1
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Liu TH, Dong XL, Chen P, Zhang Q, Zhou XL, Lu C, Pan MH. Geminin is essential for DNA re-replication in the silk gland cells of silkworms. Exp Cell Res 2022; 410:112951. [PMID: 34843715 DOI: 10.1016/j.yexcr.2021.112951] [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: 10/06/2021] [Revised: 11/22/2021] [Accepted: 11/25/2021] [Indexed: 11/18/2022]
Abstract
Endoreplication, known as endocycles or endoreduplication, is a cell cycle variant in which the genomic DNA is re-replicated without mitosis leading to polyploidy. Endoreplication is essential for the development and functioning of the different organs in animals and plants. Deletion of Geminin, a DNA replication licensing inhibitor, causes DNA re-replication or damage. However, the role of Geminin in endoreplication is still unclear. Here, we studied the role of Geminin in the endoreplication of the silk gland cells of silkworms by constructing two transgenic silkworm strains, including BmGeminin1-overexpression and BmGeminin1-RNA interference. Interference of BmGeminin1 led to body weight gain, increased silk gland volume, increased DNA content, and enhanced DNA re-replication activity relative to wild-type Dazao. Meanwhile, overexpression of BmGeminin1 showed an opposite phenotype compared to the BmGem1-RNAi strain. Furthermore, RNA-sequencing of the transgenic strains was carried out to explore how BmGeminin1 regulates DNA re-replication. Our data demonstrated a vital role of Geminin in the regulation of endoreplication in the silk gland of silkworms.
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Affiliation(s)
- Tai-Hang Liu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Department of Bioinformatics, Chongqing Medical University, No.1 Yixueyuan Road, Yuzhong District of Chongqing, 400015, China
| | - Xiao-Long Dong
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Peng Chen
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Qian Zhang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Xiao-Lin Zhou
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Cheng Lu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China.
| | - Min-Hui Pan
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China.
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2
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Control of Eukaryotic DNA Replication Initiation-Mechanisms to Ensure Smooth Transitions. Genes (Basel) 2019; 10:genes10020099. [PMID: 30700044 PMCID: PMC6409694 DOI: 10.3390/genes10020099] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Revised: 01/25/2019] [Accepted: 01/25/2019] [Indexed: 02/06/2023] Open
Abstract
DNA replication differs from most other processes in biology in that any error will irreversibly change the nature of the cellular progeny. DNA replication initiation, therefore, is exquisitely controlled. Deregulation of this control can result in over-replication characterized by repeated initiation events at the same replication origin. Over-replication induces DNA damage and causes genomic instability. The principal mechanism counteracting over-replication in eukaryotes is a division of replication initiation into two steps—licensing and firing—which are temporally separated and occur at distinct cell cycle phases. Here, we review this temporal replication control with a specific focus on mechanisms ensuring the faultless transition between licensing and firing phases.
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3
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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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4
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Parker MW, Botchan MR, Berger JM. Mechanisms and regulation of DNA replication initiation in eukaryotes. Crit Rev Biochem Mol Biol 2017; 52:107-144. [PMID: 28094588 DOI: 10.1080/10409238.2016.1274717] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cellular DNA replication is initiated through the action of multiprotein complexes that recognize replication start sites in the chromosome (termed origins) and facilitate duplex DNA melting within these regions. In a typical cell cycle, initiation occurs only once per origin and each round of replication is tightly coupled to cell division. To avoid aberrant origin firing and re-replication, eukaryotes tightly regulate two events in the initiation process: loading of the replicative helicase, MCM2-7, onto chromatin by the origin recognition complex (ORC), and subsequent activation of the helicase by its incorporation into a complex known as the CMG. Recent work has begun to reveal the details of an orchestrated and sequential exchange of initiation factors on DNA that give rise to a replication-competent complex, the replisome. Here, we review the molecular mechanisms that underpin eukaryotic DNA replication initiation - from selecting replication start sites to replicative helicase loading and activation - and describe how these events are often distinctly regulated across different eukaryotic model organisms.
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Affiliation(s)
- Matthew W Parker
- a Department of Biophysics and Biophysical Chemistry , Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - Michael R Botchan
- b Department of Molecular and Cell Biology , University of California Berkeley , Berkeley , CA , USA
| | - James M Berger
- a Department of Biophysics and Biophysical Chemistry , Johns Hopkins University School of Medicine , Baltimore , MD , USA
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5
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Kushwaha PP, Rapalli KC, Kumar S. Geminin a multi task protein involved in cancer pathophysiology and developmental process: A review. Biochimie 2016; 131:115-127. [PMID: 27702582 DOI: 10.1016/j.biochi.2016.09.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 09/29/2016] [Indexed: 02/05/2023]
Abstract
DNA replicates in a timely manner with each cell division. Multiple proteins and factors are involved in the initiation of DNA replication including a dynamic interaction between Cdc10-dependent transcript (Cdt1) and Geminin (GMNN). A conformational change between GMNN-Cdt1 heterotrimer and heterohexamer complex is responsible for licensing or inhibition of the DNA replication. This molecular switch ensures a faithful DNA replication during each S phase of cell cycle. GMNN inhibits Cdt1-mediated minichromosome maintenance helicases (MCM) loading onto the chromatin-bound origin recognition complex (ORC) which results in the inhibition of pre-replication complex assembly. GMNN modulates DNA replication by direct binding to Cdt1, and thereby alters its stability and activity. GMNN is involved in various stages of development such as pre-implantation, germ layer formation, cell commitment and specification, maintenance of genome integrity at mid blastula transition, epithelial to mesenchymal transition during gastrulation, neural development, organogenesis and axis patterning. GMNN interacts with different proteins resulting in enhanced hematopoietic stem cell activity thereby activating the development-associated genes' transcription. GMNN expression is also associated with cancer pathophysiology and development. In this review we discussed the structure and function of GMNN in detail. Inhibitors of GMNN and their role in DNA replication, repair, cell cycle and apoptosis are reviewed. Further, we also discussed the role of GMNN in virus infected host cells.
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Affiliation(s)
- Prem Prakash Kushwaha
- School of Basic and Applied Sciences, Centre for Biochemistry and Microbial Sciences, Central University of Punjab, Bathinda, 151001, India
| | - Krishna Chaitanya Rapalli
- School of Basic and Applied Sciences, Centre for Animal Sciences, Central University of Punjab, Bathinda, 151001, India
| | - Shashank Kumar
- School of Basic and Applied Sciences, Centre for Biochemistry and Microbial Sciences, Central University of Punjab, Bathinda, 151001, India.
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6
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Gillespie PJ, Neusiedler J, Creavin K, Chadha GS, Blow JJ. Cell Cycle Synchronization in Xenopus Egg Extracts. Methods Mol Biol 2016; 1342:101-47. [PMID: 26254920 DOI: 10.1007/978-1-4939-2957-3_6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Many important discoveries in cell cycle research have been made using cell-free extracts prepared from the eggs of the South African clawed frog Xenopus laevis. These extracts efficiently support the key nuclear functions of the eukaryotic cell cycle in vitro under apparently the same controls that exist in vivo. The Xenopus cell-free system is therefore uniquely suited to the study of the mechanisms, dynamics and integration of cell cycle regulated processes at a biochemical level. Here, we describe methods currently in use in our laboratory for the preparation of Xenopus egg extracts and demembranated sperm nuclei. We detail how these extracts can be used to study the key transitions of the eukaryotic cell cycle and describe conditions under which these transitions can be manipulated by addition of drugs that either retard or advance passage. In addition, we describe in detail essential techniques that provide a practical starting point for investigating the function of proteins involved in the operation of the eukaryotic cell cycle.
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Affiliation(s)
- Peter J Gillespie
- Centre for Gene Regulation & Expression, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
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7
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Rizzardi LF, Coleman KE, Varma D, Matson JP, Oh S, Cook JG. CDK1-dependent inhibition of the E3 ubiquitin ligase CRL4CDT2 ensures robust transition from S Phase to Mitosis. J Biol Chem 2014; 290:556-67. [PMID: 25411249 DOI: 10.1074/jbc.m114.614701] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Replication-coupled destruction of a cohort of cell cycle proteins ensures efficient and precise genome duplication. Three proteins destroyed during replication via the CRL4(CDT2) ubiquitin E3 ligase, CDT1, p21, and SET8 (PR-SET7), are also essential or important during mitosis, making their reaccumulation after S phase a critical cell cycle event. During early and mid-S phase and during DNA repair, proliferating cell nuclear antigen (PCNA) loading onto DNA (PCNA(DNA)) triggers the interaction between CRL4(CDT2) and its substrates, resulting in their degradation. We have discovered that, beginning in late S phase, PCNA(DNA) is no longer sufficient to trigger CRL4(CDT2)-mediated degradation. A CDK1-dependent mechanism that blocks CRL4(CDT2) activity by interfering with CDT2 recruitment to chromatin actively protects CRL4(CDT2) substrates. We postulate that deliberate override of replication-coupled destruction allows anticipatory accumulation in late S phase. We further show that (as for CDT1) de novo SET8 reaccumulation is important for normal mitotic progression. In this manner, CDK1-dependent CRL4(CDT2) inactivation contributes to efficient transition from S phase to mitosis.
