the CDC48/p97 ATPase. TRAIP-dependent CMG unloading during mitosis is also seen in C. elegans early embryos. At stalled forks, CMG removal results in fork breakage and end joining events involving deletions and templated insertions. Our results identify a mitotic pathway of global replisome disassembly that can trigger replication fork collapse and DNA rearrangements.
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Affiliation(s)
- Lin Deng
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Cell Biology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA; Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - R Alex Wu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - Remi Sonneville
- MRC Protein Phosphorylation and Ubiquitylation Unit, Sir James Black Centre, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Olga V Kochenova
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA
| | - Karim Labib
- MRC Protein Phosphorylation and Ubiquitylation Unit, Sir James Black Centre, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - David Pellman
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Cell Biology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Howard Hughes Medical Institute, Boston, MA 02115, USA.
| | - Johannes C Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston, MA 02115, USA.
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23
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Tsuda M, Ogawa S, Ooka M, Kobayashi K, Hirota K, Wakasugi M, Matsunaga T, Sakuma T, Yamamoto T, Chikuma S, Sasanuma H, Debatisse M, Doherty AJ, Fuchs RP, Takeda S. PDIP38/PolDIP2 controls the DNA damage tolerance pathways by increasing the relative usage of translesion DNA synthesis over template switching. PLoS One 2019; 14:e0213383. [PMID: 30840704 PMCID: PMC6402704 DOI: 10.1371/journal.pone.0213383] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Accepted: 02/19/2019] [Indexed: 12/05/2022] Open
Abstract
Replicative DNA polymerases are frequently stalled at damaged template strands. Stalled replication forks are restored by the DNA damage tolerance (DDT) pathways, error-prone translesion DNA synthesis (TLS) to cope with excessive DNA damage, and error-free template switching (TS) by homologous DNA recombination. PDIP38 (Pol-delta interacting protein of 38 kDa), also called Pol δ-interacting protein 2 (PolDIP2), physically associates with TLS DNA polymerases, polymerase η (Polη), Polλ, and PrimPol, and activates them in vitro. It remains unclear whether PDIP38 promotes TLS in vivo, since no method allows for measuring individual TLS events in mammalian cells. We disrupted the PDIP38 gene, generating PDIP38-/- cells from the chicken DT40 and human TK6 B cell lines. These PDIP38-/- cells did not show a significant sensitivity to either UV or H2O2, a phenotype not seen in any TLS-polymerase-deficient DT40 or TK6 mutants. DT40 provides a unique opportunity of examining individual TLS and TS events by the nucleotide sequence analysis of the immunoglobulin variable (Ig V) gene as the cells continuously diversify Ig V by TLS (non-templated Ig V hypermutation) and TS (Ig gene conversion) during in vitro culture. PDIP38-/- cells showed a shift in Ig V diversification from TLS to TS. We measured the relative usage of TLS and TS in TK6 cells at a chemically synthesized UV damage (CPD) integrated into genomic DNA. The loss of PDIP38 also caused an increase in the relative usage of TS. The number of UV-induced sister chromatid exchanges, TS events associated with crossover, was increased a few times in PDIP38-/- human and chicken cells. Collectively, the loss of PDIP38 consistently causes a shift in DDT from TLS to TS without enhancing cellular sensitivity to DNA damage. We propose that PDIP38 controls the relative usage of TLS and TS increasing usage of TLS without changing the overall capability of DDT.
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Affiliation(s)
- Masataka Tsuda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Hiroshima, Japan
| | - Saki Ogawa
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masato Ooka
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji-shi, Tokyo, Japan
| | - Kaori Kobayashi
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji-shi, Tokyo, Japan
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji-shi, Tokyo, Japan
| | - Mitsuo Wakasugi
- Faculty of Pharmacy, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan
| | - Tsukasa Matsunaga
- Faculty of Pharmacy, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan
| | - Tetsushi Sakuma
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Hiroshima, Japan
| | - Takashi Yamamoto
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Hiroshima, Japan
| | - Shunsuke Chikuma
- Department of Microbiology and Immunology, Keio University School of Medicine, Tokyo, Japan
| | - Hiroyuki Sasanuma
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Michelle Debatisse
- Institut Curie UMR 3244, Universite Pierre et Marie Curie (Paris 06), CNRS Paris, France
| | - Aidan J. Doherty
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - Robert P. Fuchs
- DNA Damage Tolerance CNRS, UMR7258, Marseille, France
- Institut Paoli-Calmettes, Marseille, France
- Aix-Marseille University, UM 105, Marseille, France
- Inserm, U1068, CRCM, Marseille, France
| | - Shunichi Takeda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- * E-mail:
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G2 Premature Chromosome Condensation/Chromosome Aberration Assay: Drug-Induced Premature Chromosome Condensation (PCC) Protocols and Cytogenetic Approaches in Mitotic Chromosome and Interphase Chromatin for Radiation Biology. Methods Mol Biol 2019; 1984:47-60. [PMID: 31267419 DOI: 10.1007/978-1-4939-9432-8_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Chromosome analysis is a fundamental technique for a wide range of cytogenetic studies. Chromosome aberrations are easily introduced by many kinds of clastogenic agents such as ionizing irradiation, UV, or alkylating agents, and damaged chromosomes may be prone to cancer. Chromosomes are conventionally prepared from mitotic cells arrested by the colcemid block method. However, obtaining of mitotic chromosomes is sometimes hampered under several circumstances, for example after high-dose (over several Gys of γ-rays) ionizing irradiation exposure accident. As a result, cytogenetic analysis will be often difficult or even impossible in such cases. Premature chromosome condensation (PCC) is an alternative technique that has proved to be a unique and useful way in chromosome analysis. Previously, PCC has been achieved following cell fusion mediated either by fusogenic viruses (for example Sendai virus) or by polyethylene glycol (PEG) (cell-fusion PCC), but the cell-fusion PCC has several drawbacks. The novel drug-induced PCC use of specific inhibitors for serine/threonine protein phosphatase was introduced about 20 years ago. This method is much simple and easy even than the conventional mitotic chromosome preparation using colcemid block protocol and the obtained PCC index (equivalent to mitotic index for metaphase chromosome) is much higher. Furthermore, this method allows the interphase chromatin to be condensed and visualized like mitotic chromosomes, and thus has been opening the way for chromosome analysis not only in metaphase chromosomes but also in interphase chromatin. The drug-induced PCC has therefore proven the usefulness in cytogenetics and other many cell biology fields. Since the first version of drug-induced PCC protocol has been published in 2009 (Gotoh, Methods in molecular biology. Humana Press, New York, 2009), many newer applications of drug-induced PCC in radiation biology and chromosome science fields in a wide range of species from animal to plant have been reported (Gotoh et al., Biomed Res 16:63-68, 1995; Lamadrid Boada et al., Mutat Res 757:45-51, 2013; Ravi et al., Biochimie 95:124-33, 2013; Ono et al., J Cell Biol 200:429-41, 2013; Vagnarelli, Exp Cell Res 318:1435-41, 2012; Roukos et al., Nat Protoc 9:2476-92, 2014; Miura and Blakely, Cytometry A 79:1016-22, 2013; Zabka et al., J Plant Physiol 174:62-70, 2015; Samaniego et al., Planta 215:195-204, 2002; Rybaczek et al., Folia Histochem Cytobiol 40:51-9, 2002; Gotoh and Durante J Cell Physiol 209:297-304, 2006). Therefore as a new edition, I will write in this chapter the drug-induced PCC technique with newer findings, in particular focused drug-induced PCC protocols in radiation biology with referring updated articles published recently.
