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Abstract
The nucleus is a cellular compartment that hosts several macro-molecular machines displaying a highly complex spatial organization. This tight architectural orchestration determines not only DNA replication and repair but also regulates gene expression. In budding yeast microtubules play a key role in structuring the nucleus since they condition the Rabl arrangement in G1 and chromosome partitioning during mitosis through their attachment to centromeres via the kinetochore proteins. Recently, we have shown that upon quiescence entry, intranuclear microtubules emanating from the spindle pole body elongate to form a highly stable bundle that spans the entire nucleus. Here, we examine some molecular mechanisms that may underlie the formation of this structure. As the intranuclear microtubule bundle causes a profound re-organization of the yeast nucleus and is required for cell survival during quiescence, we discuss the possibility that the assembly of such a structure participates in quiescence establishment.
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Affiliation(s)
- Damien Laporte
- Université de Bordeaux; Institut de Biochimie et Génétique Cellulaires; Bordeaux, France; CNRS; UMR5095 Bordeaux France; Bordeaux, France
| | - Isabelle Sagot
- Université de Bordeaux; Institut de Biochimie et Génétique Cellulaires; Bordeaux, France; CNRS; UMR5095 Bordeaux France; Bordeaux, France
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52
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Abstract
The propagation of all organisms depends on the accurate and orderly segregation of chromosomes in mitosis and meiosis. Budding yeast has long served as an outstanding model organism to identify the components and underlying mechanisms that regulate chromosome segregation. This review focuses on the kinetochore, the macromolecular protein complex that assembles on centromeric chromatin and maintains persistent load-bearing attachments to the dynamic tips of spindle microtubules. The kinetochore also serves as a regulatory hub for the spindle checkpoint, ensuring that cell cycle progression is coupled to the achievement of proper microtubule-kinetochore attachments. Progress in understanding the composition and overall architecture of the kinetochore, as well as its properties in making and regulating microtubule attachments and the spindle checkpoint, is discussed.
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53
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Magiera MM, Gueydon E, Schwob E. DNA replication and spindle checkpoints cooperate during S phase to delay mitosis and preserve genome integrity. ACTA ACUST UNITED AC 2014; 204:165-75. [PMID: 24421333 PMCID: PMC3897190 DOI: 10.1083/jcb.201306023] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Deoxyribonucleic acid (DNA) replication and chromosome segregation must occur in ordered sequence to maintain genome integrity during cell proliferation. Checkpoint mechanisms delay mitosis when DNA is damaged or upon replication stress, but little is known on the coupling of S and M phases in unperturbed conditions. To address this issue, we postponed replication onset in budding yeast so that DNA synthesis is still underway when cells should enter mitosis. This delayed mitotic entry and progression by transient activation of the S phase, G2/M, and spindle assembly checkpoints. Disabling both Mec1/ATR- and Mad2-dependent controls caused lethality in cells with deferred S phase, accompanied by Rad52 foci and chromosome missegregation. Thus, in contrast to acute replication stress that triggers a sustained Mec1/ATR response, multiple pathways cooperate to restrain mitosis transiently when replication forks progress unhindered. We suggest that these surveillance mechanisms arose when both S and M phases were coincidently set into motion by a unique ancestral cyclin-Cdk1 complex.
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Affiliation(s)
- Maria M Magiera
- Institute of Molecular Genetics, Centre National de la Recherche Scientifique Unité Mixte de Recherche 5535 and University of Montpellier, 34293 Montpellier, France
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54
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Marston AL. Chromosome segregation in budding yeast: sister chromatid cohesion and related mechanisms. Genetics 2014; 196:31-63. [PMID: 24395824 PMCID: PMC3872193 DOI: 10.1534/genetics.112.145144] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Accepted: 09/18/2013] [Indexed: 12/28/2022] Open
Abstract
Studies on budding yeast have exposed the highly conserved mechanisms by which duplicated chromosomes are evenly distributed to daughter cells at the metaphase-anaphase transition. The establishment of proteinaceous bridges between sister chromatids, a function provided by a ring-shaped complex known as cohesin, is central to accurate segregation. It is the destruction of this cohesin that triggers the segregation of chromosomes following their proper attachment to microtubules. Since it is irreversible, this process must be tightly controlled and driven to completion. Furthermore, during meiosis, modifications must be put in place to allow the segregation of maternal and paternal chromosomes in the first division for gamete formation. Here, I review the pioneering work from budding yeast that has led to a molecular understanding of the establishment and destruction of cohesion.
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Affiliation(s)
- Adele L Marston
- The Wellcome Trust Centre for Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JR, United Kingdom
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55
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Scott KC, Sullivan BA. Neocentromeres: a place for everything and everything in its place. Trends Genet 2013; 30:66-74. [PMID: 24342629 DOI: 10.1016/j.tig.2013.11.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 11/15/2013] [Accepted: 11/19/2013] [Indexed: 01/07/2023]
Abstract
Centromeres are essential for chromosome inheritance and genome stability. Centromeric proteins, including the centromeric histone centromere protein A (CENP-A), define the site of centromeric chromatin and kinetochore assembly. In many organisms, centromeres are located in or near regions of repetitive DNA. However, some atypical centromeres spontaneously form on unique sequences. These neocentromeres, or new centromeres, were first identified in humans, but have since been described in other organisms. Neocentromeres are functionally and structurally similar to endogenous centromeres, but lack the added complication of underlying repetitive sequences. Here, we discuss recent studies in chicken and fungal systems where genomic engineering can promote neocentromere formation. These studies reveal key genomic and epigenetic factors that support de novo centromere formation in eukaryotes.
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Affiliation(s)
- Kristin C Scott
- Institute for Genome Sciences & Policy, Duke University, DUMC 3382, Durham, NC 27708, USA; Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA; Division of Human Genetics, Duke University Medical Center, Durham, NC 27710, USA.
| | - Beth A Sullivan
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA; Division of Human Genetics, Duke University Medical Center, Durham, NC 27710, USA.
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56
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Laporte D, Courtout F, Salin B, Ceschin J, Sagot I. An array of nuclear microtubules reorganizes the budding yeast nucleus during quiescence. ACTA ACUST UNITED AC 2013; 203:585-94. [PMID: 24247429 PMCID: PMC3840927 DOI: 10.1083/jcb.201306075] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The microtubule cytoskeleton is a highly dynamic network. In dividing cells, its complex architecture not only influences cell shape and movement but is also crucial for chromosome segregation. Curiously, nothing is known about the behavior of this cellular machinery in quiescent cells. Here we show that, upon quiescence entry, the Saccharomyces cerevisiae microtubule cytoskeleton is drastically remodeled. Indeed, while cytoplasmic microtubules vanish, the spindle pole body (SPB) assembles a long and stable monopolar array of nuclear microtubules that spans the entire nucleus. Consequently, the nucleolus is displaced. Kinetochores remain attached to microtubule tips but lose SPB clustering and distribute along the microtubule array, leading to a large reorganization of the nucleus. When cells exit quiescence, the nuclear microtubule array slowly depolymerizes and, by pulling attached centromeres back to the SPB, allows the recovery of a typical Rabl-like configuration. Finally, mutants that do not assemble a nuclear array of microtubules are impaired for both quiescence survival and exit.
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Affiliation(s)
- Damien Laporte
- Université de Bordeaux, Institut de Biochimie et Génétique Cellulaires, F-33077 Bordeaux Cedex, France
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57
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Tanaka TU, Clayton L, Natsume T. Three wise centromere functions: see no error, hear no break, speak no delay. EMBO Rep 2013; 14:1073-83. [PMID: 24232185 PMCID: PMC3849490 DOI: 10.1038/embor.2013.181] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Accepted: 10/18/2013] [Indexed: 12/17/2022] Open
Abstract
The main function of the centromere is to promote kinetochore assembly for spindle microtubule attachment. Two additional functions of the centromere, however, are becoming increasingly clear: facilitation of robust sister-chromatid cohesion at pericentromeres and advancement of replication of centromeric regions. The combination of these three centromere functions ensures correct chromosome segregation during mitosis. Here, we review the mechanisms of the kinetochore-microtubule interaction, focusing on sister-kinetochore bi-orientation (or chromosome bi-orientation). We also discuss the biological importance of robust pericentromeric cohesion and early centromere replication, as well as the mechanisms orchestrating these two functions at the microtubule attachment site.