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Affiliation(s)
| | - Kate E Coleman
- From the Curriculum in Genetics and Molecular Biology and
| | - Dileep Varma
- the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Jacob P Matson
- the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Seeun Oh
- the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Jeanette Gowen Cook
- From the Curriculum in Genetics and Molecular Biology and the Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
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8
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Abstract
DNA replication must be tightly regulated to ensure that the genome is accurately duplicated during each cell cycle. When these regulatory mechanisms fail, replicative stress and DNA damage ensue. Activated oncogenes promote replicative stress, inducing a DNA damage response (DDR) early in tumorigenesis. Senescence or apoptosis result, forming a barrier against tumour progression. This may provide a selective pressure for acquisition of mutations in the DDR pathway during tumorigenesis. Despite its potential importance in early cancer development, the precise nature of oncogene-induced replicative stress remains poorly understood. Here, we review our current understanding of replication initiation and its regulation, describe mechanisms by which activated oncogenes might interfere with these processes and discuss how replicative stress might contribute to the genomic instability seen in cancers.
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Affiliation(s)
- Stephanie A Hills
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, EN6 3LD, UK
| | - John F X Diffley
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, EN6 3LD, UK.
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9
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Johansson P, Jeffery J, Al-Ejeh F, Schulz RB, Callen DF, Kumar R, Khanna KK. SCF-FBXO31 E3 ligase targets DNA replication factor Cdt1 for proteolysis in the G2 phase of cell cycle to prevent re-replication. J Biol Chem 2014; 289:18514-25. [PMID: 24828503 DOI: 10.1074/jbc.m114.559930] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
FBXO31 was originally identified as a putative tumor suppressor gene in breast, ovarian, hepatocellular, and prostate cancers. By screening a set of cell cycle-regulated proteins as potential FBXO31 interaction partners, we have now identified Cdt1 as a novel substrate. Cdt1 DNA replication licensing factor is part of the pre-replication complex and essential for the maintenance of genomic integrity. We show that FBXO31 specifically interacts with Cdt1 and regulates its abundance by ubiquitylation leading to subsequent degradation. We also show that Cdt1 regulation by FBXO31 is limited to the G2 phase of the cell cycle and is independent of the pathways previously described for Cdt1 proteolysis in S and G2 phase. FBXO31 targeting of Cdt1 is mediated through the N terminus of Cdt1, a region previously shown to be responsible for its cell cycle regulation. Finally, we show that Cdt1 stabilization due to FBXO31 depletion results in re-replication. Our data present an additional pathway that contributes to the FBXO31 function as a tumor suppressor.
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Affiliation(s)
- Pegah Johansson
- From the Sahlgrenska University Hospital, Department of Clinical Chemistry, Bruna Stråket 16, 41345 Gothenburg, Sweden
| | - Jessie Jeffery
- Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia
| | - Fares Al-Ejeh
- Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia
| | - Renèe B Schulz
- Centre for Personalised Cancer Medicine and Discipline of Medicine, University of Adelaide, Adelaide, South Australia 5000, Australia
| | - David F Callen
- Centre for Personalised Cancer Medicine and Discipline of Medicine, University of Adelaide, Adelaide, South Australia 5000, Australia
| | - Raman Kumar
- School of Paediatrics and Reproductive Health and Discipline of Medicine, University of Adelaide, Adelaide and Women's and Children's Health Research Institute, North Adelaide, South Australia 5006, Australia, and
| | - Kum Kum Khanna
- Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia
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10
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Molecular mechanisms of DNA replication checkpoint activation. Genes (Basel) 2014; 5:147-75. [PMID: 24705291 PMCID: PMC3978517 DOI: 10.3390/genes5010147] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 02/20/2014] [Accepted: 02/21/2014] [Indexed: 01/27/2023] Open
Abstract
The major challenge of the cell cycle is to deliver an intact, and fully duplicated, genetic material to the daughter cells. To this end, progression of DNA synthesis is monitored by a feedback mechanism known as replication checkpoint that is untimely linked to DNA replication. This signaling pathway ensures coordination of DNA synthesis with cell cycle progression. Failure to activate this checkpoint in response to perturbation of DNA synthesis (replication stress) results in forced cell division leading to chromosome fragmentation, aneuploidy, and genomic instability. In this review, we will describe current knowledge of the molecular determinants of the DNA replication checkpoint in eukaryotic cells and discuss a model of activation of this signaling pathway crucial for maintenance of genomic stability.
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11
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Dimaki M, Xouri G, Symeonidou IE, Sirinian C, Nishitani H, Taraviras S, Lygerou Z. Cell cycle-dependent subcellular translocation of the human DNA licensing inhibitor geminin. J Biol Chem 2013; 288:23953-63. [PMID: 23814078 DOI: 10.1074/jbc.m113.453092] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Once per cell cycle replication is crucial for maintaining genome integrity. Geminin interacts with the licensing factor Cdt1 to prevent untimely replication and is controlled by APC/C-dependent cell cycle specific proteolysis during mitosis and in G1. We show here that human geminin, when expressed in human cells in culture under a constitutive promoter, is excluded from the nucleus during part of the G1 phase and at the transition from G0 to G1. The N-terminal 30 amino acids of geminin, which contain its destruction box, are essential for nuclear exclusion. In addition, 30 amino acids within the central domain of geminin are required for both nuclear exclusion and nuclear accumulation. Cdt1 overexpression targets geminin to the nucleus, while reducing Cdt1 levels by RNAi leads to the appearance of endogenous geminin in the cytoplasm. Our data propose a novel means of regulating the balance of Cdt1/geminin in human cells, at the level of the subcellular localization of geminin.
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Affiliation(s)
- Maria Dimaki
- Laboratory of General Biology, School of Medicine, University of Patras, 26500 Rio, Patras, Greece
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12
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Abstract
The cell cycle ensures genome maintenance by coordinating the processes of DNA replication and chromosome segregation. Of particular importance is the irreversible transition from the G1 phase of the cell cycle to S phase. This transition marks the switch from preparing chromosomes for replication ("origin licensing") to active DNA synthesis ("origin firing"). Ubiquitin-mediated proteolysis is essential for restricting DNA replication to only once per cell cycle and is the major mechanism regulating the G1 to S phase transition. Although some changes in protein levels are attributable to regulated mRNA abundance, protein degradation elicits very rapid changes in protein abundance and is critical for the sharp and irreversible transition from one cell cycle stage to the next. Not surprisingly, regulation of the G1-to-S phase transition is perturbed in most cancer cells, and deregulation of key molecular events in G1 and S phase drives not only cell proliferation but also genome instability. In this review we focus on the mechanisms by which E3 ubiquitin ligases control the irreversible transition from G1 to S phase in mammalian cells.
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Affiliation(s)
- Lindsay F Rizzardi
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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13
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Abstract
The ubiquitin-proteasome system plays a pivotal role in the sequence of events leading to cell division known as the cell cycle. Not only does ubiquitin-mediated proteolysis constitute a critical component of the core oscillator that drives the cell cycle in all eukaryotes, it is also central to the mechanisms that ensure that the integrity of the genome is maintained. These functions are primarily carried out by two families of E3 ubiquitin ligases, the Skp/cullin/F-box-containing and anaphase-promoting complex/cyclosome complexes. However, beyond those functions associated with regulation of central cell cycle events, many peripheral cell cycle-related processes rely on ubiquitylation for signaling, homeostasis, and dynamicity, involving additional types of ubiquitin ligases and regulators. We are only beginning to understand the diversity and complexity of this regulation.
