1
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Ubieto-Capella P, Ximénez-Embún P, Giménez-Llorente D, Losada A, Muñoz J, Méndez J. A rewiring of DNA replication mediated by MRE11 exonuclease underlies primed-to-naive cell de-differentiation. Cell Rep 2024; 43:114024. [PMID: 38581679 DOI: 10.1016/j.celrep.2024.114024] [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: 09/08/2023] [Revised: 02/01/2024] [Accepted: 03/15/2024] [Indexed: 04/08/2024] Open
Abstract
Mouse embryonic stem cells (mESCs) in the primed pluripotency state, which resembles the post-implantation epiblast, can be de-differentiated in culture to a naive state that resembles the pre-implantation inner cell mass. We report that primed-to-naive mESC transition entails a significant slowdown of DNA replication forks and the compensatory activation of dormant origins. Using isolation of proteins on nascent DNA coupled to mass spectrometry, we identify key changes in replisome composition that are responsible for these effects. Naive mESC forks are enriched in MRE11 nuclease and other DNA repair proteins. MRE11 is recruited to newly synthesized DNA in response to transcription-replication conflicts, and its inhibition or genetic downregulation in naive mESCs is sufficient to restore the fork rate of primed cells. Transcriptomic analyses indicate that MRE11 exonuclease activity is required for the complete primed-to-naive mESC transition, demonstrating a direct link between DNA replication dynamics and the mESC de-differentiation process.
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Affiliation(s)
- Patricia Ubieto-Capella
- DNA Replication Group, Molecular Oncology Programme, Spanish National Cancer Research Centre (CNIO), 28029 Madrid, Spain
| | - Pilar Ximénez-Embún
- Proteomics Unit-ProteoRed-ISCIII, Biotechnology Programme, Spanish National Cancer Research Centre (CNIO), 28029 Madrid, Spain
| | - Daniel Giménez-Llorente
- Chromosome Dynamics Group, Molecular Oncology Programme, Spanish National Cancer Research Centre (CNIO), 28029 Madrid, Spain
| | - Ana Losada
- Chromosome Dynamics Group, Molecular Oncology Programme, Spanish National Cancer Research Centre (CNIO), 28029 Madrid, Spain
| | - Javier Muñoz
- Proteomics Unit-ProteoRed-ISCIII, Biotechnology Programme, Spanish National Cancer Research Centre (CNIO), 28029 Madrid, Spain
| | - Juan Méndez
- DNA Replication Group, Molecular Oncology Programme, Spanish National Cancer Research Centre (CNIO), 28029 Madrid, Spain.
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2
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Jones RM, Reynolds-Winczura A, Gambus A. A Decade of Discovery-Eukaryotic Replisome Disassembly at Replication Termination. BIOLOGY 2024; 13:233. [PMID: 38666845 PMCID: PMC11048390 DOI: 10.3390/biology13040233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Revised: 03/23/2024] [Accepted: 03/25/2024] [Indexed: 04/28/2024]
Abstract
The eukaryotic replicative helicase (CMG complex) is assembled during DNA replication initiation in a highly regulated manner, which is described in depth by other manuscripts in this Issue. During DNA replication, the replicative helicase moves through the chromatin, unwinding DNA and facilitating nascent DNA synthesis by polymerases. Once the duplication of a replicon is complete, the CMG helicase and the remaining components of the replisome need to be removed from the chromatin. Research carried out over the last ten years has produced a breakthrough in our understanding, revealing that replication termination, and more specifically replisome disassembly, is indeed a highly regulated process. This review brings together our current understanding of these processes and highlights elements of the mechanism that are conserved or have undergone divergence throughout evolution. Finally, we discuss events beyond the classic termination of DNA replication in S-phase and go over the known mechanisms of replicative helicase removal from chromatin in these particular situations.
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Affiliation(s)
- Rebecca M. Jones
- Institute of Cancer and Genomic Sciences, Birmingham Centre for Genome Biology, University of Birmingham, Birmingham B15 2TT, UK; (R.M.J.); (A.R.-W.)
- School of Biosciences, Aston University, Birmingham B4 7ET, UK
| | - Alicja Reynolds-Winczura
- Institute of Cancer and Genomic Sciences, Birmingham Centre for Genome Biology, University of Birmingham, Birmingham B15 2TT, UK; (R.M.J.); (A.R.-W.)
| | - Agnieszka Gambus
- Institute of Cancer and Genomic Sciences, Birmingham Centre for Genome Biology, University of Birmingham, Birmingham B15 2TT, UK; (R.M.J.); (A.R.-W.)
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3
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Fu Y, Lv Z, Kong D, Fan Y, Dong B. High abundance of CDC45 inhibits cell proliferation through elevation of HSPA6. Cell Prolif 2022; 55:e13257. [PMID: 35642733 PMCID: PMC9251052 DOI: 10.1111/cpr.13257] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Revised: 04/15/2022] [Accepted: 04/25/2022] [Indexed: 11/29/2022] Open
Abstract
OBJECTIVES CDC45 is the core component of CMG (CDC45-MCMs-GINS) complex that plays important role in the initial step of DNA replication in eukaryotic cells. The expression level of cdc45 is under the critical control for the accurate cell cycle progression. Loss-of-function of cdc45 has been demonstrated to inhibit cell proliferation and leads to cell death due to the inhibition of DNA replication and G1-phase arrest. An increasing of CDC45 inhibits cell proliferation as well. Nevertheless, a systematic analysis of the effect of high dose of CDC45 on cell physiology and behaviors is unclear. In the present study, we aimed to investigate the effects and mechanisms of high dose of CDC45 on cell behaviors. MATERIALS AND METHODS We overexpressed cdc45 in cultured cell lines, Ciona and Drosophila embryos, respectively. The cell cycle progression was examined by the BrdU incorporation experiment, flow cytometry and PH3 (phospho-Histone 3) staining. RNA-sequencing analysis and qRT-PCR were carried out to screen the affected genes in HeLa cells overexpressing cdc45. siRNA-mediated knockdown was performed to investigate gene functions in HeLa cells overexpressing cdc45. RESULTS We found that high level of cdc45 from different species (human, mammal, ascidian, and Drosophila) inhibited cell cycle in vitro and in vivo. High dose of CDC45 blocks cells entering into S phase. However, we failed to detect DNA damage and cell apoptosis. We identified hspa6 was the most upregulated gene in HeLa cells overexpressing cdc45 via RNA-seq analysis and qRT-PCR validation. Overexpression of Hs-hspa6 inhibited proliferation rate and DNA replication in HeLa cells, mimicking the phenotype of cdc45 overexpression. RNAi against hspa6 partially rescued the cell proliferation defect caused by high dose of CDC45. CONCLUSIONS Our study suggests that high abundance of CDC45 stops cell cycle. Instead of inducing apoptosis, excessive CDC45 prevents cell entering S phase probably due to promoting hspa6 expression.
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Affiliation(s)
- Yuanyuan Fu
- Sars‐Fang Centre, MoE Key Laboratory of Marine Genetics and BreedingCollege of Marine Life Sciences, Ocean University of ChinaQingdaoChina
| | - Zhiyi Lv
- Sars‐Fang Centre, MoE Key Laboratory of Marine Genetics and BreedingCollege of Marine Life Sciences, Ocean University of ChinaQingdaoChina
- Institute of Evolution & Marine BiodiversityOcean University of ChinaQingdaoChina
| | - Deqing Kong
- Department of BiologyPhilipps UniversityMarburgGermany
| | - Yuping Fan
- Sars‐Fang Centre, MoE Key Laboratory of Marine Genetics and BreedingCollege of Marine Life Sciences, Ocean University of ChinaQingdaoChina
| | - Bo Dong
- Sars‐Fang Centre, MoE Key Laboratory of Marine Genetics and BreedingCollege of Marine Life Sciences, Ocean University of ChinaQingdaoChina
- Institute of Evolution & Marine BiodiversityOcean University of ChinaQingdaoChina
- Laboratory for Marine Biology and BiotechnologyQingdao National Laboratory for Marine Science and TechnologyQingdaoChina
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4
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Nakatani T, Lin J, Ji F, Ettinger A, Pontabry J, Tokoro M, Altamirano-Pacheco L, Fiorentino J, Mahammadov E, Hatano Y, Van Rechem C, Chakraborty D, Ruiz-Morales ER, Arguello Pascualli PY, Scialdone A, Yamagata K, Whetstine JR, Sadreyev RI, Torres-Padilla ME. DNA replication fork speed underlies cell fate changes and promotes reprogramming. Nat Genet 2022; 54:318-327. [PMID: 35256805 PMCID: PMC8920892 DOI: 10.1038/s41588-022-01023-0] [Citation(s) in RCA: 37] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 01/27/2022] [Indexed: 01/29/2023]
Abstract
Totipotency emerges in early embryogenesis, but its molecular underpinnings remain poorly characterized. In the present study, we employed DNA fiber analysis to investigate how pluripotent stem cells are reprogrammed into totipotent-like 2-cell-like cells (2CLCs). We show that totipotent cells of the early mouse embryo have slow DNA replication fork speed and that 2CLCs recapitulate this feature, suggesting that fork speed underlies the transition to a totipotent-like state. 2CLCs emerge concomitant with DNA replication and display changes in replication timing (RT), particularly during the early S-phase. RT changes occur prior to 2CLC emergence, suggesting that RT may predispose to gene expression changes and consequent reprogramming of cell fate. Slowing down replication fork speed experimentally induces 2CLCs. In vivo, slowing fork speed improves the reprogramming efficiency of somatic cell nuclear transfer. Our data suggest that fork speed regulates cellular plasticity and that remodeling of replication features leads to changes in cell fate and reprogramming. Totipotent cells in mouse embryos and 2-cell-like cells have slow DNA replication fork speed. Perturbations that slow replication fork speed promote 2-cell-like cell emergence and improve somatic cell nuclear transfer reprogramming and formation of induced pluripotent stem cell colonies.