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Debatisse M, Rosselli F. A journey with common fragile sites: From S phase to telophase. Genes Chromosomes Cancer 2018; 58:305-316. [PMID: 30387289 DOI: 10.1002/gcc.22704] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Accepted: 10/25/2018] [Indexed: 12/17/2022] Open
Abstract
Some regions of the genome, notably common fragile sites (CFSs), are hypersensitive to replication stress and often involved in the generation of gross chromosome rearrangements in cancer cells. CFSs nest within very large genes and display cell-type-dependent instability. Fragile or not, large genes tend to replicate late in S-phase. A number of data now show that transcription perturbs replication completion across the body of large genes, particularly upon replication stress. However, the molecular mechanisms by which transcription elicits such under-replication and subsequent instability remain unclear. We present here our view of the mechanisms responsible for CFS under-replication and those allowing the cells to cope with this problem in G2 and mitosis. We notably focus on the major role played by the FANC proteins in the protection of CFSs from S phase up to late mitosis. We finally discuss a possible rationale for the conservation of large genes across vertebrate evolution.
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Affiliation(s)
- Michelle Debatisse
- CNRS UMR 8200, Equipe labellisée "La ligue Contre le Cancer", Villejuif, France.,Sorbonne Universités, UPMC Univ Paris 06, Paris, France.,Gustave Roussy Cancer Center, Villejuif, France
| | - Filippo Rosselli
- CNRS UMR 8200, Equipe labellisée "La ligue Contre le Cancer", Villejuif, France.,Gustave Roussy Cancer Center, Villejuif, France.,Université Paris Saclay - Paris Sud, Orsay, France
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26
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Abstract
The instability of chromosome fragile sites is implicated as a causative factor in several human diseases, including cancer [for common fragile sites (CFSs)] and neurological disorders [for rare fragile sites (RFSs)]. Previous studies have indicated that problems arising during DNA replication are the underlying source of this instability. Although the role of replication stress in promoting instability at CFSs is well documented, much less is known about how the fragility of RFSs arises. Many RFSs, as exemplified by expansion of a CGG trinucleotide repeat sequence in the fragile X syndrome-associated FRAXA locus, exhibit fragility in response to folate deficiency or other forms of "folate stress." We hypothesized that such folate stress, through disturbing the replication program within the pathologically expanded repeats within FRAXA, would lead to mitotic abnormalities that exacerbate locus instability. Here, we show that folate stress leads to a dramatic increase in missegregation of FRAXA coupled with the formation of single-stranded DNA bridges in anaphase and micronuclei that contain the FRAXA locus. Moreover, chromosome X aneuploidy is seen when these cells are exposed to folate deficiency for an extended period. We propose that problematic FRAXA replication during interphase leads to a failure to disjoin the sister chromatids during anaphase. This generates further instability not only at FRAXA itself but also of chromosome X. These data have wider implications for the effects of folate deficiency on chromosome instability in human cells.
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27
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Sall FB, Germini D, Kovina AP, Ribrag V, Wiels J, Toure AO, Iarovaia OV, Lipinski M, Vassetzky Y. Effect of Environmental Factors on Nuclear Organization and Transformation of Human B Lymphocytes. BIOCHEMISTRY (MOSCOW) 2018; 83:402-410. [DOI: 10.1134/s0006297918040119] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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28
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Ren L, Chen L, Wu W, Garribba L, Tian H, Liu Z, Vogel I, Li C, Hickson ID, Liu Y. Potential biomarkers of DNA replication stress in cancer. Oncotarget 2018; 8:36996-37008. [PMID: 28445142 PMCID: PMC5514887 DOI: 10.18632/oncotarget.16940] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Accepted: 03/28/2017] [Indexed: 11/25/2022] Open
Abstract
Oncogene activation is an established driver of tumorigenesis. An apparently inevitable consequence of oncogene activation is the generation of DNA replication stress (RS), a feature common to most cancer cells. RS, in turn, is a causal factor in the development of chromosome instability (CIN), a near universal feature of solid tumors. It is likely that CIN and RS are mutually reinforcing drivers that not only accelerate tumorigenesis, but also permit cancer cells to adapt to diverse and hostile environments. This article reviews the genetic changes present in cancer cells that influence oncogene-induced RS and CIN, with a particular emphasis on regions of the human genome that show enhanced sensitivity to the destabilizing effects of RS, such as common fragile sites. Because RS exists in a wide range of cancer types, we propose that the proteins involved counteracting this stress are potential biomarkers for indicating the degree of RS in cancer specimens. To test this hypothesis, we conducted a pilot study to validate whether some of proteins that are known from in vitro studies to play an essential role in the RS pathway could be suitable as a biomarker. Our results indicated that this is possible. With this review and pilot study, we aim to accelerate the development of a biomarker for analysis of RS in tumor biopsy specimens, which could ultimately help to stratify patients for different forms of therapy such as the RS inhibitors already undergoing clinical trials.