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Affiliation(s)
- Leonardo K Teixeira
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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14
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Kisielewska J, Blow JJ. Dynamic interactions of high Cdt1 and geminin levels regulate S phase in early Xenopus embryos. Development 2012; 139:63-74. [PMID: 22096080 PMCID: PMC3492748 DOI: 10.1242/dev.068676] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cdt1 plays a key role in licensing DNA for replication. In the somatic cells of metazoans, both Cdt1 and its natural inhibitor geminin show reciprocal fluctuations in their protein levels owing to cell cycle-dependent proteolysis. Here, we show that the protein levels of Cdt1 and geminin are persistently high during the rapid cell cycles of the early Xenopus embryo. Immunoprecipitation of Cdt1 and geminin complexes, together with their cell cycle spatiotemporal dynamics, strongly supports the hypothesis that Cdt1 licensing activity is regulated by periodic interaction with geminin rather than its proteolysis. Overexpression of ectopic geminin slows down, but neither arrests early embryonic cell cycles nor affects endogenous geminin levels; apparent embryonic lethality is observed around 3-4 hours after mid-blastula transition. However, functional knockdown of geminin by ΔCdt1_193-447, which lacks licensing activity and degradation sequences, causes cell cycle arrest and DNA damage in affected cells. This contributes to subsequent developmental defects in treated embryos. Our results clearly show that rapidly proliferating early Xenopus embryonic cells are able to regulate replication licensing in the persistent presence of high levels of licensing proteins by relying on changing interactions between Cdt1 and geminin during the cell cycle, but not their degradation.
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Affiliation(s)
- Jolanta Kisielewska
- University of Newcastle, The Institute for Cell and Molecular Biosciences, Framlington Place, NE2 4HH, Newcastle-Upon-Tyne, UK.
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15
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Ode KL, Fujimoto K, Kubota Y, Takisawa H. Inter-origin cooperativity of geminin action establishes an all-or-none switch for replication origin licensing. Genes Cells 2011; 16:380-96. [PMID: 21426446 DOI: 10.1111/j.1365-2443.2011.01501.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In metazoans, geminin functions as a molecular switch for preventing re-replication of chromosomal DNA. Geminin binds to and inhibits Cdt1, which is required for replication origin licensing, but little is known about the mechanisms underlying geminin's all-or-none action in licensing inhibition. Using Xenopus egg extract, we found that the all-or-none activity correlated with the formation of Cdt1 foci on chromatin, suggesting that multiple Cdt1-geminin complexes on origins cooperatively inhibit licensing. Based on experimental identification of licensing intermediates targeted by geminin and Cdt1, we developed a mathematical model of the licensing process. The model involves positive feedback owing to the cooperative action of geminin at neighboring origins and accurately accounts for the licensing activity mediated by geminin and Cdt1 in the extracts. The model also predicts that such cooperativity leads to clustering of licensing-inhibited origins, an idea that is supported by the experimentally measured distribution of inter-origin distances. We propose that geminin inhibits licensing through an inter-origin interaction, ensuring strict and coordinated control of multiple replication origins on chromosomes.
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Affiliation(s)
- Koji L Ode
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
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16
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Abstract
Eukaryotic cell cycle transitions are driven by E3 ubiquitin ligases that catalyze the ubiquitylation and destruction of specific protein targets. For example, the anaphase-promoting complex/cyclosome (APC/C) promotes the exit from mitosis via destruction of securin and mitotic cyclins, whereas CRL1(Skp2) allows entry into S phase by targeting the destruction of the cyclin-dependent kinase (CDK) inhibitor p27. Recently, an E3 ubiquitin ligase called CRL4(Cdt2) has been characterized, which couples proteolysis to DNA synthesis via an unusual mechanism that involves display of substrate degrons on the DNA polymerase processivity factor PCNA. Through its destruction of Cdt1, p21, and Set8, CRL4(Cdt2) has emerged as a master regulator that prevents rereplication in S phase. In addition, it also targets other factors such as E2F and DNA polymerase η. In this review, we discuss our current understanding of the molecular mechanism of substrate recognition by CRL4(Cdt2) and how this E3 ligase helps to maintain genome integrity.
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Affiliation(s)
- Courtney G Havens
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
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17
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Gardner L, Malik R, Shimizu Y, Mullins N, ElShamy WM. Geminin overexpression prevents the completion of topoisomerase IIα chromosome decatenation, leading to aneuploidy in human mammary epithelial cells. Breast Cancer Res 2011; 13:R53. [PMID: 21595939 PMCID: PMC3218940 DOI: 10.1186/bcr2884] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 04/16/2011] [Accepted: 05/19/2011] [Indexed: 11/10/2022] Open
Abstract
INTRODUCTION The nuclear enzyme topoisomerase IIα (TopoIIα) is able to cleave DNA in a reversible manner, making it a valuable target for agents such as etoposide that trap the enzyme in a covalent bond with the 5' DNA end to which it cleaves. This prevents DNA religation and triggers cell death in cancer cells. However, development of resistance to these agents limits their therapeutic use. In this study, we examined the therapeutic targeting of geminin for improving the therapeutic potential of TopoIIα agents. METHODS Human mammary epithelial (HME) cells and several breast cancer cell lines were used in this study. Geminin, TopoIIα and cell division cycle 7 (Cdc7) silencing were done using specific small interfering RNA. Transit or stable inducible overexpression of these proteins and casein kinase Iε (CKIε) were also used, as well as several pharmacological inhibitors that target TopoIIα, Cdc7 or CKIε. We manipulated HME cells that expressed H2B-GFP, or did not, to detect chromosome bridges. Immunoprecipitation and direct Western blot analysis were used to detect interactions between these proteins and their total expression, respectively, whereas interactions on chromosomal arms were detected using a trapped in agarose DNA immunostaining assay. TopoIIα phosphorylation by Cdc7 or CKIε was done using an in vitro kinase assay. The TopoGen decatenation kit was used to measure TopoIIα decatenation activity. Finally, a comet assay and metaphase chromosome spread were used to detect chromosome breakage and changes in chromosome condensation or numbers, respectively. RESULTS We found that geminin and TopoIIα interact primarily in G2/M/early G1 cells on chromosomes, that geminin recruits TopoIIα to chromosomal decatenation sites or vice versa and that geminin silencing in HME cells triggers the formation of chromosome bridges by suppressing TopoIIα access to chromosomal arms. CKIε kinase phosphorylates and positively regulates TopoIIα chromosome localization and function. CKIε kinase overexpression or Cdc7 kinase silencing, which we show phosphorylates TopoIIα in vitro, restored DNA decatenation and chromosome segregation in geminin-silenced cells before triggering cell death. In vivo, at normal concentration, geminin recruits the deSUMOylating sentrin-specific proteases SENP1 and SENP2 enzymes to deSUMOylate chromosome-bound TopoIIα and promote its release from chromosomes following completion of DNA decatenation. In cells overexpressing geminin, premature departure of TopoIIα from chromosomes is thought to be due to the fact that geminin recruits more of these deSUMOylating enzymes, or recruits them earlier, to bound TopoIIα. This triggers premature release of TopoIIα from chromosomes, which we propose induces aneuploidy in HME cells, since chromosome breakage generated through this mechanism were not sensed and/or repaired and the cell cycle was not arrested. Expression of mitosis-inducing proteins such as cyclin A and cell division kinase 1 was also increased in these cells because of the overexpression of geminin. CONCLUSIONS TopoIIα recruitment and its chromosome decatenation function require a normal level of geminin. Geminin silencing induces a cytokinetic checkpoint in which Cdc7 phosphorylates TopoIIα and inhibits its chromosomal recruitment and decatenation and/or segregation function. Geminin overexpression prematurely deSUMOylates TopoIIα, triggering its premature departure from chromosomes and leading to chromosomal abnormalities and the formation of aneuploid, drug-resistant cancer cells. On the basis of our findings, we propose that therapeutic targeting of geminin is essential for improving the therapeutic potential of TopoIIα agents.
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Affiliation(s)
- Lauren Gardner
- Cancer Institute, Department of Biochemistry, University of Mississippi Medical Center, Jackson, 39216, USA
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Guarino E, Shepherd MEA, Salguero I, Hua H, Deegan RS, Kearsey SE. Cdt1 proteolysis is promoted by dual PIP degrons and is modulated by PCNA ubiquitylation. Nucleic Acids Res 2011; 39:5978-90. [PMID: 21493688 PMCID: PMC3152358 DOI: 10.1093/nar/gkr222] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Cdt1 plays a critical role in DNA replication regulation by controlling licensing. In Metazoa, Cdt1 is regulated by CRL4Cdt2-mediated ubiquitylation, which is triggered by DNA binding of proliferating cell nuclear antigen (PCNA). We show here that fission yeast Cdt1 interacts with PCNA in vivo and that DNA loading of PCNA is needed for Cdt1 proteolysis after DNA damage and in S phase. Activation of this pathway by ultraviolet (UV)-induced DNA damage requires upstream involvement of nucleotide excision repair or UVDE repair enzymes. Unexpectedly, two non-canonical PCNA-interacting peptide (PIP) motifs, which both have basic residues downstream, function redundantly in Cdt1 proteolysis. Finally, we show that poly-ubiquitylation of PCNA, which occurs after DNA damage, reduces Cdt1 proteolysis. This provides a mechanism for fine-tuning the activity of the CRL4Cdt2 pathway towards Cdt1, allowing Cdt1 proteolysis to be more efficient in S phase than after DNA damage.
