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Kunchala P, Varberg JM, O'Toole E, Gardner J, Smith SE, McClain M, Jaspersen SL, Hawley RS, Gerton JL. Plasticity of the mitotic spindle in response to karyotype variation. Curr Biol 2024; 34:3416-3428.e4. [PMID: 39043187 PMCID: PMC11333012 DOI: 10.1016/j.cub.2024.06.058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 04/09/2024] [Accepted: 06/24/2024] [Indexed: 07/25/2024]
Abstract
Karyotypes, composed of chromosomes, must be accurately partitioned by the mitotic spindle for optimal cell health. However, it is unknown how underlying characteristics of karyotypes, such as chromosome number and size, govern the scaling of the mitotic spindle to ensure accurate chromosome segregation and cell proliferation. We utilize budding yeast strains engineered with fewer chromosomes, including just two "mega chromosomes," to study how spindle size and function are responsive to, and scaled by, karyotype. We determined that deletion and overexpression of spindle-related genes are detrimental to the growth of strains with two chromosomes, suggesting that mega chromosomes exert altered demands on the spindle. Using confocal microscopy, we demonstrate that cells with fewer but longer chromosomes have smaller spindle pole bodies, fewer microtubules, and longer spindles. Moreover, using electron tomography and confocal imaging, we observe elongated, bent anaphase spindles with fewer core microtubules in strains with mega chromosomes. Cells harboring mega chromosomes grow more slowly, are delayed in mitosis, and a subset struggle to complete chromosome segregation. We propose that the karyotype of the cell dictates the microtubule number, type, spindle pole body size, and spindle length, subsequently influencing the dynamics of mitosis, such as the rate of spindle elongation and the velocity of pole separation. Taken together, our results suggest that mitotic spindles are highly plastic ultrastructures that can accommodate and adjust to a variety of karyotypes, even within a species.
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Affiliation(s)
- Preethi Kunchala
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
| | - Joseph M Varberg
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Eileen O'Toole
- Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, CO 80302, USA
| | - Jennifer Gardner
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Sarah E Smith
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Melainia McClain
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Sue L Jaspersen
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - R Scott Hawley
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Jennifer L Gerton
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
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2
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Cushion TD, Leca I, Keays DA. MAPping tubulin mutations. Front Cell Dev Biol 2023; 11:1136699. [PMID: 36875768 PMCID: PMC9975266 DOI: 10.3389/fcell.2023.1136699] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Accepted: 02/02/2023] [Indexed: 02/17/2023] Open
Abstract
Microtubules are filamentous structures that play a critical role in a diverse array of cellular functions including, mitosis, nuclear translocation, trafficking of organelles and cell shape. They are composed of α/β-tubulin heterodimers which are encoded by a large multigene family that has been implicated in an umbrella of disease states collectively known as the tubulinopathies. De novo mutations in different tubulin genes are known to cause lissencephaly, microcephaly, polymicrogyria, motor neuron disease, and female infertility. The diverse clinical features associated with these maladies have been attributed to the expression pattern of individual tubulin genes, as well as their distinct Functional repertoire. Recent studies, however, have highlighted the impact of tubulin mutations on microtubule-associated proteins (MAPs). MAPs can be classified according to their effect on microtubules and include polymer stabilizers (e.g., tau, MAP2, doublecortin), destabilizers (e.g., spastin, katanin), plus-end binding proteins (e.g., EB1-3, XMAP215, CLASPs) and motor proteins (e.g., dyneins, kinesins). In this review we analyse mutation-specific disease mechanisms that influence MAP binding and their phenotypic consequences, and discuss methods by which we can exploit genetic variation to identify novel MAPs.
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Affiliation(s)
- Thomas D Cushion
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom.,Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria
| | - Ines Leca
- Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria
| | - David A Keays
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom.,Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria.,Division of Neurobiology, Department Biology II, Ludwig-Maximilians-University Munich, Munich, Germany
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3
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Ji M, Sun K, Fang H, Zhuang Z, Chen H, Chen Q, Cao Z, Wang Y, Ditta A, Khan MKR, Wang K, Wang B. Genome-wide identification and characterization of the CLASP_N gene family in upland cotton ( Gossypium hirsutum L.). PeerJ 2022; 10:e12733. [PMID: 35036102 PMCID: PMC8734470 DOI: 10.7717/peerj.12733] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 12/12/2021] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND Cytoplasmic linker-associated proteins (CLASPs) are tubule proteins that can bind to microtubules and participate in regulating the structure and function of microtubules, which significantly affects the development and growth of plants. These proteins have been identified in Arabidopsis; however, little research has been performed in upland cotton. METHODS In this study, the whole genome of the CLASP_N family was analyzed to provide theoretical support for the function of this gene family in the development of upland cotton fiber. Bioinformatics was used to analyze the family characteristics of CLASP_N in upland cotton, such as member identification, sequence characteristics, conserved domain structure and coevolutionary relationships. Real-time fluorescent quantitative PCR (qRT-PCR) was used to clarify the expression pattern of the upland cotton CLASP_N gene family in cotton fiber. RESULTS At the genome-wide level, we identified 16 upland cotton CLASP_N genes. A chromosomal localization analysis revealed that these 16 genes were located on 13 chromosomes. The motif results showed that all CLASP_N proteins have the CLASP_N domain. Gene structure analysis showed that the structure and length of exons and introns were consistent in the subgroups. In the evolutionary analysis with other species, the gene family clearly diverged from the other species in the evolutionary process. A promoter sequence analysis showed that this gene family contains a large number of cis-acting elements related to a variety of plant hormones. qRT-PCR was used to clarify the expression pattern of the upland cotton CLASP_N gene family in cotton fiber and leaves, and Gh210800 was found to be highly expressed in the later stages of fiber development. The results of this study provide a foundation for further research on the molecular role of the CLASP_N genes in cotton fiber development.
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Affiliation(s)
- Meijun Ji
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Kangtai Sun
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Hui Fang
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Zhimin Zhuang
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Haodong Chen
- Cotton Sciences Research Institute of Hunan/ National Hybrid Cotton Research Promotion Center, Changde, Hunan, China
| | - Qi Chen
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Ziyi Cao
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Yiting Wang
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Allah Ditta
- Plant Breeding and Genetics Division, Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan
| | - Muhammad Kashif Riaz Khan
- Plant Breeding and Genetics Division, Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan
| | - Kai Wang
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
| | - Baohua Wang
- School of Life Sciences, Nantong University, Nantong, Jiangsu, China
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4
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Norell S, Ortiz J, Lechner J. Slk19 enhances cross-linking of microtubules by Ase1 and Stu1. Mol Biol Cell 2021; 32:ar22. [PMID: 34495712 PMCID: PMC8693956 DOI: 10.1091/mbc.e21-05-0279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The Saccharomyces cerevisiae protein Slk19 has been shown to localize to kinetochores throughout mitosis and to the spindle midzone in anaphase. However, Slk19 clearly also has an important role for spindle formation and stabilization in prometaphase and metaphase, albeit this role is unresolved. Here we show that Slk19’s localization to metaphase spindles in vivo and to microtubules (MTs) in vitro depends on the MT cross-linking protein Ase1 and the MT cross-linking and stabilizing protein Stu1. By analyzing a slk19 mutant that specifically fails to localize to spindles and MTs, we surprisingly found that the presence of Slk19 amplified the amount of Ase1 strongly and that of Stu1 moderately at the metaphase spindle in vivo and at MTs in vitro. Furthermore, Slk19 markedly enhanced the cross-linking of MTs in vitro when added together with Ase1 or Stu1. We therefore suggest that Slk19 recruits additional Ase1 and Stu1 to the interpolar MTs (ipMTs) of metaphase spindles and thus increases their cross-linking and stabilization. This is in agreement with our observation that cells with defective Slk19 localization exhibit shorter metaphase spindles, an increased number of unaligned nuclear MTs, and most likely reduced ipMT overlaps.