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Affiliation(s)
- Tomoyuki U Tanaka
- Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
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58
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Kakui Y, Sato M, Okada N, Toda T, Yamamoto M. Microtubules and Alp7-Alp14 (TACC-TOG) reposition chromosomes before meiotic segregation. Nat Cell Biol 2013; 15:786-96. [PMID: 23770679 DOI: 10.1038/ncb2782] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Accepted: 05/10/2013] [Indexed: 12/11/2022]
Abstract
Tethering kinetochores at spindle poles facilitates their efficient capture and segregation by microtubules at mitotic onset in yeast. During meiotic prophase of fission yeast, however, kinetochores are detached from the poles, which facilitates meiotic recombination but may cause a risk of chromosome mis-segregation during meiosis. How cells circumvent this dilemma remains unclear. Here we show that an extensive microtubule array assembles from the poles at meiosis I onset and retrieves scattered kinetochores towards the poles to prevent chromosome drift. Moreover, the microtubule-associated protein complex Alp7-Alp14 (the fission yeast orthologues of mammalian TACC-TOG) is phosphorylated by Polo kinase, which promotes its meiosis-specific association to the outer kinetochore complex Nuf2-Ndc80 of scattered kinetochores, thereby assisting in capturing remote kinetochores. Although TOG was recently characterized as a microtubule polymerase, Dis1 (the other TOG orthologue in fission yeast), together with the Dam1 complex, plays a role in microtubule shortening to pull kinetochores polewards. Thus, microtubules and their binding proteins uniquely reconstitute chromosome configuration during meiosis.
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Affiliation(s)
- Yasutaka Kakui
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0032, Japan
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59
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Meyer RE, Dawson DS. Attaching to spindles before they form: do early incorrect chromosome-microtubule attachments promote meiotic segregation fidelity? Cell Cycle 2013; 12:2011-5. [PMID: 23759585 DOI: 10.4161/cc.25252] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The proper partitioning of the genome during meiosis depends on the correct segregation of chromosomes. Errors in this process result in the production of aneuploid gametes, a major cause of birth defects and infertility in humans. In order to segregate properly in meiosis, homologous chromosome partners must attach to microtubules that emanate from opposites poles of the spindle. However, a recent study in yeast has shown that, remarkably, the initial attachments between microtubules and the chromosomes are usually incorrect, which would lead to catastrophic segregation errors, but they are nearly always corrected through the detachment and reattachment of the microtubules. Here we review the reasons for the initial incorrect attachments, which stem from the timing of their formation early in the spindle assembly process, and the fact that the microtubule organizers, called spindle pole bodies in yeast, are not equal. One spindle pole body is older and better able to produce microtubules that attach to the chromosomes. We draw parallels to recent findings in animal cells and suggest that these early microtubule attachments, while often incorrect, may serve an important role in spindle assembly, which, in the long-term, promotes high-fidelity chromosome segregation.
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Affiliation(s)
- Régis E Meyer
- Cell Cycle and Cancer Biology; Oklahoma Medical Research Foundation; Oklahoma City, OK, USA
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60
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Natsume T, Müller C, Katou Y, Retkute R, Gierliński M, Araki H, Blow J, Shirahige K, Nieduszynski C, Tanaka T. Kinetochores coordinate pericentromeric cohesion and early DNA replication by Cdc7-Dbf4 kinase recruitment. Mol Cell 2013; 50:661-74. [PMID: 23746350 PMCID: PMC3679449 DOI: 10.1016/j.molcel.2013.05.011] [Citation(s) in RCA: 123] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 03/26/2013] [Accepted: 05/02/2013] [Indexed: 11/29/2022]
Abstract
Centromeres play several important roles in ensuring proper chromosome segregation. Not only do they promote kinetochore assembly for microtubule attachment, but they also support robust sister chromatid cohesion at pericentromeres and facilitate replication of centromeric DNA early in S phase. However, it is still elusive how centromeres orchestrate all these functions at the same site. Here, we show that the budding yeast Dbf4-dependent kinase (DDK) accumulates at kinetochores in telophase, facilitated by the Ctf19 kinetochore complex. This promptly recruits Sld3-Sld7 replication initiator proteins to pericentromeric replication origins so that they initiate replication early in S phase. Furthermore, DDK at kinetochores independently recruits the Scc2-Scc4 cohesin loader to centromeres in G1 phase. This enhances cohesin loading and facilitates robust pericentromeric cohesion in S phase. Thus, we have found the central mechanism by which kinetochores orchestrate early S phase DNA replication and robust sister chromatid cohesion at microtubule attachment sites.
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Affiliation(s)
- Toyoaki Natsume
- Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Carolin A. Müller
- Centre for Genetics and Genomics, School of Biology, University of Nottingham, Nottingham NG7 2UH, UK
| | - Yuki Katou
- Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan
| | - Renata Retkute
- Centre for Genetics and Genomics, School of Biology, University of Nottingham, Nottingham NG7 2UH, UK
| | - Marek Gierliński
- Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
- Data Analysis Group, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Hiroyuki Araki
- Division of Microbial Genetics, National Institute of Genetics, Mishima 411-8540, Japan
- Department of Genetics, School of Life Science, SOKENDAI, Mishima 411-8540, Japan
| | - J. Julian Blow
- Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Katsuhiko Shirahige
- Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan
| | - Conrad A. Nieduszynski
- Centre for Genetics and Genomics, School of Biology, University of Nottingham, Nottingham NG7 2UH, UK
| | - Tomoyuki U. Tanaka
- Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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61
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62
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Tanaka K. Regulatory mechanisms of kinetochore-microtubule interaction in mitosis. Cell Mol Life Sci 2013; 70:559-79. [PMID: 22752158 PMCID: PMC11113415 DOI: 10.1007/s00018-012-1057-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 05/29/2012] [Accepted: 06/11/2012] [Indexed: 12/17/2022]
Abstract
Interaction of microtubules with kinetochores is fundamental to chromosome segregation. Kinetochores initially associate with lateral surfaces of microtubules and subsequently become attached to microtubule ends. During these interactions, kinetochores can move by sliding along microtubules or by moving together with depolymerizing microtubule ends. The interplay between kinetochores and microtubules leads to the establishment of bi-orientation, which is the attachment of sister kinetochores to microtubules from opposite spindle poles, and subsequent chromosome segregation. Molecular mechanisms underlying these processes have been intensively studied over the past 10 years. Emerging evidence suggests that the KNL1-Mis12-Ndc80 (KMN) network plays a central role in connecting kinetochores to microtubules, which is under fine regulation by a mitotic kinase, Aurora B. However, a growing number of additional molecules are being shown to be involved in the kinetochore-microtubule interaction. Here I overview the current range of regulatory mechanisms of the kinetochore-microtubule interaction, and discuss how these multiple molecules contribute cooperatively to allow faithful chromosome segregation.
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Affiliation(s)
- Kozo Tanaka
- Department of Molecular Oncology, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Miyagi, Japan.
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63
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Meyer RE, Kim S, Obeso D, Straight PD, Winey M, Dawson DS. Mps1 and Ipl1/Aurora B act sequentially to correctly orient chromosomes on the meiotic spindle of budding yeast. Science 2013; 339:1071-4. [PMID: 23371552 DOI: 10.1126/science.1232518] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The conserved kinases Mps1 and Ipl1/Aurora B are critical for enabling chromosomes to attach to microtubules so that partner chromosomes will be segregated correctly from each other, but the precise roles of these kinases have been unclear. We imaged live yeast cells to elucidate the stages of chromosome-microtubule interactions and their regulation by Ipl1 and Mps1 through meiosis I. Ipl1 was found to release kinetochore-microtubule (kMT) associations after meiotic entry, liberating chromosomes to begin homologous pairing. Surprisingly, most chromosome pairs began their spindle interactions with incorrect kMT attachments. Ipl1 released these improper connections, whereas Mps1 triggered the formation of new force-generating microtubule attachments. This microtubule release and reattachment cycle could prevent catastrophic chromosome segregation errors in meiosis.
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Affiliation(s)
- Régis E Meyer
- Department of Cell Cycle and Cancer Biology, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
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64
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A structural basis for kinetochore recruitment of the Ndc80 complex via two distinct centromere receptors. EMBO J 2013; 32:409-23. [PMID: 23334295 DOI: 10.1038/emboj.2012.356] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Accepted: 12/21/2012] [Indexed: 12/30/2022] Open
Abstract
The Ndc80 complex is the key microtubule-binding element of the kinetochore. In contrast to the well-characterized interaction of Ndc80-Nuf2 heads with microtubules, little is known about how the Spc24-25 heterodimer connects to centromeric chromatin. Here, we present molecular details of Spc24-25 in complex with the histone-fold protein Cnn1/CENP-T illustrating how this connection ultimately links microtubules to chromosomes. The conserved Ndc80 receptor motif of Cnn1 is bound as an α helix in a hydrophobic cleft at the interface between Spc24 and Spc25. Point mutations that disrupt the Ndc80-Cnn1 interaction also abrogate binding to the Mtw1 complex and are lethal in yeast. We identify a Cnn1-related motif in the Dsn1 subunit of the Mtw1 complex, necessary for Ndc80 binding and essential for yeast growth. Replacing this region with the Cnn1 peptide restores viability demonstrating functionality of the Ndc80-binding module in different molecular contexts. Finally, phosphorylation of the Cnn1 N-terminus coordinates the binding of the two competing Ndc80 interaction partners. Together, our data provide structural insights into the modular binding mechanism of the Ndc80 complex to its centromere recruiters.