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Affiliation(s)
- Estrella Guarino
- Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
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19
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Yoshida K, Sugimoto N, Iwahori S, Yugawa T, Narisawa-Saito M, Kiyono T, Fujita M. CDC6 interaction with ATR regulates activation of a replication checkpoint in higher eukaryotic cells. J Cell Sci 2010; 123:225-35. [PMID: 20048340 DOI: 10.1242/jcs.058693] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
CDC6, a replication licensing protein, is partially exported to the cytoplasm in human cells through phosphorylation by Cdk during S phase, but a significant proportion remains in the nucleus. We report here that human CDC6 physically interacts with ATR, a crucial checkpoint kinase, in a manner that is stimulated by phosphorylation by Cdk. CDC6 silencing by siRNAs affected ATR-dependent inhibition of mitotic entry elicited by modest replication stress. Whereas a Cdk-phosphorylation-mimicking CDC6 mutant could rescue the checkpoint defect by CDC6 silencing, a phosphorylation-deficient mutant could not. Furthermore, we found that the CDC6-ATR interaction is conserved in Xenopus. We show that the presence of Xenopus CDC6 during S phase is essential for Xenopus ATR to bind to chromatin in response to replication inhibition. In addition, when human CDC6 amino acid fragment 180-220, which can bind to both human and Xenopus ATR, was added to Xenopus egg extracts after assembly of the pre-replication complex, Xenopus Chk1 phosphorylation was significantly reduced without lowering replication, probably through a sequestration of CDC6-mediated ATR-chromatin interaction. Thus, CDC6 might regulate replication-checkpoint activation through the interaction with ATR in higher eukaryotic cells.
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Affiliation(s)
- Kazumasa Yoshida
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
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Choschzick M, Lebeau A, Marx AH, Tharun L, Terracciano L, Heilenkötter U, Jaenicke F, Bokemeyer C, Simon R, Sauter G, Schwarz J. Overexpression of cell division cycle 7 homolog is associated with gene amplification frequency in breast cancer. Hum Pathol 2010; 41:358-65. [DOI: 10.1016/j.humpath.2009.08.008] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Revised: 06/25/2009] [Accepted: 08/04/2009] [Indexed: 11/27/2022]
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De Marco V, Gillespie PJ, Li A, Karantzelis N, Christodoulou E, Klompmaker R, van Gerwen S, Fish A, Petoukhov MV, Iliou MS, Lygerou Z, Medema RH, Blow JJ, Svergun DI, Taraviras S, Perrakis A. Quaternary structure of the human Cdt1-Geminin complex regulates DNA replication licensing. Proc Natl Acad Sci U S A 2009; 106:19807-12. [PMID: 19906994 PMCID: PMC2775996 DOI: 10.1073/pnas.0905281106] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2009] [Indexed: 01/12/2023] Open
Abstract
All organisms need to ensure that no DNA segments are rereplicated in a single cell cycle. Eukaryotes achieve this through a process called origin licensing, which involves tight spatiotemporal control of the assembly of prereplicative complexes (pre-RCs) onto chromatin. Cdt1 is a key component and crucial regulator of pre-RC assembly. In higher eukaryotes, timely inhibition of Cdt1 by Geminin is essential to prevent DNA rereplication. Here, we address the mechanism of DNA licensing inhibition by Geminin, by combining X-ray crystallography, small-angle X-ray scattering, and functional studies in Xenopus and mammalian cells. Our findings show that the Cdt1:Geminin complex can exist in two distinct forms, a "permissive" heterotrimer and an "inhibitory" heterohexamer. Specific Cdt1 residues, buried in the heterohexamer, are important for licensing. We postulate that the transition between the heterotrimer and the heterohexamer represents a molecular switch between licensing-competent and licensing-defective states.
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Affiliation(s)
- V. De Marco
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - P. J. Gillespie
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - A. Li
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | | | - E. Christodoulou
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - R. Klompmaker
- Department of Medical Oncology and Cancer Genomics Center, Laboratory of Experimental Oncology, University Medical Center Utrecht, Universiteitsweg 100, 3584CG Utrecht, The Netherlands; and
| | - S. van Gerwen
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - A. Fish
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - M. V. Petoukhov
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg, Germany
| | - M. S. Iliou
- Biology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - Z. Lygerou
- Biology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - R. H. Medema
- Department of Medical Oncology and Cancer Genomics Center, Laboratory of Experimental Oncology, University Medical Center Utrecht, Universiteitsweg 100, 3584CG Utrecht, The Netherlands; and
| | - J. J. Blow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - D. I. Svergun
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg, Germany
| | | | - A. Perrakis
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
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Narasimhachar Y, Coué M. Geminin stabilizes Cdt1 during meiosis in Xenopus oocytes. J Biol Chem 2009; 284:27235-42. [PMID: 19656945 DOI: 10.1074/jbc.m109.008854] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
During the mitotic cell cycle, Geminin can act both as a promoter and inhibitor of initiation of DNA replication. As a promoter, Geminin stabilizes Cdt1 and facilitates its accumulation leading to the assembly of the pre-replication complex on DNA. As an inhibitor, Geminin prevents Cdt1 from loading the mini-chromosome maintenance complex onto pre-replication complexes in late S, G(2), and M phases. Here we show that during meiosis Geminin functions as a stabilizer of Cdt1 promoting its accumulation for the early division cycles of the embryo. Depletion of Geminin in Xenopus immature oocytes leads to a decrease of Cdt1 protein levels during maturation and after activation of these oocytes. Injection of exogenous recombinant Geminin into the depleted oocytes rescues Cdt1 levels demonstrating that Geminin stabilizes Cdt1 during meiosis and after fertilization. Furthermore, Geminin-depleted oocytes did not replicate their DNA after meiosis I indicating that Geminin does not act as an inhibitor of initiation of DNA replication between meiosis I and meiosis II.
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Affiliation(s)
- Yadushyla Narasimhachar
- Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
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Abstract
Eukaryotic cells normally restrict genome duplication to once per cell division. In metazoa, re-replication of DNA during a single S phase seems to be prevented solely by suppressing CDT1 activity, a protein required for loading the replicative MCM DNA helicase. However, siRNA suppression of geminin (a specific inhibitor of CDT1) arrested proliferation only of cells derived from cancers by inducing DNA re-replication and DNA damage that spontaneously triggered apoptosis. None of these effects were detected either in cells derived from normal human tissues or in cells immortalized by a viral oncogene. To induce these effects in noncancer cells required suppression of both geminin and cyclin A, another cell cycle regulator. Therefore, initiating DNA replication in some cancer cells is limited solely by regulating the level of CDT1 activity with geminin, whereas noncancer cells contain additional safeguards that prevent DNA re-replication. These results show that inhibition of geminin activity could be used to selectively kill cancer cells without harming other cells.
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Affiliation(s)
- Wenge Zhu
- National Institute of Child Health and Human Development, NIH, Bethesda, Maryland 20892-2753, USA
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Sugimoto N, Yoshida K, Tatsumi Y, Yugawa T, Narisawa-Saito M, Waga S, Kiyono T, Fujita M. Redundant and differential regulation of multiple licensing factors ensures prevention of re-replication in normal human cells. J Cell Sci 2009; 122:1184-91. [DOI: 10.1242/jcs.041889] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When human cells enter S-phase, overlapping differential inhibitory mechanisms downregulate the replication licensing factors ORC1, CDC6 and Cdt1. Such regulation prevents re-replication so that deregulation of any individual factor alone would not be expected to induce overt re-replication. However, this has been challenged by the fact that overexpression of Cdt1 or Cdt1+CDC6 causes re-replication in some cancer cell lines. We thought it important to analyze licensing regulations in human non-cancerous cells that are resistant to Cdt1-induced re-replication and examined whether simultaneous deregulation of these licensing factors induces re-replication in two such cell lines, including human fibroblasts immortalized by telomerase. Individual overexpression of either Cdt1, ORC1 or CDC6 induced no detectable re-replication. However, with Cdt1+ORC1 or Cdt1+CDC6, some re-replication was detectable and coexpression of Cdt1+ORC1+CDC6 synergistically acted to give strong re-replication with increased mini-chromosome maintenance (MCM) loading. Coexpression of ORC1+CDC6 was without effect. These results suggest that, although Cdt1 regulation is the key step, differential regulation of multiple licensing factors ensures prevention of re-replication in normal human cells. Our findings also show for the first time the importance of ORC1 regulation for prevention of re-replication.