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5
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Rausch C, Weber P, Prorok P, Hörl D, Maiser A, Lehmkuhl A, Chagin VO, Casas-Delucchi CS, Leonhardt H, Cardoso MC. Developmental differences in genome replication program and origin activation. Nucleic Acids Res 2021; 48:12751-12777. [PMID: 33264404 PMCID: PMC7736824 DOI: 10.1093/nar/gkaa1124] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 10/09/2020] [Accepted: 11/04/2020] [Indexed: 12/17/2022] Open
Abstract
To ensure error-free duplication of all (epi)genetic information once per cell cycle, DNA replication follows a cell type and developmental stage specific spatio-temporal program. Here, we analyze the spatio-temporal DNA replication progression in (un)differentiated mouse embryonic stem (mES) cells. Whereas telomeres replicate throughout S-phase, we observe mid S-phase replication of (peri)centromeric heterochromatin in mES cells, which switches to late S-phase replication upon differentiation. This replication timing reversal correlates with and depends on an increase in condensation and a decrease in acetylation of chromatin. We further find synchronous duplication of the Y chromosome, marking the end of S-phase, irrespectively of the pluripotency state. Using a combination of single-molecule and super-resolution microscopy, we measure molecular properties of the mES cell replicon, the number of replication foci active in parallel and their spatial clustering. We conclude that each replication nanofocus in mES cells corresponds to an individual replicon, with up to one quarter representing unidirectional forks. Furthermore, with molecular combing and genome-wide origin mapping analyses, we find that mES cells activate twice as many origins spaced at half the distance than somatic cells. Altogether, our results highlight fundamental developmental differences on progression of genome replication and origin activation in pluripotent cells.
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Affiliation(s)
- Cathia Rausch
- Department of Biology, Technical University of Darmstadt, 64287 Darmstadt, Germany
| | - Patrick Weber
- Department of Biology, Technical University of Darmstadt, 64287 Darmstadt, Germany
| | - Paulina Prorok
- Department of Biology, Technical University of Darmstadt, 64287 Darmstadt, Germany
| | - David Hörl
- Department of Biology II, LMU Munich, 81377 Munich, Germany
| | - Andreas Maiser
- Department of Biology II, LMU Munich, 81377 Munich, Germany
| | - Anne Lehmkuhl
- Department of Biology, Technical University of Darmstadt, 64287 Darmstadt, Germany
| | - Vadim O Chagin
- Department of Biology, Technical University of Darmstadt, 64287 Darmstadt, Germany.,Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia
| | | | | | - M Cristina Cardoso
- Department of Biology, Technical University of Darmstadt, 64287 Darmstadt, Germany
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6
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Hashimoto Y, Tanaka H. Ongoing replication forks delay the nuclear envelope breakdown upon mitotic entry. J Biol Chem 2021; 296:100033. [PMID: 33148697 PMCID: PMC7948514 DOI: 10.1074/jbc.ra120.015142] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 11/02/2020] [Accepted: 11/04/2020] [Indexed: 01/22/2023] Open
Abstract
DNA replication is a major contributor to genomic instability, and protection against DNA replication perturbation is essential for normal cell division. Certain types of replication stress agents, such as aphidicolin and hydroxyurea, have been shown to cause reversible replication fork stalling, wherein replisome complexes are stably maintained with competence to restart in the S phase of the cell cycle. If these stalled forks persist into the M phase without a replication restart, replisomes are disassembled in a p97-dependent pathway and under-replicated DNA is subjected to mitotic DNA repair synthesis. Here, using Xenopus egg extracts, we investigated the consequences that arise when stalled forks are released simultaneously with the induction of mitosis. Ara-cytidine-5'-triphosphate-induced stalled forks were able to restart with the addition of excess dCTP during early mitosis before the nuclear envelope breakdown (NEB). However, stalled forks could no longer restart efficiently after the NEB. Although replisome complexes were finally disassembled in a p97-dependent manner during mitotic progression whether or not fork stalling was relieved, the timing of the NEB was delayed with the ongoing forks, rather than the stalled forks, and the delay was dependent on Wee1/Myt1 kinase activities. Thus, ongoing DNA replication was found to be directly linked to the regulation of Wee1/Myt1 kinases to modulate cyclin-dependent kinase activities because of which DNA replication and mitosis occur in a mutually exclusive and sequential manner.
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Affiliation(s)
- Yoshitami Hashimoto
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan.
| | - Hirofumi Tanaka
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
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7
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Sedlackova H, Rask MB, Gupta R, Choudhary C, Somyajit K, Lukas J. Equilibrium between nascent and parental MCM proteins protects replicating genomes. Nature 2020; 587:297-302. [PMID: 33087936 DOI: 10.1038/s41586-020-2842-3] [Citation(s) in RCA: 56] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Accepted: 07/27/2020] [Indexed: 12/14/2022]
Abstract
Minichromosome maintenance proteins (MCMs) are DNA-dependent ATPases that bind to replication origins and license them to support a single round of DNA replication. A large excess of MCM2-7 assembles on chromatin in G1 phase as pre-replication complexes (pre-RCs), of which only a fraction become the productive CDC45-MCM-GINS (CMG) helicases that are required for genome duplication1-4. It remains unclear why cells generate this surplus of MCMs, how they manage to sustain it across multiple generations, and why even a mild reduction in the MCM pool compromises the integrity of replicating genomes5,6. Here we show that, for daughter cells to sustain error-free DNA replication, their mother cells build up a nuclear pool of MCMs both by recycling chromatin-bound (parental) MCMs and by synthesizing new (nascent) MCMs. Although all MCMs can form pre-RCs, it is the parental pool that is inherently stable and preferentially matures into CMGs. By contrast, nascent MCM3-7 (but not MCM2) undergo rapid proteolysis in the cytoplasm, and their stabilization and nuclear translocation require interaction with minichromosome-maintenance complex-binding protein (MCMBP), a distant MCM paralogue7,8. By chaperoning nascent MCMs, MCMBP safeguards replicating genomes by increasing chromatin coverage with pre-RCs that do not participate on replication origins but adjust the pace of replisome movement to minimize errors during DNA replication. Consequently, although the paucity of pre-RCs in MCMBP-deficient cells does not alter DNA synthesis overall, it increases the speed and asymmetry of individual replisomes, which leads to DNA damage. The surplus of MCMs therefore increases the robustness of genome duplication by restraining the speed at which eukaryotic cells replicate their DNA. Alterations in physiological fork speed might thus explain why even a minor reduction in MCM levels destabilizes the genome and predisposes to increased incidence of tumour formation.
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Affiliation(s)
- Hana Sedlackova
- Protein Signaling Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Maj-Britt Rask
- Protein Signaling Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Rajat Gupta
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Chunaram Choudhary
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kumar Somyajit
- Protein Signaling Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Jiri Lukas
- Protein Signaling Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
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8
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Bender D, Da Silva EML, Chen J, Poss A, Gawey L, Rulon Z, Rankin S. Multivalent interaction of ESCO2 with the replication machinery is required for sister chromatid cohesion in vertebrates. Proc Natl Acad Sci U S A 2020; 117:1081-1089. [PMID: 31879348 PMCID: PMC6969535 DOI: 10.1073/pnas.1911936117] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The tethering together of sister chromatids by the cohesin complex ensures their accurate alignment and segregation during cell division. In vertebrates, sister chromatid cohesion requires the activity of the ESCO2 acetyltransferase, which modifies the Smc3 subunit of cohesin. It was shown recently that ESCO2 promotes cohesion through interaction with the MCM replicative helicase. However, ESCO2 does not significantly colocalize with the MCM complex, suggesting there are additional interactions important for ESCO2 function. Here we show that ESCO2 is recruited to replication factories, sites of DNA replication, through interaction with PCNA. We show that ESCO2 contains multiple PCNA-interaction motifs in its N terminus, each of which is essential to its ability to establish cohesion. We propose that multiple PCNA-interaction motifs embedded in a largely flexible and disordered region of the protein underlie the unique ability of ESCO2 to establish cohesion between sister chromatids precisely as they are born during DNA replication.
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Affiliation(s)
- Dawn Bender
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
- Department of Cell Biology, Oklahoma University Health Science Center, Oklahoma City, OK 73104
| | | | - Jingrong Chen
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Annelise Poss
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Lauren Gawey
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Zane Rulon
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Susannah Rankin
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104;
- Department of Cell Biology, Oklahoma University Health Science Center, Oklahoma City, OK 73104
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9
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Stinson BM, Moreno AT, Walter JC, Loparo JJ. A Mechanism to Minimize Errors during Non-homologous End Joining. Mol Cell 2019; 77:1080-1091.e8. [PMID: 31862156 DOI: 10.1016/j.molcel.2019.11.018] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 10/09/2019] [Accepted: 11/22/2019] [Indexed: 01/15/2023]
Abstract
Enzymatic processing of DNA underlies all DNA repair, yet inappropriate DNA processing must be avoided. In vertebrates, double-strand breaks are repaired predominantly by non-homologous end joining (NHEJ), which directly ligates DNA ends. NHEJ has the potential to be highly mutagenic because it uses DNA polymerases, nucleases, and other enzymes that modify incompatible DNA ends to allow their ligation. Using frog egg extracts that recapitulate NHEJ, we show that end processing requires the formation of a "short-range synaptic complex" in which DNA ends are closely aligned in a ligation-competent state. Furthermore, single-molecule imaging directly demonstrates that processing occurs within the short-range complex. This confinement of end processing to a ligation-competent complex ensures that DNA ends undergo ligation as soon as they become compatible, thereby minimizing mutagenesis. Our results illustrate how the coordination of enzymatic catalysis with higher-order structural organization of substrate maximizes the fidelity of DNA repair.
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Affiliation(s)
- Benjamin M Stinson
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Andrew T Moreno
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Johannes C Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Howard Hughes Medical Institute, Boston, MA 02115, USA.
| | - Joseph J Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
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10
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Platel M, Narassimprakash H, Ciardo D, Haccard O, Marheineke K. Genome wide decrease of DNA replication eye density at the midblastula transition of Xenopus laevis. Cell Cycle 2019; 18:1458-1472. [PMID: 31130065 PMCID: PMC6592225 DOI: 10.1080/15384101.2019.1618641] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 05/03/2019] [Accepted: 05/08/2019] [Indexed: 02/04/2023] Open
Abstract
During the first rapid divisions of early development in many species, the DNA:cytoplasm ratio increases until the midblastula transition (MBT) when transcription resumes and cell cycles lengthen. S phase is very rapid in early embryos, about 20-30 times faster than in differentiated cells. Using a combination of DNA fiber studies and a Xenopus laevis embryonic in vitro replication system, we show that S phase slows down shortly after the MBT owing to a genome wide decrease of replication eye density. Increasing the dNTP pool did not accelerate S phase or increase replication eye density implying that dNTPs are not rate limiting for DNA replication at the Xenopus MBT. Increasing the ratio of DNA:cytoplasm in egg extracts faithfully recapitulates changes in the spatial replication program in embryos, supporting the hypothesis that titration of soluble limiting factors could explain the observed changes in the DNA replication program at the MBT in Xenopus laevis.