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Affiliation(s)
- Liqun Ren
- Basic Medical Research Institute, Chengde Medical University, Chengde, China
| | - Long Chen
- Basic Medical Research Institute, Chengde Medical University, Chengde, China
| | - Wei Wu
- Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Lorenza Garribba
- Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Huanna Tian
- Basic Medical Research Institute, Chengde Medical University, Chengde, China
| | - Zihui Liu
- Pathology Department, Affiliated Hospital, Chengde Medical University, Chengde, China
| | - Ivan Vogel
- Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Chunhui Li
- Pathology Department, Affiliated Hospital, Chengde Medical University, Chengde, China
| | - Ian D Hickson
- Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark.,Center for Healthy Aging, Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Ying Liu
- Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark
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29
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Arora M, Moser J, Phadke H, Basha AA, Spencer SL. Endogenous Replication Stress in Mother Cells Leads to Quiescence of Daughter Cells. Cell Rep 2018; 19:1351-1364. [PMID: 28514656 DOI: 10.1016/j.celrep.2017.04.055] [Citation(s) in RCA: 117] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 03/23/2017] [Accepted: 04/19/2017] [Indexed: 12/17/2022] Open
Abstract
Mammalian cells have two fundamentally different states, proliferative and quiescent, but our understanding of how and why cells switch between these states is limited. We previously showed that actively proliferating populations contain a subpopulation that enters quiescence (G0) in an apparently stochastic manner. Using single-cell time-lapse imaging of CDK2 activity and DNA damage, we now show that unresolved endogenous replication stress in the previous (mother) cell cycle prompts p21-dependent entry of daughter cells into quiescence immediately after mitosis. Furthermore, the amount of time daughter cells spend in quiescence is correlated with the extent of inherited damage. Our study thus links replication errors in one cell cycle to the fate of daughter cells in the subsequent cell cycle. More broadly, this work reveals that entry into quiescence is not purely stochastic but has a strong deterministic component arising from a memory of events that occurred in the previous generation(s).
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Affiliation(s)
- Mansi Arora
- Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Justin Moser
- Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Harsha Phadke
- Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Ashik Akbar Basha
- Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Sabrina L Spencer
- Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80309, USA.
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30
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Garribba L, Wu W, Özer Ö, Bhowmick R, Hickson ID, Liu Y. Inducing and Detecting Mitotic DNA Synthesis at Difficult-to-Replicate Loci. Methods Enzymol 2018. [PMID: 29523241 DOI: 10.1016/bs.mie.2017.11.025] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Our conventional understanding of the process of DNA replication is that it occurs in the S-phase of the cell division cycle. However, during investigations into the mechanism by which common fragile sites (CFSs) drive genome instability, we observed that some DNA synthesis was still occurring in early mitosis at these loci. This curious phenomenon of mitotic DNA synthesis (which we now term "MiDAS") appears to be a form of break-induced DNA replication (BIR), a DNA repair process based on homologous recombination that has been characterized in detail only in lower eukaryotes. During MiDAS, it is proposed that parts of the human genome that are not fully replicated when cells enter mitotic prophase complete their replicative cycle at that point. To date, the loci that most depend upon this process are those whose replication can be affected by oncogene-induced DNA replication stress (RS), most notably, CFSs. From our studies, it is clear that the successful completion of MiDAS at CFSs can minimize chromosome missegregation and nondisjunction. Nevertheless, it is still not clear which loci that can undergo MiDAS, whether MiDAS is associated with mutations or genome rearrangements, or whether MiDAS really is a form of BIR. In this review, we describe methods for detecting MiDAS both in prometaphase cells and directly on isolated metaphase chromosomes. In addition, we have included methods for combining MiDAS detection either with immunofluorescence (IF) detection of proteins that are recruited to the MiDAS loci, or with fluorescence in situ hybridization using probes that target specific genomic loci.
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Affiliation(s)
- Lorenza Garribba
- Center for Chromosome Stability, University of Copenhagen, Copenhagen, Denmark
| | - Wei Wu
- Center for Chromosome Stability, University of Copenhagen, Copenhagen, Denmark
| | - Özgün Özer
- Center for Chromosome Stability, University of Copenhagen, Copenhagen, Denmark
| | - Rahul Bhowmick
- Center for Chromosome Stability, University of Copenhagen, Copenhagen, Denmark
| | - Ian D Hickson
- Center for Chromosome Stability, University of Copenhagen, Copenhagen, Denmark; Center for Healthy Aging, University of Copenhagen, Copenhagen, Denmark
| | - Ying Liu
- Center for Chromosome Stability, University of Copenhagen, Copenhagen, Denmark.
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31
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Abstract
A fragile site is a chromosomal locus that is prone to form a gap or constriction visible within a condensed metaphase chromosome, particularly following exposure of cells to DNA replication stress. Based on their frequency, fragile sites are classified as either common (CFSs; present in all individuals) or rare (RFSs; present in only a few individuals). Interest in fragile sites has remained high since their discovery in 1965, because of their association with human disease. CFSs are recognized as drivers of oncogene activation and genome instability in cancer cells, while some RFSs are associated with neurodegenerative diseases. This review summaries our current understanding of the nature and causes of fragile site "expression", including the recently characterized phenomenon of telomere fragility. In particular, we focus on a description of the methodologies and technologies for detection and analysis of chromosome fragile sites.
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32
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Irony-Tur Sinai M, Kerem B. DNA replication stress drives fragile site instability. Mutat Res 2017; 808:56-61. [PMID: 29074228 DOI: 10.1016/j.mrfmmm.2017.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 09/26/2017] [Accepted: 10/12/2017] [Indexed: 12/21/2022]
Abstract
DNA replication stress is one of the early drivers enabling the ongoing acquisition of genetic changes arising during tumorigenesis. As such, it is a feature of most pre-malignant and malignant cells. In this review article, we focus on the early events initiating DNA replication stress and the preferential sensitivity of common fragile sites (CFSs) to this stress. CFSs are specific genomic regions within the normal chromosomal structure, which appear as gaps and breaks in the metaphase chromosomes of cells grown under mild replication stress conditions. The main characteristics predisposing CFSs to instability include late replication timing, delayed replication completion, failure to activate additional origins, origin paucity along large genomic regions, collision between replication and transcription complexes along large genes, and the presence of AT-dinucleotide rich sequences. The contribution of these features to instability at CFSs during early cancer development is discussed.
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Affiliation(s)
- Michal Irony-Tur Sinai
- Department of Genetics, The Life Sciences Institute, The Hebrew University, Jerusalem, 91904, Israel
| | - Batsheva Kerem
- Department of Genetics, The Life Sciences Institute, The Hebrew University, Jerusalem, 91904, Israel.
