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Meghini F, Martins T, Zhang Q, Loyer N, Trickey M, Abula Y, Yamano H, Januschke J, Kimata Y. APC/C-dependent degradation of Spd2 regulates centrosome asymmetry in Drosophila neural stem cells. EMBO Rep 2023; 24:e55607. [PMID: 36852890 PMCID: PMC10074082 DOI: 10.15252/embr.202255607] [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: 06/17/2022] [Revised: 12/31/2022] [Accepted: 01/11/2023] [Indexed: 03/01/2023] Open
Abstract
A functional centrosome is vital for the development and physiology of animals. Among numerous regulatory mechanisms of the centrosome, ubiquitin-mediated proteolysis is known to be critical for the precise regulation of centriole duplication. However, its significance beyond centrosome copy number control remains unclear. Using an in vitro screen for centrosomal substrates of the APC/C ubiquitin ligase in Drosophila, we identify several conserved pericentriolar material (PCM) components, including the inner PCM protein Spd2. We show that Spd2 levels are controlled by the interphase-specific form of APC/C, APC/CFzr , in cultured cells and developing brains. Increased Spd2 levels compromise neural stem cell-specific asymmetric PCM recruitment and microtubule nucleation at interphase centrosomes, resulting in partial randomisation of the division axis and segregation patterns of the daughter centrosome in the following mitosis. We further provide evidence that APC/CFzr -dependent Spd2 degradation restricts the amount and mobility of Spd2 at the daughter centrosome, thereby facilitating the accumulation of Polo-dependent Spd2 phosphorylation for PCM recruitment. Our study underpins the critical role of cell cycle-dependent proteolytic regulation of the PCM in stem cells.
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Affiliation(s)
| | - Torcato Martins
- Department of Genetics, University of Cambridge, Cambridge, UK
- Department of Medical Sciences, Institute of Biomedicine-iBiMED, University of Aveiro, Aveiro, Portugal
| | - Qian Zhang
- School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | - Nicolas Loyer
- School of Life Science, University of Dundee, Dundee, UK
| | | | - Yusanjiang Abula
- School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | | | - Jens Januschke
- School of Life Science, University of Dundee, Dundee, UK
| | - Yuu Kimata
- Department of Genetics, University of Cambridge, Cambridge, UK
- School of Life Science and Technology, ShanghaiTech University, Shanghai, China
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2
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Remnant L, Kochanova NY, Reid C, Cisneros-Soberanis F, Earnshaw WC. The intrinsically disorderly story of Ki-67. Open Biol 2021; 11:210120. [PMID: 34375547 PMCID: PMC8354752 DOI: 10.1098/rsob.210120] [Citation(s) in RCA: 24] [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] [Received: 05/03/2021] [Accepted: 07/13/2021] [Indexed: 01/14/2023] Open
Abstract
Ki-67 is one of the most famous marker proteins used by histologists to identify proliferating cells. Indeed, over 30 000 articles referring to Ki-67 are listed on PubMed. Here, we review some of the current literature regarding the protein. Despite its clinical importance, our knowledge of the molecular biology and biochemistry of Ki-67 is far from complete, and its exact molecular function(s) remain enigmatic. Furthermore, reports describing Ki-67 function are often contradictory, and it has only recently become clear that this proliferation marker is itself dispensable for cell proliferation. We discuss the unusual organization of the protein and its mRNA and how they relate to various models for its function. In particular, we focus on ways in which the intrinsically disordered structure of Ki-67 might aid in the assembly of the still-mysterious mitotic chromosome periphery compartment by controlling liquid-liquid phase separation of nucleolar proteins and RNAs.
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Affiliation(s)
- Lucy Remnant
- Wellcome Centre for Cell Biology, University of Edinburgh, ICB, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - Natalia Y. Kochanova
- Wellcome Centre for Cell Biology, University of Edinburgh, ICB, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - Caitlin Reid
- Wellcome Centre for Cell Biology, University of Edinburgh, ICB, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - Fernanda Cisneros-Soberanis
- Wellcome Centre for Cell Biology, University of Edinburgh, ICB, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - William C. Earnshaw
- Wellcome Centre for Cell Biology, University of Edinburgh, ICB, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, UK
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3
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Woll KA, Van Petegem F. Calcium Release Channels: Structure and Function of IP3 Receptors and Ryanodine Receptors. Physiol Rev 2021; 102:209-268. [PMID: 34280054 DOI: 10.1152/physrev.00033.2020] [Citation(s) in RCA: 87] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ca2+-release channels are giant membrane proteins that control the release of Ca2+ from the endoplasmic and sarcoplasmic reticulum. The two members, ryanodine receptors (RyRs) and inositol-1,4,5-trisphosphate Receptors (IP3Rs), are evolutionarily related and are both activated by cytosolic Ca2+. They share a common architecture, but RyRs have evolved additional modules in the cytosolic region. Their massive size allows for the regulation by tens of proteins and small molecules, which can affect the opening and closing of the channels. In addition to Ca2+, other major triggers include IP3 for the IP3Rs, and depolarization of the plasma membrane for a particular RyR subtype. Their size has made them popular targets for study via electron microscopic methods, with current structures culminating near 3Å. The available structures have provided many new mechanistic insights int the binding of auxiliary proteins and small molecules, how these can regulate channel opening, and the mechanisms of disease-associated mutations. They also help scrutinize previously proposed binding sites, as some of these are now incompatible with the structures. Many questions remain around the structural effects of post-translational modifications, additional binding partners, and the higher-order complexes these channels can make in situ. This review summarizes our current knowledge about the structures of Ca2+-release channels and how this informs on their function.
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Affiliation(s)
- Kellie A Woll
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada
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4
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Wang LI, Das A, McKim KS. Sister centromere fusion during meiosis I depends on maintaining cohesins and destabilizing microtubule attachments. PLoS Genet 2019; 15:e1008072. [PMID: 31150390 PMCID: PMC6581285 DOI: 10.1371/journal.pgen.1008072] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 06/18/2019] [Accepted: 05/16/2019] [Indexed: 11/26/2022] Open
Abstract
Sister centromere fusion is a process unique to meiosis that promotes co-orientation of the sister kinetochores, ensuring they attach to microtubules from the same pole during metaphase I. We have found that the kinetochore protein SPC105R/KNL1 and Protein Phosphatase 1 (PP1-87B) regulate sister centromere fusion in Drosophila oocytes. The analysis of these two proteins, however, has shown that two independent mechanisms maintain sister centromere fusion. Maintenance of sister centromere fusion by SPC105R depends on Separase, suggesting cohesin proteins must be maintained at the core centromeres. In contrast, maintenance of sister centromere fusion by PP1-87B does not depend on either Separase or WAPL. Instead, PP1-87B maintains sister centromeres fusion by regulating microtubule dynamics. We demonstrate that this regulation is through antagonizing Polo kinase and BubR1, two proteins known to promote stability of kinetochore-microtubule (KT-MT) attachments, suggesting that PP1-87B maintains sister centromere fusion by inhibiting stable KT-MT attachments. Surprisingly, C(3)G, the transverse element of the synaptonemal complex (SC), is also required for centromere separation in Pp1-87B RNAi oocytes. This is evidence for a functional role of centromeric SC in the meiotic divisions, that might involve regulating microtubule dynamics. Together, we propose two mechanisms maintain co-orientation in Drosophila oocytes: one involves SPC105R to protect cohesins at sister centromeres and another involves PP1-87B to regulate spindle forces at end-on attachments.
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Affiliation(s)
- Lin-Ing Wang
- Waksman Institute and Department of Genetics, Rutgers, the State University of New Jersey, Piscataway, New Jersey, United States of America
| | - Arunika Das
- Waksman Institute and Department of Genetics, Rutgers, the State University of New Jersey, Piscataway, New Jersey, United States of America
| | - Kim S. McKim
- Waksman Institute and Department of Genetics, Rutgers, the State University of New Jersey, Piscataway, New Jersey, United States of America
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5
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Pintard L, Archambault V. A unified view of spatio-temporal control of mitotic entry: Polo kinase as the key. Open Biol 2018; 8:180114. [PMID: 30135239 PMCID: PMC6119860 DOI: 10.1098/rsob.180114] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 07/29/2018] [Indexed: 12/18/2022] Open
Abstract
The Polo kinase is an essential regulator of cell division. Its ability to regulate multiple events at distinct subcellular locations and times during mitosis is remarkable. In the last few years, a much clearer mechanistic understanding of the functions and regulation of Polo in cell division has emerged. In this regard, the importance of coupling changes in activity with changes in localization is striking, both for Polo itself and for its upstream regulators. This review brings together several new pieces of the puzzle that are gradually revealing how Polo is regulated, in space and time, to enable its functions in the early stages of mitosis in animal cells. As a result, a unified view of how mitotic entry is spatio-temporally regulated is emerging.
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Affiliation(s)
- Lionel Pintard
- Cell Cycle and Development Team, Institut Jacques Monod, UMR7592 CNRS-Université Paris Diderot, Sorbonne Paris Cité, Ligue contre le Cancer, Paris, France
- Equipe labellisée, Ligue contre le Cancer, Paris, France
| | - Vincent Archambault
- Institut de recherche en immunologie et en cancérologie, Université de Montréal, Montréal, Québec, Canada
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6
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Kachaner D, Garrido D, Mehsen H, Normandin K, Lavoie H, Archambault V. Coupling of Polo kinase activation to nuclear localization by a bifunctional NLS is required during mitotic entry. Nat Commun 2017; 8:1701. [PMID: 29167465 PMCID: PMC5700101 DOI: 10.1038/s41467-017-01876-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 10/22/2017] [Indexed: 02/07/2023] Open
Abstract
The Polo kinase is a master regulator of mitosis and cytokinesis conserved from yeasts to humans. Polo is composed of an N-term kinase domain (KD) and a C-term polo-box domain (PBD), which regulates its subcellular localizations. The PBD and KD can interact and inhibit each other, and this reciprocal inhibition is relieved when Polo is phosphorylated at its activation loop. How Polo activation and localization are coupled during mitotic entry is unknown. Here we report that PBD binding to the KD masks a nuclear localization signal (NLS). Activating phosphorylation of the KD leads to exposure of the NLS and entry of Polo into the nucleus before nuclear envelope breakdown. Failures of this mechanism result in misregulation of the Cdk1-activating Cdc25 phosphatase and lead to mitotic and developmental defects in Drosophila. These results uncover spatiotemporal mechanisms linking master regulatory enzymes during mitotic entry. Drosophila Polo kinase is the founding member of the Polo-Like Kinase (PLK) family and a master regulator of mitosis and cytokinesis. Here the authors uncover a molecular mechanism for the spatiotemporal regulation of Polo kinase during mitotic entry through a phosphorylation event that triggers nuclear import.