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65
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Richmond D, Rizkallah R, Liang F, Hurt MM, Wang Y. Slk19 clusters kinetochores and facilitates chromosome bipolar attachment. Mol Biol Cell 2013; 24:566-77. [PMID: 23283988 PMCID: PMC3583661 DOI: 10.1091/mbc.e12-07-0552] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Yeast kinetochore protein Slk19 is required for kinetochore clustering, and nocodazole exposure to slk19 mutant cells causes impaired kinetochore capture and delayed chromosome bipolar attachment after nocodazole washout. In all eukaryotic cells, DNA is packaged into multiple chromosomes that are linked to microtubules through a large protein complex called a kinetochore. Previous data show that the kinetochores are clustered together during most of the cell cycle, but the mechanism and the biological significance of kinetochore clustering are unknown. As a kinetochore protein in budding yeast, the role of Slk19 in the stability of the anaphase spindle has been well studied, but its function in chromosome segregation has remained elusive. Here we show that Slk19 is required for kinetochore clustering when yeast cells are treated with the microtubule-depolymerizing agent nocodazole. We further find that slk19Δ mutant cells exhibit delayed kinetochore capture and chromosome bipolar attachment after the disruption of the kinetochore–microtubule interaction by nocodazole, which is likely attributed to defective kinetochore clustering. In addition, we show that Slk19 interacts with itself, suggesting that the dimerization of Slk19 may mediate the interaction between kinetochores for clustering. Therefore Slk19 likely acts as kinetochore glue that clusters kinetochores to facilitate efficient and faithful chromosome segregation.
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Affiliation(s)
- Daniel Richmond
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL 32306, USA
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66
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Ma CH, Cui H, Hajra S, Rowley PA, Fekete C, Sarkeshik A, Ghosh SK, Yates JR, Jayaram M. Temporal sequence and cell cycle cues in the assembly of host factors at the yeast 2 micron plasmid partitioning locus. Nucleic Acids Res 2012; 41:2340-53. [PMID: 23275556 PMCID: PMC3575823 DOI: 10.1093/nar/gks1338] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Saccharomyces cerevisiae 2 micron plasmid exemplifies a benign but selfish genome, whose stability approaches that of the chromosomes of its host. The plasmid partitioning locus STB (stability locus) displays certain functional analogies with centromeres along with critical distinctions, a significant one being the absence of the kinetochore complex at STB. The remodels the structure of chromatin (RSC) chromatin remodeling complex, the nuclear motor Kip1, the histone H3 variant Cse4 and the cohesin complex associate with both loci. These factors appear to contribute to plasmid segregation either directly or indirectly through their roles in chromosome segregation. Assembly and disassembly of the plasmid-coded partitioning proteins Rep1 and Rep2 and host factors at STB follow a temporal hierarchy during the cell cycle. Assembly is initiated by STB association of [Rsc8-Rsc58], followed by [Rep1-Rep2-Kip1] and [Cse4-Rsc2-Sth1] recruitment, and culminates in cohesin assembly. Disassembly starts with dissociation of RSC components, is followed by cohesin disassembly and Cse4 exit during anaphase and late telophase, respectively. [Rep1-Rep2-Kip1] persists through G1 of the ensuing cell cycle. The de novo assembly of the 'partitioning complex' is cued by the innate cell cycle clock and is dependent on DNA replication. Shared functional attributes of STB and centromere (CEN) are consistent with a potential evolutionary link between them.
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Affiliation(s)
- Chien-Hui Ma
- Section of Molecular Genetics & Microbiology, University of Texas at Austin, Austin, TX 78712, USA
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67
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Roy B, Varshney N, Yadav V, Sanyal K. The process of kinetochore assembly in yeasts. FEMS Microbiol Lett 2012; 338:107-17. [PMID: 23039831 DOI: 10.1111/1574-6968.12019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2012] [Revised: 09/29/2012] [Accepted: 10/01/2012] [Indexed: 12/14/2022] Open
Abstract
High fidelity chromosome segregation is essential for efficient transfer of the genetic material from the mother to daughter cells. The kinetochore (KT), which connects the centromere DNA to the spindle apparatus, plays a pivotal role in this process. In spite of considerable divergence in the centromere DNA sequence, basic architecture of a KT is evolutionarily conserved from yeast to humans. However, the identification of a large number of KT proteins paved the way of understanding conserved and diverged regulatory steps that lead to the formation of a multiprotein KT super-complex on the centromere DNA in different organisms. Because it is a daunting task to summarize the entire spectrum of information in a minireview, we focus here on the recent understanding in the process of KT assembly in three yeasts: Saccharomyces cerevisiae, Schizosaccharomyces pombe and Candida albicans. Studies in these unicellular organisms suggest that although the basic process of KT assembly remains the same, the dependence of a conserved protein for its KT localization may vary in these organisms.
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Affiliation(s)
- Babhrubahan Roy
- Molecular Mycology Laboratory, Molecular Biology and Genetics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
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68
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Buljan VA, Damian Holsinger RM, Hambly BD, Banati RB, Ivanova EP. Intrinsic microtubule GTP-cap dynamics in semi-confined systems: kinetochore-microtubule interface. J Biol Phys 2012; 39:81-98. [PMID: 23860835 DOI: 10.1007/s10867-012-9287-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Accepted: 09/07/2012] [Indexed: 11/24/2022] Open
Abstract
In order to quantify the intrinsic dynamics associated with the tip of a GTP-cap under semi-confined conditions, such as those within a neuronal cone and at a kinetochore-microtubule interface, we propose a novel quantitative concept of critical nano local GTP-tubulin concentration (CNLC). A simulation of a rate constant of GTP-tubulin hydrolysis, under varying conditions based on this concept, generates results in the range of 0-420 s(-1). These results are in agreement with published experimental data, validating our model. The major outcome of this model is the prediction of 11 random and distinct outbursts of GTP hydrolysis per single layer of a GTP-cap. GTP hydrolysis is accompanied by an energy release and the formation of discrete expanding zones, built by less-stable, skewed GDP-tubulin subunits. We suggest that the front of these expanding zones within the walls of the microtubule represent soliton-like movements of local deformation triggered by energy released from an outburst of hydrolysis. We propose that these solitons might be helpful in addressing a long-standing question relating to the mechanism underlying how GTP-tubulin hydrolysis controls dynamic instability. This result strongly supports the prediction that large conformational movements in tubulin subunits, termed dynamic transitions, occur as a result of the conversion of chemical energy that is triggered by GTP hydrolysis (Satarić et al., Electromagn Biol Med 24:255-264, 2005). Although simple, the concept of CNLC enables the formulation of a rationale to explain the intrinsic nature of the "push-and-pull" mechanism associated with a kinetochore-microtubule complex. In addition, the capacity of the microtubule wall to produce and mediate localized spatio-temporal excitations, i.e., soliton-like bursts of energy coupled with an abundance of microtubules in dendritic spines supports the hypothesis that microtubule dynamics may underlie neural information processing including neurocomputation (Hameroff, J Biol Phys 36:71-93, 2010; Hameroff, Cognit Sci 31:1035-1045, 2007; Hameroff and Watt, J Theor Biol 98:549-561, 1982).
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Affiliation(s)
- Vlado A Buljan
- Brain and Mind Research Institute, Sydney Medical School, The University of Sydney, Sydney, NSW, 2050, Australia.