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Affiliation(s)
- Marie Platel
- Department of Genome Biology, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, University Paris‐Sud, University Paris‐Saclay, Gif‐sur‐Yvette, France
| | - Hemalatha Narassimprakash
- Department of Genome Biology, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, University Paris‐Sud, University Paris‐Saclay, Gif‐sur‐Yvette, France
| | - Diletta Ciardo
- Department of Genome Biology, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, University Paris‐Sud, University Paris‐Saclay, Gif‐sur‐Yvette, France
| | - Olivier Haccard
- Department of Genome Biology, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, University Paris‐Sud, University Paris‐Saclay, Gif‐sur‐Yvette, France
| | - Kathrin Marheineke
- Department of Genome Biology, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, University Paris‐Sud, University Paris‐Saclay, Gif‐sur‐Yvette, France
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11
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Rankin S. Reconstituting Nuclear and Chromosome Dynamics Using Xenopus Extracts. Cold Spring Harb Protoc 2019; 2019:pdb.top097105. [PMID: 30150319 DOI: 10.1101/pdb.top097105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Extracts prepared from the eggs of frogs, particularly Xenopus species, have provided critical material for seminal studies of nuclear and chromosome dynamics over several decades. Their usefulness for these types of analyses lies in several important characteristics: stockpiled nuclear components, absence of endogenous DNA, and intact and functioning signaling networks. These factors have allowed detailed molecular analyses of many aspects of chromosome biology, including DNA replication, checkpoint signaling, epigenetic control, and chromosome condensation, cohesion, and segregation. In this introduction, the preparation and application of Xenopus egg extracts for the study of chromosomes and chromatin are described in detail.
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Affiliation(s)
- Susannah Rankin
- Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104; .,Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104
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12
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Shining a Spotlight on DNA: Single-Molecule Methods to Visualise DNA. Molecules 2019; 24:molecules24030491. [PMID: 30704053 PMCID: PMC6384704 DOI: 10.3390/molecules24030491] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Revised: 01/17/2019] [Accepted: 01/29/2019] [Indexed: 11/29/2022] Open
Abstract
The ability to watch single molecules of DNA has revolutionised how we study biological transactions concerning nucleic acids. Many strategies have been developed to manipulate DNA molecules to investigate mechanical properties, dynamics and protein–DNA interactions. Imaging methods using small molecules and protein-based probes to visualise DNA have propelled our understanding of complex biochemical reactions involving DNA. This review focuses on summarising some of the methodological developments made to visualise individual DNA molecules and discusses how these probes have been used in single-molecule biophysical assays.
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13
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Ciardo D, Goldar A, Marheineke K. On the Interplay of the DNA Replication Program and the Intra-S Phase Checkpoint Pathway. Genes (Basel) 2019; 10:E94. [PMID: 30700024 PMCID: PMC6410103 DOI: 10.3390/genes10020094] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 01/23/2019] [Accepted: 01/25/2019] [Indexed: 12/12/2022] Open
Abstract
DNA replication in eukaryotes is achieved by the activation of multiple replication origins which needs to be precisely coordinated in space and time. This spatio-temporal replication program is regulated by many factors to maintain genome stability, which is frequently threatened through stresses of exogenous or endogenous origin. Intra-S phase checkpoints monitor the integrity of DNA synthesis and are activated when replication forks are stalled. Their activation leads to the stabilization of forks, to the delay of the replication program by the inhibition of late firing origins, and the delay of G2/M phase entry. In some cell cycles during early development these mechanisms are less efficient in order to allow rapid cell divisions. In this article, we will review our current knowledge of how the intra-S phase checkpoint regulates the replication program in budding yeast and metazoan models, including early embryos with rapid S phases. We sum up current models on how the checkpoint can inhibit origin firing in some genomic regions, but allow dormant origin activation in other regions. Finally, we discuss how numerical and theoretical models can be used to connect the multiple different actors into a global process and to extract general rules.
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Affiliation(s)
- Diletta Ciardo
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette CEDEX, France.
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14
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Sparks JL, Chistol G, Gao AO, Räschle M, Larsen NB, Mann M, Duxin JP, Walter JC. The CMG Helicase Bypasses DNA-Protein Cross-Links to Facilitate Their Repair. Cell 2018; 176:167-181.e21. [PMID: 30595447 DOI: 10.1016/j.cell.2018.10.053] [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: 03/09/2018] [Revised: 09/13/2018] [Accepted: 10/24/2018] [Indexed: 02/04/2023]
Abstract
Covalent DNA-protein cross-links (DPCs) impede replication fork progression and threaten genome integrity. Using Xenopus egg extracts, we previously showed that replication fork collision with DPCs causes their proteolysis, followed by translesion DNA synthesis. We show here that when DPC proteolysis is blocked, the replicative DNA helicase CMG (CDC45, MCM2-7, GINS), which travels on the leading strand template, bypasses an intact leading strand DPC. Single-molecule imaging reveals that GINS does not dissociate from CMG during bypass and that CMG slows dramatically after bypass, likely due to uncoupling from the stalled leading strand. The DNA helicase RTEL1 facilitates bypass, apparently by generating single-stranded DNA beyond the DPC. The absence of RTEL1 impairs DPC proteolysis, suggesting that CMG must bypass the DPC to enable proteolysis. Our results suggest a mechanism that prevents inadvertent CMG destruction by DPC proteases, and they reveal CMG's remarkable capacity to overcome obstacles on its translocation strand.
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Affiliation(s)
- Justin L Sparks
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Gheorghe Chistol
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Alan O Gao
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Markus Räschle
- Department of Molecular Biotechnology and Systems Biology, Technical University of Kaiserslautern, 67653 Kaiserslautern, Germany
| | - Nicolai B Larsen
- Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Matthias Mann
- Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark; Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Julien P Duxin
- Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Johannes C Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Howard Hughes Medical Institute, Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
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15
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Armas P, Calcaterra NB. G-quadruplex in animal development: Contribution to gene expression and genomic heterogeneity. Mech Dev 2018; 154:64-72. [DOI: 10.1016/j.mod.2018.05.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 04/18/2018] [Accepted: 05/09/2018] [Indexed: 12/21/2022]
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16
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Singh B, Wu PYJ. Regulation of the program of DNA replication by CDK: new findings and perspectives. Curr Genet 2018; 65:79-85. [PMID: 29926159 DOI: 10.1007/s00294-018-0860-6] [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] [Received: 06/04/2018] [Revised: 06/14/2018] [Accepted: 06/15/2018] [Indexed: 12/18/2022]
Abstract
Progression through the cell cycle is driven by the activities of the cyclin-dependent kinase (CDK) family of enzymes, which establish an ordered passage through the cell cycle phases. CDK activity is crucial for the cellular transitions from G1 to S and G2 to M, which are highly controlled to promote the faithful duplication of the genetic material and the transmission of the genome into daughter cells, respectively. While oscillations in CDK activity are essential for cell division, how its specific dynamics may shape cellular processes remains an open question. Recently, we have investigated the potential role of CDK in establishing the profile of replication initiation along the chromosomes, also referred to as the replication program. Our results demonstrated that the timing and level of CDK activity at G1/S provide two critical and independent inputs that modulate the pattern of origin usage. In this review, we will present the conclusions of our study and discuss the implications of our findings for cellular function and physiology.
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Affiliation(s)
- Balveer Singh
- CNRS, Institute of Genetics and Development of Rennes, University of Rennes, UMR 6290, 2 avenue du Pr. Léon Bernard, 35043, Rennes, France
| | - Pei-Yun Jenny Wu
- CNRS, Institute of Genetics and Development of Rennes, University of Rennes, UMR 6290, 2 avenue du Pr. Léon Bernard, 35043, Rennes, France.
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17
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Seller CA, O’Farrell PH. Rif1 prolongs the embryonic S phase at the Drosophila mid-blastula transition. PLoS Biol 2018; 16:e2005687. [PMID: 29746464 PMCID: PMC5963817 DOI: 10.1371/journal.pbio.2005687] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 05/22/2018] [Accepted: 04/23/2018] [Indexed: 01/09/2023] Open
Abstract
In preparation for dramatic morphogenetic events of gastrulation, rapid embryonic cell cycles slow at the mid-blastula transition (MBT). In Drosophila melanogaster embryos, down-regulation of cyclin-dependent kinase 1 (Cdk1) activity initiates this slowing by delaying replication of heterochromatic satellite sequences and extending S phase. We found that Cdk1 activity inhibited the chromatin association of Rap1 interacting factor 1 (Rif1), a candidate repressor of replication. Furthermore, Rif1 bound selectively to satellite sequences following Cdk1 down-regulation at the MBT. In the next S phase, Rif1 dissociated from different satellites in an orderly schedule that anticipated their replication. Rif1 lacking potential phosphorylation sites failed to dissociate and dominantly prevented completion of replication. Loss of Rif1 in mutant embryos shortened the post-MBT S phase and rescued embryonic cell cycles disrupted by depletion of the S phase–promoting kinase, cell division cycle 7 (Cdc7). Our work shows that Rif1 and S phase kinases compose a replication timer controlling first the developmental onset of late replication and then the precise schedule of replication within S phase. In addition, we describe how onset of late replication fits into the progressive maturation of heterochromatin during development. Cells divide rapidly in the early embryos of most animals. However, during a conserved period of development known as the mid-blastula transition (MBT), the cell cycle slows down dramatically. In Drosophila embryos, genome duplication abruptly slows to initiate this cell cycle prolongation. This is achieved through the onset of late replication, a well-recognized phenomenon in which specific sequences of the genome await replication until long after other sequences have finished. Even though this temporal program of replication is a major determinant of the duration of S phase, the factors involved in this process remain unknown. Here, we use genetics and real-time microscopy to visualize replication in developing fly embryos and show that the protein Rap1 interacting factor 1 (Rif1) mediates the introduction of late replication at the MBT. We find that at this stage, Rif1 binds to and selectively delays the replication of large blocks of repetitive DNA known as satellite sequences. During the rapid cell cycles before the MBT, we show that the cyclin-dependent kinase 1 (Cdk1) prevents Rif1 from slowing down DNA replication by driving its removal from the chromatin. The developmental down-regulation of Cdk1 at the MBT allows Rif1 to associate with the satellite sequences and initiate cell cycle slowing. Our work provides new insights into the temporal programming of S phase and into the embryonic origin of late replication.