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Affiliation(s)
- Sarina Norell
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120 Heidelberg, Germany
| | - Jennifer Ortiz
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120 Heidelberg, Germany
| | - Johannes Lechner
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120 Heidelberg, Germany
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5
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Hassell DS, Steingesser MG, Denney AS, Johnson CR, McMurray MA. Chemical rescue of mutant proteins in living Saccharomyces cerevisiae cells by naturally occurring small molecules. G3-GENES GENOMES GENETICS 2021; 11:6323229. [PMID: 34544143 PMCID: PMC8496222 DOI: 10.1093/g3journal/jkab252] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 06/29/2021] [Indexed: 11/14/2022]
Abstract
Intracellular proteins function in a complex milieu wherein small molecules influence protein folding and act as essential cofactors for enzymatic reactions. Thus protein function depends not only on amino acid sequence but also on the concentrations of such molecules, which are subject to wide variation between organisms, metabolic states, and environmental conditions. We previously found evidence that exogenous guanidine reverses the phenotypes of specific budding yeast septin mutants by binding to a WT septin at the former site of an Arg side chain that was lost during fungal evolution. Here, we used a combination of targeted and unbiased approaches to look for other cases of "chemical rescue" by naturally occurring small molecules. We report in vivo rescue of hundreds of Saccharomyces cerevisiae mutants representing a variety of genes, including likely examples of Arg or Lys side chain replacement by the guanidinium ion. Failed rescue of targeted mutants highlight features required for rescue, as well as key differences between the in vitro and in vivo environments. Some non-Arg mutants rescued by guanidine likely result from "off-target" effects on specific cellular processes in WT cells. Molecules isosteric to guanidine and known to influence protein folding had a range of effects, from essentially none for urea, to rescue of a few mutants by DMSO. Strikingly, the osmolyte trimethylamine-N-oxide rescued ∼20% of the mutants we tested, likely reflecting combinations of direct and indirect effects on mutant protein function. Our findings illustrate the potential of natural small molecules as therapeutic interventions and drivers of evolution.
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Affiliation(s)
- Daniel S Hassell
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Marc G Steingesser
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Ashley S Denney
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Courtney R Johnson
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Michael A McMurray
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
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6
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How Essential Kinesin-5 Becomes Non-Essential in Fission Yeast: Force Balance and Microtubule Dynamics Matter. Cells 2020; 9:cells9051154. [PMID: 32392819 PMCID: PMC7290485 DOI: 10.3390/cells9051154] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 05/01/2020] [Accepted: 05/04/2020] [Indexed: 12/13/2022] Open
Abstract
The bipolar mitotic spindle drives accurate chromosome segregation by capturing the kinetochore and pulling each set of sister chromatids to the opposite poles. In this review, we describe recent findings on the multiple pathways leading to bipolar spindle formation in fission yeast and discuss these results from a broader perspective. The roles of three mitotic kinesins (Kinesin-5, Kinesin-6 and Kinesin-14) in spindle assembly are depicted, and how a group of microtubule-associated proteins, sister chromatid cohesion and the kinetochore collaborate with these motors is shown. We have paid special attention to the molecular pathways that render otherwise essential Kinesin-5 to become non-essential: how cells build bipolar mitotic spindles without the need for Kinesin-5 and where the alternate forces come from are considered. We highlight the force balance for bipolar spindle assembly and explain how outward and inward forces are generated by various ways, in which the proper fine-tuning of microtubule dynamics plays a crucial role. Overall, these new pathways have illuminated the remarkable plasticity and adaptability of spindle mechanics. Kinesin molecules are regarded as prospective targets for cancer chemotherapy and many specific inhibitors have been developed. However, several hurdles have arisen against their clinical implementation. This review provides insight into possible strategies to overcome these challenges.
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7
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Abstract
CLIP-associating proteins (CLASPs) form an evolutionarily conserved family of regulatory factors that control microtubule dynamics and the organization of microtubule networks. The importance of CLASP activity has been appreciated for some time, but until recently our understanding of the underlying molecular mechanisms remained basic. Over the past few years, studies of, for example, migrating cells, neuronal development, and microtubule reorganization in plants, along with in vitro reconstitutions, have provided new insights into the cellular roles and molecular basis of CLASP activity. In this Cell Science at a Glance article and the accompanying poster, we will summarize some of these recent advances, emphasizing how they impact our current understanding of CLASP-mediated microtubule regulation.
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Affiliation(s)
- Elizabeth J Lawrence
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA
| | - Marija Zanic
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA
- Department of Chemical and Biomolecular Engineering, and Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
| | - Luke M Rice
- Department of Biophysics and Department of Biochemistry, UT Southwestern Medical Center, Dallas, TX 75390, USA
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8
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Varshney N, Som S, Chatterjee S, Sridhar S, Bhattacharyya D, Paul R, Sanyal K. Spatio-temporal regulation of nuclear division by Aurora B kinase Ipl1 in Cryptococcus neoformans. PLoS Genet 2019; 15:e1007959. [PMID: 30763303 PMCID: PMC6392335 DOI: 10.1371/journal.pgen.1007959] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 02/27/2019] [Accepted: 01/11/2019] [Indexed: 11/29/2022] Open
Abstract
The nuclear division takes place in the daughter cell in the basidiomycetous budding yeast Cryptococcus neoformans. Unclustered kinetochores gradually cluster and the nucleus moves to the daughter bud as cells enter mitosis. Here, we show that the evolutionarily conserved Aurora B kinase Ipl1 localizes to the nucleus upon the breakdown of the nuclear envelope during mitosis in C. neoformans. Ipl1 is shown to be required for timely breakdown of the nuclear envelope as well. Ipl1 is essential for viability and regulates structural integrity of microtubules. The compromised stability of cytoplasmic microtubules upon Ipl1 depletion results in a significant delay in kinetochore clustering and nuclear migration. By generating an in silico model of mitosis, we previously proposed that cytoplasmic microtubules and cortical dyneins promote atypical nuclear division in C. neoformans. Improving the previous in silico model by introducing additional parameters, here we predict that an effective cortical bias generated by cytosolic Bim1 and dynein regulates dynamics of kinetochore clustering and nuclear migration. Indeed, in vivo alterations of Bim1 or dynein cellular levels delay nuclear migration. Results from in silico model and localization dynamics by live cell imaging suggests that Ipl1 spatio-temporally influences Bim1 or/and dynein activity along with microtubule stability to ensure timely onset of nuclear division. Together, we propose that the timely breakdown of the nuclear envelope by Ipl1 allows its own nuclear entry that helps in spatio-temporal regulation of nuclear division during semi-open mitosis in C. neoformans. Unlike the model ascomycetous budding yeast Saccharomyces cerevisiae, microtubule organizing centers (MTOCs) coalesce to form the spindle pole body (SPB) in C. neoformans. This process also ensures unclustered kinetochores to gradually cluster in this organism. As C. neoformans cells enter mitosis, the nuclear envelope ruptures and the nucleus eventually moves to the daughter bud before division. Here, we combine cell and systems biology techniques to understand the key determinants of nuclear division in C. neoformans. We show that the evolutionarily conserved Aurora B kinase Ipl1 enters the nucleus during the mitotic phase as cells undergo semi-open mitosis. Ipl1 regulates dynamics of cytoplasmic microtubules, cytosolic proteins such as Bim1 and dynein-mediated cortical forces and integrity of the nuclear envelope to ensure timely kinetochore clustering and nuclear division in this medically relevant human pathogenic budding yeast.