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33
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García-Pichardo D, Cañas JC, García-Rubio ML, Gómez-González B, Rondón AG, Aguilera A. Histone Mutants Separate R Loop Formation from Genome Instability Induction. Mol Cell 2017; 66:597-609.e5. [PMID: 28575656 DOI: 10.1016/j.molcel.2017.05.014] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 04/03/2017] [Accepted: 05/15/2017] [Indexed: 01/02/2023]
Abstract
R loops have positive physiological roles, but they can also be deleterious by causing genome instability, and the mechanisms for this are unknown. Here we identified yeast histone H3 and H4 mutations that facilitate R loops but do not cause instability. R loops containing single-stranded DNA (ssDNA), versus RNA-DNA hybrids alone, were demonstrated using ssDNA-specific human AID and bisulfite. Notably, they are similar size regardless of whether or not they induce genome instability. Contrary to mutants causing R loop-mediated instability, these histone mutants do not accumulate H3 serine-10 phosphate (H3S10-P). We propose a two-step mechanism in which, first, an altered chromatin facilitates R loops, and second, chromatin is modified, including H3S10-P, as a requisite for compromising genome integrity. Consistently, these histone mutations suppress the high H3S10 phosphorylation and genomic instability of hpr1 and sen1 mutants. Therefore, contrary to what was previously believed, R loops do not cause genome instability by themselves.
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Affiliation(s)
- Desiré García-Pichardo
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville 41092, Spain
| | - Juan C Cañas
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville 41092, Spain
| | - María L García-Rubio
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville 41092, Spain
| | - Belén Gómez-González
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville 41092, Spain
| | - Ana G Rondón
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville 41092, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville 41092, Spain.
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Bhatia V, Herrera-Moyano E, Aguilera A, Gómez-González B. The Role of Replication-Associated Repair Factors on R-Loops. Genes (Basel) 2017; 8:E171. [PMID: 28653981 PMCID: PMC5541304 DOI: 10.3390/genes8070171] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Revised: 06/19/2017] [Accepted: 06/20/2017] [Indexed: 12/12/2022] Open
Abstract
The nascent RNA can reinvade the DNA double helix to form a structure termed the R-loop, where a single-stranded DNA (ssDNA) is accompanied by a DNA-RNA hybrid. Unresolved R-loops can impede transcription and replication processes and lead to genomic instability by a mechanism still not fully understood. In this sense, a connection between R-loops and certain chromatin markers has been reported that might play a key role in R-loop homeostasis and genome instability. To counteract the potential harmful effect of R-loops, different conserved messenger ribonucleoprotein (mRNP) biogenesis and nuclear export factors prevent R-loop formation, while ubiquitously-expressed specific ribonucleases and DNA-RNA helicases resolve DNA-RNA hybrids. However, the molecular events associated with R-loop sensing and processing are not yet known. Given that R-loops hinder replication progression, it is plausible that some DNA replication-associated factors contribute to dissolve R-loops or prevent R-loop mediated genome instability. In support of this, R-loops accumulate in cells depleted of the BRCA1, BRCA2 or the Fanconi anemia (FA) DNA repair factors, indicating that they play an active role in R-loop dissolution. In light of these results, we review our current view of the role of replication-associated DNA repair pathways in preventing the harmful consequences of R-loops.
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Affiliation(s)
- Vaibhav Bhatia
- Andalusian Center for Molecular Biology and Regenerative Medicine-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Av. Américo Vespucio 24, 41092 Seville, Spain.
| | - Emilia Herrera-Moyano
- Andalusian Center for Molecular Biology and Regenerative Medicine-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Av. Américo Vespucio 24, 41092 Seville, Spain.
| | - Andrés Aguilera
- Andalusian Center for Molecular Biology and Regenerative Medicine-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Av. Américo Vespucio 24, 41092 Seville, Spain.
| | - Belén Gómez-González
- Andalusian Center for Molecular Biology and Regenerative Medicine-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Av. Américo Vespucio 24, 41092 Seville, Spain.
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35
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S-phase checkpoint regulations that preserve replication and chromosome integrity upon dNTP depletion. Cell Mol Life Sci 2017; 74:2361-2380. [PMID: 28220209 PMCID: PMC5487892 DOI: 10.1007/s00018-017-2474-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 12/29/2016] [Accepted: 01/23/2017] [Indexed: 11/18/2022]
Abstract
DNA replication stress, an important source of genomic instability, arises upon different types of DNA replication perturbations, including those that stall replication fork progression. Inhibitors of the cellular pool of deoxynucleotide triphosphates (dNTPs) slow down DNA synthesis throughout the genome. Following depletion of dNTPs, the highly conserved replication checkpoint kinase pathway, also known as the S-phase checkpoint, preserves the functionality and structure of stalled DNA replication forks and prevents chromosome fragmentation. The underlying mechanisms involve pathways extrinsic to replication forks, such as those involving regulation of the ribonucleotide reductase activity, the temporal program of origin firing, and cell cycle transitions. In addition, the S-phase checkpoint modulates the function of replisome components to promote replication integrity. This review summarizes the various functions of the replication checkpoint in promoting replication fork stability and genome integrity in the face of replication stress caused by dNTP depletion.
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36
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Prado F, Maya D. Regulation of Replication Fork Advance and Stability by Nucleosome Assembly. Genes (Basel) 2017; 8:genes8020049. [PMID: 28125036 PMCID: PMC5333038 DOI: 10.3390/genes8020049] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/04/2017] [Accepted: 01/16/2017] [Indexed: 12/13/2022] Open
Abstract
The advance of replication forks to duplicate chromosomes in dividing cells requires the disassembly of nucleosomes ahead of the fork and the rapid assembly of parental and de novo histones at the newly synthesized strands behind the fork. Replication-coupled chromatin assembly provides a unique opportunity to regulate fork advance and stability. Through post-translational histone modifications and tightly regulated physical and genetic interactions between chromatin assembly factors and replisome components, chromatin assembly: (1) controls the rate of DNA synthesis and adjusts it to histone availability; (2) provides a mechanism to protect the integrity of the advancing fork; and (3) regulates the mechanisms of DNA damage tolerance in response to replication-blocking lesions. Uncoupling DNA synthesis from nucleosome assembly has deleterious effects on genome integrity and cell cycle progression and is linked to genetic diseases, cancer, and aging.
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Affiliation(s)
- Felix Prado
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), Spanish National Research Council (CSIC), Seville 41092, Spain.
| | - Douglas Maya
- Department of Genome Biology, Andalusian Molecular Biology and Regenerative Medicine Center (CABIMER), Spanish National Research Council (CSIC), Seville 41092, Spain.