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Affiliation(s)
- Charles A. Seller
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Patrick H. O’Farrell
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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18
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Biochemical Fractionation of Time-Resolved Drosophila Embryos Reveals Similar Transcriptomic Alterations in Replication Checkpoint and Histone mRNA Processing Mutants. J Mol Biol 2017; 429:3264-3279. [DOI: 10.1016/j.jmb.2017.01.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 01/28/2017] [Accepted: 01/30/2017] [Indexed: 11/22/2022]
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19
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The Intra-S Checkpoint Responses to DNA Damage. Genes (Basel) 2017; 8:genes8020074. [PMID: 28218681 PMCID: PMC5333063 DOI: 10.3390/genes8020074] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 02/08/2017] [Accepted: 02/08/2017] [Indexed: 02/03/2023] Open
Abstract
Faithful duplication of the genome is a challenge because DNA is susceptible to damage by a number of intrinsic and extrinsic genotoxins, such as free radicals and UV light. Cells activate the intra-S checkpoint in response to damage during S phase to protect genomic integrity and ensure replication fidelity. The checkpoint prevents genomic instability mainly by regulating origin firing, fork progression, and transcription of G1/S genes in response to DNA damage. Several studies hint that regulation of forks is perhaps the most critical function of the intra-S checkpoint. However, the exact role of the checkpoint at replication forks has remained elusive and controversial. Is the checkpoint required for fork stability, or fork restart, or to prevent fork reversal or fork collapse, or activate repair at replication forks? What are the factors that the checkpoint targets at stalled replication forks? In this review, we will discuss the various pathways activated by the intra-S checkpoint in response to damage to prevent genomic instability.
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20
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Regulation of DNA Replication in Early Embryonic Cleavages. Genes (Basel) 2017; 8:genes8010042. [PMID: 28106858 PMCID: PMC5295036 DOI: 10.3390/genes8010042] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/06/2017] [Accepted: 01/11/2017] [Indexed: 11/18/2022] Open
Abstract
Early embryonic cleavages are characterized by short and highly synchronous cell cycles made of alternating S- and M-phases with virtually absent gap phases. In this contracted cell cycle, the duration of DNA synthesis can be extraordinarily short. Depending on the organism, the whole genome of an embryo is replicated at a speed that is between 20 to 60 times faster than that of a somatic cell. Because transcription in the early embryo is repressed, DNA synthesis relies on a large stockpile of maternally supplied proteins stored in the egg representing most, if not all, cellular genes. In addition, in early embryonic cell cycles, both replication and DNA damage checkpoints are inefficient. In this article, we will review current knowledge on how DNA synthesis is regulated in early embryos and discuss possible consequences of replicating chromosomes with little or no quality control.
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21
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Acevedo J, Yan S, Michael WM. Direct Binding to Replication Protein A (RPA)-coated Single-stranded DNA Allows Recruitment of the ATR Activator TopBP1 to Sites of DNA Damage. J Biol Chem 2016; 291:13124-31. [PMID: 27129245 DOI: 10.1074/jbc.m116.729194] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Indexed: 12/29/2022] Open
Abstract
A critical event for the ability of cells to tolerate DNA damage and replication stress is activation of the ATR kinase. ATR activation is dependent on the BRCT (BRCA1 C terminus) repeat-containing protein TopBP1. Previous work has shown that recruitment of TopBP1 to sites of DNA damage and stalled replication forks is necessary for downstream events in ATR activation; however, the mechanism for this recruitment was not known. Here, we use protein binding assays and functional studies in Xenopus egg extracts to show that TopBP1 makes a direct interaction, via its BRCT2 domain, with RPA-coated single-stranded DNA. We identify a point mutant that abrogates this interaction and show that this mutant fails to accumulate at sites of DNA damage and that the mutant cannot activate ATR. These data thus supply a mechanism for how the critical ATR activator, TopBP1, senses DNA damage and stalled replication forks to initiate assembly of checkpoint signaling complexes.
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Affiliation(s)
- Julyana Acevedo
- From the Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089 and
| | - Shan Yan
- the Department of Biological Sciences, University of North Carolina, Charlotte, North Carolina 28223
| | - W Matthew Michael
- From the Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089 and
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22
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Löb D, Lengert N, Chagin VO, Reinhart M, Casas-Delucchi CS, Cardoso MC, Drossel B. 3D replicon distributions arise from stochastic initiation and domino-like DNA replication progression. Nat Commun 2016; 7:11207. [PMID: 27052359 PMCID: PMC4829661 DOI: 10.1038/ncomms11207] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 03/02/2016] [Indexed: 01/02/2023] Open
Abstract
DNA replication dynamics in cells from higher eukaryotes follows very complex but highly efficient mechanisms. However, the principles behind initiation of potential replication origins and emergence of typical patterns of nuclear replication sites remain unclear. Here, we propose a comprehensive model of DNA replication in human cells that is based on stochastic, proximity-induced replication initiation. Critical model features are: spontaneous stochastic firing of individual origins in euchromatin and facultative heterochromatin, inhibition of firing at distances below the size of chromatin loops and a domino-like effect by which replication forks induce firing of nearby origins. The model reproduces the empirical temporal and chromatin-related properties of DNA replication in human cells. We advance the one-dimensional DNA replication model to a spatial model by taking into account chromatin folding in the nucleus, and we are able to reproduce the spatial and temporal characteristics of the replication foci distribution throughout S-phase.
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Affiliation(s)
- D. Löb
- Department of Physics, Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
| | - N. Lengert
- Department of Physics, Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
| | - V. O. Chagin
- Laboratory of Chromosome Stability, Institute of Cytology, St Petersburg 194064, Russia
- Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - M. Reinhart
- Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - C. S. Casas-Delucchi
- Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - M. C. Cardoso
- Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - B. Drossel
- Department of Physics, Institute for Condensed Matter Physics, Technische Universität Darmstadt, 64289 Darmstadt, Germany
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23
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The N Terminus of the Retinoblastoma Protein Inhibits DNA Replication via a Bipartite Mechanism Disrupted in Partially Penetrant Retinoblastomas. Mol Cell Biol 2015; 36:832-45. [PMID: 26711265 DOI: 10.1128/mcb.00636-15] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 12/22/2015] [Indexed: 02/01/2023] Open
Abstract
The N-terminal domain of the retinoblastoma (Rb) tumor suppressor protein (RbN) harbors in-frame exon deletions in partially penetrant hereditary retinoblastomas and is known to impair cell growth and tumorigenesis. However, how such RbN deletions contribute to Rb tumor- and growth-suppressive functions is unknown. Here we establish that RbN directly inhibits DNA replication initiation and elongation using a bipartite mechanism involving N-terminal exons lost in cancer. Specifically, Rb exon 7 is necessary and sufficient to target and inhibit the replicative CMG helicase, resulting in the accumulation of inactive CMGs on chromatin. An independent N-terminal loop domain, which forms a projection, specifically blocks DNA polymerase α (Pol-α) and Ctf4 recruitment without affecting DNA polymerases ε and δ or the CMG helicase. Individual disruption of exon 7 or the projection in RbN or Rb, as occurs in inherited cancers, partially impairs the ability of Rb/RbN to inhibit DNA replication and block G1-to-S cell cycle transit. However, their combined loss abolishes these functions of Rb. Thus, Rb growth-suppressive functions include its ability to block replicative complexes via bipartite, independent, and additive N-terminal domains. The partial loss of replication, CMG, or Pol-α control provides a potential molecular explanation for how N-terminal Rb loss-of-function deletions contribute to the etiology of partially penetrant retinoblastomas.
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24
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Siefert JC, Clowdus EA, Sansam CL. Cell cycle control in the early embryonic development of aquatic animal species. Comp Biochem Physiol C Toxicol Pharmacol 2015; 178:8-15. [PMID: 26475527 PMCID: PMC4755307 DOI: 10.1016/j.cbpc.2015.10.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Revised: 10/07/2015] [Accepted: 10/09/2015] [Indexed: 01/02/2023]
Abstract
The cell cycle is integrated with many aspects of embryonic development. Not only is proper control over the pace of cell proliferation important, but also the timing of cell cycle progression is coordinated with transcription, cell migration, and cell differentiation. Due to the ease with which the embryos of aquatic organisms can be observed and manipulated, they have been a popular choice for embryologists throughout history. In the cell cycle field, aquatic organisms have been extremely important because they have played a major role in the discovery and analysis of key regulators of the cell cycle. In particular, the frog Xenopus laevis has been instrumental for understanding how the basic embryonic cell cycle is regulated. More recently, the zebrafish has been used to understand how the cell cycle is remodeled during vertebrate development and how it is regulated during morphogenesis. This review describes how some of the unique strengths of aquatic species have been leveraged for cell cycle research and suggests how species such as Xenopus and zebrafish will continue to reveal the roles of the cell cycle in human biology and disease.
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Affiliation(s)
- Joseph C Siefert
- Oklahoma Medical Research Foundation, Cell Cycle and Cancer Biology Research Program, Oklahoma City, OK, USA; University of Oklahoma Health Sciences Center, Department of Cell Biology, Oklahoma City, OK, USA
| | - Emily A Clowdus
- Oklahoma Medical Research Foundation, Cell Cycle and Cancer Biology Research Program, Oklahoma City, OK, USA; University of Oklahoma Health Sciences Center, Department of Cell Biology, Oklahoma City, OK, USA
| | - Christopher L Sansam
- Oklahoma Medical Research Foundation, Cell Cycle and Cancer Biology Research Program, Oklahoma City, OK, USA; University of Oklahoma Health Sciences Center, Department of Cell Biology, Oklahoma City, OK, USA.