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Affiliation(s)
- Neha Varshney
- Molecular Mycology Laboratory, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, India
| | - Subhendu Som
- Department of Solid State Physics, Indian Association for the Cultivation of Science, Kolkata, India
| | - Saptarshi Chatterjee
- Department of Solid State Physics, Indian Association for the Cultivation of Science, Kolkata, India
| | - Shreyas Sridhar
- Molecular Mycology Laboratory, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, India
| | - Dibyendu Bhattacharyya
- Tata Memorial Centre, Advanced Centre for Treatment Research and Education in Cancer, Kharghar, Navi Mumbai, India
| | - Raja Paul
- Department of Solid State Physics, Indian Association for the Cultivation of Science, Kolkata, India
- * E-mail: (RP); (KS)
| | - Kaustuv Sanyal
- Molecular Mycology Laboratory, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore, India
- * E-mail: (RP); (KS)
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9
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Lawrence EJ, Arpag G, Norris SR, Zanic M. Human CLASP2 specifically regulates microtubule catastrophe and rescue. Mol Biol Cell 2018. [PMID: 29540526 PMCID: PMC5935067 DOI: 10.1091/mbc.e18-01-0016] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Cytoplasmic linker-associated proteins (CLASPs) are microtubule-associated proteins essential for microtubule regulation in many cellular processes. However, the molecular mechanisms underlying CLASP activity are not understood. Here, we use purified protein components and total internal reflection fluorescence microscopy to investigate the effects of human CLASP2 on microtubule dynamics in vitro. We demonstrate that CLASP2 suppresses microtubule catastrophe and promotes rescue without affecting the rates of microtubule growth or shrinkage. Strikingly, when CLASP2 is combined with EB1, a known binding partner, the effects on microtubule dynamics are strongly enhanced. We show that synergy between CLASP2 and EB1 is dependent on a direct interaction, since a truncated EB1 protein that lacks the CLASP2-binding domain does not enhance CLASP2 activity. Further, we find that EB1 targets CLASP2 to microtubules and increases the dwell time of CLASP2 at microtubule tips. Although the temporally averaged microtubule growth rates are unaffected by CLASP2, we find that microtubules grown with CLASP2 display greater variability in growth rates. Our results provide insight into the regulation of microtubule dynamics by CLASP proteins and highlight the importance of the functional interplay between regulatory proteins at dynamic microtubule ends.
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Affiliation(s)
- Elizabeth J Lawrence
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240
| | - Göker Arpag
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240
| | - Stephen R Norris
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240
| | - Marija Zanic
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240.,Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37240.,Department of Biochemistry, Vanderbilt University, Nashville, TN 37240
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10
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Kolenda C, Ortiz J, Pelzl M, Norell S, Schmeiser V, Lechner J. Unattached kinetochores drive their own capturing by sequestering a CLASP. Nat Commun 2018; 9:886. [PMID: 29491436 PMCID: PMC5830412 DOI: 10.1038/s41467-018-03108-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 01/17/2018] [Indexed: 12/24/2022] Open
Abstract
Kinetochores that are not attached to microtubules prevent chromosome missegregation via the spindle assembly checkpoint. We show that they also promote their own capturing. Similar to what governs the localization of spindle assembly checkpoint proteins, the phosphorylation of Spc105 by Mps1 allows unattached kinetochores to sequester Stu1 in cooperation with Slk19. The withdrawal of Stu1, a CLASP essential for spindle integrity, from microtubules and attached kinetochores disrupts the organization of the spindle and thus allows the enhanced formation of dynamic random microtubules that span the nucleus and are ideal to capture unattached kinetochores. The enhanced formation of nuclear random microtubules does not occur if Stu1 sequestering to unattached kinetochores fails and the spindle remains uncompromised. Consequently, these cells exhibit a severely decreased capturing efficiency. After the capturing event, Stu1 is relocated to the capturing microtubule and prevents precocious microtubule depolymerization as long as kinetochores are laterally or incompletely end-on attached. Kinetochores (KT) that are not attached to microtubules prevent chromosome missegregation via the spindle assembly checkpoint. Here the authors show that Mps1 localizes Stu1 at unattached KTs together with Slk19, causing a reorganization of the nuclear MT network that favors the capturing of unattached KT.
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Affiliation(s)
- Caroline Kolenda
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120, Heidelberg, Germany
| | - Jennifer Ortiz
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120, Heidelberg, Germany
| | - Marina Pelzl
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120, Heidelberg, Germany
| | - Sarina Norell
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120, Heidelberg, Germany
| | - Verena Schmeiser
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120, Heidelberg, Germany
| | - Johannes Lechner
- Biochemie-Zentrum der Universität Heidelberg, INF 328, 69120, Heidelberg, Germany.
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11
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Vasileva V, Gierlinski M, Yue Z, O'Reilly N, Kitamura E, Tanaka TU. Molecular mechanisms facilitating the initial kinetochore encounter with spindle microtubules. J Cell Biol 2017; 216:1609-1622. [PMID: 28446512 PMCID: PMC5461016 DOI: 10.1083/jcb.201608122] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 02/15/2017] [Accepted: 04/03/2017] [Indexed: 12/11/2022] Open
Abstract
The initial kinetochore (KT) encounter with a spindle microtubule (MT) is one of the rate-limiting steps in establishing proper KT–MT interaction during mitosis. This study reveals how multiple factors cooperate to facilitate the KT encounter with a spindle MT. In particular, it highlights the important roles of KT-derived MTs in this process. The initial kinetochore (KT) encounter with a spindle microtubule (MT; KT capture) is one of the rate-limiting steps in establishing proper KT–MT interaction during mitosis. KT capture is facilitated by multiple factors, such as MT extension in various directions, KT diffusion, and MT pivoting. In addition, KTs generate short MTs, which subsequently interact with a spindle MT. KT-derived MTs may facilitate KT capture, but their contribution is elusive. In this study, we find that Stu1 recruits Stu2 to budding yeast KTs, which promotes MT generation there. By removing Stu2 specifically from KTs, we show that KT-derived MTs shorten the half-life of noncaptured KTs from 48–49 s to 28–34 s. Using computational simulation, we found that multiple factors facilitate KT capture redundantly or synergistically. In particular, KT-derived MTs play important roles both by making a significant contribution on their own and by synergistically enhancing the effects of KT diffusion and MT pivoting. Our study reveals fundamental mechanisms facilitating the initial KT encounter with spindle MTs.
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Affiliation(s)
- Vanya Vasileva
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Marek Gierlinski
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK.,Data Analysis Group, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Zuojun Yue
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Nicola O'Reilly
- Lincoln's Inn Fields Laboratory, The Francis Crick Institute, London WC2A 3LY, England, UK
| | - Etsushi Kitamura
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Tomoyuki U Tanaka
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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12
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Prajapati HK, Rizvi SMA, Rathore I, Ghosh SK. Microtubule-associated proteins, Bik1 and Bim1, are required for faithful partitioning of the endogenous 2 micron plasmids in budding yeast. Mol Microbiol 2017; 103:1046-1064. [PMID: 28004422 DOI: 10.1111/mmi.13608] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/13/2016] [Indexed: 12/01/2022]
Abstract
The 2 μ plasmid of budding yeast shows high mitotic stability similar to that of chromosomes by using its self-encoded systems, namely partitioning and amplification. The partitioning system consists of the plasmid-borne proteins Rep1, Rep2 and a cis-acting locus STB that, along with several host factors, ensures efficient segregation of the plasmid. The plasmids show high stability as they presumably co-segregate with chromosomes through utilization of various host factors. To acquire these host factors, the plasmids are thought to localize to a certain sub-nuclear locale probably assisted by the motor protein, Kip1 and microtubules. Here, we show that the microtubule-associated proteins Bik1 and Bim1 are also important host factors in this process, perhaps by acting as an adapter between the plasmid and the motor and thus helping to anchor the plasmid to microtubules. Abrogation of Kip1 recruitment at STB in the absence of Bik1 argues for its function at STB upstream of Kip1. Consistent with this, both Bik1 and Bim1 associate with plasmids without any assistance from the Rep proteins. As observed earlier with other host factors, lack of Bik1 or Bim1 also causes a cohesion defect between sister plasmids leading to plasmid missegregation.