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Feng W, Chakraborty A. Fragility Extraordinaire: Unsolved Mysteries of Chromosome Fragile Sites. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1042:489-526. [PMID: 29357071 DOI: 10.1007/978-981-10-6955-0_21] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Chromosome fragile sites are a fascinating cytogenetic phenomenon now widely implicated in a slew of human diseases ranging from neurological disorders to cancer. Yet, the paths leading to these revelations were far from direct, and the number of fragile sites that have been molecularly cloned with known disease-associated genes remains modest. Moreover, as more fragile sites were being discovered, research interests in some of the earliest discovered fragile sites ebbed away, leaving a number of unsolved mysteries in chromosome biology. In this review we attempt to recount some of the early discoveries of fragile sites and highlight those phenomena that have eluded intense scrutiny but remain extremely relevant in our understanding of the mechanisms of chromosome fragility. We then survey the literature for disease association for a comprehensive list of fragile sites. We also review recent studies addressing the underlying cause of chromosome fragility while highlighting some ongoing debates. We report an observed enrichment for R-loop forming sequences in fragile site-associated genes than genomic average. Finally, we will leave the reader with some lingering questions to provoke discussion and inspire further scientific inquiries.
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Affiliation(s)
- Wenyi Feng
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY, USA.
| | - Arijita Chakraborty
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY, USA
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Richard P, Manley JL. R Loops and Links to Human Disease. J Mol Biol 2016; 429:3168-3180. [PMID: 27600412 DOI: 10.1016/j.jmb.2016.08.031] [Citation(s) in RCA: 125] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 08/26/2016] [Accepted: 08/31/2016] [Indexed: 12/13/2022]
Abstract
Aberrant R-loop structures are increasingly being realized as an important contributor to human disease. R loops, which are mainly co-transcriptional, abundant RNA/DNA hybrids, form naturally and can indeed be beneficial for transcription regulation at certain loci. However, their unwanted persistence elsewhere or in particular situations can lead to DNA double-strand breaks, chromosome rearrangements, and hypermutation, which are all sources of genomic instability. Mutations in genes involved in R-loop resolution or mutations leading to R-loop formation at specific genes affect the normal physiology of the cell. We discuss here the examples of diseases for which a link with R loops has been described, as well as how disease-causing mutations might participate in the development and/or progression of diseases that include repeat-associated conditions, other neurological disorders, and cancers.
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Affiliation(s)
- Patricia Richard
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
| | - James L Manley
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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Condensin I and II behaviour in interphase nuclei and cells undergoing premature chromosome condensation. Chromosome Res 2016; 24:243-69. [PMID: 27008552 DOI: 10.1007/s10577-016-9519-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 03/07/2016] [Indexed: 10/22/2022]
Abstract
Condensin is an integral component of the mitotic chromosome condensation machinery, which ensures orderly segregation of chromosomes during cell division. In metazoans, condensin exists as two complexes, condensin I and II. It is not yet clear what roles these complexes may play outside mitosis, and so we have examined their behaviour both in normal interphase and in premature chromosome condensation (PCC). We find that a small fraction of condensin I is retained in interphase nuclei, and our data suggests that this interphase nuclear condensin I is active in both gene regulation and chromosome condensation. Furthermore, live cell imaging demonstrates condensin II dramatically increases on G1 nuclei following completion of mitosis. Our PCC studies show condensins I and II and topoisomerase II localise to the chromosome axis in G1-PCC and G2/M-PCC, while KIF4 binding is altered. Individually, condensins I and II are dispensable for PCC. However, when both are knocked out, G1-PCC chromatids are less well structured. Our results define new roles for the condensins during interphase and provide new information about the mechanism of PCC.
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Leibowitz ML, Zhang CZ, Pellman D. Chromothripsis: A New Mechanism for Rapid Karyotype Evolution. Annu Rev Genet 2015; 49:183-211. [DOI: 10.1146/annurev-genet-120213-092228] [Citation(s) in RCA: 123] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Mitchell L. Leibowitz
- Department of Pediatric Oncology,
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115;
| | - Cheng-Zhong Zhang
- Department of Pediatric Oncology,
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215;
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115;
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142;
| | - David Pellman
- Department of Pediatric Oncology,
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115;
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142;
- Howard Hughes Medical Institute, Boston, Massachusetts 02115
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García-Rubio ML, Pérez-Calero C, Barroso SI, Tumini E, Herrera-Moyano E, Rosado IV, Aguilera A. The Fanconi Anemia Pathway Protects Genome Integrity from R-loops. PLoS Genet 2015; 11:e1005674. [PMID: 26584049 PMCID: PMC4652862 DOI: 10.1371/journal.pgen.1005674] [Citation(s) in RCA: 216] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 10/26/2015] [Indexed: 11/19/2022] Open
Abstract
Co-transcriptional RNA-DNA hybrids (R loops) cause genome instability. To prevent harmful R loop accumulation, cells have evolved specific eukaryotic factors, one being the BRCA2 double-strand break repair protein. As BRCA2 also protects stalled replication forks and is the FANCD1 member of the Fanconi Anemia (FA) pathway, we investigated the FA role in R loop-dependent genome instability. Using human and murine cells defective in FANCD2 or FANCA and primary bone marrow cells from FANCD2 deficient mice, we show that the FA pathway removes R loops, and that many DNA breaks accumulated in FA cells are R loop-dependent. Importantly, FANCD2 foci in untreated and MMC-treated cells are largely R loop dependent, suggesting that the FA functions at R loop-containing sites. We conclude that co-transcriptional R loops and R loop-mediated DNA damage greatly contribute to genome instability and that one major function of the FA pathway is to protect cells from R loops. R loops are co-transcriptional RNA-DNA hybrids that can have a physiological role in transcription and replication, but also may be a major threat to genome stability. To avoid the deleterious effects of R loops, specific factors prevent their formation or facilitate their removal. The double-strand break repair factor BRCA2 is among those that prevent R-loop accumulation. As BRCA2 also protects stalled replication forks and is the FANCD1 member of the Fanconi Anemia (FA) pathway, we studied the role of this pathway in preventing R loop accumulation and R loop-dependent genome instability. Using human and murine cells defective in FANCD2 or FANCA and primary bone marrow cells derived from FANCD2 deficient mice, we show that the FA pathway removes R loops and that many DNA breaks accumulated in FA cells are R loop-dependent. Importantly, FANCD2 foci accumulation is largely R loop-dependent, suggesting that the FA functions at R loop-containing sites. The FA pathway is primarily known as a DNA interstrand crosslinks (ICLs) repair pathway. Our findings reveal a novel function of the FA pathway in preventing R loop-mediated DNA damage, providing new clues to understand the relevance of R-loops as a natural source of genome instability and the way they are processed.