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Affiliation(s)
- David Kachaner
- Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7.,Département de biochimie et médecine moléculaire, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7
| | - Damien Garrido
- Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7.,Département de biochimie et médecine moléculaire, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7
| | - Haytham Mehsen
- Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7
| | - Karine Normandin
- Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7
| | - Hugo Lavoie
- Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7
| | - Vincent Archambault
- Institute for Research in Immunology and Cancer, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7. .,Département de biochimie et médecine moléculaire, Université de Montréal, C.P. 6128 Succursale Centre-Ville, Montréal, QC, Canada, H3C 3J7.
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7
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An Amino-Terminal Polo Kinase Interaction Motif Acts in the Regulation of Centrosome Formation and Reveals a Novel Function for centrosomin (cnn) in Drosophila. Genetics 2016; 201:685-706. [PMID: 26447129 DOI: 10.1534/genetics.115.181842] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The formation of the pericentriolar matrix (PCM) and a fully functional centrosome in syncytial Drosophila melanogaster embryos requires the rapid transport of Cnn during initiation of the centrosome replication cycle. We show a Cnn and Polo kinase interaction is apparently required during embryogenesis and involves the exon 1A-initiating coding exon, suggesting a subset of Cnn splice variants is regulated by Polo kinase. During PCM formation exon 1A Cnn-Long Form proteins likely bind Polo kinase before phosphorylation by Polo for Cnn transport to the centrosome. Loss of either of these interactions in a portion of the total Cnn protein pool is sufficient to remove native Cnn from the pool, thereby altering the normal localization dynamics of Cnn to the PCM. Additionally, Cnn-Short Form proteins are required for polar body formation, a process known to require Polo kinase after the completion of meiosis. Exon 1A Cnn-LF and Cnn-SF proteins, in conjunction with Polo kinase, are required at the completion of meiosis and for the formation of functional centrosomes during early embryogenesis.
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8
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Lin CH, Li H, Lee YN, Cheng YJ, Wu RM, Chien CT. Lrrk regulates the dynamic profile of dendritic Golgi outposts through the golgin Lava lamp. J Cell Biol 2015. [PMID: 26216903 PMCID: PMC4523617 DOI: 10.1083/jcb.201411033] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Lrrk regulates Golgi outpost (GOP) dynamics in dendrites by antagonizing the interaction between the golgin Lva and dynein heavy chain at GOPs, thereby disrupting minus end–directed transport along dendritic microtubules by dynein. Constructing the dendritic arbor of neurons requires dynamic movements of Golgi outposts (GOPs), the prominent component in the dendritic secretory pathway. GOPs move toward dendritic ends (anterograde) or cell bodies (retrograde), whereas most of them remain stationary. Here, we show that Leucine-rich repeat kinase (Lrrk), the Drosophila melanogaster homologue of Parkinson’s disease–associated Lrrk2, regulates GOP dynamics in dendrites. Lrrk localized at stationary GOPs in dendrites and suppressed GOP movement. In Lrrk loss-of-function mutants, anterograde movement of GOPs was enhanced, whereas Lrrk overexpression increased the pool size of stationary GOPs. Lrrk interacted with the golgin Lava lamp and inhibited the interaction between Lva and dynein heavy chain, thus disrupting the recruitment of dynein to Golgi membranes. Whereas overexpression of kinase-dead Lrrk caused dominant-negative effects on GOP dynamics, overexpression of the human LRRK2 mutant G2019S with augmented kinase activity promoted retrograde movement. Our study reveals a pathogenic pathway for LRRK2 mutations causing dendrite degeneration.
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Affiliation(s)
- Chin-Hsien Lin
- Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan Department of Neurology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 100, Taiwan
| | - Hsun Li
- Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan Taiwan International Graduate Program in Interdisciplinary Neuroscience, National Yang-Ming University and Academia Sinica, Taipei 115, Taiwan
| | - Yi-Nan Lee
- Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan
| | - Ying-Ju Cheng
- Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan
| | - Ruey-Meei Wu
- Department of Neurology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 100, Taiwan
| | - Cheng-Ting Chien
- Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan
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9
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Platani M, Trinkle-Mulcahy L, Porter M, Jeyaprakash AA, Earnshaw WC. Mio depletion links mTOR regulation to Aurora A and Plk1 activation at mitotic centrosomes. J Cell Biol 2015; 210:45-62. [PMID: 26124292 PMCID: PMC4494011 DOI: 10.1083/jcb.201410001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Coordination of cell growth and proliferation in response to nutrient supply is mediated by mammalian target of rapamycin (mTOR) signaling. In this study, we report that Mio, a highly conserved member of the SEACAT/GATOR2 complex necessary for the activation of mTORC1 kinase, plays a critical role in mitotic spindle formation and subsequent chromosome segregation by regulating the proper concentration of active key mitotic kinases Plk1 and Aurora A at centrosomes and spindle poles. Mio-depleted cells showed reduced activation of Plk1 and Aurora A kinase at spindle poles and an impaired localization of MCAK and HURP, two key regulators of mitotic spindle formation and known substrates of Aurora A kinase, resulting in spindle assembly and cytokinesis defects. Our results indicate that a major function of Mio in mitosis is to regulate the activation/deactivation of Plk1 and Aurora A, possibly by linking them to mTOR signaling in a pathway to promote faithful mitotic progression.
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Affiliation(s)
- Melpomeni Platani
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, Scotland, UK
| | - Laura Trinkle-Mulcahy
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H8M5, Canada Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Ontario K1H8M5, Canada
| | - Michael Porter
- Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - A Arockia Jeyaprakash
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, Scotland, UK
| | - William C Earnshaw
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, Scotland, UK
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10
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Hyun SY, Sarantuya B, Lee HJ, Jang YJ. APC/C(Cdh1)-dependent degradation of Cdc20 requires a phosphorylation on CRY-box by Polo-like kinase-1 during somatic cell cycle. Biochem Biophys Res Commun 2013; 436:12-8. [PMID: 23643811 DOI: 10.1016/j.bbrc.2013.04.073] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 04/26/2013] [Indexed: 10/26/2022]
Abstract
Cdc20 is an activator of the anaphase-promoting complex (APC/C), and APC/C(Cdc20) is essential for metaphase-anaphase transition. To allow progression beyond mitosis, Cdc20 is degraded through KEN-box-dependent APC/C(Cdh1) activity. Mammalian Cdc20 contains the CRY box, a second APC/C(Cdh1)-dependent degron, but the molecular mechanism in degradation process remains undefined. Polo-like kinase-1 (Plk1) is an essential mitotic kinase regulating various targets in kinetochore, centrosome, and midbody for proper mitotic progression. Plk1 directly bound to Cdc20 and phosphorylates it on serine-170 located in CRY-box. Whereas wild-type Cdc20 was degraded according to progress cell cycle beyond mitosis, the phosphorylation-defective mutant, which serine-170 was changed into alanine, was not destroyed in early G1 phase. The phosphorylation on serine-170 by Plk1 was important for ubiquitination and Cdh1-dependent proteolysis. However, this modification by Plk1 on CRY box had no effect on the subcellular localization of Cdc20 and the formation of APC/C-inhibitory checkpoint complexes under spindle assembly checkpoint. This mechanism will be the first finding of inhibitory phosphorylation related to Cdc20 instability.
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Affiliation(s)
- Sun-Yi Hyun
- Laboratory of Cell Cycle & Signal Transduction, World Class University, Department of NanoBioMedical Science, Dankook University, 29 Anseo-Dong, Cheonan-Si, Chungnam 330-714, South Korea
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11
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Pek JW, Ng BF, Kai T. Polo-mediated phosphorylation of Maelstrom regulates oocyte determination during oogenesis in Drosophila. Development 2012; 139:4505-13. [DOI: 10.1242/dev.082867] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In Drosophila, Maelstrom is a conserved component of the perinuclear nuage, a germline-unique structure that appears to serve as a site for Piwi-interacting RNA (piRNA) production to repress deleterious transposons. Maelstrom also functions in the nucleus as a transcriptional regulator to repress the expression of microRNA-7, a process that is essential for the proper differentiation of germline stem cells. In this paper, we report another function of Maelstrom in regulating oocyte determination independently of its transposon silencing and germline stem cell differentiation activities. In Drosophila, the conserved serine 138 residue in Maelstrom is required for its phosphorylation, an event that promotes oocyte determination. Phosphorylation of Maelstrom is required for the repression of the pachytene checkpoint protein Sir2, but not for transposon silencing or for germline stem cell differentiation. We identify Polo as a kinase that mediates the phosphorylation of Maelstrom. Our results suggest that the Polo-mediated phosphorylation of Maelstrom may be a mechanism that controls oocyte determination by inactivating the pachytene checkpoint via the repression of Sir2 in Drosophila ovaries.
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Affiliation(s)
- Jun Wei Pek
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore 117604
| | - Bing Fu Ng
- Department of Biological Sciences, National University of Singapore, Singapore 117604
| | - Toshie Kai
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore 117604
- Department of Biological Sciences, National University of Singapore, Singapore 117604
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12
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Abstract
New findings reveal that, in Caenorhabditis elegans embryos, the centrosome provides signals that induce cell polarization, independently of its function as the microtubule-organizing center.
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13
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Olszak AM, van Essen D, Pereira AJ, Diehl S, Manke T, Maiato H, Saccani S, Heun P. Heterochromatin boundaries are hotspots for de novo kinetochore formation. Nat Cell Biol 2011; 13:799-808. [PMID: 21685892 DOI: 10.1038/ncb2272] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Accepted: 04/28/2011] [Indexed: 12/14/2022]
Abstract
The centromere-specific histone H3 variant CENH3 (also known as CENP-A) is considered to be an epigenetic mark for establishment and propagation of centromere identity. Pulse induction of CENH3 (Drosophila CID) in Schneider S2 cells leads to its incorporation into non-centromeric regions and generates CID islands that resist clearing from chromosome arms for multiple cell generations. We demonstrate that CID islands represent functional ectopic kinetochores, which are non-randomly distributed on the chromosome and show a preferential localization near telomeres and pericentric heterochromatin in transcriptionally silent, intergenic chromatin domains. Although overexpression of heterochromatin protein 1 (HP1) or increasing histone acetylation interferes with CID island formation on a global scale, induction of a locally defined region of synthetic heterochromatin by targeting HP1-LacI fusions to stably integrated Lac operator arrays produces a proximal hotspot for CID deposition. These data indicate that the characteristics of regions bordering heterochromatin promote de novo kinetochore assembly and thereby contribute to centromere identity.