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Affiliation(s)
- Hemant Kumar Prajapati
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India
| | - Syed Meraj Azhar Rizvi
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India
| | - Ishan Rathore
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India
| | - Santanu K Ghosh
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India
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13
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Fraschini R. Factors that Control Mitotic Spindle Dynamics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 925:89-101. [PMID: 27722958 DOI: 10.1007/5584_2016_74] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Mitosis is the last phase of the cell cycle and it leads to the formation of two daughter cells with the same genetic information. This process must occurr in a very precise way and this task is essential to preserve genetic stability and to maintain cell viability. Accurate chromosome segregation during mitosis is brought about by an important cellular organelle: the mitotic spindle. This structure is made of microtubules, polymers of alpha and beta tubulin, and it is highly dynamic during the cell cycle: it emanates from two microtubules organizing centers (Spindle Pole Bodies, SPBs, in yeast) that are essential to build a short bipolar spindle, and it undergoes two steps of elongation during anaphase A and anaphase B in order to separate sister chromatids. Several proteins are involved in the control of mitotic spindle dynamics and their activity is tightly coordinated with other cell cycle events and with cell cycle progression.
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Affiliation(s)
- Roberta Fraschini
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Piazza della Scienza 2, 20126, Milan, Italy.
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14
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Funk C, Schmeiser V, Ortiz J, Lechner J. A TOGL domain specifically targets yeast CLASP to kinetochores to stabilize kinetochore microtubules. ACTA ACUST UNITED AC 2014; 205:555-71. [PMID: 24862575 PMCID: PMC4033772 DOI: 10.1083/jcb.201310018] [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] [Indexed: 01/05/2023]
Abstract
The two different TOGL domains of the budding yeast CLASP Stu1 are responsible for its distinct mitotic activities, and these activities are only partially mediated by tight microtubule binding. Cytoplasmic linker–associated proteins (CLASPs) are proposed to function in cell division based on their ability to bind tubulin via arrayed tumor overexpressed gene (TOG)–like (TOGL) domains. Structure predictions suggest that CLASPs have at least two TOGL domains. We show that only TOGL2 of Saccharomyces cerevisiae CLASP Stu1 binds to tubulin and is required for polymerization of spindle microtubules (MTs) in vivo. In contrast, TOGL1 recruits Stu1 to kinetochores (KTs), where it is essential for the stability and tension-dependent regulation of KT MTs. Stu1 is also recruited to spindle MTs by different mechanisms depending on the mitotic phase: in metaphase, Stu1 binds directly to the MT lattice, whereas in anaphase, it is localized indirectly to the spindle midzone. In both phases, the activity of TOGL2 is essential for interpolar MT stability, whereas TOGL1 is not involved. Thus, the two TOGL domains of yeast CLASP have different activities and execute distinct mitotic functions.
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Affiliation(s)
- Caroline Funk
- Biochemie-Zentrum der Universität Heidelberg, 69120 Heidelberg, Germany
| | - Verena Schmeiser
- Biochemie-Zentrum der Universität Heidelberg, 69120 Heidelberg, Germany
| | - Jennifer Ortiz
- Biochemie-Zentrum der Universität Heidelberg, 69120 Heidelberg, Germany
| | - Johannes Lechner
- Biochemie-Zentrum der Universität Heidelberg, 69120 Heidelberg, Germany
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15
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Leano JB, Rogers SL, Slep KC. A cryptic TOG domain with a distinct architecture underlies CLASP-dependent bipolar spindle formation. Structure 2014; 21:939-50. [PMID: 23727231 DOI: 10.1016/j.str.2013.04.018] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 04/08/2013] [Accepted: 04/18/2013] [Indexed: 01/29/2023]
Abstract
CLASP is a key regulator of microtubule (MT) dynamics and bipolar mitotic spindle structure with CLASP mutants displaying a distinctive monopolar spindle phenotype. It has been postulated that cryptic TOG domains underlie CLASP’s ability to regulate MT dynamics. Here, we report the crystal structure of a cryptic TOG domain (TOG2) from human CLASP1, demonstrating the presence of a TOG array in the CLASP family. Strikingly, CLASP1 TOG2 exhibits a convex architecture across the tubulin-binding surface that contrasts with the flat tubulin-binding surface of XMAP215 family TOG domains. Mutations in key conserved TOG2 determinants abrogate the ability of CLASP mutants to rescue bipolar spindle formation in Drosophila cells depleted of endogenous CLASP. These findings highlight the common mechanistic use of TOG domains in XMAP215 and CLASP families to regulate MT dynamics and suggest that differential TOG domain architecture may confer distinct functions to these critical cytoskeletal regulators.
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Affiliation(s)
- Jonathan B Leano
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
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16
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Abstract
The Saccharomyces cerevisiae mitotic spindle in budding yeast is exemplified by its simplicity and elegance. Microtubules are nucleated from a crystalline array of proteins organized in the nuclear envelope, known as the spindle pole body in yeast (analogous to the centrosome in larger eukaryotes). The spindle has two classes of nuclear microtubules: kinetochore microtubules and interpolar microtubules. One kinetochore microtubule attaches to a single centromere on each chromosome, while approximately four interpolar microtubules emanate from each pole and interdigitate with interpolar microtubules from the opposite spindle to provide stability to the bipolar spindle. On the cytoplasmic face, two to three microtubules extend from the spindle pole toward the cell cortex. Processes requiring microtubule function are limited to spindles in mitosis and to spindle orientation and nuclear positioning in the cytoplasm. Microtubule function is regulated in large part via products of the 6 kinesin gene family and the 1 cytoplasmic dynein gene. A single bipolar kinesin (Cin8, class Kin-5), together with a depolymerase (Kip3, class Kin-8) or minus-end-directed kinesin (Kar3, class Kin-14), can support spindle function and cell viability. The remarkable feature of yeast cells is that they can survive with microtubules and genes for just two motor proteins, thus providing an unparalleled system to dissect microtubule and motor function within the spindle machine.
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17
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Woodruff JB, Drubin DG, Barnes G. Mitotic spindle disassembly occurs via distinct subprocesses driven by the anaphase-promoting complex, Aurora B kinase, and kinesin-8. ACTA ACUST UNITED AC 2011; 191:795-808. [PMID: 21079246 PMCID: PMC2983061 DOI: 10.1083/jcb.201006028] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A large-scale analysis of spindle disassembly in budding yeast identifies factors required for disengagement of spindle halves, arrest of spindle elongation, and depolymerization of interpolar microtubules. The mitotic spindle is a complex and dynamic structure. Although much has been learned about how spindles assemble and mediate chromosome segregation, how spindles rapidly and irreversibly disassemble during telophase is less clear. We used synthetic lethal screens in budding yeast to identify mutants defective in spindle disassembly. Real-time, live cell imaging analysis of spindle disassembly was performed on nine mutants defective in this process. Results of this analysis suggest that spindle disassembly is achieved by mechanistically distinct but functionally overlapping subprocesses: disengagement of the spindle halves, arrest of spindle elongation, and initiation of interpolar microtubule depolymerization. These subprocesses are largely governed by the anaphase-promoting complex, Aurora B kinase, and kinesin-8. Combinatorial inhibition of these subprocesses yielded cells with hyperstable spindle remnants and dramatic defects in cell cycle progression, establishing that rapid spindle disassembly is crucial for cell proliferation.