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Affiliation(s)
- María L. García-Rubio
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Seville, Spain
| | - Carmen Pérez-Calero
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Seville, Spain
| | - Sonia I. Barroso
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Seville, Spain
| | - Emanuela Tumini
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Seville, Spain
| | - Emilia Herrera-Moyano
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Seville, Spain
| | - Iván V. Rosado
- Instituto de Biomedicina de Sevilla-Hospital Virgen del Rocío, Seville, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Seville, Spain
- * E-mail:
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Menolfi D, Delamarre A, Lengronne A, Pasero P, Branzei D. Essential Roles of the Smc5/6 Complex in Replication through Natural Pausing Sites and Endogenous DNA Damage Tolerance. Mol Cell 2015; 60:835-46. [PMID: 26698660 PMCID: PMC4691243 DOI: 10.1016/j.molcel.2015.10.023] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 10/02/2015] [Accepted: 10/09/2015] [Indexed: 02/07/2023]
Abstract
The essential functions of the conserved Smc5/6 complex remain elusive. To uncover its roles in genome maintenance, we established Saccharomyces cerevisiae cell-cycle-regulated alleles that enable restriction of Smc5/6 components to S or G2/M. Unexpectedly, the essential functions of Smc5/6 segregated fully and selectively to G2/M. Genetic screens that became possible with generated alleles identified processes that crucially rely on Smc5/6 specifically in G2/M: metabolism of DNA recombination structures triggered by endogenous replication stress, and replication through natural pausing sites located in late-replicating regions. In the first process, Smc5/6 modulates remodeling of recombination intermediates, cooperating with dissolution activities. In the second, Smc5/6 prevents chromosome fragility and toxic recombination instigated by prolonged pausing and the fork protection complex, Tof1-Csm3. Our results thus dissect Smc5/6 essential roles and reveal that combined defects in DNA damage tolerance and pausing site-replication cause recombination-mediated DNA lesions, which we propose to drive developmental and cancer-prone disorders. Cell-cycle-regulated alleles reveal Smc5/6-essential functions to segregate in G2/M Genetic screen with new hypomorphic allele identifies processes relying on Smc5/6 Smc5/6 acts on recombination structures triggered by endogenous replication stress Smc5/6 prevents fragility and mediates replication through natural pausing sites
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Affiliation(s)
- Demis Menolfi
- IFOM, the FIRC Institute of Molecular Oncology, Via Adamello 16, 20139, Milan, Italy
| | - Axel Delamarre
- IGH, Institute of Human Genetics CNRS UPR 1142, 141 rue de la Cardonille F-34396 Cedex 5, Montpellier, France
| | - Armelle Lengronne
- IGH, Institute of Human Genetics CNRS UPR 1142, 141 rue de la Cardonille F-34396 Cedex 5, Montpellier, France
| | - Philippe Pasero
- IGH, Institute of Human Genetics CNRS UPR 1142, 141 rue de la Cardonille F-34396 Cedex 5, Montpellier, France
| | - Dana Branzei
- IFOM, the FIRC Institute of Molecular Oncology, Via Adamello 16, 20139, Milan, Italy.
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Santos-Pereira JM, Aguilera A. R loops: new modulators of genome dynamics and function. Nat Rev Genet 2015; 16:583-97. [PMID: 26370899 DOI: 10.1038/nrg3961] [Citation(s) in RCA: 528] [Impact Index Per Article: 58.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
R loops are nucleic acid structures composed of an RNA-DNA hybrid and a displaced single-stranded DNA. Recently, evidence has emerged that R loops occur more often in the genome and have greater physiological relevance, including roles in transcription and chromatin structure, than was previously predicted. Importantly, however, R loops are also a major threat to genome stability. For this reason, several DNA and RNA metabolism factors prevent R-loop formation in cells. Dysfunction of these factors causes R-loop accumulation, which leads to replication stress, genome instability, chromatin alterations or gene silencing, phenomena that are frequently associated with cancer and a number of genetic diseases. We review the current knowledge of the mechanisms controlling R loops and their putative relationship with disease.
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Affiliation(s)
- José M Santos-Pereira
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Av. Américo Vespucio s/n, Seville 41092, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Av. Américo Vespucio s/n, Seville 41092, Spain
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Zhang CZ, Spektor A, Cornils H, Francis JM, Jackson EK, Liu S, Meyerson M, Pellman D. Chromothripsis from DNA damage in micronuclei. Nature 2015; 522:179-84. [PMID: 26017310 PMCID: PMC4742237 DOI: 10.1038/nature14493] [Citation(s) in RCA: 777] [Impact Index Per Article: 86.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Accepted: 04/20/2015] [Indexed: 01/01/2023]
Abstract
Genome sequencing has uncovered a new mutational phenomenon in cancer and congenital disorders called chromothripsis. Chromothripsis is characterized by extensive genomic rearrangements and an oscillating pattern of DNA copy number levels, all curiously restricted to one or a few chromosomes. The mechanism for chromothripsis is unknown, but we previously proposed that it could occur through the physical isolation of chromosomes in aberrant nuclear structures called micronuclei. Here, using a combination of live cell imaging and single-cell genome sequencing, we demonstrate that micronucleus formation can indeed generate a spectrum of genomic rearrangements, some of which recapitulate all known features of chromothripsis. These events are restricted to the mis-segregated chromosome and occur within one cell division. We demonstrate that the mechanism for chromothripsis can involve the fragmentation and subsequent reassembly of a single chromatid from a micronucleus. Collectively, these experiments establish a new mutational process of which chromothripsis is one extreme outcome.