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Affiliation(s)
- Agata M Olszak
- Max Planck Institute of Immunobiology and Epigenetics, Stübeweg 51, 79108 Freiburg, Germany
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14
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Bahassi EM. Polo-like kinases and DNA damage checkpoint: beyond the traditional mitotic functions. Exp Biol Med (Maywood) 2011; 236:648-57. [PMID: 21558091 DOI: 10.1258/ebm.2011.011011] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Polo-like kinases (Plks) are a family of serine-threonine kinases that play a pivotal role in cell cycle progression and in cellular response to DNA damage. The Plks are highly conserved from yeast to mammals. There are five Plk family members (Plk1-5) in humans, of which Plk1, is the best characterized. The Plk1 isoform is being aggressively pursued as a target for cancer therapy, following observations that this protein is overexpressed in human tumors and is actively involved in malignant transformation. The roles of Plks in mitotic entry, spindle pole functions and cytokinesis are well established and have been the subject of several recent reviews. In this review, we discuss functions of Plks other than their classical roles in mitotic progression. When cells incur DNA damage, they activate checkpoint mechanisms that result in cell cycle arrest and allow time for repair. If the damage is extensive and cannot be repaired, cells will undergo cell death by apoptosis. If the damage is repaired, cells can resume cycling, as part of the process known as checkpoint recovery. If the damage is not repaired or incompletely repaired, cells can override the checkpoint and resume cycling with damaged DNA, a process called checkpoint adaptation. The Plks play a role in all three outcomes and their involvement in these processes will be the subject of this review.
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Affiliation(s)
- El Mustapha Bahassi
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH 45267-0562, USA.
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15
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Myer DL, Robbins SB, Yin M, Boivin GP, Liu Y, Greis KD, Bahassi EM, Stambrook PJ. Absence of polo-like kinase 3 in mice stabilizes Cdc25A after DNA damage but is not sufficient to produce tumors. Mutat Res 2011; 714:1-10. [PMID: 21376736 DOI: 10.1016/j.mrfmmm.2011.02.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Revised: 01/05/2011] [Accepted: 02/15/2011] [Indexed: 11/29/2022]
Abstract
The polo-like kinases (Plks1-5) are emerging as an important class of proteins involved in many facets of cell cycle regulation and response to DNA damage and stress. Here we show that Plk3 phosphorylates the key cell cycle protein phosphatase Cdc25A on two serine residues in its cyclinB/cdk1 docking domain and regulates its stability in response to DNA damage. We generated a Plk3 knock-out mouse and show that Cdc25A protein from Plk3-deficient cells is less susceptible to DNA damage-mediated degradation than cells with functional Plk3. We also show that absence of Plk3 correlates with loss of the G1/S cell cycle checkpoint. However, neither this compromised DNA damage checkpoint nor reduced susceptibility to proteasome-mediated degradation after DNA damage translated into a significant increase in tumor incidence in the Plk3-deficient mice.
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Affiliation(s)
- David L Myer
- Department of Molecular Genetics, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0524, USA
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16
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Negishi T, Kumano G, Nishida H. Polo-like kinase 1 is required for localization of Posterior End Mark protein to the centrosome-attracting body and unequal cleavages in ascidian embryos. Dev Growth Differ 2011; 53:76-87. [PMID: 21261613 DOI: 10.1111/j.1440-169x.2010.01231.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In ascidian embryos, the posterior-localized maternal factor Posterior End Mark (PEM) is responsible for patterning embryos along the anterior-posterior axis with regard to both cleavage pattern involving unequal cell divisions and gene expression. Although PEM plays important roles in embryogenesis, its mechanism of action is still unclear because PEM has no known functional domain. In the present study, we explored the candidate of PEM partner proteins in Halocynthia roretzi using yeast two-hybrid screening. We isolated a homologue of Polo-like kinase 1 (Plk1), a key regulator of cell division and highly conserved in eukaryotes, as the first potential binding partner of PEM. We biochemically confirmed that interaction occurred between the Plk1 and PEM proteins. Immunostaining showed that Plk1 protein concentrates in the centrosome-attracting body (CAB) at the posterior pole, where PEM protein is also localized. The CAB is a subcellular structure that plays an important role in generating the posterior cleavage pattern. Plk1 localization to the CAB was dependent on the cell cycle phases during unequal cleavage. Inhibition of Plk1 with specific drugs resulted in failure of the nucleus to migrate towards the posterior pole and formation of a microtubule bundle between the CAB and a centrosome, similarly to inhibition of PEM function, suggesting that both proteins are involved in the same process of unequal cleavages. This interrupted nuclear migration was rescued by overexpression of PEM. In Plk1-inhibited embryos, the localization of PEM protein to the CAB was impaired, indicating that Plk1 is required for appropriate localization of PEM.
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Affiliation(s)
- Takefumi Negishi
- Department of Biological Sciences, Osaka University, Toyonaka, Japan.
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17
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Torras-Llort M, Medina-Giró S, Moreno-Moreno O, Azorín F. A conserved arginine-rich motif within the hypervariable N-domain of Drosophila centromeric histone H3 (CenH3) mediates BubR1 recruitment. PLoS One 2010; 5:e13747. [PMID: 21060784 PMCID: PMC2966416 DOI: 10.1371/journal.pone.0013747] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Accepted: 10/07/2010] [Indexed: 12/13/2022] Open
Abstract
Background Centromere identity is determined epigenetically by deposition of CenH3, a centromere-specific histone H3 variant that dictates kinetochore assembly. The molecular basis of the contribution of CenH3 to centromere/kinetochore functions is, however, incompletely understood, as its interactions with the rest of centromere/kinetochore components remain largely uncharacterised at the molecular/structural level. Principal Findings Here, we report on the contribution of Drosophila CenH3CID to recruitment of BubR1, a conserved kinetochore protein that is a core component of the spindle attachment checkpoint (SAC). This interaction is mediated by the N-terminal domain of CenH3CID (NCenH3CID), as tethering NCenH3CID to an ectopic reporter construct results in BubR1 recruitment and BubR1-dependent silencing of the reporter gene. Here, we also show that this interaction depends on a short arginine (R)-rich motif and that, most remarkably, it appears to be evolutionarily conserved, as tethering constructs carrying the highly divergent NCenH3 of budding yeast and human also induce silencing of the reporter. Interestingly, though NCenH3 shows an exceedingly low degree of conservation, the presence of R-rich motives is a common feature of NCenH3 from distant species. Finally, our results also indicate that two other conserved sequence motives within NCenH3CID might also be involved in interactions with kinetochore components. Conclusions These results unveil an unexpected contribution of the hypervariable N-domain of CenH3 to recruitment of kinetochore components, identifying simple R-rich motives within it as evolutionary conserved structural determinants involved in BubR1 recruitment.
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Affiliation(s)
- Mònica Torras-Llort
- Institute of Molecular Biology of Barcelona, CSIC, and Institute for Research in Biomedicine, IRB Barcelona, Barcelona, Spain
| | - Sònia Medina-Giró
- Institute of Molecular Biology of Barcelona, CSIC, and Institute for Research in Biomedicine, IRB Barcelona, Barcelona, Spain
| | - Olga Moreno-Moreno
- Institute of Molecular Biology of Barcelona, CSIC, and Institute for Research in Biomedicine, IRB Barcelona, Barcelona, Spain
| | - Fernando Azorín
- Institute of Molecular Biology of Barcelona, CSIC, and Institute for Research in Biomedicine, IRB Barcelona, Barcelona, Spain
- * E-mail:
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18
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Andrysik Z, Bernstein WZ, Deng L, Myer DL, Li YQ, Tischfield JA, Stambrook PJ, Bahassi EM. The novel mouse Polo-like kinase 5 responds to DNA damage and localizes in the nucleolus. Nucleic Acids Res 2010; 38:2931-43. [PMID: 20100802 PMCID: PMC2875007 DOI: 10.1093/nar/gkq011] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Polo-like kinases (Plk1-4) are emerging as an important class of proteins involved in many aspects of cell cycle regulation and response to DNA damage. Here, we report the cloning of a fifth member of the polo-like kinase family named Plk5. DNA and protein sequence analyses show that Plk5 shares more similarities with Plk2 and Plk3 than with Plk1 and Plk4. Consistent with this observation, we show that mouse Plk5 is a DNA damage inducible gene. Mouse Plk5 protein localizes predominantly to the nucleolus, and deletion of a putative nucleolus localization signal (NoLS) within its N-terminal moiety disrupts its nucleolar localization. Ectopic expression of Plk5 leads to cell cycle arrest in G1, decreased DNA synthesis, and to apoptosis, a characteristic it shares with Plk3. Interestingly, in contrast to mouse Plk5 gene, the sequence of human Plk5 contains a stop codon that produces a truncated protein lacking part of the kinase domain.
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Affiliation(s)
- Zdenek Andrysik
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA
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19
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Blagden SP, Gatt MK, Archambault V, Lada K, Ichihara K, Lilley KS, Inoue YH, Glover DM. Drosophila Larp associates with poly(A)-binding protein and is required for male fertility and syncytial embryo development. Dev Biol 2009; 334:186-97. [PMID: 19631203 DOI: 10.1016/j.ydbio.2009.07.016] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Revised: 07/02/2009] [Accepted: 07/14/2009] [Indexed: 10/20/2022]
Abstract
As the influence of mRNA translation upon cell cycle regulation becomes clearer, we searched for genes that might specify such control in Drosophila. A maternal-effect lethal screen identified mutants in the Drosophila gene for Larp (La-related protein) which displayed maternal-effect lethality and male sterility. A role for La protein has already been implicated in mRNA translation whereas Larp has been proposed to regulate mRNA stability. Here we demonstrate that Larp exists in a physical complex with, and also interacts genetically with, the translation regulator poly(A)-binding protein (PABP). Most mutant alleles of pAbp are embryonic lethal. However hypomorphic pAbp alleles show similar meiotic defects to larp mutants. We find that larp mutant-derived syncytial embryos show a range of mitotic phenotypes, including failure of centrosomes to migrate around the nuclear envelope, detachment of centrosomes from spindle poles, the formation of multipolar spindle arrays and cytokinetic defects. We discuss why the syncytial mitotic cycles and male meiosis should have a particularly sensitive requirement for Larp proteins in regulating not only transcript stability but also potentially the translation of mRNAs.