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Affiliation(s)
- Jeffrey B Woodruff
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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18
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Al-Bassam J, Kim H, Brouhard G, van Oijen A, Harrison SC, Chang F. CLASP promotes microtubule rescue by recruiting tubulin dimers to the microtubule. Dev Cell 2010; 19:245-58. [PMID: 20708587 DOI: 10.1016/j.devcel.2010.07.016] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 04/12/2010] [Accepted: 06/30/2010] [Indexed: 10/19/2022]
Abstract
Spatial regulation of microtubule (MT) dynamics contributes to cell polarity and cell division. MT rescue, in which a MT stops shrinking and reinitiates growth, is the least understood aspect of MT dynamics. Cytoplasmic Linker Associated Proteins (CLASPs) are a conserved class of MT-associated proteins that contribute to MT stabilization and rescue in vivo. We show here that the Schizosaccharomyces pombe CLASP, Cls1p, is a homodimer that binds an alphabeta-tubulin heterodimer through conserved TOG-like domains. In vitro, CLASP increases MT rescue frequency, decreases MT catastrophe frequency, and moderately decreases MT disassembly rate. CLASP binds stably to the MT lattice, recruits tubulin, and locally promotes rescues. Mutations in the CLASP TOG domains demonstrate that tubulin binding is critical for its rescue activity. We propose a mechanism for rescue in which CLASP-tubulin dimer complexes bind along the MT lattice and reverse MT depolymerization with their bound tubulin dimer.
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Affiliation(s)
- Jawdat Al-Bassam
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
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19
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Gouveia SM, Akhmanova A. Cell and Molecular Biology of Microtubule Plus End Tracking Proteins. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2010; 285:1-74. [DOI: 10.1016/b978-0-12-381047-2.00001-3] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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20
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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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21
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Chiroli E, Rancati G, Catusi I, Lucchini G, Piatti S. Cdc14 inhibition by the spindle assembly checkpoint prevents unscheduled centrosome separation in budding yeast. Mol Biol Cell 2009; 20:2626-37. [PMID: 19339280 DOI: 10.1091/mbc.e08-11-1150] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The spindle assembly checkpoint (SAC) is an evolutionarily conserved surveillance mechanism that delays anaphase onset and mitotic exit in response to the lack of kinetochore attachment. The target of the SAC is the E3 ubiquitin ligase anaphase-promoting complex (APC) bound to its Cdc20 activator. The Cdc20/APC complex is in turn required for sister chromatid separation and mitotic exit through ubiquitin-mediated proteolysis of securin, thus relieving inhibition of separase that unties sister chromatids. Separase is also involved in the Cdc-fourteen early anaphase release (FEAR) pathway of nucleolar release and activation of the Cdc14 phosphatase, which regulates several microtubule-linked processes at the metaphase/anaphase transition and also drives mitotic exit. Here, we report that the SAC prevents separation of microtubule-organizing centers (spindle pole bodies [SPBs]) when spindle assembly is defective. Under these circumstances, failure of SAC activation causes unscheduled SPB separation, which requires Cdc20/APC, the FEAR pathway, cytoplasmic dynein, and the actin cytoskeleton. We propose that, besides inhibiting sister chromatid separation, the SAC preserves the accurate transmission of chromosomes also by preventing SPBs to migrate far apart until the conditions to assemble a bipolar spindle are satisfied.
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Affiliation(s)
- Elena Chiroli
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, 20126 Milan, Italy
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22
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Bratman SV, Chang F. Mechanisms for maintaining microtubule bundles. Trends Cell Biol 2008; 18:580-6. [PMID: 18951798 DOI: 10.1016/j.tcb.2008.09.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 09/04/2008] [Accepted: 09/05/2008] [Indexed: 10/21/2022]
Abstract
The dynamics of microtubules (MTs) are crucial to many of their functions. Certain MT structures, such as the mitotic spindle apparatus, exhibit high MT turnover yet maintain their mass stably through long periods of time. Here, we highlight what are emerging as two important mechanisms for maintaining MT bundles: the first, MT nucleation from pre-existing MTs by means of gamma-tubulin-containing complexes; and the second, MT 'rescue' by the stabilizing protein CLASP. As examples, we describe recent advances in understanding the assembly and maintenance of simple MT bundles in fission yeast and plant cells, which have implications for the bundles of the animal mitotic spindle.
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Affiliation(s)
- Scott V Bratman
- Microbiology Department, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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23
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Bannigan A, Lizotte-Waniewski M, Riley M, Baskin TI. Emerging molecular mechanisms that power and regulate the anastral mitotic spindle of flowering plants. ACTA ACUST UNITED AC 2008; 65:1-11. [PMID: 17968986 DOI: 10.1002/cm.20247] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Flowering plants, lacking centrosomes as well as dynein, assemble their mitotic spindle via a pathway that is distinct visually and molecularly from that of animals and yeast. The molecular components underlying mitotic spindle assembly and function in plants are beginning to be discovered. Here, we review recent evidence suggesting the preprophase band in plants functions analogously to the centrosome in animals in establishing spindle bipolarity, and we review recent progress characterizing the roles of specific motor proteins in plant mitosis. Loss of function of certain minus-end-directed KIN-14 motor proteins causes a broadening of the spindle pole; whereas, loss of function of a KIN-5 causes the formation of monopolar spindles, resembling those formed when the homologous motor protein (e.g., Eg5) is knocked out in animal cells. We present a phylogeny of the kinesin-5 motor domain, which shows deep divergence among plant sequences, highlighting possibilities for specialization. Finally, we review information concerning the roles of selected structural proteins at mitosis as well as recent findings concerning regulation of M-phase in plants. Insight into the mitotic spindle will be obtained through continued comparison of mitotic mechanisms in a diversity of cells.
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Affiliation(s)
- Alex Bannigan
- Biology Department, University of Massachusetts, Amherst, Massachusetts 01003, USA
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24
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The Saccharomyces cerevisiae homolog of p24 is essential for maintaining the association of p150Glued with the dynactin complex. Genetics 2008; 178:703-9. [PMID: 18245366 DOI: 10.1534/genetics.107.079103] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Stu1 is the Saccharomyces cerevisiae member of the CLASP family of microtubule plus-end tracking proteins and is essential for spindle formation. A genomewide screen for gene deletions that are lethal in combination with the temperature-sensitive stu1-5 allele identified ldb18Delta. ldb18Delta cells exhibit defects in spindle orientation similar to those caused by a block in the dynein pathway. Consistent with this observation, ldb18Delta is synthetic lethal with mutations affecting the Kar9 spindle orientation pathway, but not with those affecting the dynein pathway. We show that Ldb18 is a component of dynactin, a complex required for dynein activity in yeast and mammalian cells. Ldb18 shares modest sequence and structural homology with the mammalian dynactin component p24. It interacts with dynactin proteins in two-hybrid and co-immunoprecipitation assays, and comigrates with them as a 20 S complex during sucrose gradient sedimentation. In ldb18Delta cells, the interaction between Nip100 (p150(Glued)) and Jnm1 (dynamitin) is disrupted, while the interaction between Jnm1 and Arp1 is not affected. These results indicate that p24 is required for attachment of the p150(Glued) arm to dynamitin and the remainder of the dynactin complex. The genetic interaction of ldb18Delta with stu1-5 also supports the notion that dynein/dynactin helps to generate a spindle pole separating force.
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25
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Bratman SV, Chang F. Stabilization of overlapping microtubules by fission yeast CLASP. Dev Cell 2008; 13:812-27. [PMID: 18061564 DOI: 10.1016/j.devcel.2007.10.015] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Revised: 08/10/2007] [Accepted: 10/29/2007] [Indexed: 10/22/2022]
Abstract
Many microtubule (MT) structures contain dynamic MTs that are bundled and stabilized in overlapping arrays. CLASPs are conserved MT-binding proteins implicated in the regulation of MT plus ends. Here, we show that the Schizosaccharomyces pombe CLASP, cls1p/peg1p, mediates the stabilization of overlapping MTs within the mitotic spindle and interphase bundles. cls1p localizes to these regions but not to interphase MT plus ends. Inactivation of cls1p leads to the rapid depolymerization of spindle midzone MTs. cls1p also stabilizes a subset of MTs within interphase bundles. cls1p prevents disassembly of the entire microtubule, while still allowing for plus-end growth. It has no measurable effects on MT nucleation, polymerization, catastrophe, or bundling. A direct interaction with ase1p (PRC1/MAP65) targets cls1p to regions of antiparallel MT overlap. These findings show how a MT-stabilizing factor attached to specific sites on MTs can help to generate MT structures that have both dynamic and stable components.