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Affiliation(s)
- Nozomi Sugimoto
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
- Faculty of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyouku, Tokyo 112-8679, Japan
| | - Kazumasa Yoshida
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Yasutoshi Tatsumi
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
- Division of Biochemistry, Chiba Cancer Center Research Institute, 666-2 Nitona, Chuohku, Chiba 260-8717, Japan
| | - Takashi Yugawa
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Mako Narisawa-Saito
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Shou Waga
- Faculty of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyouku, Tokyo 112-8679, Japan
| | - Tohru Kiyono
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Masatoshi Fujita
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
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Tsuyama T, Watanabe S, Aoki A, Cho Y, Seki M, Enomoto T, Tada S. Repression of nascent strand elongation by deregulated Cdt1 during DNA replication in Xenopus egg extracts. Mol Biol Cell 2008; 20:937-47. [PMID: 19064889 DOI: 10.1091/mbc.e08-06-0613] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Excess Cdt1 reportedly induces rereplication of chromatin in cultured cells and Xenopus egg extracts, suggesting that the regulation of Cdt1 activity by cell cycle-dependent proteolysis and expression of the Cdt1 inhibitor geminin is crucial for the inhibition of chromosomal overreplication between S phase and metaphase. We analyzed the consequences of excess Cdt1 for DNA replication and found that increased Cdt1 activity inhibited the elongation of nascent strands in Xenopus egg extracts. In Cdt1-supplemented extracts, overreplication was remarkably induced by the further addition of the Cdt1-binding domain of geminin (Gem79-130), which lacks licensing inhibitor activity. Further analyses indicated that fully active geminin, as well as Gem79-130, restored nascent strand elongation in Cdt1-supplemented extracts even after the Cdt1-induced stalling of replication fork elongation had been established. Our results demonstrate an unforeseen, negative role for Cdt1 in elongation and suggest that its function in the control of replication should be redefined. We propose a novel surveillance mechanism in which Cdt1 blocks nascent chain elongation after detecting illegitimate activation of the licensing system.
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Affiliation(s)
- Takashi Tsuyama
- Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Miyagi, 980-8578, Japan
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26
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Salabat MR, Melstrom LG, Strouch MJ, Ding XZ, Milam BM, Ujiki MB, Chen C, Pelling JC, Rao S, Grippo PJ, McGarry TJ, Bentrem DJ. Geminin is overexpressed in human pancreatic cancer and downregulated by the bioflavanoid apigenin in pancreatic cancer cell lines. Mol Carcinog 2008; 47:835-44. [DOI: 10.1002/mc.20441] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Kim Y, Starostina NG, Kipreos ET. The CRL4Cdt2 ubiquitin ligase targets the degradation of p21Cip1 to control replication licensing. Genes Dev 2008; 22:2507-19. [PMID: 18794348 DOI: 10.1101/gad.1703708] [Citation(s) in RCA: 192] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The faithful replication of genomic DNA is crucial for maintaining genome stability. In eukaryotes, DNA rereplication is prevented by the temporal regulation of replication licensing. Replication-licensing factors are required to form prereplicative complexes during G1 phase, but are inactivated in S phase to prevent rereplication. A vertebrate CUL4 CRL ubiquitin ligase (CRL4) complex containing Cdt2 as the substrate recognition subunit promotes proper DNA replication, in part, by degrading the replication-licensing factor Cdt1 during S phase. We show that the Caenorhabditis elegans CRL4(Cdt2) complex has a conserved role in degrading Cdt1. Furthermore, we show that CRL4(Cdt2) restrains replication licensing in both C. elegans and humans by targeting the degradation of the cyclin-dependent kinase (CDK) inhibitors CKI-1 and p21(Cip1), respectively. Human CRL4(Cdt2) targets the degradation of p21 in S phase, with the in vivo ubiquitylation of p21 by CRL4(Cdt2) dependent on p21 binding to PCNA. Inactivation of Cdt2 induces rereplication, which requires the presence of the CDK inhibitor p21. Strikingly, coinactivation of CRL4(Cdt2) and SCF(Skp2) (which redundantly targets p21 degradation) prevents the nuclear export of the replication-licensing factor Cdc6 during S phase, and the block on nuclear export is dependent on p21. Our work defines the degradation of p21 as a critical aspect of replication licensing in human cells.
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Affiliation(s)
- Youngjo Kim
- Department of Cellular Biology, University of Georgia, Athens, Georgia 30602 USA
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28
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Lutzmann M, Méchali M. MCM9 binds Cdt1 and is required for the assembly of prereplication complexes. Mol Cell 2008; 31:190-200. [PMID: 18657502 DOI: 10.1016/j.molcel.2008.07.001] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2007] [Revised: 03/04/2008] [Accepted: 07/01/2008] [Indexed: 02/03/2023]
Abstract
Prereplication complexes (pre-RCs) define potential origins of DNA replication and allow the recruitment of the replicative DNA helicase MCM2-7. Here, we characterize MCM9, a member of the MCM2-8 family. We demonstrate that MCM9 binds to chromatin in an ORC-dependent manner and is required for the recruitment of the MCM2-7 helicase onto chromatin. Its depletion leads to a block in pre-RC assembly, as well as DNA replication inhibition. We show that MCM9 forms a stable complex with the licensing factor Cdt1, preventing an excess of geminin on chromatin during the licensing reaction. Our data suggest that MCM9 is an essential activating linker between Cdt1 and the MCM2-7 complex, required for loading the MCM2-7 helicase onto DNA replication origins. Thus, Cdt1, with its two opposing regulatory binding factors MCM9 and geminin, appears to be a major platform on the pre-RC to integrate cell-cycle signals.
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Affiliation(s)
- Malik Lutzmann
- Institute of Human Genetics, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France
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Liu E, Lee AYL, Chiba T, Olson E, Sun P, Wu X. The ATR-mediated S phase checkpoint prevents rereplication in mammalian cells when licensing control is disrupted. ACTA ACUST UNITED AC 2007; 179:643-57. [PMID: 18025301 PMCID: PMC2080923 DOI: 10.1083/jcb.200704138] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
DNA replication in eukaryotic cells is tightly controlled by a licensing mechanism, ensuring that each origin fires once and only once per cell cycle. We demonstrate that the ataxia telangiectasia and Rad3 related (ATR)–mediated S phase checkpoint acts as a surveillance mechanism to prevent rereplication. Thus, disruption of licensing control will not induce significant rereplication in mammalian cells when the ATR checkpoint is intact. We also demonstrate that single-stranded DNA (ssDNA) is the initial signal that activates the checkpoint when licensing control is compromised in mammalian cells. We demonstrate that uncontrolled DNA unwinding by minichromosome maintenance proteins upon Cdt1 overexpression is an important mechanism that leads to ssDNA accumulation and checkpoint activation. Furthermore, we show that replication protein A 2 and retinoblastoma protein are both downstream targets for ATR that are important for the inhibition of DNA rereplication. We reveal the molecular mechanisms by which the ATR-mediated S phase checkpoint pathway prevents DNA rereplication and thus significantly improve our understanding of how rereplication is prevented in mammalian cells.
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Affiliation(s)
- Enbo Liu
- Department of Molecular Experimental Medicine and 2Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
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30
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Gillespie PJ, Khoudoli GA, Stewart G, Swedlow JR, Blow J. ELYS/MEL-28 chromatin association coordinates nuclear pore complex assembly and replication licensing. Curr Biol 2007; 17:1657-62. [PMID: 17825564 PMCID: PMC2267255 DOI: 10.1016/j.cub.2007.08.041] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Revised: 07/27/2007] [Accepted: 08/10/2007] [Indexed: 10/30/2022]
Abstract
Xenopus egg extract supports all the major cell-cycle transitions in vitro. We have used a proteomics approach to identify proteins whose abundance on chromatin changes during the course of an in vitro cell cycle. One of the proteins we identified was ELYS/MEL-28, which has recently been described as the earliest-acting factor known to be required for nuclear pore complex (NPC) assembly [1-4]. ELYS interacts with the Nup107-160 complex and is required for its association with chromatin. ELYS contains an AT-hook domain, which we show binds to chromatin with a high affinity. This domain can compete with full-length ELYS for chromatin association, thereby blocking NPC assembly. This provides evidence that ELYS interacts directly with chromatin and that this interaction is essential for NPC assembly and compartmentalization of chromosomal DNA within the cell. Furthermore, we detected a physical association on chromatin between ELYS and the Mcm2-7 replication-licensing proteins. ELYS chromatin loading, NPC assembly, and nuclear growth were delayed when Mcm2-7 was prevented from loading onto chromatin. Because nuclear assembly is required to shut down licensing prior to entry into S phase, our results suggest a mechanism by which these two early cell-cycle events are coordinated with one another.