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69
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Bock LJ, Pagliuca C, Kobayashi N, Grove RA, Oku Y, Shrestha K, Alfieri C, Golfieri C, Oldani A, Maschio MD, Bermejo R, Hazbun TR, Tanaka TU, De Wulf P. Cnn1 inhibits the interactions between the KMN complexes of the yeast kinetochore. Nat Cell Biol 2012; 14:614-24. [PMID: 22561345 PMCID: PMC3438452 DOI: 10.1038/ncb2495] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Accepted: 04/02/2012] [Indexed: 12/16/2022]
Abstract
Kinetochores attach the replicated chromosomes to the mitotic spindle and orchestrate their transmission to the daughter cells. Kinetochore-spindle binding and chromosome segregation are mediated by the multi-copy KNL1(Spc105), MIS12(Mtw1) and NDC80(Ndc80) complexes that form the so-called KMN network. KMN-spindle attachment is regulated by the Aurora B(Ipl1) and MPS1(Mps1) kinases. It is unclear whether other mechanisms exist that support KMN activity during the cell cycle. Using budding yeast, we show that kinetochore protein Cnn1 localizes to the base of the Ndc80 complex and promotes a functionally competent configuration of the KMN network. Cnn1 regulates KMN activity in a spatiotemporal manner by inhibiting the interaction between its complexes. Cnn1 activity peaks in anaphase and is driven by the Cdc28, Mps1 and Ipl1 kinases.
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Affiliation(s)
- Lucy J. Bock
- European Institute of Oncology, Department of Experimental Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Cinzia Pagliuca
- European Institute of Oncology, Department of Experimental Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Norihiko Kobayashi
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Ryan A. Grove
- Department of Medicinal Chemistry and Molecular Pharmacology, Center for Cancer Research, Purdue University, West Lafayette, Indiana 47907-2091, USA
| | - Yusuke Oku
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Kriti Shrestha
- Department of Medicinal Chemistry and Molecular Pharmacology, Center for Cancer Research, Purdue University, West Lafayette, Indiana 47907-2091, USA
| | - Claudio Alfieri
- European Institute of Oncology, Department of Experimental Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Cristina Golfieri
- European Institute of Oncology, Department of Experimental Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Amanda Oldani
- FIRC Institute of Molecular Oncology Foundation, 20139 Milan, Italy
| | - Marianna Dal Maschio
- European Institute of Oncology, Department of Experimental Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Rodrigo Bermejo
- Instituto de Biología Funcional y Genómica, CSIC, Universidad de Salamanca, 37008 Salamanca, Spain
| | - Tony R. Hazbun
- Department of Medicinal Chemistry and Molecular Pharmacology, Center for Cancer Research, Purdue University, West Lafayette, Indiana 47907-2091, USA
| | - Tomoyuki U. Tanaka
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Peter De Wulf
- European Institute of Oncology, Department of Experimental Oncology, Via Adamello 16, 20139 Milan, Italy
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70
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Abstract
Mitosis is the process by which eukaryotic cells organize and segregate their chromosomes in preparation for cell division. It is accomplished by a cellular machine composed largely of microtubules (MTs) and their associated proteins. This article reviews literature on mitosis from a biophysical point of view, drawing attention to the assembly and motility processes required to do this complex job with precision. Work from both the recent and the older literature is integrated into a description of relevant biological events and the experiments that probe their mechanisms. Theoretical work on specific subprocesses is also reviewed. Our goal is to provide a document that will expose biophysicists to the fascination of this quite amazing process and provide them with a good background from which they can pursue their own research interests in the subject.
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71
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Guacci V, Koshland D. Cohesin-independent segregation of sister chromatids in budding yeast. Mol Biol Cell 2012; 23:729-39. [PMID: 22190734 PMCID: PMC3279399 DOI: 10.1091/mbc.e11-08-0696] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2011] [Revised: 12/01/2011] [Accepted: 12/12/2011] [Indexed: 12/02/2022] Open
Abstract
Cohesin generates cohesion between sister chromatids, which enables chromosomes to form bipolar attachments to the mitotic spindle and segregate. Cohesin also functions in chromosome condensation, transcriptional regulation, and DNA damage repair. Here we analyze the role of acetylation in modulating cohesin functions and how it affects budding yeast viability. Previous studies show that cohesion establishment requires Eco1p-mediated acetylation of the cohesin subunit Smc3p at residue K113. Smc3p acetylation was proposed to promote establishment by merely relieving Wpl1p inhibition because deletion of WPL1 bypasses the lethality of an ECO1 deletion (eco1Δ wpl1Δ). We find that little, if any, cohesion is established in eco1Δ wpl1Δ cells, indicating that Eco1p performs a function beyond antagonizing Wpl1p. Cohesion also fails to be established when SMC3 acetyl-mimics (K113Q or K112R,K113Q) are the sole functional SMC3s in cells. These results suggest that Smc3p acetylation levels affect establishment. It is remarkable that, despite their severe cohesion defect, eco1Δ wpl1Δ and smc3-K112R,K113Q strains are viable because a cohesin-independent mechanism enables bipolar attachment and segregation. This alternative mechanism is insufficient for smc3-K113Q strain viability. Smc3-K113Q is defective for condensation, whereas eco1Δ wpl1Δ and smc3-K112R,K113Q strains are competent for condensation. We suggest that Smc3p acetylation and Wpl1p antagonistically regulate cohesin's essential role in condensation.
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Affiliation(s)
- Vincent Guacci
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
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72
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Kinetochore-dependent microtubule rescue ensures their efficient and sustained interactions in early mitosis. Dev Cell 2012; 21:920-33. [PMID: 22075150 PMCID: PMC3277888 DOI: 10.1016/j.devcel.2011.09.006] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 08/14/2011] [Accepted: 09/12/2011] [Indexed: 12/16/2022]
Abstract
How kinetochores regulate microtubule dynamics to ensure proper kinetochore-microtubule interactions is unknown. Here, we studied this during early mitosis in Saccharomyces cerevisiae. When a microtubule shrinks and its plus end reaches a kinetochore bound to its lateral surface, the microtubule end attempts to tether the kinetochore. This process often fails and, responding to this failure, microtubule rescue (conversion from shrinkage to growth) occurs, preventing kinetochore detachment from the microtubule end. This rescue is promoted by Stu2 transfer (ortholog of vertebrate XMAP215/ch-TOG) from the kinetochore to the microtubule end. Meanwhile, microtubule rescue distal to the kinetochore is also promoted by Stu2, which is transported by a kinesin-8 motor Kip3 along the microtubule from the kinetochore. Microtubule extension following rescue facilitates interaction with other widely scattered kinetochores, diminishing long delays in collecting the complete set of kinetochores by microtubules. Thus, kinetochore-dependent microtubule rescue ensures efficient and sustained kinetochore-microtubule interactions in early mitosis.
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73
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Ohkuni K, Kitagawa K. Endogenous transcription at the centromere facilitates centromere activity in budding yeast. Curr Biol 2011; 21:1695-703. [PMID: 22000103 DOI: 10.1016/j.cub.2011.08.056] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Revised: 05/06/2011] [Accepted: 08/23/2011] [Indexed: 11/15/2022]
Abstract
BACKGROUND The centromere (CEN) DNA-kinetochore complex is the specialized chromatin structure that mediates chromosome attachment to the spindle and is required for high-fidelity chromosome segregation. Although kinetochore function is conserved from budding yeast to humans, it was thought that transcription had no role in centromere function in budding yeast, in contrast to other eukaryotes including fission yeast. RESULTS We report here that transcription at the centromere facilitates centromere activity in the budding yeast Saccharomyces cerevisiae. We identified transcripts at CEN DNA and found that Cbf1, which is a transcription factor that binds to CEN DNA, is required for transcription at CEN DNA. Chromosome instability of cbf1Δ cells is suppressed by transcription driven from an artificial promoter. Furthermore, we have identified Ste12, which is a transcription factor, and Dig1, a Ste12 inhibitor, as a novel CEN-associated protein complex by an in vitro kinetochore assembly system. Dig1 represses Ste12-dependent transcription at the centromere. CONCLUSIONS Our studies reveal that transcription at the centromere plays an important role in centromere function in budding yeast.