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Affiliation(s)
- Scott V Bratman
- Microbiology Department, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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26
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Tanaka TU, Stark MJR, Tanaka K. Kinetochore capture and bi-orientation on the mitotic spindle. Nat Rev Mol Cell Biol 2007; 6:929-42. [PMID: 16341079 DOI: 10.1038/nrm1764] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Kinetochores are large protein complexes that are formed on chromosome regions known as centromeres. For high-fidelity chromosome segregation, kinetochores must be correctly captured on the mitotic spindle before anaphase onset. During prometaphase, kinetochores are initially captured by a single microtubule that extends from a spindle pole and are then transported poleward along the microtubule. 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 - this is known as bi-orientation. Here we discuss the molecular mechanisms of these processes, by focusing on budding yeast and drawing comparisons with other organisms.
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Affiliation(s)
- Tomoyuki U Tanaka
- School of Life Sciences, University of Dundee, Wellcome Trust Biocentre, Dow Street, Dundee, DD1 5EH, UK.
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27
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Tsvetkov AS, Samsonov A, Akhmanova A, Galjart N, Popov SV. Microtubule-binding proteins CLASP1 and CLASP2 interact with actin filaments. ACTA ACUST UNITED AC 2007; 64:519-30. [PMID: 17342765 DOI: 10.1002/cm.20201] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Cell morphogenesis requires dynamic communication between actin filaments and microtubules which is mediated, at least in part, by direct structural links between the two cytoskeletal systems. Here, we examined interaction between the CLIP-associated proteins (CLASP) CLASP1 and CLASP2, and actin filaments. We demonstrate that, in addition to a well-established association with the distal ends of microtubules, CLASP2alpha co-localizes with stress fibers, and that both CLASP1alpha and CLASP2alpha co-immunoprecipitate with actin. GFP-CLASP2alpha exhibits retrograde flow in the lamellipodia of Xenopus primary fibroblasts and in the filopodia of Xenopus spinal cord neurons. A deletion mapping analysis reveals that both the microtubule-binding domain of CLASP2 (which is homologous between all CLASPs) and the N-terminal dis1/TOG domain of CLASP2alpha (which is homologous between alpha isoforms) possess actin-binding activity. Fluorescence resonance energy transfer experiments demonstrate significant energy transfer between YFP-CLASP2alpha and CFP-actin. Our results indicate that CLASPs function as actin/microtubule crosslinkers in interphase cells. We propose that CLASPs facilitate recognition of actin filaments by the plus ends of growing microtubules at the initial stages of actin-microtubule interaction. Cell Motil.
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Affiliation(s)
- Andrey S Tsvetkov
- Department of Physiology and Biophysics M/C 901, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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28
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Khmelinskii A, Lawrence C, Roostalu J, Schiebel E. Cdc14-regulated midzone assembly controls anaphase B. ACTA ACUST UNITED AC 2007; 177:981-93. [PMID: 17562791 PMCID: PMC2064359 DOI: 10.1083/jcb.200702145] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Spindle elongation in anaphase of mitosis is a cell cycle–regulated process that requires coordination between polymerization, cross-linking, and sliding of microtubules (MTs). Proteins that assemble at the spindle midzone may be important for this process. In this study, we show that Ase1 and the separase–Slk19 complex drive midzone assembly in yeast. Whereas the conserved MT-bundling protein Ase1 establishes a midzone, separase–Slk19 is required to focus and center midzone components. An important step leading to spindle midzone assembly is the dephosphorylation of Ase1 by the protein phosphatase Cdc14 at the beginning of anaphase. Failure to dephosphorylate Ase1 delocalizes midzone proteins and delays the second, slower phase of anaphase B. In contrast, in cells expressing nonphosphorylated Ase1, anaphase spindle extension is faster, and spindles frequently break. Cdc14 also controls the separase–Slk19 complex indirectly via the Aurora B kinase. Thus, Cdc14 regulates spindle midzone assembly and function directly through Ase1 and indirectly via the separase–Slk19 complex.
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Affiliation(s)
- Anton Khmelinskii
- Zentrum für Molekulare Biologie der Universität Heidelberg, 69120 Heidelberg, Germany
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29
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Ma L, McQueen J, Cuschieri L, Vogel J, Measday V. Spc24 and Stu2 promote spindle integrity when DNA replication is stalled. Mol Biol Cell 2007; 18:2805-16. [PMID: 17507656 PMCID: PMC1949354 DOI: 10.1091/mbc.e06-09-0882] [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: 12/22/2022] Open
Abstract
The kinetochore, a protein complex that links chromosomes to microtubules (MTs), is required to prevent spindle expansion during S phase in budding yeast, but the mechanism of how the kinetochore maintains integrity of the bipolar spindle before mitosis is not well understood. Here, we demonstrate that a mutation of Spc24, a component of the conserved Ndc80 kinetochore complex, causes lethality when cells are exposed to the DNA replication inhibitor hydroxyurea (HU) due to premature spindle expansion and segregation of incompletely replicated DNA. Overexpression of Stu1, a CLASP-related MT-associated protein or a truncated form of the XMAP215 orthologue Stu2 rescues spc24-9 HU lethality and prevents spindle expansion. Truncated Stu2 likely acts in a dominant-negative manner, because overexpression of full-length STU2 does not rescue spc24-9 HU lethality, and spindle expansion in spc24-9 HU-treated cells requires active Stu2. Stu1 and Stu2 localize to the kinetochore early in the cell cycle and Stu2 kinetochore localization depends on Spc24. We propose that mislocalization of Stu2 results in premature spindle expansion in S phase stalled spc24-9 mutants. Identifying factors that restrain spindle expansion upon inhibition of DNA replication is likely applicable to the mechanism by which spindle elongation is regulated during a normal cell cycle.
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Affiliation(s)
- Lina Ma
- *Genetics Graduate Program and
- Wine Research Centre/Michael Smith Laboratories, Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada; and
| | - Jennifer McQueen
- *Genetics Graduate Program and
- Wine Research Centre/Michael Smith Laboratories, Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada; and
| | | | - Jackie Vogel
- Department of Biology and
- Developmental Biology Research Initiative, McGill University, Montreal, QC, H3A 1B1 Canada
| | - Vivien Measday
- Wine Research Centre/Michael Smith Laboratories, Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada; and
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30
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Mimori-Kiyosue Y, Grigoriev I, Sasaki H, Matsui C, Akhmanova A, Tsukita S, Vorobjev I. Mammalian CLASPs are required for mitotic spindle organization and kinetochore alignment. Genes Cells 2006; 11:845-57. [PMID: 16866869 DOI: 10.1111/j.1365-2443.2006.00990.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
CLASP1 and CLASP2 are homologous mammalian proteins, which associate with the ends of growing microtubules, as well as the cell cortex and the kinetochores of mitotic chromosomes. Previous studies have shown that in interphase cells CLASPs can attach microtubule plus ends to the cortex and stabilize them by repeatedly rescuing them from depolymerization. Here we show that CLASP1 and 2 play similar and redundant roles in organizing the mitotic apparatus in HeLa cells. Simultaneous depletion of both CLASPs causes mitotic spindle defects and a significant metaphase delay, which often results in abnormal exit from mitosis. Metaphase delay is associated with decreased kinetochore tension, increased kinetochore oscillations and more rapid microtubule growth. We show that the association of CLASP2 with the kinetochores relies on its C-terminal domain, but is independent of microtubules or association with CLIP-170. We propose that CLASPs exhibit at the kinetochores an activity similar to that at the cortex, providing apparent stabilization of microtubules by locally reducing the amplitude of growth/shortening episodes at the microtubule ends. This local stabilization of microtubules is essential for the formation of normal metaphase spindle, completion of anaphase and cytokinesis.