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25
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MCM Paradox: Abundance of Eukaryotic Replicative Helicases and Genomic Integrity. Mol Biol Int 2014; 2014:574850. [PMID: 25386362 PMCID: PMC4217321 DOI: 10.1155/2014/574850] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Accepted: 09/30/2014] [Indexed: 12/03/2022] Open
Abstract
As a crucial component of DNA replication licensing system, minichromosome maintenance (MCM) 2–7 complex acts as the eukaryotic DNA replicative helicase. The six related MCM proteins form a heterohexamer and bind with ORC, CDC6, and Cdt1 to form the prereplication complex. Although the MCMs are well known as replicative helicases, their overabundance and distribution patterns on chromatin present a paradox called the “MCM paradox.” Several approaches had been taken to solve the MCM paradox and describe the purpose of excess MCMs distributed beyond the replication origins. Alternative functions of these MCMs rather than a helicase had also been proposed. This review focuses on several models and concepts generated to solve the MCM paradox coinciding with their helicase function and provides insight into the concept that excess MCMs are meant for licensing dormant origins as a backup during replication stress. Finally, we extend our view towards the effect of alteration of MCM level. Though an excess MCM constituent is needed for normal cells to withstand stress, there must be a delineation of the threshold level in normal and malignant cells. This review also outlooks the future prospects to better understand the MCM biology.
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26
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Zierhut C, Jenness C, Kimura H, Funabiki H. Nucleosomal regulation of chromatin composition and nuclear assembly revealed by histone depletion. Nat Struct Mol Biol 2014; 21:617-25. [PMID: 24952593 PMCID: PMC4082469 DOI: 10.1038/nsmb.2845] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 05/23/2014] [Indexed: 12/13/2022]
Abstract
Nucleosomes are the fundamental unit of chromatin, but analysis of transcription-independent nucleosome functions has been complicated by the gene-expression changes resulting from histone manipulation. Here we solve this dilemma by developing Xenopus laevis egg extracts deficient for nucleosome formation and by analyzing the proteomic landscape and behavior of nucleosomal chromatin and nucleosome-free DNA. We show that although nucleosome-free DNA can recruit nuclear-envelope membranes, nucleosomes are required for spindle assembly and for formation of the lamina and of nuclear pore complexes (NPCs). We show that, in addition to the Ran G-nucleotide exchange factor RCC1, ELYS, the initiator of NPC formation, fails to associate with naked DNA but directly binds histone H2A-H2B dimers and nucleosomes. Tethering ELYS and RCC1 to DNA bypasses the requirement for nucleosomes in NPC formation in a synergistic manner. Thus, the minimal essential function of nucleosomes in NPC formation is to recruit RCC1 and ELYS.
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Affiliation(s)
- Christian Zierhut
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, New York, USA
| | - Christopher Jenness
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, New York, USA
| | - Hiroshi Kimura
- 1] Graduate School of Frontier Biosciences, Osaka University, Suita, Japan. [2] Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, Suita, Japan
| | - Hironori Funabiki
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, New York, USA
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27
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Bellelli R, Castellone MD, Guida T, Limongello R, Dathan NA, Merolla F, Cirafici AM, Affuso A, Masai H, Costanzo V, Grieco D, Fusco A, Santoro M, Carlomagno F. NCOA4 transcriptional coactivator inhibits activation of DNA replication origins. Mol Cell 2014; 55:123-37. [PMID: 24910095 DOI: 10.1016/j.molcel.2014.04.031] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2013] [Revised: 03/31/2014] [Accepted: 04/28/2014] [Indexed: 11/19/2022]
Abstract
NCOA4 is a transcriptional coactivator of nuclear hormone receptors that undergoes gene rearrangement in human cancer. By combining studies in Xenopus laevis egg extracts and mouse embryonic fibroblasts (MEFs), we show here that NCOA4 is a minichromosome maintenance 7 (MCM7)-interacting protein that is able to control DNA replication. Depletion-reconstitution experiments in Xenopus laevis egg extracts indicate that NCOA4 acts as an inhibitor of DNA replication origin activation by regulating CMG (CDC45/MCM2-7/GINS) helicase. NCOA4(-/-) MEFs display unscheduled origin activation and reduced interorigin distance; this results in replication stress, as shown by the presence of fork stalling, reduction of fork speed, and premature senescence. Together, our findings indicate that NCOA4 acts as a regulator of DNA replication origins that helps prevent inappropriate DNA synthesis and replication stress.
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Affiliation(s)
- Roberto Bellelli
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Maria Domenica Castellone
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Teresa Guida
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Roberto Limongello
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | | | - Francesco Merolla
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Anna Maria Cirafici
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Andrea Affuso
- Animal Model Facility, Biogem s.c.a.r.l., 83031 Ariano Irpino, Avellino, Italy
| | - Hisao Masai
- Tokyo Metropolitan Institute of Medical Sciences, 156-8506 Tokyo, Japan
| | - Vincenzo Costanzo
- London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms EN6 3LD, UK
| | - Domenico Grieco
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Alfredo Fusco
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy
| | - Massimo Santoro
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy.
| | - Francesca Carlomagno
- Istituto di Endocrinologia ed Oncologia Sperimentale del CNR/Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università di Napoli "Federico II," 80131 Naples, Italy.
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28
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Bernis C, Forbes DJ. Analysis of nuclear reconstitution, nuclear envelope assembly, and nuclear pore assembly using Xenopus in vitro assays. Methods Cell Biol 2014; 122:165-91. [PMID: 24857730 DOI: 10.1016/b978-0-12-417160-2.00008-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The large and complex eukaryotic nucleus is the arbiter of DNA replication, RNA transcription, splicing, and ribosome assembly. With the advent of in vitro nuclear reconstitution extracts derived from Xenopus eggs in the 1980s, it became possible to assemble multiple nuclei in vitro around added DNA or chromatin substrates. Such reconstituted nuclei contain a nuclear lamina, double nuclear membranes, nuclear pores, and are competent for DNA replication and nuclear import. In vitro nuclear reconstitution has allowed the assembly of "wild-type" and "biochemically mutant" nuclei in which the impact of individual components can be assessed. Here, we describe protocols for preparation of the nuclear reconstitution extract, nuclear reconstitution in vitro, assessment of nuclear membrane integrity, and a more specialized assay for nuclear pore assembly into preformed pore-free nuclear intermediates.
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Affiliation(s)
- Cyril Bernis
- Cell and Developmental Biology, University of California, San Diego, California, USA
| | - Douglass J Forbes
- Cell and Developmental Biology, University of California, San Diego, California, USA
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29
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Abstract
The minichromosome maintenance (MCM) complex, which plays multiple important roles in DNA replication, is loaded onto chromatin following mitosis, remains on chromatin until the completion of DNA synthesis, and then is unloaded by a poorly defined mechanism that involves the MCM binding protein (MCM-BP). Here we show that MCM-BP directly interacts with the ubiquitin-specific protease USP7, that this interaction occurs predominantly on chromatin, and that MCM-BP can tether USP7 to MCM proteins. Detailed biochemical and structure analyses of the USP7-MCM-BP interaction showed that the (155)PSTS(158) MCM-BP sequence mediates critical interactions with the TRAF domain binding pocket of USP7. Analysis of the effects of USP7 knockout on DNA replication revealed that lack of USP7 results in slowed progression through late S phase without globally affecting the fork rate or origin usage. Lack of USP7 also resulted in increased levels of MCM proteins on chromatin, and investigation of the cause of this increase revealed a defect in the dissociation of MCM proteins from chromatin in mid- to late S phase. This role of USP7 mirrors the previously described role for MCM-BP in MCM complex unloading and suggests that USP7 works with MCM-BP to unload MCM complexes from chromatin at the end of S phase.
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30
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Murphy CM, Michael WM. Control of DNA replication by the nucleus/cytoplasm ratio in Xenopus. J Biol Chem 2013; 288:29382-93. [PMID: 23986447 DOI: 10.1074/jbc.m113.499012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The nucleus/cytoplasm (N/C) ratio controls S phase dynamics in many biological systems, most notably the abrupt remodeling of the cell cycle that occurs at the midblastula transition in early Xenopus laevis embryos. After an initial series of rapid cleavage cycles consisting only of S and M phases, a critical N/C ratio is reached, which causes a sharp increase in the length of S phase as the cell cycle is reconfigured to resemble somatic cell cycles. How the N/C ratio determines the length of S phase has been a longstanding problem in developmental biology. Using Xenopus egg extracts, we show that DNA replication at high N/C ratio is restricted by one or more limiting substances. We report here that the protein phosphatase PP2A, in conjunction with its B55α regulatory subunit, becomes limiting for replication origin firing at high N/C ratio, and this in turn leads to reduced origin activation and an increase in the time required to complete S phase. Increasing the levels of PP2A catalytic subunit or B55α experimentally restores rapid DNA synthesis at high N/C ratio. Inversely, reduction of PP2A or B55α levels sharply extends S phase even in low N/C extracts. These results identify PP2A-B55α as a link between DNA replication and N/C ratio in egg extracts and suggest a mechanism that may influence the onset of the midblastula transition in vivo.
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Affiliation(s)
- Christopher M Murphy
- From the Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089 and
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31
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Collart C, Allen GE, Bradshaw CR, Smith JC, Zegerman P. Titration of four replication factors is essential for the Xenopus laevis midblastula transition. Science 2013; 341:893-6. [PMID: 23907533 PMCID: PMC3898016 DOI: 10.1126/science.1241530] [Citation(s) in RCA: 163] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The rapid, reductive early divisions of many metazoan embryos are followed by the midblastula transition (MBT), during which the cell cycle elongates and zygotic transcription begins. It has been proposed that the increasing nuclear to cytoplasmic (N/C) ratio is critical for controlling the events of the MBT. We show that four DNA replication factors--Cut5, RecQ4, Treslin, and Drf1--are limiting for replication initiation at increasing N/C ratios in vitro and in vivo in Xenopus laevis. The levels of these factors regulate multiple events of the MBT, including the slowing of the cell cycle, the onset of zygotic transcription, and the developmental activation of the kinase Chk1. This work provides a mechanism for how the N/C ratio controls the MBT and shows that the regulation of replication initiation is fundamental for normal embryogenesis.