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Affiliation(s)
- Kentaro Ohkuni
- Center for Childhood Cancer, The Research Institute, Nationwide Children's Hospital, Columbus, OH 43205, USA
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74
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Buttrick GJ, Meadows JC, Lancaster TC, Vanoosthuyse V, Shepperd LA, Hoe KL, Kim DU, Park HO, Hardwick KG, Millar JBA. Nsk1 ensures accurate chromosome segregation by promoting association of kinetochores to spindle poles during anaphase B. Mol Biol Cell 2011; 22:4486-502. [PMID: 21965289 PMCID: PMC3226469 DOI: 10.1091/mbc.e11-07-0608] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Nsk1 is a novel fission yeast protein that binds the nucleolus during interphase and the nucleoplasm during early mitosis. After anaphase and following dephosphorylation by Clp1, Nsk1 binds the kinetochore–spindle pole junction and maintains accurate chromosome segregation by promoting the association of kinetochores to spindle poles during anaphase B. Type 1 phosphatase (PP1) antagonizes Aurora B kinase to stabilize kinetochore–microtubule attachments and to silence the spindle checkpoint. We screened for factors that exacerbate the growth defect of Δdis2 cells, which lack one of two catalytic subunits of PP1 in fission yeast, and identified Nsk1, a novel protein required for accurate chromosome segregation. During interphase, Nsk1 resides in the nucleolus but spreads throughout the nucleoplasm as cells enter mitosis. Following dephosphorylation by Clp1 (Cdc14-like) phosphatase and at least one other phosphatase, Nsk1 localizes to the interface between kinetochores and the inner face of the spindle pole body during anaphase. In the absence of Nsk1, some kinetochores become detached from spindle poles during anaphase B. If this occurs late in anaphase B, then the sister chromatids of unclustered kinetochores segregate to the correct daughter cell. These unclustered kinetochores are efficiently captured, retrieved, bioriented, and segregated during the following mitosis, as long as Dis2 is present. However, if kinetochores are detached from a spindle pole early in anaphase B, then these sister chromatids become missegregated. These data suggest Nsk1 ensures accurate chromosome segregation by promoting the tethering of kinetochores to spindle poles during anaphase B.
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Affiliation(s)
- Graham J Buttrick
- Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, United Kingdom
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75
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Misregulation of Scm3p/HJURP causes chromosome instability in Saccharomyces cerevisiae and human cells. PLoS Genet 2011; 7:e1002303. [PMID: 21980305 PMCID: PMC3183075 DOI: 10.1371/journal.pgen.1002303] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Accepted: 07/29/2011] [Indexed: 11/19/2022] Open
Abstract
The kinetochore (centromeric DNA and associated proteins) is a key determinant for high fidelity chromosome transmission. Evolutionarily conserved Scm3p is an essential component of centromeric chromatin and is required for assembly and function of kinetochores in humans, fission yeast, and budding yeast. Overexpression of HJURP, the mammalian homolog of budding yeast Scm3p, has been observed in lung and breast cancers and is associated with poor prognosis; however, the physiological relevance of these observations is not well understood. We overexpressed SCM3 and HJURP in Saccharomyces cerevisiae and HJURP in human cells and defined domains within Scm3p that mediate its chromosome loss phenotype. Our results showed that the overexpression of SCM3 (GALSCM3) or HJURP (GALHJURP) caused chromosome loss in a wild-type yeast strain, and overexpression of HJURP led to mitotic defects in human cells. GALSCM3 resulted in reduced viability in kinetochore mutants, premature separation of sister chromatids, and reduction in Cse4p and histone H4 at centromeres. Overexpression of CSE4 or histone H4 suppressed chromosome loss and restored levels of Cse4p at centromeres in GALSCM3 strains. Using mutant alleles of scm3, we identified a domain in the N-terminus of Scm3p that mediates its interaction with CEN DNA and determined that the chromosome loss phenotype of GALSCM3 is due to centromeric association of Scm3p devoid of Cse4p/H4. Furthermore, we determined that similar to other systems the centromeric association of Scm3p is cell cycle regulated. Our results show that altered stoichiometry of Scm3p/HJURP, Cse4p, and histone H4 lead to defects in chromosome segregation. We conclude that stringent regulation of HJURP and SCM3 expression are critical for genome stability.
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76
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Wadsworth P, Lee WL, Murata T, Baskin TI. Variations on theme: spindle assembly in diverse cells. PROTOPLASMA 2011; 248:439-46. [PMID: 20830494 PMCID: PMC5290749 DOI: 10.1007/s00709-010-0205-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 08/26/2010] [Indexed: 05/18/2023]
Abstract
The mitotic spindle faithfully separates the genetic material, and has been reverently observed for well over a century. Across eukaryotes, while the mechanisms for moving chromosomes seem quite conserved, mechanisms for assembling the spindle often seem distinct. Two major pathways for spindle assembly are known, one based on centrosomes and the other based on chromatin, and these pathways are usually considered to be fundamentally different. We review observations of spindle assembly in animals, fungi, and plants, and argue that microtubule assembly at a particular location, centrosomes, or chromatin, reflects contingent, cell-type specific factors, rather than reflecting a fundamental distinction in the process of spindle building. We hypothesize that the essential process for spindle assembly is the motor-driven organization of microtubules that accumulate in the form of dense bundles at or near the chromosomes.
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Affiliation(s)
- Patricia Wadsworth
- Department of Biology, Morrill Science Center, University of Massachusetts, Amherst, MA 01003, USA.
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77
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Abstract
Malaria is caused by intraerythrocytic protozoan parasites belonging to Plasmodium spp. (phylum Apicomplexa) that produce significant morbidity and mortality, mostly in developing countries. Plasmodium parasites have a complex life cycle that includes multiple stages in anopheline mosquito vectors and vertebrate hosts. During the life cycle, the parasites undergo several cycles of extreme population growth within a brief span, and this is critical for their continued transmission and a contributing factor for their pathogenesis in the host. As with other eukaryotes, successful mitosis is an essential requirement for Plasmodium reproduction; however, some aspects of Plasmodium mitosis are quite distinct and not fully understood. In this review, we will discuss the current understanding of the architecture and key events of mitosis in Plasmodium falciparum and related parasites and compare them with the traditional mitotic events described for other eukaryotes.
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78
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Maure JF, Komoto S, Oku Y, Mino A, Pasqualato S, Natsume K, Clayton L, Musacchio A, Tanaka TU. The Ndc80 loop region facilitates formation of kinetochore attachment to the dynamic microtubule plus end. Curr Biol 2011; 21:207-13. [PMID: 21256019 PMCID: PMC3052438 DOI: 10.1016/j.cub.2010.12.050] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Revised: 11/21/2010] [Accepted: 12/23/2010] [Indexed: 10/24/2022]
Abstract
Proper chromosome segregation in mitosis relies on correct kinetochore-microtubule (KT-MT) interactions. The KT initially interacts with the lateral surface of a single MT (lateral attachment) extending from a spindle pole and is subsequently anchored at the plus end of the MT (end-on attachment). The conversion from lateral to end-on attachment is crucial because end-on attachment is more robust and thought to be necessary to sustain KT-MT attachment when tension is applied across sister KTs upon their biorientation. The mechanism for this conversion is still elusive. The Ndc80 complex is an essential component of the KT-MT interface, and here we studied a role of the Ndc80 loop region, a distinct motif looping out from the coiled-coil shaft of the complex, in Saccharomyces cerevisiae. With deletions or mutations of the loop region, the lateral KT-MT attachment occurred normally; however, subsequent conversion to end-on attachment was defective, leading to failure in sister KT biorientation. The Ndc80 loop region was required for Ndc80-Dam1 interaction and KT loading of the Dam1 complex, which in turn supported KT tethering to the dynamic MT plus end. The Ndc80 loop region, therefore, has an important role in the conversion from lateral to end-on attachment, a crucial maturation step of KT-MT interaction.
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Affiliation(s)
- Jean-François Maure
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, Dundee DD1 5EH, UK
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79
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Tension directly stabilizes reconstituted kinetochore-microtubule attachments. Nature 2010; 468:576-9. [PMID: 21107429 DOI: 10.1038/nature09594] [Citation(s) in RCA: 328] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2010] [Accepted: 10/19/2010] [Indexed: 11/08/2022]
Abstract
Kinetochores are macromolecular machines that couple chromosomes to dynamic microtubule tips during cell division, thereby generating force to segregate the chromosomes. Accurate segregation depends on selective stabilization of correct 'bi-oriented' kinetochore-microtubule attachments, which come under tension as the result of opposing forces exerted by microtubules. Tension is thought to stabilize these bi-oriented attachments indirectly, by suppressing the destabilizing activity of a kinase, Aurora B. However, a complete mechanistic understanding of the role of tension requires reconstitution of kinetochore-microtubule attachments for biochemical and biophysical analyses in vitro. Here we show that native kinetochore particles retaining the majority of kinetochore proteins can be purified from budding yeast and used to reconstitute dynamic microtubule attachments. Individual kinetochore particles maintain load-bearing associations with assembling and disassembling ends of single microtubules for >30 min, providing a close match to the persistent coupling seen in vivo between budding yeast kinetochores and single microtubules. Moreover, tension increases the lifetimes of the reconstituted attachments directly, through a catch bond-like mechanism that does not require Aurora B. On the basis of these findings, we propose that tension selectively stabilizes proper kinetochore-microtubule attachments in vivo through a combination of direct mechanical stabilization and tension-dependent phosphoregulation.