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31
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Wittmann T, Waterman-Storer CM. Spatial regulation of CLASP affinity for microtubules by Rac1 and GSK3beta in migrating epithelial cells. ACTA ACUST UNITED AC 2005; 169:929-39. [PMID: 15955847 PMCID: PMC2171640 DOI: 10.1083/jcb.200412114] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Proteins that in cells specifically bind to growing microtubule plus ends (+TIPs) are thought to play important roles in polarization of the cytoskeleton. However, most +TIPs do not show a bias of their microtubule-binding behavior toward different subcellular regions. Here, we examine the dynamics of the +TIP CLASP in migrating PtK1 epithelial cells. We find that, although CLASPs track microtubule plus ends in the cell body, they dynamically decorate the entire microtubule lattice in the leading edge lamella and lamellipodium. Microtubule lattice binding is mediated by the COOH-terminal region of the CLASP microtubule-binding domain and is regulated downstream of Rac1. Phosphorylation of sites in the NH2-terminal part of the microtubule-binding domain by glycogen synthase kinase 3beta likely regulates the affinity of CLASPs for microtubule lattices. These results demonstrate the striking difference of the microtubule cytoskeleton in the lamella as compared with the cell body and provide the first direct observation of subcellular regulation of a microtubule-associated protein in migrating cells.
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Affiliation(s)
- Torsten Wittmann
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
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Maiato H, DeLuca J, Salmon ED, Earnshaw WC. The dynamic kinetochore-microtubule interface. J Cell Sci 2005; 117:5461-77. [PMID: 15509863 DOI: 10.1242/jcs.01536] [Citation(s) in RCA: 282] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The kinetochore is a control module that both powers and regulates chromosome segregation in mitosis and meiosis. The kinetochore-microtubule interface is remarkably fluid, with the microtubules growing and shrinking at their point of attachment to the kinetochore. Furthermore, the kinetochore itself is highly dynamic, its makeup changing as cells enter mitosis and as it encounters microtubules. Active kinetochores have yet to be isolated or reconstituted, and so the structure remains enigmatic. Nonetheless, recent advances in genetic, bioinformatic and imaging technology mean we are now beginning to understand how kinetochores assemble, bind to microtubules and release them when the connections made are inappropriate, and also how they influence microtubule behaviour. Recent work has begun to elucidate a pathway of kinetochore assembly in animal cells; the work has revealed that many kinetochore components are highly dynamic and that some cycle between kinetochores and spindle poles along microtubules. Further studies of the kinetochore-microtubule interface are illuminating: (1) the role of the Ndc80 complex and components of the Ran-GTPase system in microtubule attachment, force generation and microtubule-dependent inactivation of kinetochore spindle checkpoint activity; (2) the role of chromosomal passenger proteins in the correction of kinetochore attachment errors; and (3) the function of microtubule plus-end tracking proteins, motor depolymerases and other proteins in kinetochore movement on microtubules and movement coupled to microtubule poleward flux.
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Affiliation(s)
- Helder Maiato
- Laboratory of Cell Regulation, NYSDH-Division of Molecular Medicine, Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY 12201-0509, USA
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Mimori-Kiyosue Y, Grigoriev I, Lansbergen G, Sasaki H, Matsui C, Severin F, Galjart N, Grosveld F, Vorobjev I, Tsukita S, Akhmanova A. CLASP1 and CLASP2 bind to EB1 and regulate microtubule plus-end dynamics at the cell cortex. ACTA ACUST UNITED AC 2005; 168:141-53. [PMID: 15631994 PMCID: PMC2171674 DOI: 10.1083/jcb.200405094] [Citation(s) in RCA: 320] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
CLIP-associating protein (CLASP) 1 and CLASP2 are mammalian microtubule (MT) plus-end binding proteins, which associate with CLIP-170 and CLIP-115. Using RNA interference in HeLa cells, we show that the two CLASPs play redundant roles in regulating the density, length distribution and stability of interphase MTs. In HeLa cells, both CLASPs concentrate on the distal MT ends in a narrow region at the cell margin. CLASPs stabilize MTs by promoting pauses and restricting MT growth and shortening episodes to this peripheral cell region. We demonstrate that the middle part of CLASPs binds directly to EB1 and to MTs. Furthermore, we show that the association of CLASP2 with the cell cortex is MT independent and relies on its COOH-terminal domain. Both EB1- and cortex-binding domains of CLASP are required to promote MT stability. We propose that CLASPs can mediate interactions between MT plus ends and the cell cortex and act as local rescue factors, possibly through forming a complex with EB1 at MT tips.
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Affiliation(s)
- Yuko Mimori-Kiyosue
- KAN Research Institute, Kyoto Research Park, Shimogyo-ku, Kyoto 600-8815, Japan
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Higuchi T, Uhlmann F. Stabilization of microtubule dynamics at anaphase onset promotes chromosome segregation. Nature 2005; 433:171-6. [PMID: 15650742 PMCID: PMC2586334 DOI: 10.1038/nature03240] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2004] [Accepted: 11/29/2004] [Indexed: 11/09/2022]
Abstract
Microtubules of the mitotic spindle form the structural basis for chromosome segregation. In metaphase, microtubules show high dynamic instability, which is thought to aid the 'search and capture' of chromosomes for bipolar alignment on the spindle. Microtubules suddenly become more stable at the onset of anaphase, but how this change in microtubule behaviour is regulated and how important it is for the ensuing chromosome segregation are unknown. Here we show that in the budding yeast Saccharomyces cerevisiae, activation of the phosphatase Cdc14 at anaphase onset is both necessary and sufficient for silencing microtubule dynamics. Cdc14 is activated by separase, the protease that triggers sister chromatid separation, linking the onset of anaphase to microtubule stabilization. If sister chromatids separate in the absence of Cdc14 activity, microtubules maintain high dynamic instability; this correlates with defects in both the movement of chromosomes to the spindle poles (anaphase A) and the elongation of the anaphase spindle (anaphase B). Cdc14 promotes localization of microtubule-stabilizing proteins to the anaphase spindle, and dephosphorylation of the kinetochore component Ask1 contributes to both the silencing of microtubule turnover and successful anaphase A.
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Affiliation(s)
- Toru Higuchi
- Chromosome Segregation Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, 44 Lincoln's Inn Fields, London WC2A 3PX, UK
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Maiato H, Sampaio P, Sunkel CE. Microtubule-associated proteins and their essential roles during mitosis. ACTA ACUST UNITED AC 2005; 241:53-153. [PMID: 15548419 DOI: 10.1016/s0074-7696(04)41002-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Microtubules play essential roles during mitosis, including chromosome capture, congression, and segregation. In addition, microtubules are also required for successful cytokinesis. At the heart of these processes is the ability of microtubules to do work, a property that derives from their intrinsic dynamic behavior. However, if microtubule dynamics were not properly regulated, it is certain that microtubules alone could not accomplish any of these tasks. In vivo, the regulation of microtubule dynamics is the responsibility of microtubule-associated proteins. Among these, we can distinguish several classes according to their function: (1) promotion and stabilization of microtubule polymerization, (2) destabilization or severance of microtubules, (3) functioning as linkers between various structures, or (4) motility-related functions. Here we discuss how the various properties of microtubule-associated proteins can be used to assemble an efficient mitotic apparatus capable of ensuring the bona fide transmission of the genetic information in animal cells.