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Affiliation(s)
- Cheng-Zhong Zhang
- 1] Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [3] Broad Institute of Harvard and MIT, Cambridge, Massachusetts 02142, USA [4] Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Alexander Spektor
- 1] Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA [3] Department of Radiation Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA
| | - Hauke Cornils
- 1] Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Joshua M Francis
- 1] Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Broad Institute of Harvard and MIT, Cambridge, Massachusetts 02142, USA
| | - Emily K Jackson
- 1] Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA [3] Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA
| | - Shiwei Liu
- 1] Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Matthew Meyerson
- 1] Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Broad Institute of Harvard and MIT, Cambridge, Massachusetts 02142, USA [3] Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA [4] Center for Cancer Genome Discovery, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA
| | - David Pellman
- 1] Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA [2] Broad Institute of Harvard and MIT, Cambridge, Massachusetts 02142, USA [3] Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA [4] Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA
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Replication stress in Mammalian cells and its consequences for mitosis. Genes (Basel) 2015; 6:267-98. [PMID: 26010955 PMCID: PMC4488665 DOI: 10.3390/genes6020267] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Revised: 05/15/2015] [Accepted: 05/18/2015] [Indexed: 12/23/2022] Open
Abstract
The faithful transmission of genetic information to daughter cells is central to maintaining genomic stability and relies on the accurate and complete duplication of genetic material during each cell cycle. However, the genome is routinely exposed to endogenous and exogenous stresses that can impede the progression of replication. Such replication stress can be an early cause of cancer or initiate senescence. Replication stress, which primarily occurs during S phase, results in consequences during mitosis, jeopardizing chromosome segregation and, in turn, genomic stability. The traces of replication stress can be detected in the daughter cells during G1 phase. Alterations in mitosis occur in two types: 1) local alterations that correspond to breaks, rearrangements, intertwined DNA molecules or non-separated sister chromatids that are confined to the region of the replication dysfunction; 2) genome-wide chromosome segregation resulting from centrosome amplification (although centrosomes do not contain DNA), which amplifies the local replication stress to the entire genome. Here, we discuss the endogenous causes of replication perturbations, the mechanisms of replication fork restart and the consequences for mitosis, chromosome segregation and genomic stability.
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Ambroziak W, Koziorowski D, Duszyc K, Górka-Skoczylas P, Potulska-Chromik A, Sławek J, Hoffman-Zacharska D. Genomic instability in the PARK2 locus is associated with Parkinson's disease. J Appl Genet 2015; 56:451-461. [PMID: 25833766 PMCID: PMC4617850 DOI: 10.1007/s13353-015-0282-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 03/05/2015] [Accepted: 03/05/2015] [Indexed: 12/01/2022]
Abstract
Parkinson’s disease (PD) is a common neurodegenerative disorder affecting mostly elderly people, although there is a group of patients developing so-called early-onset PD (EOPD). Mutations in the PARK2 gene are a common cause of autosomal recessive EOPD. PARK2 belongs to the family of extremely large human genes which are often localised in genomic common fragile sites (CFSs) and exhibit gross instability. PARK2 is located in the centre of FRA6E, the third most mutation-susceptible CFS of the human genome. The gene encompasses a region of 1.3 Mbp and, among its mutations, large rearrangements of single or multiple exons account for around 50 %. We performed an analysis of the PARK2 gene in a group of 344 PD patients with EOPD and classical form of the disease. Copy number changes were first identified using multiplex ligation probe amplification (MLPA), with their ranges characterised by array comparative genomic hybridisation (aCGH). Exact breakpoints were mapped using direct sequencing. Rearrangements were found in eight subjects, including five deletions and three duplications. Rearrangements were mostly non-recurrent and no repetitive sequences or extended homologies were identified in the regions flanking breakpoint junctions. However, in most cases, 1–3 bp microhomologies were present, strongly suggesting that microhomology-mediated mechanisms, specifically non-homologous end joining (NHEJ) and fork stalling and template switching (FoSTeS)/microhomology-mediated break-induced replication (MMBIR), are predominantly involved in the rearrangement processes in this genomic region.
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Affiliation(s)
- Wojciech Ambroziak
- Department of Medical Genetics, Institute of Mother and Child, Kasprzaka 17A, 01-211, Warsaw, Poland.,Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Pawińskiego 5a, 02-106, Warsaw, Poland
| | - Dariusz Koziorowski
- Department of Neurology, Faculty of Heath Science, Medical University of Warsaw, Kondratowicza 8, 03-242, Warsaw, Poland
| | - Kinga Duszyc
- Department of Medical Genetics, Institute of Mother and Child, Kasprzaka 17A, 01-211, Warsaw, Poland.,Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Pawińskiego 5a, 02-106, Warsaw, Poland
| | - Paulina Górka-Skoczylas
- Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Pawińskiego 5a, 02-106, Warsaw, Poland
| | - Anna Potulska-Chromik
- Department of Neurology, Medical University of Warsaw, Banacha 1, 02-097, Warsaw, Poland
| | - Jarosław Sławek
- Department of Neurological and Psychiatric Nursing, Medical University of Gdańsk, Dębinki 7, 80-952, Gdańsk, Poland
| | - Dorota Hoffman-Zacharska
- Department of Medical Genetics, Institute of Mother and Child, Kasprzaka 17A, 01-211, Warsaw, Poland. .,Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Pawińskiego 5a, 02-106, Warsaw, Poland.
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Gotoh E. Drug-induced premature chromosome condensation (PCC) protocols: cytogenetic approaches in mitotic chromosome and interphase chromatin. Methods Mol Biol 2015; 1288:53-66. [PMID: 25827875 DOI: 10.1007/978-1-4939-2474-5_5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Chromosome analysis is a fundamental technique which is used in wide areas of cytogenetic study including karyotyping species, hereditary diseases diagnosis, or chromosome biology study. Chromosomes are usually prepared from mitotic cells arrested by colcemid block protocol. However, obtaining mitotic chromosomes is often hampered under several circumstances. As a result, cytogenetic analysis will be sometimes difficult or even impossible in such cases. Premature chromosome condensation (PCC) (see Note 1) is an alternative method that has proved to be a unique and useful way in chromosome analysis. Former, PCC has been achieved following cell fusion method (cell-fusion PCC) mediated either by fusogenic viruses (e.g., Sendai virus) or cell fusion chemicals (e.g., polyethylene glycol), but the cell fusion PCC has several drawbacks. The novel drug-induced PCC using protein phosphatase inhibitors was introduced about 20 years ago. This method is much simpler and easier even than the conventional mitotic chromosome preparation protocol use with colcemid block and furthermore obtained PCC index (equivalent to mitotic index for metaphase chromosome) is usually much higher than colcemid block method. Moreover, this method allows the interphase chromatin to be condensed to visualize like mitotic chromosomes. Therefore drug-induced PCC has opened the way for chromosome analysis not only in metaphase chromosomes but also in interphase chromatin. The drug-induced PCC has thus proven the usefulness in cytogenetics and other cell biology fields. For this second edition version, updated modifications/changes are supplemented in Subheadings 2, 3, and 4, and a new section describing the application of PCC in chromosome science fields is added with citation of updated references.