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80
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Kinetochore-microtubule interactions: steps towards bi-orientation. EMBO J 2010; 29:4070-82. [PMID: 21102558 DOI: 10.1038/emboj.2010.294] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2010] [Accepted: 10/29/2010] [Indexed: 11/08/2022] Open
Abstract
Eukaryotic cells segregate their chromosomes accurately to opposite poles during mitosis, which is necessary for maintenance of their genetic integrity. This process mainly relies on the forces generated by kinetochore-microtubule (KT-MT) attachment. During prometaphase, the KT initially interacts with a single MT extending from a spindle pole and then moves towards a spindle pole. Subsequently, MTs from the other spindle pole also interact with the KT. Eventually, one sister KT becomes attached to MTs from one pole while the other sister to those from the other pole (sister KT bi-orientation). If sister KTs interact with MTs with aberrant orientation, this must be corrected to attain proper bi-orientation (error correction) before the anaphase is initiated. Here, I discuss how KTs initially interact with MTs and how this interaction develops into bi-orientation; both processes are fundamentally crucial for proper chromosome segregation in the subsequent anaphase.
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81
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Cdc14-dependent dephosphorylation of a kinetochore protein prior to anaphase in Saccharomyces cerevisiae. Genetics 2010; 186:1487-91. [PMID: 20923974 DOI: 10.1534/genetics.110.123653] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The budding yeast Cdc14 phosphatase reverses Cdk1 phosphorylation to promote mitotic exit. Although Cdc14 activity is thought to be restricted to anaphase, we found that dephosphorylation of the Dsn1 kinetochore protein in metaphase requires Cdc14. These data suggest that there is a nonnucleolar pool of active Cdc14 prior to anaphase.
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82
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Brito IL, Monje-Casas F, Amon A. The Lrs4-Csm1 monopolin complex associates with kinetochores during anaphase and is required for accurate chromosome segregation. Cell Cycle 2010; 9:3611-8. [PMID: 20818155 DOI: 10.4161/cc.9.17.12885] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Lrs4 and Csm1, components of the monopolin complex, localize to the rDNA where they regulate rDNA maintenance and segregation. During meiosis, the complex also associates with kinetochores to bring about sister kinetochore co-orientation, an essential aspect of meiosis I chromosome segregation. We show here that the Lrs4-Csm1 complex associates with kinetochores during mitosis. This kinetochore localization is observed during anaphase and depends on the on the Mitotic Exit Network, a signaling cascade essential for the completion of mitosis. Furthermore, we find that Lrs4 and Csm1 are important for chromosome segregation fidelity. Our results reveal a previously unanticipated function for Lrs4-Csm1 in mitotic chromosome segregation.
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Affiliation(s)
- Ilana L Brito
- David H. Koch Institute for Integrative Cancer Research and Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA
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83
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Abstract
Duplication of chromosomal DNA is a temporally and spatially regulated process. The timing of DNA replication initiation at various origins is highly coordinated; some origins fire early and others late during S phase. Moreover, inside the nuclei, the bulk of DNA replication is physically organized in replication factories, consisting of DNA polymerases and other replication proteins. In this review article, we discuss how DNA replication is organized and regulated spatially within the nucleus and how this spatial organization is linked to temporal regulation. We focus on DNA replication in budding yeast and fission yeast and, where applicable, compare yeast DNA replication with that in bacteria and metazoans.
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Affiliation(s)
- Toyoaki Natsume
- Wellcome Trust Centre for Gene Regulation and Expression, University of Dundee, Dundee, DD1 5EH, UK
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84
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Tanaka K, Kitamura E, Tanaka TU. Live-cell analysis of kinetochore-microtubule interaction in budding yeast. Methods 2010; 51:206-13. [PMID: 20117214 PMCID: PMC2954359 DOI: 10.1016/j.ymeth.2010.01.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Accepted: 01/14/2010] [Indexed: 12/02/2022] Open
Abstract
Kinetochore capture and transport by spindle microtubules plays a crucial role in high-fidelity chromosome segregation, although its detailed mechanism has remained elusive. It has been difficult to observe individual kinetochore-microtubule interactions because multiple kinetochores are captured by microtubules during a short period within a small space. We have developed a method to visualize individual kinetochore-microtubule interactions in Saccharomyces cerevisiae, by isolating one of the kinetochores from others through regulation of the activity of a centromere. We detail this technique, which we call 'centromere reactivation system', for dissection of the process of kinetochore capture and transport on mitotic spindle. Kinetochores are initially captured by the side of microtubules extending from a spindle pole, and subsequently transported poleward along them, which is an evolutionarily conserved process from yeast to vertebrate cells. Our system, in combination with amenable yeast genetics, has proved useful to elucidate the molecular mechanisms of kinetochore-microtubule interactions. We discuss practical considerations for applying our system to live cell imaging using fluorescence microscopy.
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Affiliation(s)
- Kozo Tanaka
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK
- Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi, Japan
| | - Etsushi Kitamura
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK
| | - Tomoyuki U. Tanaka
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK
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85
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Kitamura E, Tanaka K, Komoto S, Kitamura Y, Antony C, Tanaka TU. Kinetochores generate microtubules with distal plus ends: their roles and limited lifetime in mitosis. Dev Cell 2010; 18:248-59. [PMID: 20159595 PMCID: PMC2828607 DOI: 10.1016/j.devcel.2009.12.018] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2009] [Revised: 10/28/2009] [Accepted: 12/17/2009] [Indexed: 11/28/2022]
Abstract
In early mitosis, microtubules can be generated at kinetochores as well as at spindle poles. However, the role and regulation of kinetochore-derived microtubules have been unclear. In general, metaphase spindle microtubules are oriented such that their plus ends bind to kinetochores. However, we now have evidence that, during early mitosis in budding yeast, microtubules are generated at kinetochores with distal plus ends. These kinetochore-derived microtubules interact along their length with microtubules that extend from a spindle pole, facilitating kinetochore loading onto the lateral surface of spindle pole microtubules. Once kinetochores are loaded, microtubules are no longer generated at kinetochores, and those that remain disappear rapidly and do not contribute to the metaphase spindle. Stu2 (the ortholog of vertebrate XMAP215/ch-TOG) localizes to kinetochores and plays a central role in regulating kinetochore-derived microtubules. Our work provides insight into microtubule generation at kinetochores and the mechanisms that facilitate initial kinetochore interaction with spindle pole microtubules.
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Affiliation(s)
- Etsushi Kitamura
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, Dundee DD1 5EH, UK
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86
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Keating P, Rachidi N, Tanaka TU, Stark MJR. Ipl1-dependent phosphorylation of Dam1 is reduced by tension applied on kinetochores. J Cell Sci 2010; 122:4375-82. [PMID: 19923271 DOI: 10.1242/jcs.055566] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The conserved Aurora B protein kinase (Ipl1 in Saccharomyces cerevisiae) is essential for ensuring that sister kinetochores become attached to microtubules from opposite spindle poles (bi-orientation) before anaphase onset. When sister chromatids become attached to microtubules from a single pole, Aurora B/Ipl1 facilitates turnover of kinetochore-microtubule attachments. This process requires phosphorylation by Aurora B/Ipl1 of kinetochore components such as Dam1 in yeast. Once bi-orientation is established and tension is applied on kinetochores, Aurora B/Ipl1 must stop promoting this turnover, otherwise correct attachment would never be stabilised. How this is achieved remains elusive: it might be due to dephosphorylation of Aurora B/Ipl1 substrates at kinetochores, or might take place independently, for example because of conformational changes in kinetochores. Here, we show that Ipl1-dependent phosphorylation at crucial sites on Dam1 is maximal during S phase and minimal during metaphase, matching the cell cycle window when chromosome bi-orientation occurs. Intriguingly, when we reduced tension at kinetochores through failure to establish sister chromatid cohesion, Dam1 phosphorylation persisted in metaphase-arrested cells. We propose that Aurora B/Ipl1-facilitated bi-orientation is stabilised in response to tension at kinetochores by dephosphorylation of Dam1, resulting in termination of kinetochore-microtubule attachment turnover.