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Affiliation(s)
- Clara Collart
- Wellcome Trust/Cancer Research UK Gurdon Institute, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge CB2 1QN, UK
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK
| | - George E. Allen
- Wellcome Trust/Cancer Research UK Gurdon Institute, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge CB2 1QN, UK
| | - Charles R. Bradshaw
- Wellcome Trust/Cancer Research UK Gurdon Institute, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge CB2 1QN, UK
| | - James C. Smith
- MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK
| | - Philip Zegerman
- Wellcome Trust/Cancer Research UK Gurdon Institute, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge CB2 1QN, UK
- Department of Zoology, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge CB2 1QN, UK
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32
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Gaggioli V, Le Viet B, Germe T, Hyrien O. DNA topoisomerase IIα controls replication origin cluster licensing and firing time in Xenopus egg extracts. Nucleic Acids Res 2013; 41:7313-31. [PMID: 23757188 PMCID: PMC3753627 DOI: 10.1093/nar/gkt494] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Sperm chromatin incubated in Xenopus egg extracts undergoes origin licensing and nuclear assembly before DNA replication. We found that depletion of DNA topoisomerase IIα (topo IIα), the sole topo II isozyme of eggs and its inhibition by ICRF-193, which clamps topo IIα around DNA have opposite effects on these processes. ICRF-193 slowed down replication origin cluster activation and fork progression in a checkpoint-independent manner, without altering replicon size. In contrast, topo IIα depletion accelerated origin cluster activation, and topo IIα add-back negated overinitiation. Therefore, topo IIα is not required for DNA replication, but topo IIα clamps slow replication, probably by forming roadblocks. ICRF-193 had no effect on DNA synthesis when added after nuclear assembly, confirming that topo IIα activity is dispensable for replication and revealing that topo IIα clamps formed on replicating DNA do not block replication, presumably because topo IIα acts behind and not in front of forks. Topo IIα depletion increased, and topo IIα addition reduced, chromatin loading of MCM2-7 replicative helicase, whereas ICRF-193 did not affect MCM2-7 loading. Therefore, topo IIα restrains MCM2-7 loading in an ICRF-193-resistant manner during origin licensing, suggesting a model for establishing the sequential firing of origin clusters.
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Affiliation(s)
- Vincent Gaggioli
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), S2-Génomique Fonctionnelle, CNRS UMR8197, Inserm U1024, 46 rue d'Ulm, 75005 Paris, France
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33
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Song J, Lafont A, Chen J, Wu FM, Shirahige K, Rankin S. Cohesin acetylation promotes sister chromatid cohesion only in association with the replication machinery. J Biol Chem 2012; 287:34325-36. [PMID: 22896698 PMCID: PMC3464539 DOI: 10.1074/jbc.m112.400192] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 08/10/2012] [Indexed: 11/06/2022] Open
Abstract
Acetylation of the Smc3 subunit of cohesin is essential to establish functional cohesion between sister chromatids. Smc3 acetylation is catalyzed by members of the Eco family of acetyltransferases, although the mechanism by which acetylation is regulated and how it promotes cohesion are largely unknown. In vertebrates, the cohesin complex binds to chromatin during mitotic exit and is converted to a functional form during or shortly after DNA replication. The conserved proliferating cell nuclear antigen-interacting protein box motif in yeast Eco1 is required for function, and cohesin is acetylated during the S phase. This has led to the notion that acetylation of cohesin is stimulated by interaction of Eco1 with the replication machinery. Here we show that in vertebrates Smc3 acetylation occurs independently of DNA replication. Smc3 is readily acetylated before replication is initiated and after DNA replication is complete. However, we also show that functional acetylation occurs only in association with the replication machinery: disruption of the interaction between XEco2 and proliferating cell nuclear antigen prevents cohesion establishment while having little impact on the overall levels of Smc3 acetylation. These results demonstrate that Smc3 acetylation can occur throughout interphase but that only acetylation in association with the replication fork promotes sister chromatid cohesion. These data reveal how the generation of cohesion is limited to the appropriate time and place during the cell cycle and provide insight into the mechanism by which acetylation ensures cohesion.
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Affiliation(s)
- Jianhua Song
- From the Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Andrea Lafont
- From the Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Jingrong Chen
- From the Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
| | - Frank M. Wu
- the Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, and
| | - Katsuhiko Shirahige
- the Institute of Molecular and Cellular Biosciences, University of Tokyo, Yayoi, Tokyo 113-0032 Japan
| | - Susannah Rankin
- From the Program in Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104
- the Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, and
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34
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Loveland AB, Habuchi S, Walter JC, van Oijen AM. A general approach to break the concentration barrier in single-molecule imaging. Nat Methods 2012; 9:987-92. [PMID: 22961247 PMCID: PMC3610324 DOI: 10.1038/nmeth.2174] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Accepted: 08/09/2012] [Indexed: 02/04/2023]
Abstract
Single-molecule fluorescence imaging is often incompatible with physiological protein concentrations, as fluorescence background overwhelms an individual molecule's signal. We solve this problem with a new imaging approach called PhADE (PhotoActivation, Diffusion and Excitation). A protein of interest is fused to a photoactivatable protein (mKikGR) and introduced to its surface-immobilized substrate. After photoactivation of mKikGR near the surface, rapid diffusion of the unbound mKikGR fusion out of the detection volume eliminates background fluorescence, whereupon the bound molecules are imaged. We labeled the eukaryotic DNA replication protein flap endonuclease 1 with mKikGR and added it to replication-competent Xenopus laevis egg extracts. PhADE imaging of high concentrations of the fusion construct revealed its dynamics and micrometer-scale movements on individual, replicating DNA molecules. Because PhADE imaging is in principle compatible with any photoactivatable fluorophore, it should have broad applicability in revealing single-molecule dynamics and stoichiometry of macromolecular protein complexes at previously inaccessible fluorophore concentrations.
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Affiliation(s)
- Anna B. Loveland
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
- Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA
| | - Satoshi Habuchi
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Johannes C. Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Antoine M. van Oijen
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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35
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Williams HL, Gottesman ME, Gautier J. Replication-independent repair of DNA interstrand crosslinks. Mol Cell 2012; 47:140-7. [PMID: 22658724 DOI: 10.1016/j.molcel.2012.05.001] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 03/19/2012] [Accepted: 04/17/2012] [Indexed: 12/24/2022]
Abstract
DNA interstrand crosslinks (ICLs) are cytotoxic lesions that covalently link opposite strands of the DNA helix and block DNA unwinding. ICLs are repaired during and outside S phase, and replication-independent ICL repair (RIR) is critical to maintain genomic integrity and to allow transcription in nondividing or slowly dividing cells. Here, we show that the Y family DNA polymerase kappa (Pol κ) is essential for RIR of a site-specific ICL lesion in Xenopus egg extracts, and that both its catalytic activity and UBZ domains are required for this function. We also demonstrate a requirement for PCNA and its modification on lysine 164. Finally, we show that Pol κ participates in ICL repair in mammalian cells, particularly in G0. Our results identify key components of the RIR pathway and begin to unravel its mechanism.
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Affiliation(s)
- Hannah L Williams
- Institute for Cancer Genetics, Department of Genetics and Development, Columbia University, New York, NY 10032, USA
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36
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Abstract
The duration of S phase in early embryos is often short, and then increases as development proceeds because of the appearance of late-replicating regions of the genome. In the April 1, 2012, issue of Genes & Development, Farrell and colleagues (pp. 714-725) demonstrate that the down-regulation of cyclin-dependent kinase 1 (Cdk1) activity triggers the onset of late-replicating DNA and an increase in S-phase length in Drosophila embryos, revealing an unexpected role for Cdk1 in replication control during development.
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Affiliation(s)
- Robert J Duronio
- Department of Biology, Department of Genetics, Lineberger Comprehensive Cancer Center, Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, NC 27599, USA.
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37
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Farrell JA, Shermoen AW, Yuan K, O'Farrell PH. Embryonic onset of late replication requires Cdc25 down-regulation. Genes Dev 2012; 26:714-25. [PMID: 22431511 DOI: 10.1101/gad.186429.111] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The Drosophila midblastula transition (MBT), a major event in embryogenesis, remodels and slows the cell cycle. In the pre-MBT cycles, all genomic regions replicate simultaneously in rapid S phases that alternate with mitosis, skipping gap phases. At the MBT, down-regulation of Cdc25 phosphatase and the resulting inhibitory phosphorylation of the mitotic kinase Cdk1 create a G2 pause in interphase 14. However, an earlier change in interphase 14 is the prolongation of S phase. While the signals modifying S phase are unknown, the onset of late replication-where replication of constitutively heterochromatic satellite sequences is delayed-extends S-phase 14. We injected Cdc25 mRNA to bypass the developmentally programmed down-regulation of Cdc25 at the MBT. Introduction of either Cdc25 isoform (String or Twine) or enhanced Cdk1 activity triggered premature replication of late-replicating sequences, even after their specification, and thereby shortened S phase. Reciprocally, reduction of Cdk1 activity by knockdown of mitotic cyclins extended pre-MBT S phase. These findings suggest that high Cdc25 and Cdk1 contribute to the speed of the rapid, pre-MBT S phases and that down-regulation of these activities plays a broader role in MBT-associated changes than was previously suspected.
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Affiliation(s)
- Jeffrey A Farrell
- Department of Biochemistry, University of California at San Francisco, San Francisco, California 94143, USA
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38
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McLellan JL, O'Neil NJ, Barrett I, Ferree E, van Pel DM, Ushey K, Sipahimalani P, Bryan J, Rose AM, Hieter P. Synthetic lethality of cohesins with PARPs and replication fork mediators. PLoS Genet 2012; 8:e1002574. [PMID: 22412391 PMCID: PMC3297586 DOI: 10.1371/journal.pgen.1002574] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 01/16/2012] [Indexed: 12/11/2022] Open
Abstract
Synthetic lethality has been proposed as a way to leverage the genetic differences found in tumor cells to affect their selective killing. Cohesins, which tether sister chromatids together until anaphase onset, are mutated in a variety of tumor types. The elucidation of synthetic lethal interactions with cohesin mutants therefore identifies potential therapeutic targets. We used a cross-species approach to identify robust negative genetic interactions with cohesin mutants. Utilizing essential and non-essential mutant synthetic genetic arrays in Saccharomyces cerevisiae, we screened genome-wide for genetic interactions with hypomorphic mutations in cohesin genes. A somatic cell proliferation assay in Caenorhabditis elegans demonstrated that the majority of interactions were conserved. Analysis of the interactions found that cohesin mutants require the function of genes that mediate replication fork progression. Conservation of these interactions between replication fork mediators and cohesin in both yeast and C. elegans prompted us to test whether other replication fork mediators not found in the yeast were required for viability in cohesin mutants. PARP1 has roles in the DNA damage response but also in the restart of stalled replication forks. We found that a hypomorphic allele of the C. elegans SMC1 orthologue, him-1(e879), genetically interacted with mutations in the orthologues of PAR metabolism genes resulting in a reduced brood size and somatic cell defects. We then demonstrated that this interaction is conserved in human cells by showing that PARP inhibitors reduce the viability of cultured human cells depleted for cohesin components. This work demonstrates that large-scale genetic interaction screening in yeast can identify clinically relevant genetic interactions and suggests that PARP inhibitors, which are currently undergoing clinical trials as a treatment of homologous recombination-deficient cancers, may be effective in treating cancers that harbor cohesin mutations.