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Affiliation(s)
- Peter J. Gillespie
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Guennadi A. Khoudoli
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Graeme Stewart
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Jason R. Swedlow
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - J. Julian Blow
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
- Corresponding author
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Luo L, Uerlings Y, Happel N, Asli NS, Knoetgen H, Kessel M. Regulation of geminin functions by cell cycle-dependent nuclear-cytoplasmic shuttling. Mol Cell Biol 2007; 27:4737-44. [PMID: 17470552 PMCID: PMC1951490 DOI: 10.1128/mcb.00123-07] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Revised: 02/27/2007] [Accepted: 04/18/2007] [Indexed: 12/24/2022] Open
Abstract
The geminin protein functions both as a DNA rereplication inhibitor through association with Cdt1 and as a repressor of Hox gene transcription through the polycomb pathway. Here, we report that the functions of avian geminin are coordinated with and regulated by cell cycle-dependent nuclear-cytoplasmic shuttling. In S phase, geminin enters nuclei and inhibits both loading of the minichromosome maintenance (MCM) complex onto chromatin and Hox gene transcription. At the end of mitosis, geminin is exported from nuclei by the exportin protein Crm1 and is unavailable in the nucleus during the next G(1) phase, thus ensuring proper chromatin loading of the MCM complex and Hox gene transcription. This mechanism for regulating the functions of geminin adds to distinct mechanisms, such as protein degradation and ubiquitination, applied in other vertebrates.
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Affiliation(s)
- Lingfei Luo
- Department of Molecular Cell Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
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Shrestha P, Saito T, Hama S, Arifin MT, Kajiwara Y, Yamasaki F, Hidaka T, Sugiyama K, Kurisu K. Geminin: a good prognostic factor in high-grade astrocytic brain tumors. Cancer 2007; 109:949-56. [PMID: 17262828 DOI: 10.1002/cncr.22474] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND Geminin is a nuclear protein that belongs to the DNA replication inhibitor group. It inhibits DNA replication by preventing Cdt1 from loading minichromosome maintenance protein onto chromatin, as is required for DNA replication. For this study, the authors investigated geminin expression in high-grade astrocytic tumors, including anaplastic astrocytoma (AA) and glioblastoma multiforme (GBM), with a view to predicting clinical outcomes on this basis in patients with these malignant brain tumors. METHODS Immunohistochemistry was used to detect geminin expression in 51 patients with high-grade astrocytic tumors (19 AA and 32 GBM). Samples were categorized by taking the median value as the cut-off point for constructing Kaplan-Meier curves. The relation of geminin expression to clinical outcome in these malignant brain tumors was analyzed by using the Kaplan-Meier method and a Cox proportional hazards regression model. RESULTS Geminin was expressed in all high-grade astrocytomas (mean geminin labeling index [LI], 24.90%). Kaplan-Meier curves showed that the group with higher geminin LI (>or=22.50%) had a better prognosis than the group with lower LI (<22.50%; P = .0296). Similarly, the Cox regression analysis showed that geminin expression has a significant correlation with survival in patients with high-grade astrocytoma (P = .0278), especially in an early stage. CONCLUSIONS Although it is an inhibitor of DNA proliferation and, thus, is a cell cycle inhibitor, geminin expression was found in all malignant astrocytic tumors. The geminin LI was a significant predictive factor of outcomes in patients with high-grade astrocytoma, with higher expression indicating a good prognosis.
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Affiliation(s)
- Prabin Shrestha
- Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan
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Arias EE, Walter JC. Strength in numbers: preventing rereplication via multiple mechanisms in eukaryotic cells. Genes Dev 2007; 21:497-518. [PMID: 17344412 DOI: 10.1101/gad.1508907] [Citation(s) in RCA: 313] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In eukaryotic cells, prereplication complexes (pre-RCs) are assembled on chromatin in the G1 phase, rendering origins of DNA replication competent to initiate DNA synthesis. When DNA replication commences in S phase, pre-RCs are disassembled, and multiple initiations from the same origin do not occur because new rounds of pre-RC assembly are inhibited. In most experimental organisms, multiple mechanisms that prevent pre-RC assembly have now been identified, and rereplication within the same cell cycle can be induced through defined perturbations of these mechanisms. This review summarizes the diverse array of inhibitory pathways used by different organisms to prevent pre-RC assembly, and focuses on the challenge of understanding how in any one cell type, various mechanisms cooperate to strictly enforce once per cell cycle regulation of DNA replication.
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Affiliation(s)
- Emily E Arias
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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Davidson IF, Li A, Blow JJ. Deregulated replication licensing causes DNA fragmentation consistent with head-to-tail fork collision. Mol Cell 2006; 24:433-43. [PMID: 17081992 PMCID: PMC1819398 DOI: 10.1016/j.molcel.2006.09.010] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Revised: 08/07/2006] [Accepted: 09/18/2006] [Indexed: 12/29/2022]
Abstract
Correct regulation of the replication licensing system ensures that no DNA is rereplicated in a single cell cycle. When the licensing protein Cdt1 is overexpressed in G2 phase of the cell cycle, replication origins are relicensed and the DNA is rereplicated. At the same time, checkpoint pathways are activated that block further cell cycle progression. We have studied the consequence of deregulating the licensing system by adding recombinant Cdt1 to Xenopus egg extracts. We show that Cdt1 induces checkpoint activation and the appearance of small fragments of double-stranded DNA. DNA fragmentation and strong checkpoint activation are dependent on uncontrolled rereplication and do not occur after a single coordinated round of rereplication. The DNA fragments are composed exclusively of rereplicated DNA. The unusual characteristics of these fragments suggest that they result from head-to-tail collision (rear ending) of replication forks chasing one another along the same DNA template.
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Affiliation(s)
- Iain F. Davidson
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Anatoliy Li
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - J. Julian Blow
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
- Corresponding author
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Lutzmann M, Maiorano D, Méchali M. A Cdt1-geminin complex licenses chromatin for DNA replication and prevents rereplication during S phase in Xenopus. EMBO J 2006; 25:5764-74. [PMID: 17124498 PMCID: PMC1698883 DOI: 10.1038/sj.emboj.7601436] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Accepted: 10/06/2006] [Indexed: 12/20/2022] Open
Abstract
Initiation of DNA synthesis involves the loading of the MCM2-7 helicase onto chromatin by Cdt1 (origin licensing). Geminin is thought to prevent relicensing by binding and inhibiting Cdt1. Here we show, using Xenopus egg extracts, that geminin binding to Cdt1 is not sufficient to block its activity and that a Cdt1-geminin complex licenses chromatin, but prevents rereplication, working as a molecular switch at replication origins. We demonstrate that geminin is recruited to chromatin already during licensing, while bulk geminin is recruited at the onset of S phase. A recombinant Cdt1-geminin complex binds chromatin, interacts with the MCM2-7 complex and licenses chromatin once per cell cycle. Accordingly, while recombinant Cdt1 induces rereplication in G1 or G2 and activates an ATM/ATR-dependent checkpoint, the Cdt1-geminin complex does not. We further demonstrate that the stoichiometry of the Cdt1-geminin complex regulates its activity. Our results suggest a model in which the MCM2-7 helicase is loaded onto chromatin by a Cdt1-geminin complex, which is inactivated upon origin firing by binding additional geminin. This origin inactivation reaction does not occur if only free Cdt1 is present on chromatin.
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Affiliation(s)
| | | | - Marcel Méchali
- Institute of Human Genetics, CNRS, Montpellier, France
- Institute of Human Genetics, CNRS, Genome Dynamics and Development, 141, rue de la Cardonille, Montpellier 34396, France. Tel.: +33 499 619 917; Fax: +33 499 619 920; E-mail:
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36
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Fujita M. Cdt1 revisited: complex and tight regulation during the cell cycle and consequences of deregulation in mammalian cells. Cell Div 2006; 1:22. [PMID: 17042960 PMCID: PMC1621056 DOI: 10.1186/1747-1028-1-22] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2006] [Accepted: 10/17/2006] [Indexed: 12/31/2022] Open
Abstract
In eukaryotic cells, replication of genomic DNA initiates from multiple replication origins distributed on multiple chromosomes. To ensure that each origin is activated precisely only once during each S phase, a system has evolved which features periodic assembly and disassembly of essential pre-replication complexes (pre-RCs) at replication origins. The pre-RC assembly reaction involves the loading of a presumptive replicative helicase, the MCM2-7 complexes, onto chromatin by the origin recognition complex (ORC) and two essential factors, CDC6 and Cdt1. The eukaryotic cell cycle is driven by the periodic activation and inactivation of cyclin-dependent kinases (Cdks) and assembly of pre-RCs can only occur during the low Cdk activity period from late mitosis through G1 phase, with inappropriate re-assembly suppressed during S, G2, and M phases. It was originally suggested that inhibition of Cdt1 function after S phase in vertebrate cells is due to geminin binding and that Cdt1 hyperfunction resulting from Cdt1-geminin imbalance induces re-replication. However, recent progress has revealed that Cdt1 activity is more strictly regulated by two other mechanisms in addition to geminin: (1) functional and SCFSkp2-mediated proteolytic regulation through phosphorylation by Cdks; and (2) replication-coupled proteolysis mediated by the Cullin4-DDB1Cdt2 ubiquitin ligase and PCNA, an eukaryotic sliding clamp stimulating replicative DNA polymerases. The tight regulation implies that Cdt1 control is especially critical for the regulation of DNA replication in mammalian cells. Indeed, Cdt1 overexpression evokes chromosomal damage even without re-replication. Furthermore, deregulated Cdt1 induces chromosomal instability in normal human cells. Since Cdt1 is overexpressed in cancer cells, this could be a new molecular mechanism leading to carcinogenesis. In this review, recent insights into Cdt1 function and regulation in mammalian cells are discussed.