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Affiliation(s)
- Patrick Keating
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, MSI/WTB Complex, University of Dundee, Dundee, DD1 5EH, UK
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87
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Ortiz J, Funk C, Schäfer A, Lechner J. Stu1 inversely regulates kinetochore capture and spindle stability. Genes Dev 2009; 23:2778-91. [PMID: 19952112 DOI: 10.1101/gad.541309] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The Saccharomyces cerevisiae CLASP (CLIP-associated protein) Stu1 is essential for the establishment and maintenance of the mitotic spindle. Furthermore, Stu1 localizes to kinetochores. Here we show that, in prometaphase, Stu1 assembles in an Ndc80-dependent manner exclusively at kinetochores that are not attached to microtubules. Stu1 relocates to microtubules when a captured kinetochore reaches a spindle pole. This relocation does not depend on kinetochore biorientation, but requires a functional DASH complex. Stu1 at detached kinetochores facilitates kinetochore capturing. Furthermore, since most of the nuclear Stu1 is sequestered by one or a few detached kinetochores, the presence of detached kinetochores prevents Stu1 from localizing the spindle, and therefore from stabilizing the spindle. Thus, the sequestering of Stu1 by detached kinetochores serves as a checkpoint that keeps spindle poles in close proximity until all kinetochores are captured. This is likely to facilitate kinetochore biorientation. In agreement with the findings described above, a kinetochore mutant (okp1-52) that fails to release Stu1 from the kinetochore displays a severe spindle defect upon spindle pole body separation, and this defect can be rescued by destroying the okp1-52 kinetochore.
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Affiliation(s)
- Jennifer Ortiz
- Biochemie-Zentrum der Universität Heidelberg, 69120 Heidelberg, Germany
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88
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Tanaka K, Hirota T. Chromosome segregation machinery and cancer. Cancer Sci 2009; 100:1158-65. [PMID: 19432891 PMCID: PMC11158954 DOI: 10.1111/j.1349-7006.2009.01178.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Revised: 03/19/2009] [Accepted: 03/24/2009] [Indexed: 12/30/2022] Open
Abstract
Loss or gain of chromosomes is associated with many cancer cells. This property, called chromosome instability, might arise from a lesion in the chromosome segregation machinery. Essential for chromosome segregation are the proper connection of microtubules to kinetochores, and the synchronous segregation of sister chromatids in anaphase. Accuracy of these processes is ensured by two sophisticated machineries called the correction mechanism and the spindle assembly checkpoint. Here we outline the current understanding of the underlying mechanisms, and highlight recent challenging experiments to address how chromosome segregation failure might relate to tumorigenesis. Understanding these mechanisms may lead to the discovery of new and improved anticancer therapies.
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Affiliation(s)
- Kozo Tanaka
- Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan
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89
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Efficient chromosome biorientation and the tension checkpoint in Saccharomyces cerevisiae both require Bir1. Mol Cell Biol 2009; 29:4552-62. [PMID: 19528231 DOI: 10.1128/mcb.01911-08] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Accurate chromosome segregation requires the capture of sister kinetochores by microtubules from opposite spindle poles prior to the initiation of anaphase, a state termed chromosome biorientation. In the budding yeast Saccharomyces cerevisiae, the conserved protein kinase Ipl1 (Aurora B in metazoans) is critical for ensuring correct chromosomal alignment. Ipl1 associates with its activators Sli15 (INCENP), Nbl1 (Borealin), and Bir1 (Survivin), but while Sli15 clearly functions with Ipl1 to promote chromosome biorientation, the role of Bir1 has been uncertain. Using a temperature-sensitive bir1 mutant (bir1-17), we show that Bir1 is needed to permit efficient chromosome biorientation. However, once established, chromosome biorientation is maintained in bir1-17 cells at the restrictive temperature. Ipl1 is partially delocalized in bir1-17 cells, and its protein kinase activity is markedly reduced under nonpermissive conditions. bir1-17 cells arrest normally in response to microtubule depolymerization but fail to delay anaphase when sister kinetochore tension is reduced. Thus, Bir1 is required for the tension checkpoint. Despite their robust mitotic arrest in response to nocodazole, bir1-17 cells are hypersensitive to microtubule-depolymerizing drugs and show a more severe biorientation defect on recovery from nocodazole treatment. The role of Bir1 therefore may become more critical when spindle formation is delayed.
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90
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Cui H, Ghosh SK, Jayaram M. The selfish yeast plasmid uses the nuclear motor Kip1p but not Cin8p for its localization and equal segregation. J Cell Biol 2009; 185:251-64. [PMID: 19364922 PMCID: PMC2700366 DOI: 10.1083/jcb.200810130] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Accepted: 03/23/2009] [Indexed: 01/31/2023] Open
Abstract
The 2 micron plasmid of Saccharomyces cerevisiae uses the Kip1 motor, but not the functionally redundant Cin8 motor, for its precise nuclear localization and equal segregation. The timing and lifetime of Kip1p association with the plasmid partitioning locus STB are consistent with Kip1p being an authentic component of the plasmid partitioning complex. Kip1-STB association is not blocked by disassembling the mitotic spindle. Lack of Kip1p disrupts recruitment of the cohesin complex at STB and cohesion of replicated plasmid molecules. Colocalization of a 2 micron reporter plasmid with Kip1p in close proximity to the spindle pole body is reminiscent of that of a CEN reporter plasmid. Absence of Kip1p displaces the plasmid from this nuclear address, where it has the potential to tether to a chromosome or poach chromosome segregation factors. Exploiting Kip1p, which is subsidiary to Cin8p for chromosome segregation, to direct itself to a "partitioning center" represents yet another facet of the benign parasitism of the yeast plasmid.
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Affiliation(s)
- Hong Cui
- Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, TX 78712, USA
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91
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Tartakoff AM, Jaiswal P. Nuclear fusion and genome encounter during yeast zygote formation. Mol Biol Cell 2009; 20:2932-42. [PMID: 19369416 DOI: 10.1091/mbc.e08-12-1193] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
When haploid cells of Saccharomyces cerevisiae are crossed, parental nuclei congress and fuse with each other. To investigate underlying mechanisms, we have developed assays that evaluate the impact of drugs and mutations. Nuclear congression is inhibited by drugs that perturb the actin and tubulin cytoskeletons. Nuclear envelope (NE) fusion consists of at least five steps in which preliminary modifications are followed by controlled flux of first outer and then inner membrane proteins, all before visible dilation of the waist of the nucleus or coalescence of the parental spindle pole bodies. Flux of nuclear pore complexes occurs after dilation. Karyogamy requires both the Sec18p/NSF ATPase and ER/NE luminal homeostasis. After fusion, chromosome tethering keeps tagged parental genomes separate from each other. The process of NE fusion and evidence of genome independence in yeast provide a prototype for understanding related events in higher eukaryotes.
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Affiliation(s)
- Alan Michael Tartakoff
- Pathology Department and Cell Biology Program, Case Western Reserve University, Cleveland, OH 44106, USA.
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92
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Abstract
Asymmetric cell division is of fundamental importance in biology as it allows for the establishment of separate cell lineages during the development of multicellular organisms. Although microbial systems, including the yeast Saccharomyces cerevisiae, are excellent models of asymmetric cell division, this phenotype occurs in all cell divisions; consequently, models of lineage-specific segregation patterns in these systems do not exist. Here, we report the first example of lineage-specific asymmetric division in yeast. We used fluorescent tags to show that components of the yeast kinetochore, the protein complex that anchors chromosomes to the mitotic spindle, divide asymmetrically in a single postmeiotic lineage. This phenotype is not seen in vegetatively dividing haploid or diploid cells. This kinetochore asymmetry suggests a mechanism for the selective segregation of sister centromeres to daughter cells to establish different cell lineages or fates. These results provide a mechanistic link between lineage-defining asymmetry of metazoa with unicellular eukaryotes.
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93
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Ebrahimi H, Donaldson AD. Release of yeast telomeres from the nuclear periphery is triggered by replication and maintained by suppression of Ku-mediated anchoring. Genes Dev 2009; 22:3363-74. [PMID: 19056887 DOI: 10.1101/gad.486208] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The perinuclear localization of Saccharomyces cerevisiae telomeres provides a useful model for studying mechanisms that control chromosome positioning. Telomeres tend to be localized at the nuclear periphery during early interphase, but following S phase they delocalize and remain randomly positioned within the nucleus. We investigated whether DNA replication causes telomere delocalization from the nuclear periphery. Using live-cell fluorescence microscopy, we show that delaying DNA replication causes a corresponding delay in the dislodgment of telomeres from the nuclear envelope, demonstrating that replication of individual telomeres causes their delocalization. Telomere delocalization is not simply the result of recruitment to a replication factory in the nuclear interior, since we found that telomeric DNA replication can occur either at the nuclear periphery or in the nuclear interior. The telomere-binding complex Ku is one of the factors that localizes telomeres to the nuclear envelope. Using a gene locus tethering assay, we show that Ku-mediated peripheral positioning is switched off after DNA replication. Based on these findings, we propose that DNA replication causes telomere delocalization by triggering stable repression of the Ku-mediated anchoring pathway. In addition to maintaining genetic information, DNA replication may therefore regulate subnuclear organization of chromatin.