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Affiliation(s)
- Hélder Maiato
- Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150-180 Porto, Portugal
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Maiato H, Khodjakov A, Rieder CL. Drosophila CLASP is required for the incorporation of microtubule subunits into fluxing kinetochore fibres. Nat Cell Biol 2004; 7:42-7. [PMID: 15592460 PMCID: PMC2596653 DOI: 10.1038/ncb1207] [Citation(s) in RCA: 152] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2004] [Accepted: 11/23/2004] [Indexed: 01/08/2023]
Abstract
The motion of a chromosome during mitosis is mediated by a bundle of microtubules, termed a kinetochore fibre (K-fibre), which connects the kinetochore of the chromosome to a spindle pole. Once formed, mature K-fibres maintain a steady state length because the continuous addition of microtubule subunits onto microtubule plus ends at the kinetochore is balanced by their removal at their minus ends within the pole. This condition is known as 'microtubule poleward flux'. Chromosome motion and changes in position are then driven by changes in K-fibre length, which in turn are controlled by changes in the rates at which microtubule subunits are added at the kinetochore and/or removed from the pole. A key to understanding the role of flux in mitosis is to identify the molecular factors that drive it. Here we use Drosophila melanogaster S2 cells expressing alpha-tubulin tagged with green fluorescent protein, RNA interference, laser microsurgery and photobleaching to show that the kinetochore protein MAST/Orbit - the single CLASP orthologue in Drosophila - is an essential component for microtubule subunit incorporation into fluxing K-fibres.
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Affiliation(s)
- Helder Maiato
- Laboratory of Cell Regulation, Wadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA
| | - Alexey Khodjakov
- Laboratory of Cell Regulation, Wadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA
- Department of Biomedical Sciences, State University of New York, Albany, NY 12222, USA
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Conly L. Rieder
- Laboratory of Cell Regulation, Wadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA
- Department of Biomedical Sciences, State University of New York, Albany, NY 12222, USA
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
- Correspondence should be addressed to C.L.R. (e-mail )
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Abstract
Drosophila melanogaster is an excellent model for studying mitosis. Syncytial embryos are amenable to time-lapse imaging of hundreds of synchronously dividing spindles, allowing the quantitation of spindle and chromosome dynamics with unprecedented fidelity. Other Drosophila cell types, including neuroblasts, cultured cells, spermatocytes and oocytes, contain spindles that differ in their design, providing cells amenable to different types of experiments and allowing identification of common core mechanisms. The function of mitotic proteins can be studied using mutants, inhibitor microinjection and RNA interference (RNAi) to identify the full inventory of mitotic proteins encoded by the genome. Here, we review recent advances in understanding how ensembles of mitotic proteins coordinate spindle assembly and chromosome motion in this system.
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Affiliation(s)
- Mijung Kwon
- Department of Pediatric Oncology, The Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA
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You L, Gillilan R, Huffaker TC. Model for the yeast cofactor A-beta-tubulin complex based on computational docking and mutagensis. J Mol Biol 2004; 341:1343-54. [PMID: 15321725 DOI: 10.1016/j.jmb.2004.06.081] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2004] [Revised: 06/24/2004] [Accepted: 06/29/2004] [Indexed: 11/16/2022]
Abstract
Virtually every biological process involves protein-protein contact but relatively few protein-protein complexes have been solved by X-ray crystallography. As more individual protein structures become available, computational methods are likely to play increasingly important roles in defining these interactions. Tubulin folding and dimer formation are complex processes requiring a variety of protein cofactors. One of these is cofactor A, which interacts with beta-tubulin prior to assembly of the alpha-tubulin-beta-tubulin heterodimer. In the yeast Saccharomyces cerevisiae, beta-tubulin is encoded by TUB2 and cofactor A by RBL2. We have used computational docking and site-directed mutagenesis to generate a model of the Rbl2-Tub2 complex from the solved structures of these two proteins. Residues in the N termini and the loops of the Rbl2 homodimer appear to mediate binding to beta-tubulin. These interact with beta-tubulin residues in the region that contains helices H9 and H10. Rbl2 and alpha-tubulin share overlapping binding sites on the beta-tubulin molecule providing a structural explanation for the mutually exclusive binding of Rbl2 and alpha-tubulin to beta-tubulin.
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Affiliation(s)
- Liru You
- Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
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Maiato H, Fairley EAL, Rieder CL, Swedlow JR, Sunkel CE, Earnshaw WC. Human CLASP1 is an outer kinetochore component that regulates spindle microtubule dynamics. Cell 2003; 113:891-904. [PMID: 12837247 DOI: 10.1016/s0092-8674(03)00465-3] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
One of the most intriguing aspects of mitosis is the ability of kinetochores to hold onto plus ends of microtubules that are actively gaining or losing tubulin subunits. Here, we show that CLASP1, a microtubule-associated protein, localizes preferentially near the plus ends of growing spindle microtubules and is also a component of a kinetochore region that we term the outer corona. A truncated form of CLASP1 lacking the kinetochore binding domain behaves as a dominant negative, leading to the formation of radial arrays of microtubule bundles that are highly resistant to depolymerization. Microinjection of CLASP1-specific antibodies suppresses microtubule dynamics at kinetochores and throughout the spindle, resulting in the formation of monopolar asters with chromosomes buried in the interior. Incubation with microtubule-stabilizing drugs rescues the kinetochore association with microtubule plus ends at the periphery of the asters. Our data suggest that CLASP1 is required at kinetochores for attached microtubules to exhibit normal dynamic behavior.
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Affiliation(s)
- Helder Maiato
- Chromosome Structure Group, Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, University of Edinburgh, Swann Building, King's Buildings, Mayfield Road, EH9 3JR, Scotland, Edinburgh, United Kingdom
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Schuyler SC, Liu JY, Pellman D. The molecular function of Ase1p: evidence for a MAP-dependent midzone-specific spindle matrix. Microtubule-associated proteins. J Cell Biol 2003; 160:517-28. [PMID: 12591913 PMCID: PMC2173742 DOI: 10.1083/jcb.200210021] [Citation(s) in RCA: 168] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The midzone is the domain of the mitotic spindle that maintains spindle bipolarity during anaphase and generates forces required for spindle elongation (anaphase B). Although there is a clear role for microtubule (MT) motor proteins at the spindle midzone, less is known about how microtubule-associated proteins (MAPs) contribute to midzone organization and function. Here, we report that budding yeast Ase1p is a member of a conserved family of midzone-specific MAPs. By size exclusion chromatography and velocity sedimentation, both Ase1p in extracts and purified Ase1p behaved as a homodimer. Ase1p bound and bundled MTs in vitro. By live cell microscopy, loss of Ase1p resulted in a specific defect: premature spindle disassembly in mid-anaphase. Furthermore, when overexpressed, Ase1p was sufficient to trigger spindle elongation in S phase-arrested cells. FRAP revealed that Ase1p has both a very slow rate of turnover within the midzone and limited lateral diffusion along spindle MTs. We propose that Ase1p functions as an MT cross-bridge that imparts matrix-like characteristics to the midzone. MT-dependent networks of spindle midzone MAPs may be one molecular basis for the postulated spindle matrix.
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Affiliation(s)
- Scott C Schuyler
- Department of Pediatric Oncology, The Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA
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Abstract
New evidence that cortical actin patches and the endocytic machinery share components supports the idea that actin patches are in fact transient membrane coats at the initial stage of endocytosis. Recent studies of actin cables have identified formins as the core of a novel actin-filament-assembling machine. Meanwhile, microtubule-binding proteins have been found in the kinetochore, and factors affecting microtubule dynamic instability have been identified.
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Affiliation(s)
- Daniel Schott
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
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42
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Abstract
Successful mitosis requires coordinated activities of microtubules and numerous associated proteins. A recent study implicates the microtubule-associated protein MAST/Orbit in a surprisingly wide array of mitotic activities, ranging from maintaining mitotic spindle bipolarity to tethering chromosomes to the ends of microtubules.
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Affiliation(s)
- David J Sharp
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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