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Affiliation(s)
- Jessica L. McLellan
- Department of Medical Genetics, University of British Columbia, Vancouver, Canada
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Nigel J. O'Neil
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Irene Barrett
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Elizabeth Ferree
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Derek M. van Pel
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
- Department of Biochemistry, University of British Columbia, Vancouver, Canada
| | - Kevin Ushey
- Department of Statistics, University of British Columbia, Vancouver, Canada
| | - Payal Sipahimalani
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
| | - Jennifer Bryan
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
- Department of Statistics, University of British Columbia, Vancouver, Canada
| | - Ann M. Rose
- Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | - Philip Hieter
- Department of Medical Genetics, University of British Columbia, Vancouver, Canada
- Michael Smith Laboratories, University of British Columbia, Vancouver, Canada
- Department of Biochemistry, University of British Columbia, Vancouver, Canada
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39
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Errico A, Costanzo V. Mechanisms of replication fork protection: a safeguard for genome stability. Crit Rev Biochem Mol Biol 2012; 47:222-35. [DOI: 10.3109/10409238.2012.655374] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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40
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Sasaki T, Li A, Gillespie PJ, Blow JJ, Gilbert DM. Evidence for a mammalian late-G1 phase inhibitor of replication licensing distinct from geminin or Cdk activity. Nucleus 2011; 2:455-64. [PMID: 21983086 DOI: 10.4161/nucl.2.5.17859] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Pre-replication complexes (pre-RCs) are assembled onto DNA during late mitosis and G1 to license replication origins for use in S phase. In order to prevent re-replication of DNA, licensing must be completely shutdown prior to entry into S phase. While mechanisms preventing re-replication during S phase and mitosis have been elucidated, the means by which cells first prevent licensing during late G1 phase are poorly understood. We have employed a hybrid mammalian / Xenopus egg extract replication system to dissect activities that inhibit replication licensing at different stages of the cell cycle in Chinese Hamster Ovary (CHO) cells. We find that soluble extracts from mitotic cells inhibit licensing through a combination of geminin and Cdk activities, while extracts from S-phase cells inhibit licensing predominantly through geminin alone. Surprisingly however, geminin did not accumulate until after cells enter S phase. Unlike extracts from cells in early G1 phase, extracts from late G1 phase and early S phase cells contained an inhibitor of licensing that could not be accounted for by either geminin or Cdk. Moreover, inhibiting cyclin and geminin protein synthesis or inhibiting Cdk activity early in G1 phase did not prevent the appearance of inhibitory activity. These results suggest that a soluble inhibitor of replication licensing appears prior to entry into S phase that is distinct from either geminin or Cdk activity. Our hybrid system should permit the identification of this and other novel cell cycle regulatory activities.
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Affiliation(s)
- Takayo Sasaki
- Department of Biological Science, Florida State University, Tallahassee, FL, USA
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41
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Cayrou C, Coulombe P, Vigneron A, Stanojcic S, Ganier O, Peiffer I, Rivals E, Puy A, Laurent-Chabalier S, Desprat R, Méchali M. Genome-scale analysis of metazoan replication origins reveals their organization in specific but flexible sites defined by conserved features. Genome Res 2011; 21:1438-49. [PMID: 21750104 DOI: 10.1101/gr.121830.111] [Citation(s) in RCA: 248] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In metazoans, thousands of DNA replication origins (Oris) are activated at each cell cycle. Their genomic organization and their genetic nature remain elusive. Here, we characterized Oris by nascent strand (NS) purification and a genome-wide analysis in Drosophila and mouse cells. We show that in both species most CpG islands (CGI) contain Oris, although methylation is nearly absent in Drosophila, indicating that this epigenetic mark is not crucial for defining the activated origin. Initiation of DNA synthesis starts at the borders of CGI, resulting in a striking bimodal distribution of NS, suggestive of a dual initiation event. Oris contain a unique nucleotide skew around NS peaks, characterized by G/T and C/A overrepresentation at the 5' and 3' of Ori sites, respectively. Repeated GC-rich elements were detected, which are good predictors of Oris, suggesting that common sequence features are part of metazoan Oris. In the heterochromatic chromosome 4 of Drosophila, Oris correlated with HP1 binding sites. At the chromosome level, regions rich in Oris are early replicating, whereas Ori-poor regions are late replicating. The genome-wide analysis was coupled with a DNA combing analysis to unravel the organization of Oris. The results indicate that Oris are in a large excess, but their activation does not occur at random. They are organized in groups of site-specific but flexible origins that define replicons, where a single origin is activated in each replicon. This organization provides both site specificity and Ori firing flexibility in each replicon, allowing possible adaptation to environmental cues and cell fates.
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42
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Cdc45 limits replicon usage from a low density of preRCs in mammalian cells. PLoS One 2011; 6:e17533. [PMID: 21390258 PMCID: PMC3046982 DOI: 10.1371/journal.pone.0017533] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Accepted: 02/08/2011] [Indexed: 12/16/2022] Open
Abstract
Little is known about mammalian preRC stoichiometry, the number of preRCs on chromosomes, and how this relates to replicon size and usage. We show here that, on average, each 100-kb of the mammalian genome contains a preRC composed of approximately one ORC hexamer, 4–5 MCM hexamers, and 2 Cdc6. Relative to these subunits, ∼0.35 total molecules of the pre-Initiation Complex factor Cdc45 are present. Thus, based on ORC availability, somatic cells contain ∼70,000 preRCs of this average total stoichiometry, although subunits may not be juxtaposed with each other. Except for ORC, the chromatin-bound complement of preRC subunits is even lower. Cdc45 is present at very low levels relative to the preRC subunits, but is highly stable, and the same limited number of stable Cdc45 molecules are present from the beginning of S-phase to its completion. Efforts to artificially increase Cdc45 levels through ectopic expression block cell growth. However, microinjection of excess purified Cdc45 into S-phase nuclei activates additional replication foci by three-fold, indicating that Cdc45 functions to activate dormant preRCs and is rate-limiting for somatic replicon usage. Paradoxically, although Cdc45 colocalizes in vivo with some MCM sites and is rate-limiting for DNA replication to occur, neither Cdc45 nor MCMs colocalize with active replication sites. Embryonic metazoan chromatin consists of small replicons that are used efficiently via an excess of preRC subunits. In contrast, somatic mammalian cells contain a low density of preRCs, each containing only a few MCMs that compete for limiting amounts of Cdc45. This provides a molecular explanation why, relative to embryonic replicon dynamics, somatic replicons are, on average, larger and origin efficiency tends to be lower. The stable, continuous, and rate-limiting nature of Cdc45 suggests that Cdc45 contributes to the staggering of replicon usage throughout S-phase, and that replicon activation requires reutilization of existing Cdc45 during S-phase.
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43
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Vastag L, Jorgensen P, Peshkin L, Wei R, Rabinowitz JD, Kirschner MW. Remodeling of the metabolome during early frog development. PLoS One 2011; 6:e16881. [PMID: 21347444 PMCID: PMC3035664 DOI: 10.1371/journal.pone.0016881] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Accepted: 01/04/2011] [Indexed: 12/27/2022] Open
Abstract
A rapid series of synchronous cell divisions initiates embryogenesis in many animal species, including the frog Xenopus laevis. After many of these cleavage cycles, the nuclear to cytoplasmic ratio increases sufficiently to somehow cause cell cycles to elongate and become asynchronous at the mid-blastula transition (MBT). We have discovered that an unanticipated remodeling of core metabolic pathways occurs during the cleavage cycles and the MBT in X. laevis, as evidenced by widespread changes in metabolite abundance. While many of the changes in metabolite abundance were consistently observed, it was also evident that different female frogs laid eggs with different levels of at least some metabolites. Metabolite tracing with heavy isotopes demonstrated that alanine is consumed to generate energy for the early embryo. dATP pools were found to decline during the MBT and we have confirmed that maternal pools of dNTPs are functionally exhausted at the onset of the MBT. Our results support an alternative hypothesis that the cell cycle lengthening at the MBT is triggered not by a limiting maternal protein, as is usually proposed, but by a decline in dNTP pools brought about by the exponentially increasing demands of DNA synthesis.
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Affiliation(s)
- Livia Vastag
- Carl Icahn Laboratory, Department of Chemistry and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Paul Jorgensen
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Leonid Peshkin
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Ru Wei
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
| | - Joshua D. Rabinowitz
- Carl Icahn Laboratory, Department of Chemistry and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Marc W. Kirschner
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
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Ott E, Norio P, Ritzi M, Schildkraut C, Schepers A. The dyad symmetry element of Epstein-Barr virus is a dominant but dispensable replication origin. PLoS One 2011; 6:e18609. [PMID: 21603652 PMCID: PMC3095595 DOI: 10.1371/journal.pone.0018609] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2010] [Accepted: 03/07/2011] [Indexed: 01/13/2023] Open
Abstract
OriP, the latent origin of Epstein-Barr virus (EBV), consists of two essential elements: the dyad symmetry (DS) and the family of repeats (FR). The function of these elements has been predominantly analyzed in plasmids transfected into transformed cells. Here, we examined the molecular functions of DS in its native genomic context and at an ectopic position in the mini-EBV episome. Mini-EBV plasmids contain 41% of the EBV genome including all information required for the proliferation of human B cells. Both FR and DS function independently of their genomic context. We show that DS is the most active origin of replication present in the mini-EBV genome regardless of its location, and it is characterized by the binding of the origin recognition complex (ORC) allowing subsequent replication initiation. Surprisingly, the integrity of oriP is not required for the formation of the pre-replicative complex (pre-RC) at or near DS. In addition we show that initiation events occurring at sites other than the DS are also limited to once per cell cycle and that they are ORC-dependent. The deletion of DS increases initiation from alternative origins, which are normally used very infrequently in the mini-EBV genome. The sequence-independent distribution of ORC-binding, pre-RC-assembly, and initiation patterns indicates that a large number of silent origins are present in the mini-EBV genome. We conclude that, in mini-EBV genomes lacking the DS element, the absence of a strong ORC binding site results in an increase of ORC binding at dispersed sites.