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Affiliation(s)
- Masatoshi Fujita
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan.
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Matsuno K, Kumano M, Kubota Y, Hashimoto Y, Takisawa H. The N-terminal noncatalytic region of Xenopus RecQ4 is required for chromatin binding of DNA polymerase alpha in the initiation of DNA replication. Mol Cell Biol 2006; 26:4843-52. [PMID: 16782873 PMCID: PMC1489170 DOI: 10.1128/mcb.02267-05] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Recruitment of DNA polymerases onto replication origins is a crucial step in the assembly of eukaryotic replication machinery. A previous study in budding yeast suggests that Dpb11 controls the recruitment of DNA polymerases alpha and epsilon onto the origins. Sld2 is an essential replication protein that interacts with Dpb11, but no metazoan homolog has yet been identified. We isolated Xenopus RecQ4 as a candidate Sld2 homolog. RecQ4 is a member of the metazoan RecQ helicase family, and its N-terminal region shows sequence similarity with Sld2. In Xenopus egg extracts, RecQ4 is essential for the initiation of DNA replication, in particular for chromatin binding of DNA polymerase alpha. An N-terminal fragment of RecQ4 devoid of the helicase domain could rescue the replication activity of RecQ4-depleted extracts, and antibody against the fragment inhibited DNA replication and chromatin binding of the polymerase. Further, N-terminal fragments of RecQ4 physically interacted with Cut5, a Xenopus homolog of Dpb11, and their ability to bind to Cut5 closely correlated with their ability to rescue the replication activity of the depleted extracts. Our data suggest that RecQ4 performs an essential role in the assembly of replication machinery through interaction with Cut5 in vertebrates.
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Affiliation(s)
- Kumiko Matsuno
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
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38
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Tatsumi Y, Sugimoto N, Yugawa T, Narisawa-Saito M, Kiyono T, Fujita M. Deregulation of Cdt1 induces chromosomal damage without rereplication and leads to chromosomal instability. J Cell Sci 2006; 119:3128-40. [PMID: 16835273 DOI: 10.1242/jcs.03031] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The activity of human Cdt1 is negatively regulated by multiple mechanisms. This suggests that Cdt1 deregulation may have a deleterious effect. Indeed, it has been suggested that overexpression of Cdt1 can induce rereplication in cancer cells and that rereplication activates Ataxia-telangiectasia-mutated (ATM) kinase and/or ATM- and Rad3-related (ATR) kinase-dependent checkpoint pathways. In this report, we highlight a new and interesting aspect of Cdt1 deregulation: data from several different systems all strongly indicate that unregulated Cdt1 overexpression at pathophysiological levels can induce chromosomal damage other than rereplication in non-transformed cells. The most important finding in these studies is that deregulated Cdt1 induces chromosomal damage and activation of the ATM-Chk2 DNA damage checkpoint pathway even in quiescent cells. These Cdt1 activities are negatively regulated by cyclin A/Cdks, probably through modification by phosphorylation. Furthermore, we found that deregulated Cdt1 induces chromosomal instability in normal human cells. Since Cdt1 is overexpressed in cancer cells, this would be a new molecular mechanism leading to carcinogenesis.
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Affiliation(s)
- Yasutoshi Tatsumi
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
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39
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Boos A, Lee A, Thompson DM, Kroll KL. Subcellular translocation signals regulate Geminin activity during embryonic development. Biol Cell 2006; 98:363-75. [PMID: 16464175 DOI: 10.1042/bc20060007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
BACKGROUND INFORMATION Geminin (Gem) is a protein with roles in regulating both the fidelity of DNA replication and cell fate during embryonic development. The distribution of Gem is predominantly nuclear in cells undergoing the cell cycle. Previous studies have demonstrated that Gem performs multiple activities in the nucleus and that regulation of Gem activation requires nuclear import in at least one context. In the present study, we defined structural and mechanistic features underlying subcellular localization of Gem and tested whether regulation of the subcellular localization of Gem has an impact on its activity in cell fate specification during embryonic development. RESULTS We determined that nuclear localization of Gem is dependent on a bipartite NLS (nuclear localization signal) in the N-terminus of Xenopus Gem protein. This bipartite motif mapped to a Gem N-terminal region previously shown to regulate neural cell fate acquisition. Microinjection into Xenopus embryos demonstrated that import-deficient Gem was incapable of modulating ectodermal cell fate, but that this activity was rescued by fusion to a heterologous NLS. Cross-species comparison of Gem protein sequences revealed that the Xenopus bipartite signal is conserved in many non-mammalian vertebrates, but not in mammalian species assessed. Instead, we found that human Gem employs an alternative N-terminal motif to regulate the protein's nuclear localization. Finally, we found that additional mechanisms contributed to regulating the subcellular localization of Gem. These included a link to Crm1-dependent nuclear export and the observation that Cdt1, a protein in the pre-replication complex, could also mediate nuclear import of Gem. CONCLUSIONS We have defined new structural and regulatory features of Gem, and showed that the activity of Gem in regulating cell fate, in addition to its cell-cycle-regulatory activity, requires control of its subcellular localization. Our data suggest that rather than being constitutively nuclear, Gem may undergo nucleocytoplasmic shuttling through several mechanisms involving distinct protein motifs. The use of multiple mechanisms for modulating Gem subcellular localization is congruent with observations that Gem levels and activity must be stringently controlled during cell-cycle progression and embryonic development.
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Affiliation(s)
- Aline Boos
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA
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40
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DePamphilis ML, Blow JJ, Ghosh S, Saha T, Noguchi K, Vassilev A. Regulating the licensing of DNA replication origins in metazoa. Curr Opin Cell Biol 2006; 18:231-9. [PMID: 16650748 DOI: 10.1016/j.ceb.2006.04.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Accepted: 04/04/2006] [Indexed: 01/19/2023]
Abstract
Eukaryotic DNA replication is a highly conserved process; the proteins and sequence of events that replicate animal genomes are remarkably similar to those that replicate yeast genomes. Moreover, the assembly of prereplication complexes at DNA replication origins ('DNA licensing') is regulated in all eukaryotes so that no origin fires more than once in a single cell cycle. And yet there are significant differences between species both in the selection of replication origins and in the way in which these origins are licensed to operate. Moreover, these differences impart advantages to multicellular animals and plants that facilitate their development, such as better control over endoreduplication, flexibility in origin selection, and discrimination between quiescent and proliferative states.
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Affiliation(s)
- Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Building 6/3A-15, 9000 Rockville Pike, Bethesda, MD 20892-2753, USA.
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41
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Iizuka M, Matsui T, Takisawa H, Smith MM. Regulation of replication licensing by acetyltransferase Hbo1. Mol Cell Biol 2006; 26:1098-108. [PMID: 16428461 PMCID: PMC1347032 DOI: 10.1128/mcb.26.3.1098-1108.2006] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The initiation of DNA replication is tightly regulated in eukaryotic cells to ensure that the genome is precisely duplicated once and only once per cell cycle. This is accomplished by controlling the assembly of a prereplicative complex (pre-RC) which involves the sequential binding to replication origins of the origin recognition complex (ORC), Cdc6/Cdc18, Cdt1, and the minichromosome maintenance complex (Mcm2-Mcm7, or Mcm2-7). Several mechanisms of pre-RC regulation are known, including ATP utilization, cyclin-dependent kinase levels, protein turnover, and Cdt1 binding by geminin. Histone acetylation may also affect the initiation of DNA replication, but at present neither the enzymes nor the steps involved are known. Here, we show that Hbo1, a member of the MYST histone acetyltransferase family, is a previously unrecognized positive regulatory factor for pre-RC assembly. When Hbo1 expression was inhibited in human cells, Mcm2-7 failed to associate with chromatin even though ORC and Cdc6 loading was normal. When Xenopus egg extracts were immunodepleted of Xenopus Hbo1 (XHbo1), chromatin binding of Mcm2-7 was lost, and DNA replication was abolished. The binding of Mcm2-7 to chromatin in XHbo1-depleted extracts could be restored by the addition of recombinant Cdt1.