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Affiliation(s)
- Sarah P Blagden
- Cancer Research UK Cell Cycle Genetics Group, University of Cambridge, Department of Genetics, Cambridge CB2 3EH, UK
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20
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Vanderheyden V, Wakai T, Bultynck G, De Smedt H, Parys JB, Fissore RA. Regulation of inositol 1,4,5-trisphosphate receptor type 1 function during oocyte maturation by MPM-2 phosphorylation. Cell Calcium 2009; 46:56-64. [PMID: 19482353 PMCID: PMC2774721 DOI: 10.1016/j.ceca.2009.04.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Revised: 04/27/2009] [Accepted: 04/28/2009] [Indexed: 11/30/2022]
Abstract
Egg activation and further embryo development require a sperm-induced intracellular Ca(2+) signal at the time of fertilization. Prior to fertilization, the egg's Ca(2+) machinery is therefore optimized. To this end, during oocyte maturation, the sensitivity, i.e. the Ca(2+) releasing ability, of the inositol 1,4,5-trisphosphate receptor type 1 (IP(3)R1), which is responsible for most of this Ca(2+) release, markedly increases. In this study, the recently discovered specific Polo-like kinase (Plk) inhibitor BI2536 was used to investigate the role of Plk1 in this process. BI2536 inactivates Plk1 in oocytes at the early stages of maturation and significantly decreases IP(3)R1 phosphorylation at an MPM-2 epitope at this stage. Moreover, this decrease in Plk1-dependent MPM-2 phosphorylation significantly lowers IP(3)R1 sensitivity. Finally, using in vitro phosphorylation techniques we identified T(2656) as a major Plk1 site on IP(3)R1. We therefore propose that the initial increase in IP(3)R1 sensitivity during oocyte maturation is underpinned by IP(3)R1 phosphorylation at an MPM-2 epitope(s).
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Affiliation(s)
- Veerle Vanderheyden
- Laboratory of Molecular and Cellular Signalling, Department of Molecular Cell Biology, K.U. Leuven, Campus Gasthuisberg, O&N1 Bus 802, B-3000 Leuven, Belgium
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21
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Vanderheyden V, Devogelaere B, Missiaen L, De Smedt H, Bultynck G, Parys JB. Regulation of inositol 1,4,5-trisphosphate-induced Ca2+ release by reversible phosphorylation and dephosphorylation. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1793:959-70. [PMID: 19133301 DOI: 10.1016/j.bbamcr.2008.12.003] [Citation(s) in RCA: 151] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Revised: 11/27/2008] [Accepted: 12/03/2008] [Indexed: 12/12/2022]
Abstract
The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) is a universal intracellular Ca2+-release channel. It is activated after cell stimulation and plays a crucial role in the initiation and propagation of the complex spatio-temporal Ca2+ signals that control cellular processes as different as fertilization, cell division, cell migration, differentiation, metabolism, muscle contraction, secretion, neuronal processing, and ultimately cell death. To achieve these various functions, often in a single cell, exquisite control of the Ca2+ release is needed. This review aims to highlight how protein kinases and protein phosphatases can interact with the IP3R or with associated proteins and so provide a large potential for fine tuning the Ca2+-release activity and for creating efficient Ca2+ signals in subcellular microdomains.
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Affiliation(s)
- Veerle Vanderheyden
- Laboratory of Molecular and Cellular Signalling, Department Molecular and Cellular Biology, Campus Gasthuisberg O/N1-K. U. Leuven, Herestraat 49-Bus 802, B-3000 Leuven, Belgium
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22
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Sequestration of Polo kinase to microtubules by phosphopriming-independent binding to Map205 is relieved by phosphorylation at a CDK site in mitosis. Genes Dev 2008; 22:2707-20. [PMID: 18832073 DOI: 10.1101/gad.486808] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The conserved Polo kinase controls multiple events in mitosis and cytokinesis. Although Polo-like kinases are regulated by phosphorylation and proteolysis, control of subcellular localization plays a major role in coordinating their mitotic functions. This is achieved largely by the Polo-Box Domain, which binds prephosphorylated targets. However, it remains unclear whether and how Polo might interact with partner proteins when priming mitotic kinases are inactive. Here we show that Polo associates with microtubules in interphase and cytokinesis, through a strong interaction with the microtubule-associated protein Map205. Surprisingly, this interaction does not require priming phosphorylation of Map205, and the Polo-Box Domain of Polo is required but not sufficient for this interaction. Moreover, phosphorylation of Map205 at a CDK site relieves this interaction. Map205 can stabilize Polo and inhibit its cellular activity in vivo. In syncytial embryos, the centrosome defects observed in polo hypomorphs are enhanced by overexpression of Map205 and suppressed by its deletion. We propose that Map205-dependent targeting of Polo to microtubules provides a stable reservoir of Polo that can be rapidly mobilized by the activity of Cdk1 at mitotic entry.
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23
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Kosodo Y, Toida K, Dubreuil V, Alexandre P, Schenk J, Kiyokage E, Attardo A, Mora-Bermúdez F, Arii T, Clarke JDW, Huttner WB. Cytokinesis of neuroepithelial cells can divide their basal process before anaphase. EMBO J 2008; 27:3151-63. [PMID: 18971946 DOI: 10.1038/emboj.2008.227] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Accepted: 10/02/2008] [Indexed: 11/09/2022] Open
Abstract
Neuroepithelial (NE) cells, the primary stem and progenitor cells of the vertebrate central nervous system, are highly polarized and elongated. They retain a basal process extending to the basal lamina, while undergoing mitosis at the apical side of the ventricular zone. By studying NE cells in the embryonic mouse, chick and zebrafish central nervous system using confocal microscopy, electron microscopy and time-lapse imaging, we show here that the basal process of these cells can split during M phase. Splitting occurred in the basal-to-apical direction and was followed by inheritance of the processes by either one or both daughter cells. A cluster of anillin, an essential component of the cytokinesis machinery, appeared at the distal end of the basal process in prophase and was found to colocalize with F-actin at bifurcation sites, in both proliferative and neurogenic NE cells. GFP-anillin in the basal process moved apically to the cell body prior to anaphase onset, followed by basal-to-apical ingression of the cleavage furrow in telophase. The splitting of the basal process of M-phase NE cells has implications for cleavage plane orientation and the relationship between mitosis and cytokinesis.
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Affiliation(s)
- Yoichi Kosodo
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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24
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Von Stetina JR, Tranguch S, Dey SK, Lee LA, Cha B, Drummond-Barbosa D. alpha-Endosulfine is a conserved protein required for oocyte meiotic maturation in Drosophila. Development 2008; 135:3697-706. [PMID: 18927152 DOI: 10.1242/dev.025114] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Meiosis is coupled to gamete development and must be well regulated to prevent aneuploidy. During meiotic maturation, Drosophila oocytes progress from prophase I to metaphase I. The molecular factors controlling meiotic maturation timing, however, are poorly understood. We show that Drosophila alpha-endosulfine (endos) plays a key role in this process. endos mutant oocytes have a prolonged prophase I and fail to progress to metaphase I. This phenotype is similar to that of mutants of cdc2 (synonymous with cdk1) and of twine, the meiotic homolog of cdc25, which is required for Cdk1 activation. We found that Twine and Polo kinase levels are reduced in endos mutants, and identified Early girl (Elgi), a predicted E3 ubiquitin ligase, as a strong Endos-binding protein. In elgi mutant oocytes, the transition into metaphase I occurs prematurely, but Polo and Twine levels are unaffected. These results suggest that Endos controls meiotic maturation by regulating Twine and Polo levels, and, independently, by antagonizing Elgi. Finally, germline-specific expression of the human alpha-endosulfine ENSA rescues the endos mutant meiotic defects and infertility, and alpha-endosulfine is expressed in mouse oocytes, suggesting potential conservation of its meiotic function.
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Affiliation(s)
- Jessica R Von Stetina
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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25
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Williams B, Leung G, Maiato H, Wong A, Li Z, Williams EV, Kirkpatrick C, Aquadro CF, Rieder CL, Goldberg ML. Mitch a rapidly evolving component of the Ndc80 kinetochore complex required for correct chromosome segregation in Drosophila. J Cell Sci 2007; 120:3522-33. [PMID: 17895365 DOI: 10.1242/jcs.012112] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We identified an essential kinetochore protein, Mitch, from a genetic screen in D. melanogaster. Mitch localizes to the kinetochore, and its targeting is independent of microtubules (MTs) and several other known kinetochore components. Animals carrying mutations in mitch die as late third-instar larvae; mitotic neuroblasts in larval brains exhibit high levels of aneuploidy. Analysis of fixed D. melanogaster brains and mitch RNAi in cultured cells, as well as video recordings of cultured mitch mutant neuroblasts, reveal that chromosome alignment in mitch mutants is compromised during spindle formation, with many chromosomes displaying persistent mono-orientation. These misalignments lead to aneuploidy during anaphase. Mutations in mitch also disrupt chromosome behavior during both meiotic divisions in spermatocytes: the entire chromosome complement often moves to only one spindle pole. Mutant mitotic cells exhibit contradictory behavior with respect to the spindle assembly checkpoint (SAC). Anaphase onset is delayed in untreated cells, probably because incorrect kinetochore attachment maintains the SAC. However, mutant brain cells and mitch RNAi cells treated with MT poisons prematurely disjoin their chromatids, and exit mitosis. These data suggest that Mitch participates in SAC signaling that responds specifically to disruptions in spindle microtubule dynamics. The mitch gene corresponds to the transcriptional unit CG7242, and encodes a protein that is a possible ortholog of the Spc24 or Spc25 subunit of the Ndc80 kinetochore complex. Despite the crucial role of Mitch in cell division, the mitch gene has evolved very rapidly among species in the genus Drosophila.