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Affiliation(s)
- Elisabeth Ott
- Department of Gene Vectors, Helmholtz Zentrum München, München, Germany
| | - Paolo Norio
- Department of Cell Biology (CH 416), Albert Einstein College of Medicine, New York, New York, United States of America
| | - Marion Ritzi
- Department of Gene Vectors, Helmholtz Zentrum München, München, Germany
| | - Carl Schildkraut
- Department of Cell Biology (CH 416), Albert Einstein College of Medicine, New York, New York, United States of America
- * E-mail: (AS); (CS)
| | - Aloys Schepers
- Department of Gene Vectors, Helmholtz Zentrum München, München, Germany
- * E-mail: (AS); (CS)
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Nishiyama A, Frappier L, Méchali M. MCM-BP regulates unloading of the MCM2-7 helicase in late S phase. Genes Dev 2010; 25:165-75. [PMID: 21196493 DOI: 10.1101/gad.614411] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Origins of DNA replication are licensed by recruiting MCM2-7 to assemble the prereplicative complex (pre-RC). How MCM2-7 is inactivated or removed from chromatin at the end of S phase is still unclear. Here, we show that MCM-BP can disassemble the MCM2-7 complex and might function as an unloader of MCM2-7 from chromatin. In Xenopus egg extracts, MCM-BP exists in a stable complex with MCM7, but is not associated with the MCM2-7 hexameric complex. MCM-BP accumulates in nuclei in late S phase, well after the loading of MCM2-7 onto chromatin. MCM-BP immunodepletion in Xenopus egg extracts inhibits replication-dependent MCM dissociation without affecting pre-RC formation and DNA replication. When excess MCM-BP is incubated with Xenopus egg extracts or immunopurified MCM2-7, it binds to MCM proteins and promotes disassembly of the MCM2-7 complex. Recombinant MCM-BP also releases MCM2-7 from isolated late-S-phase chromatin, but this activity is abolished when DNA replication is blocked. MCM-BP silencing in human cells also delays MCM dissociation in late S phase. We propose that MCM-BP plays a key role in the mechanism by which pre-RC is cleared from replicated DNA in vertebrate cells.
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Richard DJ, Bolderson E, Khanna KK. Multiple human single-stranded DNA binding proteins function in genome maintenance: structural, biochemical and functional analysis. Crit Rev Biochem Mol Biol 2010; 44:98-116. [PMID: 19367476 DOI: 10.1080/10409230902849180] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
DNA exists predominantly in a duplex form that is preserved via specific base pairing. This base pairing affords a considerable degree of protection against chemical or physical damage and preserves coding potential. However, there are many situations, e.g. during DNA damage and programmed cellular processes such as DNA replication and transcription, in which the DNA duplex is separated into two single-stranded DNA (ssDNA) strands. This ssDNA is vulnerable to attack by nucleases, binding by inappropriate proteins and chemical attack. It is very important to control the generation of ssDNA and protect it when it forms, and for this reason all cellular organisms and many viruses encode a ssDNA binding protein (SSB). All known SSBs use an oligosaccharide/oligonucleotide binding (OB)-fold domain for DNA binding. SSBs have multiple roles in binding and sequestering ssDNA, detecting DNA damage, stimulating strand-exchange proteins and helicases, and mediation of protein-protein interactions. Recently two additional human SSBs have been identified that are more closely related to bacterial and archaeal SSBs. Prior to this it was believed that replication protein A, RPA, was the only human equivalent of bacterial SSB. RPA is thought to be required for most aspects of DNA metabolism including DNA replication, recombination and repair. This review will discuss in further detail the biological pathways in which human SSBs function.
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Affiliation(s)
- Derek J Richard
- Cancer and Cell Biology Division, The Queensland Institute of Medical Research, 300 Herston Road, Herston, QLD 4006, Australia
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Liachko I, Bhaskar A, Lee C, Chung SCC, Tye BK, Keich U. A comprehensive genome-wide map of autonomously replicating sequences in a naive genome. PLoS Genet 2010; 6:e1000946. [PMID: 20485513 PMCID: PMC2869322 DOI: 10.1371/journal.pgen.1000946] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Accepted: 04/09/2010] [Indexed: 11/19/2022] Open
Abstract
Eukaryotic chromosomes initiate DNA synthesis from multiple replication origins. The machinery that initiates DNA synthesis is highly conserved, but the sites where the replication initiation proteins bind have diverged significantly. Functional comparative genomics is an obvious approach to study the evolution of replication origins. However, to date, the Saccharomyces cerevisiae replication origin map is the only genome map available. Using an iterative approach that combines computational prediction and functional validation, we have generated a high-resolution genome-wide map of DNA replication origins in Kluyveromyces lactis. Unlike other yeasts or metazoans, K. lactis autonomously replicating sequences (KlARSs) contain a 50 bp consensus motif suggestive of a dimeric structure. This motif is necessary and largely sufficient for initiation and was used to dependably identify 145 of the up to 156 non-repetitive intergenic ARSs projected for the K. lactis genome. Though similar in genome sizes, K. lactis has half as many ARSs as its distant relative S. cerevisiae. Comparative genomic analysis shows that ARSs in K. lactis and S. cerevisiae preferentially localize to non-syntenic intergenic regions, linking ARSs with loci of accelerated evolutionary change.
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Affiliation(s)
- Ivan Liachko
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Anand Bhaskar
- Department of Computer Science, Cornell University, Ithaca, New York, United States of America
| | - Chanmi Lee
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Shau Chee Claire Chung
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Bik-Kwoon Tye
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
- * E-mail:
| | - Uri Keich
- School of Mathematics and Statistics F07, University of Sydney, Sydney, Australia
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Van C, Yan S, Michael WM, Waga S, Cimprich KA. Continued primer synthesis at stalled replication forks contributes to checkpoint activation. ACTA ACUST UNITED AC 2010; 189:233-46. [PMID: 20385778 PMCID: PMC2856894 DOI: 10.1083/jcb.200909105] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
An increased number of primer–template junctions generated by PCNA, Pol-δ, and Pol-ε at stalled replication forks activates Chk1. Stalled replication forks activate and are stabilized by the ATR (ataxia-telangiectasia mutated and Rad3 related)-mediated checkpoint, but ultimately, they must also recover from the arrest. Although primed single-stranded DNA (ssDNA) is sufficient for checkpoint activation, it is still unknown how this signal is generated at a stalled replication fork. Furthermore, it is not clear how recovery and fork restart occur in higher eukaryotes. Using Xenopus laevis egg extracts, we show that DNA replication continues at a stalled fork through the synthesis and elongation of new primers independent of the checkpoint. This synthesis is dependent on the activity of proliferating cell nuclear antigen, Pol-δ, and Pol-ε, and it contributes to the phosphorylation of Chk1. We also used defined DNA structures to show that for a fixed amount of ssDNA, increasing the number of primer–template junctions strongly enhances Chk1 phosphorylation. These results suggest that new primers are synthesized at stalled replication forks by the leading and lagging strand polymerases and that accumulation of these primers may contribute to checkpoint activation.
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Affiliation(s)
- Christopher Van
- Department of Chemical and Systems Biology, Stanford University, Stanford, CA 94305, USA
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Differences in the DNA replication of unicellular eukaryotes and metazoans: known unknowns. EMBO Rep 2010; 11:270-8. [PMID: 20203697 DOI: 10.1038/embor.2010.27] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Accepted: 01/28/2010] [Indexed: 01/01/2023] Open
Abstract
Although the basic mechanisms of DNA synthesis are conserved across species, there are differences between simple and complex organisms. In contrast to lower eukaryotes, replication origins in complex eukaryotes lack DNA sequence specificity, can be activated in response to stressful conditions and require poorly conserved factors for replication firing. The response to replication fork damage is monitored by conserved proteins, such as the TIPIN-TIM-CLASPIN complex. The absence of this complex induces severe effects on yeast replication, whereas in higher eukaryotes it is only crucial when the availability of replication origins is limiting. Finally, the dependence of DNA replication on homologous recombination proteins such as RAD51 and the MRE11-RAD50-NBS1 complex is also different; they are dispensable for yeast S-phase but essential for accurate DNA replication in metazoans under unchallenged conditions. The reasons for these differences are not yet understood. Here, we focus on some of these known unknowns of DNA replication.
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Terret ME, Sherwood R, Rahman S, Qin J, Jallepalli PV. Cohesin acetylation speeds the replication fork. Nature 2009; 462:231-4. [PMID: 19907496 PMCID: PMC2777716 DOI: 10.1038/nature08550] [Citation(s) in RCA: 187] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Accepted: 09/30/2009] [Indexed: 12/31/2022]
Abstract
Cohesin not only links sister chromatids but also inhibits the transcriptional machinery's interaction with and movement along chromatin. In contrast, replication forks must traverse such cohesin-associated obstructions to duplicate the entire genome in S phase. How this occurs is unknown. Through single-molecule analysis, we demonstrate that the replication factor C (RFC)-CTF18 clamp loader (RFC(CTF18)) controls the velocity, spacing and restart activity of replication forks in human cells and is required for robust acetylation of cohesin's SMC3 subunit and sister chromatid cohesion. Unexpectedly, we discovered that cohesin acetylation itself is a central determinant of fork processivity, as slow-moving replication forks were found in cells lacking the Eco1-related acetyltransferases ESCO1 or ESCO2 (refs 8-10) (including those derived from Roberts' syndrome patients, in whom ESCO2 is biallelically mutated) and in cells expressing a form of SMC3 that cannot be acetylated. This defect was a consequence of cohesin's hyperstable interaction with two regulatory cofactors, WAPL and PDS5A (refs 12, 13); removal of either cofactor allowed forks to progress rapidly without ESCO1, ESCO2, or RFC(CTF18). Our results show a novel mechanism for clamp-loader-dependent fork progression, mediated by the post-translational modification and structural remodelling of the cohesin ring. Loss of this regulatory mechanism leads to the spontaneous accrual of DNA damage and may contribute to the abnormalities of the Roberts' syndrome cohesinopathy.
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Affiliation(s)
- Marie-Emilie Terret
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 USA
| | - Rebecca Sherwood
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 USA
| | - Sadia Rahman
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 USA
| | - Jun Qin
- Center for Molecular Discovery, Verna and Marrs McLean, Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030 USA
| | - Prasad V. Jallepalli
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 USA
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