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Affiliation(s)
- Eisuke Gotoh
- Department of Radiology, Jikei University School of Medicine, 3-25-8, Nishi-Shimbashi, Minato-ku, Tokyo, 105-8461, Japan,
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PUL21a-Cyclin A2 interaction is required to protect human cytomegalovirus-infected cells from the deleterious consequences of mitotic entry. PLoS Pathog 2014; 10:e1004514. [PMID: 25393019 PMCID: PMC4231158 DOI: 10.1371/journal.ppat.1004514] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Accepted: 10/11/2014] [Indexed: 12/02/2022] Open
Abstract
Entry into mitosis is accompanied by dramatic changes in cellular architecture, metabolism and gene expression. Many viruses have evolved cell cycle arrest strategies to prevent mitotic entry, presumably to ensure sustained, uninterrupted viral replication. Here we show for human cytomegalovirus (HCMV) what happens if the viral cell cycle arrest mechanism is disabled and cells engaged in viral replication enter into unscheduled mitosis. We made use of an HCMV mutant that, due to a defective Cyclin A2 binding motif in its UL21a gene product (pUL21a), has lost its ability to down-regulate Cyclin A2 and, therefore, to arrest cells at the G1/S transition. Cyclin A2 up-regulation in infected cells not only triggered the onset of cellular DNA synthesis, but also promoted the accumulation and nuclear translocation of Cyclin B1-CDK1, premature chromatin condensation and mitotic entry. The infected cells were able to enter metaphase as shown by nuclear lamina disassembly and, often irregular, metaphase spindle formation. However, anaphase onset was blocked by the still intact anaphase promoting complex/cyclosome (APC/C) inhibitory function of pUL21a. Remarkably, the essential viral IE2, but not the related chromosome-associated IE1 protein, disappeared upon mitotic entry, suggesting an inherent instability of IE2 under mitotic conditions. Viral DNA synthesis was impaired in mitosis, as demonstrated by the abnormal morphology and strongly reduced BrdU incorporation rates of viral replication compartments. The prolonged metaphase arrest in infected cells coincided with precocious sister chromatid separation and progressive fragmentation of the chromosomal material. We conclude that the Cyclin A2-binding function of pUL21a contributes to the maintenance of a cell cycle state conducive for the completion of the HCMV replication cycle. Unscheduled mitotic entry during the course of the HCMV replication has fatal consequences, leading to abortive infection and cell death. Cyclin A2 is a key regulator of the cell division cycle. Interactors of Cyclin A2 typically contain short sequence elements (RXL/Cy motifs) that bind with high affinity to a hydrophobic patch in the Cyclin A2 protein. Two types of RXL/Cy-containing factors are known: i) cyclin-dependent kinase (CDK) substrates, which are processed by the CDK subunit that complexes to Cyclin A2, and ii) CDK inhibitors, which stably associate to Cyclin A2-CDK due to the lack of CDK phosphorylation sites. Human cytomegalovirus (HCMV) has evolved a novel type of RXL/Cy-containing protein. Its UL21a gene product, a small and highly unstable protein, binds to Cyclin A2 via an RXL/Cy motif in its N-terminus, leading to efficient degradation of Cyclin A2 by the proteasome. Here, we show that this mechanism is not only essential for viral inhibition of cellular DNA synthesis, but also to prevent entry of infected cells into mitosis. Unscheduled mitotic entry is followed by aberrant spindle formation, metaphase arrest, precocious separation of sister chromatids, chromosomal fragmentation and cell death. Viral DNA replication and expression of the essential viral IE2 protein are abrogated in mitosis. Thus, pUL21a-Cyclin A2 interaction protects HCMV from a collapse of viral and cellular functions in mitosis.
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Georgakilas AG, Tsantoulis P, Kotsinas A, Michalopoulos I, Townsend P, Gorgoulis VG. Are common fragile sites merely structural domains or highly organized "functional" units susceptible to oncogenic stress? Cell Mol Life Sci 2014; 71:4519-44. [PMID: 25238782 PMCID: PMC4232749 DOI: 10.1007/s00018-014-1717-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 08/28/2014] [Indexed: 01/07/2023]
Abstract
Common fragile sites (CFSs) are regions of the genome with a predisposition to DNA double-strand breaks in response to intrinsic (oncogenic) or extrinsic replication stress. CFS breakage is a common feature in carcinogenesis from its earliest stages. Given that a number of oncogenes and tumor suppressors are located within CFSs, a question that emerges is whether fragility in these regions is only a structural “passive” incident or an event with a profound biological effect. Furthermore, there is sparse evidence that other elements, like non-coding RNAs, are positioned with them. By analyzing data from various libraries, like miRbase and ENCODE, we show a prevalence of various cancer-related genes, miRNAs, and regulatory binding sites, such as CTCF within CFSs. We propose that CFSs are not only susceptible structural domains, but highly organized “functional” entities that when targeted, severe repercussion for cell homeostasis occurs.
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Affiliation(s)
- Alexandros G Georgakilas
- Physics Department, School of Applied Mathematical and Physical Sciences, National Technical University of Athens (NTUA), Zografou, 15780, Athens, Greece
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Toledo LI, Altmeyer M, Rask MB, Lukas C, Larsen DH, Povlsen LK, Bekker-Jensen S, Mailand N, Bartek J, Lukas J. ATR prohibits replication catastrophe by preventing global exhaustion of RPA. Cell 2014; 155:1088-103. [PMID: 24267891 DOI: 10.1016/j.cell.2013.10.043] [Citation(s) in RCA: 634] [Impact Index Per Article: 63.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 08/19/2013] [Accepted: 10/18/2013] [Indexed: 11/26/2022]
Abstract
ATR, activated by replication stress, protects replication forks locally and suppresses origin firing globally. Here, we show that these functions of ATR are mechanistically coupled. Although initially stable, stalled forks in ATR-deficient cells undergo nucleus-wide breakage after unscheduled origin firing generates an excess of single-stranded DNA that exhausts the nuclear pool of RPA. Partial reduction of RPA accelerated fork breakage, and forced elevation of RPA was sufficient to delay such "replication catastrophe" even in the absence of ATR activity. Conversely, unscheduled origin firing induced breakage of stalled forks even in cells with active ATR. Thus, ATR-mediated suppression of dormant origins shields active forks against irreversible breakage via preventing exhaustion of nuclear RPA. This study elucidates how replicating genomes avoid destabilizing DNA damage. Because cancer cells commonly feature intrinsically high replication stress, this study also provides a molecular rationale for their hypersensitivity to ATR inhibitors.
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Affiliation(s)
- Luis Ignacio Toledo
- Chromosome Stability and Dynamics Group, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
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