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Affiliation(s)
- Masayoshi Iizuka
- Department of Microbiology, University of Virginia Health System, P.O. Box 800734, Charlottesville, VA 22908-0734, USA
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42
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Maiorano D, Lutzmann M, Méchali M. MCM proteins and DNA replication. Curr Opin Cell Biol 2006; 18:130-6. [PMID: 16495042 DOI: 10.1016/j.ceb.2006.02.006] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Accepted: 02/09/2006] [Indexed: 12/30/2022]
Abstract
The MCM proteins identify a group of ten conserved factors functioning in the replication of the genomes of archae and eukaryotic organisms. Among these, MCM2-7 proteins are related to each other and form a family of DNA helicases implicated at the initiation step of DNA synthesis. Recently this family expanded by the identification of two additional members that appear to be present only in multicellular organisms, MCM8 and MCM9. The function of MCM8 is distinct from that of MCM2-7 proteins, while the function of MCM9 is unknown. MCM1 and MCM10 are not related to this family, nor to each other, but also function in DNA synthesis.
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Affiliation(s)
- Domenico Maiorano
- Institute of Human Genetics, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France.
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43
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Nishitani H, Sugimoto N, Roukos V, Nakanishi Y, Saijo M, Obuse C, Tsurimoto T, Nakayama KI, Nakayama K, Fujita M, Lygerou Z, Nishimoto T. Two E3 ubiquitin ligases, SCF-Skp2 and DDB1-Cul4, target human Cdt1 for proteolysis. EMBO J 2006; 25:1126-36. [PMID: 16482215 PMCID: PMC1409712 DOI: 10.1038/sj.emboj.7601002] [Citation(s) in RCA: 308] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Accepted: 01/23/2006] [Indexed: 12/25/2022] Open
Abstract
Replication licensing is carefully regulated to restrict replication to once in a cell cycle. In higher eukaryotes, regulation of the licensing factor Cdt1 by proteolysis and Geminin is essential to prevent re-replication. We show here that the N-terminal 100 amino acids of human Cdt1 are recognized for proteolysis by two distinct E3 ubiquitin ligases during S-G2 phases. Six highly conserved amino acids within the 10 first amino acids of Cdt1 are essential for DDB1-Cul4-mediated proteolysis. This region is also involved in proteolysis following DNA damage. The second E3 is SCF-Skp2, which recognizes the Cy-motif-mediated Cyclin E/A-cyclin-dependent kinase-phosphorylated region. Consistently, in HeLa cells cosilenced of Skp2 and Cul4, Cdt1 remained stable in S-G2 phases. The Cul4-containing E3 is active during ongoing replication, while SCF-Skp2 operates both in S and G2 phases. PCNA binds to Cdt1 through the six conserved N-terminal amino acids. PCNA is essential for Cul4- but not Skp2-directed degradation during DNA replication and following ultraviolet-irradiation. Our data unravel multiple distinct pathways regulating Cdt1 to block re-replication.
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Affiliation(s)
- Hideo Nishitani
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Higashi-ku, Fukuoka, Japan.
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44
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Green BM, Morreale RJ, Ozaydin B, Derisi JL, Li JJ. Genome-wide mapping of DNA synthesis in Saccharomyces cerevisiae reveals that mechanisms preventing reinitiation of DNA replication are not redundant. Mol Biol Cell 2006; 17:2401-14. [PMID: 16481397 PMCID: PMC1446083 DOI: 10.1091/mbc.e05-11-1043] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
To maintain genomic stability, reinitiation of eukaryotic DNA replication within a single cell cycle is blocked by multiple mechanisms that inactivate or remove replication proteins after G1 phase. Consistent with the prevailing notion that these mechanisms are redundant, we previously showed that simultaneous deregulation of three replication proteins, ORC, Cdc6, and Mcm2-7, was necessary to cause detectable bulk re-replication in G2/M phase in Saccharomyces cerevisiae. In this study, we used microarray comparative genomic hybridization (CGH) to provide a more comprehensive and detailed analysis of re-replication. This genome-wide analysis suggests that reinitiation in G2/M phase primarily occurs at a subset of both active and latent origins, but is independent of chromosomal determinants that specify the use and timing of these origins in S phase. We demonstrate that re-replication can be induced within S phase, but differs in amount and location from re-replication in G2/M phase, illustrating the dynamic nature of DNA replication controls. Finally, we show that very limited re-replication can be detected by microarray CGH when only two replication proteins are deregulated, suggesting that the mechanisms blocking re-replication are not redundant. Therefore we propose that eukaryotic re-replication at levels below current detection limits may be more prevalent and a greater source of genomic instability than previously appreciated.
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Affiliation(s)
- Brian M Green
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94143-2200, USA
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45
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Arias EE, Walter JC. PCNA functions as a molecular platform to trigger Cdt1 destruction and prevent re-replication. Nat Cell Biol 2005; 8:84-90. [PMID: 16362051 DOI: 10.1038/ncb1346] [Citation(s) in RCA: 243] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Accepted: 12/05/2005] [Indexed: 01/20/2023]
Abstract
Ubiquitin-mediated proteolysis of the replication licensing factor Cdt1 (Cdc10-dependent transcript 1) in S phase is a key mechanism that limits DNA replication to a single round per cell cycle in metazoans. In Xenopus egg extracts, Cdt1 is destroyed on chromatin during DNA replication. Here, we report that replication-dependent proteolysis of Cdt1 requires its interaction with proliferating cell nuclear antigen (PCNA), a homotrimeric processivity factor for DNA polymerases. Cdt1 binds to PCNA through a consensus PCNA-interaction motif that is conserved in Cdt1 of all metazoans, and removal of PCNA from egg extracts inhibits replication-dependent Cdt1 destruction. Mutation of the PCNA-interaction motif yields a stabilized Cdt1 protein that induces re-replication. DDB1, a component of the Cul4 E3 ubiquitin ligase that mediates human Cdt1 proteolysis in response to DNA damage, is also required for replication-dependent Cdt1 destruction. Cdt1 and DDB1 interact in extracts, and DDB1 chromatin loading is dependent on the binding of Cdt1 to PCNA, which indicates that PCNA docking activates the pre-formed Cdt1-Cul4(DDB1) ligase complex. Thus, PCNA functions as a platform for Cdt1 destruction, ensuring efficient and temporally restricted inactivation of a key cell-cycle regulator.
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Affiliation(s)
- Emily E Arias
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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46
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Abstract
To ensure its duplication, chromosomal DNA must be precisely duplicated in each cell cycle, with no sections left unreplicated, and no sections replicated more than once. Eukaryotic cells achieve this by dividing replication into two non-overlapping phases. During late mitosis and G1, replication origins are 'licensed' for replication by loading the minichromosome maintenance (Mcm) 2-7 proteins to form a pre-replicative complex. Mcm2-7 proteins are then essential for initiating and elongating replication forks during S phase. Recent data have provided biochemical and structural insight into the process of replication licensing and the mechanisms that regulate it during the cell cycle.
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Affiliation(s)
- J Julian Blow
- Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, UK.
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47
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Yanagi KI, Mizuno T, Tsuyama T, Tada S, Iida Y, Sugimoto A, Eki T, Enomoto T, Hanaoka F. Caenorhabditis elegans Geminin Homologue Participates in Cell Cycle Regulation and Germ Line Development. J Biol Chem 2005; 280:19689-94. [PMID: 15811859 DOI: 10.1074/jbc.c500070200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Cdt1 is an essential component for the assembly of a pre-replicative complex. Cdt1 activity is inhibited by geminin, which also participates in neural development and embryonic differentiation in many eukaryotes. Although Cdt1 homologues have been identified in organisms ranging from yeast to human, geminin homologues had not been described for Caenorhabditis elegans and fungi. Here, we identify the C. elegans geminin, GMN-1. Biochemical analysis reveals that GMN-1 associates with C. elegans CDT-1, the Hox protein NOB-1, and the Six protein CEH-32. GMN-1 inhibits not only the interaction between mouse Cdt1 and Mcm6 but also licensing activity in Xenopus egg extracts. RNA interference-mediated reduction of GMN-1 is associated with enlarged germ nuclei with aberrant nucleolar morphology, severely impaired gametogenesis, and chromosome bridging in intestinal cells. We conclude that the Cdt1-geminin system is conserved throughout metazoans and that geminin has evolved in these taxa to regulate proliferation and differentiation by directly interacting with Cdt1 and homeobox proteins.
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Affiliation(s)
- Ken-ichiro Yanagi
- Cellular Physiology Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama, Japan
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