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Affiliation(s)
- Byron Williams
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA
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26
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D'Avino PP, Archambault V, Przewloka MR, Zhang W, Lilley KS, Laue E, Glover DM. Recruitment of Polo kinase to the spindle midzone during cytokinesis requires the Feo/Klp3A complex. PLoS One 2007; 2:e572. [PMID: 17593971 PMCID: PMC1894651 DOI: 10.1371/journal.pone.0000572] [Citation(s) in RCA: 45] [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: 03/27/2007] [Accepted: 06/02/2007] [Indexed: 12/27/2022] Open
Abstract
Background Polo-like kinases control multiple events during cell division, including mitotic entry, centrosome organization, spindle formation, chromosome segregation and cytokinesis. Their roles during cytokinesis, however, are not well understood because the requirement of these kinases during early stages of mitosis complicates the study of their functions after anaphase onset. Methodology/Principal Findings We used time-lapse microscopy to analyze the dynamics of Polo::GFP in Drosophila tissue culture cells during mitosis. After anaphase onset, Polo::GFP concentrated at the spindle midzone, but also diffused along the entire length of the central spindle. Using RNA interference we demonstrate that the microtubule-associated proteins Feo and Klp3A are required for Polo recruitment to the spindle midzone, but not the kinesin Pavarotti as previously thought. Moreover, we show that Feo and Klp3A form a complex and that Polo co-localizes with both proteins during cytokinesis. Conclusion/Significance Our results reveal that the Feo/Klp3A complex is necessary for Polo recruitment to the spindle midzone. A similar finding has also been recently reported in mammalian cells [1], suggesting that this basic mechanism has been conserved during evolution, albeit with some differences. Finally, since cleavage furrow formation and ingression are unaffected following feo RNAi, our data imply that Polo recruitment to the central spindle is not required for furrowing, but some other aspect of cytokinesis.
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Affiliation(s)
- Pier Paolo D'Avino
- Cancer Research UK Cell Cycle Genetics Research Group, Department of Genetics, University of Cambridge, Cambridge, United Kingdom.
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27
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White AE, Leslie ME, Calvi BR, Marzluff WF, Duronio RJ. Developmental and cell cycle regulation of the Drosophila histone locus body. Mol Biol Cell 2007; 18:2491-502. [PMID: 17442888 PMCID: PMC1924828 DOI: 10.1091/mbc.e06-11-1033] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Cyclin E/Cdk2 is necessary for replication-dependent histone mRNA biosynthesis, but how it controls this process in early development is unknown. We show that in Drosophila embryos the MPM-2 monoclonal antibody, raised against a phosphoepitope from human mitotic cells, detects Cyclin E/Cdk2-dependent nuclear foci that colocalize with nascent histone transcripts. These foci are coincident with the histone locus body (HLB), a Cajal body-like nuclear structure associated with the histone locus and enriched in histone pre-mRNA processing factors such as Lsm11, a core component of the U7 small nuclear ribonucleoprotein. Using MPM-2 and anti-Lsm11 antibodies, we demonstrate that the HLB is absent in the early embryo and occurs when zygotic histone transcription begins during nuclear cycle 11. Whereas the HLB is found in all cells after its formation, MPM-2 labels the HLB only in cells with active Cyclin E/Cdk2. MPM-2 and Lsm11 foci are present in embryos lacking the histone locus, and MPM-2 foci are present in U7 mutants, which cannot correctly process histone pre-mRNA. These data indicate that MPM-2 recognizes a Cdk2-regulated protein that assembles into the HLB independently of histone mRNA biosynthesis. HLB foci are present in histone deletion embryos, although the MPM-2 foci are smaller, and some Lsm11 foci are not associated with MPM-2 foci, suggesting that the histone locus is important for HLB integrity.
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Affiliation(s)
| | | | - Brian R. Calvi
- Department of Biology, Syracuse University, Syracuse, NY 13244
| | - William F. Marzluff
- *Department of Biology
- Curriculum in Genetics and Molecular Biology
- Department of Biochemistry and Biophysics, and
- Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, NC 27599; and
| | - Robert J. Duronio
- *Department of Biology
- Curriculum in Genetics and Molecular Biology
- Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, NC 27599; and
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28
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Escargueil A, Larsen A. Mitosis-specific MPM-2 phosphorylation of DNA topoisomerase IIalpha is regulated directly by protein phosphatase 2A. Biochem J 2007; 403:235-42. [PMID: 17212588 PMCID: PMC1874246 DOI: 10.1042/bj20061460] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Recent results suggest a role for topoIIalpha (topoisomerase IIalpha) in the fine-tuning of mitotic entry. Mitotic entry is accompanied by the formation of specific phosphoepitopes such as MPM-2 (mitotic protein monoclonal 2) that are believed to control mitotic processes. Surprisingly, the MPM-2 kinase of topoIIalpha was identified as protein kinase CK2, otherwise known as a constitutive interphase kinase. This suggested the existence of alternative pathways for the creation of mitotic phosphoepitopes, different from the classical pathway where the substrate is phosphorylated by a mitotic kinase. In the present paper, we report that topoIIalpha is co-localized with both CK2 and PP2A (protein phosphatase 2A) during interphase. Simultaneous incubation of purified topoIIalpha with CK2 and PP2A had minimal influence on the total phosphorylation levels of topoIIalpha, but resulted in complete disappearance of the MPM-2 phosphoepitope owing to opposite sequence preferences of CK2 and PP2A. Accordingly, short-term exposure of interphase cells to okadaic acid, a selective PP2A inhibitor, was accompanied by the specific appearance of the MPM-2 phosphoepitope on topoIIalpha. During early mitosis, PP2A was translocated from the nucleus, while CK2 remained in the nucleus until pro-metaphase thus permitting the formation of the MPM-2 phosphoepitope. These results underline the importance of protein phosphatases as an alternative way of creating cell-cycle-specific phosphoepitopes.
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Affiliation(s)
- Alexandre E. Escargueil
- Group of Cancer Biology and Therapeutics, Inserm U673, Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75572 Paris Cedex 12, France, and Université Pierre et Marie Curie, Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75572 Paris Cedex 12, France
| | - Annette K. Larsen
- Group of Cancer Biology and Therapeutics, Inserm U673, Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75572 Paris Cedex 12, France, and Université Pierre et Marie Curie, Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75572 Paris Cedex 12, France
- To whom correspondence should be addressed (email )
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Joachimiak E, Pucciarelli S, Barchetta S, Ballarini P, Kaczanowska J, Miceli C. Cell Cycle-dependent Expression of γ-Tubulin in the Amicronuclear Ciliate Tetrahymena pyriformis. Protist 2007; 158:39-50. [PMID: 17023214 DOI: 10.1016/j.protis.2006.08.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2006] [Accepted: 08/01/2006] [Indexed: 10/24/2022]
Abstract
In ciliates, different microtubular structures are nucleated from diverse Microtubule Organizing Centers (MTOCs). gamma-Tubulin is a tubulin superfamily member that plays an essential role in microtubule nucleation at the MTOCs. However, little is known about mechanisms regulating the activity of gamma-tubulin on different MTOCs and during the cell cycle. In Tetrahymena thermophila, the alpha- and beta-tubulin expression is regulated mainly at the transcriptional level, and changes in the ratio of polymerized/unpolymerized tubulin dimers lead to an increase or decrease of alpha- and beta-tubulin transcription. This study deals with the characterization of gamma-tubulin in the amicronuclear ciliate Tetrahymena pyriformis. Sequence analysis revealed some specific substitutions in nucleotide-binding loops characteristic of the Tetrahymena genus and putative conserved phosphorylation sites located on the external surface of the gamma-tubulin molecule. gamma-Tubulin expression during the cell cycle, in the presence of microtubular poisons and after deciliation, was also characterized. We found that gamma-tubulin mRNA levels are correlated with basal body proliferation and gamma-tubulin nuclear localization. We also found that gamma-tubulin expression changes during anti-microtubular drugs treatment, but does not changes during reciliation. These findings suggest a relationship between the level of unpolymerized tubulin dimers and gamma-tubulin transcription.
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Affiliation(s)
- Ewa Joachimiak
- Department of Molecular, Cellular and Animal Biology, University of Camerino, Camerino 62032, v. Camerini 2, Italy
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30
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McInnes C, Mazumdar A, Mezna M, Meades C, Midgley C, Scaerou F, Carpenter L, Mackenzie M, Taylor P, Walkinshaw M, Fischer PM, Glover D. Inhibitors of Polo-like kinase reveal roles in spindle-pole maintenance. Nat Chem Biol 2006; 2:608-17. [PMID: 17028581 DOI: 10.1038/nchembio825] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2006] [Accepted: 08/24/2006] [Indexed: 01/08/2023]
Abstract
Polo-like kinases (Plks) have several functions in mitotic progression and are upregulated in many tumor types. Small-molecule Plk inhibitors would be valuable as tools for studying Plk biology and for developing antitumor agents. Guided by homology modeling of the Plk1 kinase domain, we have discovered a chemical series that shows potent and selective Plk1 inhibition. The effects of one such optimized benzthiazole N-oxide, cyclapolin 1 (1), on purified centrosomes indicate that Plks are required to generate MPM2 epitopes, recruit gamma-tubulin and enable nucleation of microtubules. The compound can also promote loss of centrosome integrity and microtubule nucleating ability apparently through increased accessibility of protein phosphatases. We show that treatment of living S2 cells with cyclapolin 1 leads to collapsed spindles, in contrast to the metaphase-arrested bipolar spindles observed after RNAi. This different response to protein depletion and protein inhibition may have significance in the development of antitumor agents.
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31
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Cesario JM, Jang JK, Redding B, Shah N, Rahman T, McKim KS. Kinesin 6 family member Subito participates in mitotic spindle assembly and interacts with mitotic regulators. J Cell Sci 2006; 119:4770-80. [PMID: 17077127 DOI: 10.1242/jcs.03235] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Drosophila Subito is a kinesin 6 family member and ortholog of mitotic kinesin-like protein (MKLP2) in mammalian cells. Based on the previously established requirement for Subito in meiotic spindle formation and for MKLP2 in cytokinesis, we investigated the function of Subito in mitosis. During metaphase, Subito localized to microtubules at the center of the mitotic spindle, probably interpolar microtubules that originate at the poles and overlap in antiparallel orientation. Consistent with this localization pattern, subito mutants improperly assembled microtubules at metaphase, causing activation of the spindle assembly checkpoint and lagging chromosomes at anaphase. These results are the first demonstration of a kinesin 6 family member with a function in mitotic spindle assembly, possibly involving the interpolar microtubules. However, the role of Subito during mitotic anaphase resembles other kinesin 6 family members. Subito localizes to the spindle midzone at anaphase and is required for the localization of Polo, Incenp and Aurora B. Genetic evidence suggested that the effects of subito mutants are attenuated as a result of redundant mechanisms for spindle assembly and cytokinesis. For example, subito double mutants with ncd, polo, Aurora B or Incenp mutations were synthetic lethal with severe defects in microtubule organization.