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Affiliation(s)
- Hani Ebrahimi
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland, United Kingdom
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94
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Abstract
For high-fidelity chromosome segregation, kinetochores must be properly captured by spindle microtubules, but the mechanisms of initial kinetochore capture have remained elusive. Observation of individual kinetochore-microtubule interaction has been difficult, because multiple kinetochores are captured by microtubules during a short period and within a small space. By isolating one of the kinetochores from others through regulation of the activity of a centromere, we could visualize individual kinetochore-microtubule interactions in Saccharomyces cerevisiae. This technique, which we have called the 'centromere reactivation system', allowed us to dissect the process of kinetochore capture and transport on the mitotic spindle into several steps, thus enabling us to identify genes involved in each step. Kinetochores are captured by the side of microtubules extending from a spindle pole, and subsequently transported poleward along them. This process is evolutionarily conserved from yeast to vertebrate cells. Therefore, our system has proved useful in elucidating the underlying mechanisms of kinetochore capture by spindle microtubules.
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Affiliation(s)
- Kozo Tanaka
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK
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95
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Liu H, Liang F, Jin F, Wang Y. The coordination of centromere replication, spindle formation, and kinetochore-microtubule interaction in budding yeast. PLoS Genet 2008; 4:e1000262. [PMID: 19023403 PMCID: PMC2577889 DOI: 10.1371/journal.pgen.1000262] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2008] [Accepted: 10/16/2008] [Indexed: 01/12/2023] Open
Abstract
The kinetochore is a protein complex that assembles on centromeric DNA to mediate chromosome–microtubule interaction. Most eukaryotic cells form the spindle and establish kinetochore–microtubule interaction during mitosis, but budding yeast cells finish these processes in S-phase. It has long been noticed that the S-phase spindle in budding yeast is shorter than that in metaphase, but the biological significance of this short S-phase spindle structure remains unclear. We addressed this issue by using ask1-3, a temperature-sensitive kinetochore mutant that exhibits partially elongated spindles at permissive temperature in the presence of hydroxyurea (HU), a DNA synthesis inhibitor. After exposure to and removal of HU, ask1-3 cells show a delayed anaphase entry. This delay depends on the spindle checkpoint, which monitors kinetochore–microtubule interaction defects. Overproduction of microtubule-associated protein Ase1 or Cin8 also induces spindle elongation in HU-arrested cells. The spindle checkpoint-dependent anaphase entry delay is also observed after ASE1 or CIN8 overexpression in HU-arrested cells. Therefore, the shorter spindle in S-phase cells is likely to facilitate proper chromosome–microtubule interaction. The interaction of spindle microtubules with chromosomes is essential for proper segregation of chromosomes into two daughter cells. Most eukaryotic cells form spindles and establish the chromosome–microtubule interaction after DNA replication, but the chromosomes in budding yeast are attached by spindle microtubules before the completion of DNA replication. Interestingly, when yeast cells are arrested in S-phase by hydroxyurea, a DNA synthesis inhibitor, they show a unique spindle structure that is shorter than the metaphase spindle. The focus of this study is to address how the shorter S-phase spindle benefits chromosome–microtubule interaction. We found that the increase in spindle length in yeast cells that are arrested in S-phase results in an improper chromosome–microtubule interaction. It is likely that the shorter S-phase spindle facilitates chromosome capture by microtubules as well as the generation of tension on chromosomes, which is critical for flawless chromosome segregation.
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Affiliation(s)
- Hong Liu
- Department of Biological Sciences, Florida State University, Tallahassee, Florida, United States of America
| | - Fengshan Liang
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
| | - Fengzhi Jin
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
| | - Yanchang Wang
- Department of Biological Sciences, Florida State University, Tallahassee, Florida, United States of America
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, Florida, United States of America
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
- * E-mail:
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96
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New insights into the chromosome cycle. Conference on the Replication & Segregation of Chromosomes. EMBO Rep 2008; 9:1177-81. [PMID: 18974771 DOI: 10.1038/embor.2008.203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Accepted: 10/09/2008] [Indexed: 12/11/2022] Open
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97
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Tanaka TU. Bi-orienting chromosomes: acrobatics on the mitotic spindle. Chromosoma 2008; 117:521-33. [PMID: 18677502 DOI: 10.1007/s00412-008-0173-5] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 06/05/2008] [Accepted: 06/07/2008] [Indexed: 11/28/2022]
Abstract
To maintain their genetic integrity, eukaryotic cells must segregate their chromosomes properly to opposite poles during mitosis. This process mainly depends on the forces generated by microtubules that attach to kinetochores. During prometaphase, kinetochores initially interact with a single microtubule that extends from a spindle pole and then move towards a spindle pole. Subsequently, microtubules that extend from the other spindle pole also interact with kinetochores and, eventually, each sister kinetochore attaches to microtubules that extend from opposite poles (sister kinetochore bi-orientation). If sister kinetochores interact with microtubules in wrong orientation, this must be corrected before the onset of anaphase. Here, I discuss the processes leading to bi-orientation and the mechanisms ensuring this pivotal state that is required for proper chromosome segregation.
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Affiliation(s)
- Tomoyuki U Tanaka
- Wellcome Trust Centre for Gene Regulation & Expression, College of Life Sciences, University of Dundee, Dundee, Scotland.
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98
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99
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Tanaka TU, Desai A. Kinetochore-microtubule interactions: the means to the end. Curr Opin Cell Biol 2008; 20:53-63. [PMID: 18182282 PMCID: PMC2358929 DOI: 10.1016/j.ceb.2007.11.005] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Accepted: 11/26/2007] [Indexed: 01/08/2023]
Abstract
Kinetochores are proteinaceous complexes containing dozens of components; they are assembled at centromeric DNA regions and provide the major microtubule attachment site on chromosomes during cell division. Recent studies have defined the kinetochore components comprising the direct interface with spindle microtubules, primarily through structural and functional analysis of the Ndc80 and Dam1 complexes. These studies have facilitated our understanding of how kinetochores remain attached to the end of dynamic microtubules and how proper orientation of a kinetochore-microtubule attachment is promoted on the mitotic spindle. In this article, we review these recent studies and summarize their key findings.
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Affiliation(s)
- Tomoyuki U Tanaka
- Wellcome Trust Centre for Gene Regulation & Expression, College of Life Sciences, University of Dundee, MSI/WTB/JBC Complex, Dundee, UK.
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100
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Maure JF, Kitamura E, Tanaka TU. Mps1 kinase promotes sister-kinetochore bi-orientation by a tension-dependent mechanism. Curr Biol 2007; 17:2175-82. [PMID: 18060784 PMCID: PMC2515371 DOI: 10.1016/j.cub.2007.11.032] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 11/13/2007] [Accepted: 11/13/2007] [Indexed: 10/26/2022]
Abstract
Segregation of sister chromatids to opposite spindle poles during anaphase is dependent on the prior capture of sister kinetochores by microtubules extending from opposite spindle poles (bi-orientation). If sister kinetochores attach to microtubules from the same pole (syntelic attachment), the kinetochore-spindle pole connections must be re-oriented to be converted to proper bi-orientation. This re-orientation is facilitated by Aurora B kinase (Ipl1 in budding yeast), which eliminates kinetochore-spindle pole connections that do not generate tension. Mps1 is another evolutionarily conserved protein kinase, required for spindle-assembly checkpoint and, in some organisms, for duplication of microtubule-organizing centers. Separately from these functions, however, Mps1 has an important role in chromosome segregation. Here we show that, in budding yeast, Mps1 has a crucial role in establishing sister-kinetochore bi-orientation on the mitotic spindle. Failure in bi-orientation with inactive Mps1 is not due to a lack of kinetochore-spindle pole connections by microtubules, but due to a defect in properly orienting the connections. Mps1 promotes re-orientation of kinetochore-spindle pole connections and eliminates those that do not generate tension between sister kinetochores. We did not find evidence that Ipl1 regulates Mps1 or vice versa; therefore, they play similar, but possibly independent, roles in facilitating bi-orientation.
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Affiliation(s)
- Jean-François Maure
- Wellcome Trust Centre for Gene Regulation & Expression, College of Life Sciences, University of Dundee, MSI/WTB/JBC Complex, Dundee DD1 5EH, UK
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