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Affiliation(s)
- Jeff M Cesario
- Waksman Institute and Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8020, USA
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32
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Feng Y, Yuan JH, Maloid SC, Fisher R, Copeland TD, Longo DL, Conrads TP, Veenstra TD, Ferris A, Hughes S, Dimitrov DS, Ferris DK. Polo-like kinase 1-mediated phosphorylation of the GTP-binding protein Ran is important for bipolar spindle formation. Biochem Biophys Res Commun 2006; 349:144-52. [PMID: 16930555 DOI: 10.1016/j.bbrc.2006.08.028] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2006] [Accepted: 08/03/2006] [Indexed: 01/21/2023]
Abstract
Polo-like kinase functions are essential for the establishment of a normal bipolar mitotic spindle, although precisely how Plk1 regulates the spindle is uncertain. In this study, we report that the small GTP/GDP-binding protein Ran is associated with Plk1. Plk1 is capable of phosphorylating co-immunoprecipitated Ran in vitro on serine-135 and Ran is phosphorylated in vivo at the same site during mitosis when Plk1 is normally activated. Cell cultures over-expressing a Ran S135D mutant have significantly higher numbers of abnormal mitotic cells than those over-expressing either wild-type or S135A Ran. The abnormalities in S135D mutant cells are similar to cells over-expressing Plk1. Our data suggests that Ran is a physiological substrate of Plk1 and that Plk1 regulates the spindle organization partially through its phosphorylation on Ran.
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Affiliation(s)
- Yang Feng
- Laboratory of Cancer Prevention, NCI at Frederick, Frederick, MD, USA; Nanobiology Program, CCR, NCI at Frederick, Frederick, MD, USA.
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33
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Heun P, Erhardt S, Blower MD, Weiss S, Skora AD, Karpen GH. Mislocalization of the Drosophila centromere-specific histone CID promotes formation of functional ectopic kinetochores. Dev Cell 2006; 10:303-15. [PMID: 16516834 PMCID: PMC3192491 DOI: 10.1016/j.devcel.2006.01.014] [Citation(s) in RCA: 272] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2005] [Revised: 01/09/2006] [Accepted: 01/27/2006] [Indexed: 01/14/2023]
Abstract
The centromere-specific histone variant CENP-A (CID in Drosophila) is a structural and functional foundation for kinetochore formation and chromosome segregation. Here, we show that overexpressed CID is mislocalized into normally noncentromeric regions in Drosophila tissue culture cells and animals. Analysis of mitoses in living and fixed cells reveals that mitotic delays, anaphase bridges, chromosome fragmentation, and cell and organismal lethality are all direct consequences of CID mislocalization. In addition, proteins that are normally restricted to endogenous kinetochores assemble at a subset of ectopic CID incorporation regions. The presence of microtubule motors and binding proteins, spindle attachments, and aberrant chromosome morphologies demonstrate that these ectopic kinetochores are functional. We conclude that CID mislocalization promotes formation of ectopic centromeres and multicentric chromosomes, which causes chromosome missegregation, aneuploidy, and growth defects. Thus, CENP-A mislocalization is one possible mechanism for genome instability during cancer progression, as well as centromere plasticity during evolution.
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Affiliation(s)
- Patrick Heun
- Department of Genome Biology Lawrence Berkeley National Lab One Cyclotron Road
- Department of Molecular and Cell Biology University of California, Berkeley Berkeley, California 94720
| | - Sylvia Erhardt
- Department of Genome Biology Lawrence Berkeley National Lab One Cyclotron Road
- Department of Molecular and Cell Biology University of California, Berkeley Berkeley, California 94720
| | - Michael D. Blower
- Department of Molecular and Cell Biology University of California, Berkeley Berkeley, California 94720
| | - Samara Weiss
- Department of Genome Biology Lawrence Berkeley National Lab One Cyclotron Road
- Department of Molecular and Cell Biology University of California, Berkeley Berkeley, California 94720
| | - Andrew D. Skora
- Department of Biology Johns Hopkins University 3400 North Charles Street Baltimore, Maryland 21208
| | - Gary H. Karpen
- Department of Genome Biology Lawrence Berkeley National Lab One Cyclotron Road
- Department of Molecular and Cell Biology University of California, Berkeley Berkeley, California 94720
- Correspondence:
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Pearson J, Godinho SA, Tavares A, Glover DM. Heterologous expression of mammalian Plk1 in Drosophila reveals divergence from Polo during late mitosis. Exp Cell Res 2006; 312:770-81. [PMID: 16412419 DOI: 10.1016/j.yexcr.2005.11.031] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Revised: 11/07/2005] [Accepted: 11/29/2005] [Indexed: 10/25/2022]
Abstract
Drosophila Polo kinase is the founder member of a conserved kinase family required for multiple stages of mitosis. We assessed the ability of mouse Polo-like kinase 1 (Plk1) to perform the multiple mitotic functions of Polo kinase, by expressing a Plk1-GFP fusion in Drosophila. Consistent with the previously reported localization of Polo kinase, Plk1-GFP was strongly localized to centrosomes and recruited to the centromeric regions of condensing chromosomes during early mitosis. However, in contrast to a functional Polo-GFP fusion, Plk1-GFP failed to localize to the central spindle midzone in both syncytial embryo mitosis and the conventional mitoses of cellularized embryos and S2 cells. Moreover, unlike endogenous Polo kinase and Polo-GFP, Plk1-GFP failed to associate with the contractile ring. Expression of Plk1-GFP enhanced the lethality of hypomorphic polo mutants and disrupted the organization of the actinomyosin cytoskeleton in a dominant-negative manner. Taken together, our results suggest that endogenous Polo kinase has specific roles in regulating actinomyosin rearrangements during Drosophila mitoses that its mammalian counterpart, Plk1, cannot fulfill. Consistent with this hypothesis, we observed defects in the cortical recruitment of myosin and myosin regulatory light chain in Polo deficient cells.
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Affiliation(s)
- John Pearson
- Cancer Research UK Cell Cycle Genetics Research Group, University of Cambridge, Department of Genetics, Downing Street, Cambridge CB2 3EH, UK.
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35
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Tapia C, Kutzner H, Mentzel T, Savic S, Baumhoer D, Glatz K. Two mitosis-specific antibodies, MPM-2 and phospho-histone H3 (Ser28), allow rapid and precise determination of mitotic activity. Am J Surg Pathol 2006; 30:83-9. [PMID: 16330946 DOI: 10.1097/01.pas.0000183572.94140.43] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Mitotic figure (MF) counting is important in the evaluation of many tumor types. Inadequate fixation, crush artefacts, the presence of many apoptoses, or the rarity of MFs in a given lesion can make the determination of the mitotic index a very time-consuming or even impossible task, especially for novices. We evaluated the potential of the two commercially available mitotic markers MPM-2 and Phospho-Histone H3 Ser28 (PHH3) for improving mitotic counting. Formalin-fixed tissue of 1 lymphoma, 19 epithelial, 25 mesenchymal, and 10 melanocytic tumors was immunohistochemically stained with both antibodies. Mitotic counts of each tumor sample were determined by a pathologist and three residents in the hematoxylin and eosin and in both immunohistochemical stainings. Because of the higher sensitivity of the immunohistochemical stainings for MFs, average mitotic counts per 10 HPF were higher with MPM-2 (11.0) and PHH3 (10.1) than with hematoxylin and eosin (5.9) staining. The precise distinction of MFs from apoptoses and the visualization of the distribution of MFs uncovering mitotic hotspots, even at low magnification, turned out to be major advantages of both mitotic markers. In addition, the average time needed to establish the mitotic count was reduced by 40.3% with MPM-2 and by 50.4% with PHH3. MPM-2 and PHH3 were subjectively rated by all pathologists involved in this study to be very helpful in mitotic counting, especially in melanocytic and mesenchymal lesions but less so in epithelial tumors. Both markers have hence been successfully introduced in our laboratory for the routine assessment of MFs in melanocytic and mesenchymal tumors.
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Affiliation(s)
- Coya Tapia
- Institute for Pathology, University Hospital, Schönbeinstrasse 40, 4031 Basel, Switzerland
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36
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Lingle WL, Lukasiewicz K, Salisbury JL. Deregulation of the centrosome cycle and the origin of chromosomal instability in cancer. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 570:393-421. [PMID: 18727509 DOI: 10.1007/1-4020-3764-3_14] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Although we have begun to tap into the mechanisms behind Boveri's initial observation that supernumerary centrosomes cause chromosome missegregation in sea urchin eggs, there is still much left to discover with regard to chromosomal instability in cancer. Many of the molecular players involved in regulation of the centrosome and cell cycles, and the coupling of the two cycles to produce a bipolar mitotic spindle have been identified. One theme that has become apparent is that cross talk and interrelatedness of the pathways serve to provide redundant mechanisms to maintain genomic integrity. In spite of this, cells occasionally fall prey to insults that initiate and maintain the chromosomal instability that results in viable malignant tumours. Deregulation of centrosome structure is an integral aspect of the origin of chromosomal instability in many cancers. There are numerous routes to centrosome amplification including: environmental insults such as ionising radiation and exposure to estrogen (Li et al., 2005); failure of cytokinesis; and activating mutations in key regulators of centrosome structure and function. There are two models for initiation of centrosome amplification (Figure 2). In the first, centrosome duplication and chromosome replication remain coupled and cells enter G2 with 4N chromosomes and duplicated centrosomes. However, these cells may fail to complete mitosis, and thus reenter G1 as tetraploid cells with amplified centrosomes. In the second, the centrosome cycle is uncoupled from chromosome replication and cells go through one or more rounds of centriole/centrosome duplication in the absence of chromosome replication. If these cells then go through chromosome replication accompanied by another round of centrosome duplication, cells complete G2 with 4N chromosomes and more than 2 centrosomes, and therefore are predisposed to generate multipolar mitotic spindles. Fragmentation of centrosomes due to ionising radiation is a variation of the second model. Once centrosome amplification is present, even in a diploid cell, that cell has the potential to yield viable aneuploid progeny. The telophase cell in Figure 3C illustrates this scenario. In a normal telophase configuration, the total number of chromosomes is 92 (resulting from the segregation of 46 pairs of chromatids), with each daughter nucleus containing 46 individual chromosomes. Based on the number of kinetochore signals present, the lower nucleus in Figure 3C has approximately 28 chromosomes, and the elongate upper nucleus has approximately 60, for a total of 88. Due to superimposition of kinetochores in this maximum projection image, 88 is an underestimate of the actual number of kinetochores and is not significantly different from the expected total of 92. A cell resulting from the lower nucleus with only around 28 chromosomes would probably not be viable, much as Boveri's experiments indicated. However, the upper nucleus with at least 60 chromosomes could be viable. This cell would enter G1 as hypotriploid (69 chromosomes = triploid) with 2 centrosomes. During S and G2, the centrosomes and chromosomes would double, and the following mitosis could be tetrapolar with a 6N chromosome content. When centrosome amplification is accompanied by permissive lapses in cell cycle checkpoints, the potential for malignant growth is present. These lapses could result from specific genetic mutations and amplifications, epigenetic gene silencing, or from massive chromosomal instability caused by the centrosome amplification. Centrosome amplification, therefore, can serve to exacerbate and/or generate genetic instabilities associated with cancers.
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Affiliation(s)
- Wilma L Lingle
- Mayo Clinic College of Medicine, Mayo Clinic Foundation, Mayo Clinic Cancer Center, Rochester, Minnesota 55905, USA
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37
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Lange BMH, Kirfel G, Gestmann I, Herzog V, González C. Structure and microtubule-nucleation activity of isolated Drosophila embryo centrosomes characterized by whole mount scanning and transmission electron microscopy. Histochem Cell Biol 2005; 124:325-34. [PMID: 16091939 DOI: 10.1007/s00418-005-0032-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/05/2005] [Indexed: 11/29/2022]
Abstract
Experimental approaches in Drosophila melanogaster over the last 20 years have played a fundamental role in elucidating the function, structure and molecular composition of the centrosome. However, quantitative data on the structure and function of the Drosophila centrosome are still lacking. This study uses, for the first time, whole mount electron microscopy in combination with negative staining on isolated centrosomes from the early Drosophila embryos to analyze its dimensions, structure and capacity to nucleate microtubules in vitro. We show that these organelles are on average 0.75 microm in diameter and have abundant pericentriolar material which often appears fibrillar and with bulbous protrusions. Corresponding to the abundant pericentriolar material, extensive microtubule nucleation occurs. Quantification of the number of microtubules nucleated showed that 50-300 active nucleation sites are present. We examined via electron microscopy immunogold labeling the distribution of gamma-tubulin, CNN, Asp and the MPM-2 epitopes that are phosphorylated through Polo and the Cdk1 kinase. The distribution of these proteins is homogeneous, with the MPM-2 epitopes exhibiting the highest density. In contrast, centrosomal subdomains are identified using a centriole marker to relate centrosome size to the centriole number by electron microscopy. In conclusion, we present a clear-cut technique assaying and quantifying the microtubule nucleation capacity and antigen distribution complementing molecular studies on centrosome protein complexes, cell organelle assembly and protein composition.
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Affiliation(s)
- B M H Lange
- Max-Planck Institute for Molecular Genetics, Vertebrate Genomics, Ihnestr. 73, 14195 Berlin, Germany.
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38
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Jang JK, Rahman T, McKim KS. The kinesinlike protein Subito contributes to central spindle assembly and organization of the meiotic spindle in Drosophila oocytes. Mol Biol Cell 2005; 16:4684-94. [PMID: 16055508 PMCID: PMC1237074 DOI: 10.1091/mbc.e04-11-0964] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In the oocytes of many species, bipolar spindles form in the absence of centrosomes. Drosophila melanogaster oocyte chromosomes have a major role in nucleating microtubules, which precedes the bundling and assembly of these microtubules into a bipolar spindle. Here we present evidence that a region similar to the anaphase central spindle functions to organize acentrosomal spindles. Subito mutants are characterized by the formation of tripolar or monopolar spindles and nondisjunction of homologous chromosomes at meiosis I. Subito encodes a kinesinlike protein and associates with the meiotic central spindle, consistent with its classification in the Kinesin 6/MKLP1 family. This class of proteins is known to be required for cytokinesis, but our results suggest a new function in spindle formation. The meiotic central spindle appears during prometaphase and includes passenger complex proteins such as AurB and Incenp. Unlike mitotic cells, the passenger proteins do not associate with centromeres before anaphase. In the absence of Subito, central spindle formation is defective and AurB and Incenp fail to properly localize. We propose that Subito is required for establishing and/or maintaining the central spindle in Drosophila oocytes, and this substitutes for the role of centrosomes in organizing the bipolar spindle.
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Affiliation(s)
- J K Jang
- Waksman Institute and Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8020, USA
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Slawson C, Zachara NE, Vosseller K, Cheung WD, Lane MD, Hart GW. Perturbations in O-linked beta-N-acetylglucosamine protein modification cause severe defects in mitotic progression and cytokinesis. J Biol Chem 2005; 280:32944-56. [PMID: 16027160 DOI: 10.1074/jbc.m503396200] [Citation(s) in RCA: 222] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dynamic modification of nuclear and cytoplasmic proteins with O-linked beta-N-acetylglucosamine (O-GlcNAc) is a regulatory post-translational modification that is rapidly responsive to morphogens, hormones, nutrients, and cellular stress. Here we show that O-GlcNAc is an important regulator of the cell cycle. Increased O-GlcNAc (pharmacologically or genetically) results in growth defects linked to delays in G2/M progression, altered mitotic phosphorylation, and cyclin expression. Overexpression of O-GlcNAcase, the enzyme that removes O-GlcNAc, induces a mitotic exit phenotype accompanied by a delay in mitotic phosphorylation, altered cyclin expression, and pronounced disruption in nuclear organization. Overexpression of the O-GlcNAc transferase, the enzyme that adds O-GlcNAc, results in a polyploid phenotype with faulty cytokinesis. Notably, O-GlcNAc transferase is concentrated at the mitotic spindle and midbody at M phase. These data suggest that dynamic O-GlcNAc processing is a pivotal regulatory component of the cell cycle, controlling cell cycle progression by regulating mitotic phosphorylation, cyclin expression, and cell division.
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Affiliation(s)
- Chad Slawson
- Department of Biological Chemistry, the Johns Hopkins School of Medicine, Baltimore, Maryland 21205-2185, USA
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40
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Clarke AS, Tang TTL, Ooi DLY, Orr-Weaver TL. POLO kinase regulates the Drosophila centromere cohesion protein MEI-S332. Dev Cell 2005; 8:53-64. [PMID: 15621529 DOI: 10.1016/j.devcel.2004.12.003] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2004] [Revised: 08/02/2004] [Accepted: 12/03/2004] [Indexed: 11/18/2022]
Abstract
Accurate segregation of chromosomes is critical to ensure that each daughter cell receives the full genetic complement. Maintenance of cohesion between sister chromatids, especially at centromeres, is required to segregate chromosomes precisely during mitosis and meiosis. The Drosophila protein MEI-S332, the founding member of a conserved protein family, is essential in meiosis for maintaining cohesion at centromeres until sister chromatids separate at the metaphase II/anaphase II transition. MEI-S332 localizes onto centromeres in prometaphase of mitosis or meiosis I, remaining until sister chromatids segregate. We elucidated a mechanism for controlling release of MEI-S332 from centromeres via phosphorylation by POLO kinase. We demonstrate that POLO antagonizes MEI-S332 cohesive function and that full POLO activity is needed to remove MEI-S332 from centromeres, yet this delocalization is not required for sister chromatid separation. POLO phosphorylates MEI-S332 in vitro, POLO and MEI-S332 bind each other, and mutation of POLO binding sites prevents MEI-S332 dissociation from centromeres.
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Affiliation(s)
- Astrid S Clarke
- Whitehead Institute for Biomedical Research, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
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41
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Yan X, Wu Y, Li Q, Cao L, Liu X, Saiyin H, Yu L. Cloning and characterization of a novel human Aurora C splicing variant. Biochem Biophys Res Commun 2005; 328:353-61. [PMID: 15670791 DOI: 10.1016/j.bbrc.2004.12.168] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Indexed: 10/25/2022]
Abstract
In the last 10 years, Aurora kinases have emerged as the key proteins regulating many events during cell mitosis. Despite the wealth of studies on human Aurora A and B, little is known about human Aurora C. Here we report a novel splicing variant of Aurora C, named as Aurora C-SV (Aurora C splicing variant), which encodes a 290-amino-acid protein. By RT-PCR analysis in various tissues, Aurora C-SV, like Aurora C, was found to be expressed at the highest level in human testis. The in vitro kinase assay showed that this Aurora C-SV phosphorylated MBP, and its T179A mutant lost the kinase activity. During cell mitosis, Aurora C-SV-EGFP associated with chromosomes in prophase and metaphase, and then transferred to the central spindle midzone and the cortex where the contract ring formed during the transition from anaphase to telophase. It then remained in the midbody during cytokinesis. Therefore, we speculated that Aurora C-SV might also contribute to the regulation of chromosome segregation and cytokinesis.
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Affiliation(s)
- Xiaomei Yan
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai 200433, PR China
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42
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Glover DM. Polo kinase and progression through M phase in Drosophila: a perspective from the spindle poles. Oncogene 2005; 24:230-7. [PMID: 15640838 DOI: 10.1038/sj.onc.1208279] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Genes for the mitotic kinases Polo and Aurora A were first identified in Drosophila through screens of maternal effect lethal mutations for defects in spindle pole behaviour. These enzymes have been shown to be highly conserved and required for multiple functions in mitosis. Polo is stabilized at the centrosome by association with Hsp90. It is required for centrosome maturation on M-phase entry in order to recruit the gamma-tubulin ring complex and activate the abnormal spindle protein, Asp. These events facilitate the nucleation of minus ends of microtubules at the centrosome. The localization of Polo at the kinetochore and the mid-zone of the central spindle together with the phenotypes of polo mutants point to functions at the metaphase to anaphase transition and in cytokinesis. The latter are mediated, at least in part, through the Pavarotti kinesin-like motor protein and its conserved counterparts in other metazoans.
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Affiliation(s)
- David M Glover
- Cancer Research UK Cell Cycle Genetics Research Group, Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK.
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43
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Sumara I, Giménez-Abián JF, Gerlich D, Hirota T, Kraft C, de la Torre C, Ellenberg J, Peters JM. Roles of polo-like kinase 1 in the assembly of functional mitotic spindles. Curr Biol 2005; 14:1712-22. [PMID: 15458642 DOI: 10.1016/j.cub.2004.09.049] [Citation(s) in RCA: 263] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2004] [Revised: 08/26/2004] [Accepted: 08/31/2004] [Indexed: 11/20/2022]
Abstract
BACKGROUND The stable association of chromosomes with both poles of the mitotic spindle (biorientation) depends on spindle pulling forces. These forces create tension across sister kinetochores and are thought to stabilize microtubule-kinetochore interactions and to silence the spindle checkpoint. Polo-like kinase 1 (Plk1) has been implicated in regulating centrosome maturation, mitotic entry, sister chromatid cohesion, the anaphase-promoting complex/cyclosome (APC/C), and cytokinesis, but it is unknown if Plk1 controls chromosome biorientation. RESULTS We have analyzed Plk1 functions in synchronized mammalian cells by RNA interference (RNAi). Plk1-depleted cells enter mitosis after a short delay, accumulate in a preanaphase state, and subsequently often die by apoptosis. Spindles in Plk1-depleted cells lack focused poles and are not associated with centrosomes. Chromosomes attach to these spindles, but the checkpoint proteins Mad2, BubR1, and CENP-E are enriched at many kinetochores. When Plk1-depleted cells are treated with the Aurora B inhibitor Hesperadin, which silences the spindle checkpoint by stabilizing microtubule-kinetochore interactions, cells degrade APC/C substrates and exit mitosis without chromosome segregation and cytokinesis. Experiments with monopolar spindles that are induced by the kinesin inhibitor Monastrol indicate that Plk1 is required for the assembly of spindles that are able to generate poleward pulling forces. CONCLUSIONS Our results imply that Plk1 is not essential for mitotic entry and APC/C activation but is required for proper spindle assembly and function. In Plk1-depleted cells spindles may not be able to create enough tension across sister kinetochores to stabilize microtubule-kinetochore interactions and to silence the spindle checkpoint.
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Affiliation(s)
- Izabela Sumara
- Research Institute of Molecular Pathology, Dr. Bohr-Gasse 7, 1030 Vienna, Austria
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44
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Abstract
Polo-like kinases play critical roles during multiple stages of cell cycle progression. All Polo-like kinases contain an N-terminal Ser/Thr kinase catalytic domain and a C-terminal region that contains one or two Polo-boxes. For Polo-like kinase 1, 2, and 3, and their homologs, the entire C-terminal region, including both Polo-boxes, functions as a single modular phosphoserine/threonine-binding domain known as the Polo-box domain (PBD). In the absence of a bound substrate, the PBD inhibits the basal activity of the kinase domain. Phosphorylation-dependent binding of the PBD to its ligands releases the kinase domain, while simultaneously localizing Polo-like kinases to specific subcellular structures. These observations suggest two different models for how the PBD integrates signals arising from other mitotic kinases to target the activated kinase towards distinct substrates. The recent X-ray crystal structures of the PBD provide insights into the structural basis for PBD function and kinase regulation. Molecular modelling of the structure of the isolated kinase domain reveals a potential basis for motif-dependent substrate specificity.
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Affiliation(s)
- Drew M Lowery
- Center for Cancer Research, E18-580, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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45
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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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46
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Jang YJ, Ji JH, Ahn JH, Hoe KL, Won M, Im DS, Chae SK, Song S, Yoo HS. Polo-box motif targets a centrosome regulator, RanGTPase. Biochem Biophys Res Commun 2004; 325:257-64. [PMID: 15522227 DOI: 10.1016/j.bbrc.2004.10.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2004] [Indexed: 10/26/2022]
Abstract
Mammalian polo-like kinase (Plk) acts at various stages in early and late mitosis. Plk1 localizes in the centrosome, the central spindle, the midbody as well as the kinetochore. The non-catalytic region in the C-terminus of Plk1 has conserved sequence motifs, named polo-boxes. These motifs are important for Plk localization. GFP protein fused with the core sequences of polo-box (50 amino acids) localized Plk to target organelles. We screened for Plk interacting proteins by constructing a tandem repeat of the polo-box motif, and used it as bait in the two-hybrid system with HeLa cell cDNA library. RanGTPase was detected as a positive clone. Through in vitro and in vivo protein binding analysis in synchronized cells by thymidine block and by nocodazole treatment, we confirmed the interaction between endogenous Ran and Plk1. We showed that endogenous Ran and Plk1 proteins were co-localized to centrosomes, which is a major target organelle of endogenous Plk1, in early mitotic cells by immunofluorescence. Finally, we demonstrated that Plk1 phosphorylated RanBPM, a Ran-binding protein in microtubule organizing center, through the interaction with Ran. These data suggested that the core motif of polo-box is sufficient for Plk1-targeting, and that Plk1 may play roles in centrosome through recruitment and/or activation of Ran/RanBPM proteins.
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Affiliation(s)
- Young-Joo Jang
- Genome Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 52 Oeun-Dong, Yusong-Gu, Daejeon 305-333, Republic of Korea.
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47
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de Cárcer G. Heat shock protein 90 regulates the metaphase-anaphase transition in a polo-like kinase-dependent manner. Cancer Res 2004; 64:5106-12. [PMID: 15289312 DOI: 10.1158/0008-5472.can-03-2214] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We have shown previously that the molecular chaperone heat shock protein 90 (Hsp90) is required for a proper centrosome function. Indeed, this Hsp90 function seems to be reflected in Polo-like kinase stability. Inhibition of Hsp90 in HeLa cells results in cell cycle arrest either in G2 stage or at the metaphase-anaphase transition. Here, we show that this inhibition leads to inactivation of the anaphase-promoting complex or cyclosome by both dephosphorylation and induction of the spindle assembly checkpoint. Hsp90 inhibition compromises two of the main mitotic kinases, Polo-like kinase 1 (Plk1) and cdc2. Interestingly, this mitotic arrest does not occur in certain tumor cell lines where Hsp90 and Plk1 are not associated. Those cells are able to process mitosis successfully and have an active Plk1 despite Hsp90 inactivation. Therefore, it seems that Hsp90 regulates completion of mitosis depending on its association with Plk1.
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Affiliation(s)
- Guillermo de Cárcer
- Molecular Oncology Programme, Centro Nacional de Investigaciones Oncológicas, Melchior Fernandez Almagro 3, 28029 Madrid, Spain.
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48
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Barr FA, Silljé HHW, Nigg EA. Polo-like kinases and the orchestration of cell division. Nat Rev Mol Cell Biol 2004; 5:429-40. [PMID: 15173822 DOI: 10.1038/nrm1401] [Citation(s) in RCA: 854] [Impact Index Per Article: 42.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Francis A Barr
- Department of Cell Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
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49
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Coelho PA, Queiroz-Machado J, Sunkel CE. Condensin-dependent localisation of topoisomerase II to an axial chromosomal structure is required for sister chromatid resolution during mitosis. J Cell Sci 2004; 116:4763-76. [PMID: 14600262 DOI: 10.1242/jcs.00799] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Assembly of compact mitotic chromosomes and resolution of sister chromatids are two essential processes for the correct segregation of the genome during mitosis. Condensin, a five-subunit protein complex, is thought to be required for chromosome condensation. However, recent genetic analysis suggests that condensin is only essential to resolve sister chromatids. To study further the function of condensin we have depleted DmSMC4, a subunit of the complex, from Drosophila S2 cells by dsRNA-mediated interference. Cells lacking DmSMC4 assemble short mitotic chromosomes with unresolved sister chromatids where Barren, a non-SMC subunit of the complex is unable to localise. Topoisomerase II, however, binds mitotic chromatin after depletion of DmSMC4 but it is no longer confined to a central axial structure and becomes diffusely distributed all over the chromatin. Furthermore, cell extracts from DmSMC4 dsRNA-treated cells show significantly reduced topoisomerase II-dependent DNA decatenation activity in vitro. Nevertheless, DmSMC4-depleted chromosomes have centromeres and kinetochores that are able to segregate, although sister chromatid arms form extensive chromatin bridges during anaphase. These chromatin bridges do not result from inappropriate maintenance of sister chromatid cohesion by DRAD21, a subunit of the cohesin complex. Moreover, depletion of DmSMC4 prevents premature sister chromatid separation, caused by removal of DRAD21, allowing cells to exit mitosis with chromatin bridges. Our results suggest that condensin is required so that an axial chromatid structure can be organised where topoisomerase II can effectively promote sister chromatid resolution.
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Affiliation(s)
- Paula A Coelho
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
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50
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Logarinho E, Bousbaa H, Dias JM, Lopes C, Amorim I, Antunes-Martins A, Sunkel CE. Different spindle checkpoint proteins monitor microtubule attachment and tension at kinetochores in Drosophila cells. J Cell Sci 2004; 117:1757-71. [PMID: 15075237 DOI: 10.1242/jcs.01033] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The spindle assembly checkpoint detects errors in kinetochore attachment to the spindle including insufficient microtubule occupancy and absence of tension across bi-oriented kinetochore pairs. Here, we analyse how the kinetochore localization of the Drosophila spindle checkpoint proteins Bub1, Mad2, Bub3 and BubR1, behave in response to alterations in microtubule binding or tension. To analyse the behaviour in the absence of tension, we treated S2 cells with low doses of taxol to disrupt microtubule dynamics and tension, but not kinetochore-microtubule occupancy. Under these conditions, we found that Mad2 and Bub1 do not accumulate at metaphase kinetochores whereas BubR1 does. Consistently, in mono-oriented chromosomes, both kinetochores accumulate BubR1 whereas Bub1 and Mad2 only localize at the unattached kinetochore. To study the effect of tension we analysed the kinetochore localization of spindle checkpoint proteins in relation to tension-sensitive kinetochore phosphorylation recognised by the 3F3/2 antibody. Using detergent-extracted S2 cells as a system in which kinetochore phosphorylation can be easily manipulated, we observed that BubR1 and Bub3 accumulation at kinetochores is dependent on the presence of phosphorylated 3F3/2 epitopes. However, Bub1 and Mad2 localize at kinetochores regardless of the 3F3/2 phosphorylation state. Altogether, our results suggest that spindle checkpoint proteins sense distinct aspects of kinetochore interaction with the spindle, with Mad2 and Bub1 monitoring microtubule occupancy while BubR1 and Bub3 monitor tension across attached kinetochores.
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Affiliation(s)
- Elsa Logarinho
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
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