1
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Polverino F, Mastrangelo A, Guarguaglini G. Contribution of AurkA/TPX2 Overexpression to Chromosomal Imbalances and Cancer. Cells 2024; 13:1397. [PMID: 39195284 DOI: 10.3390/cells13161397] [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: 07/12/2024] [Revised: 08/14/2024] [Accepted: 08/15/2024] [Indexed: 08/29/2024] Open
Abstract
The AurkA serine/threonine kinase is a key regulator of cell division controlling mitotic entry, centrosome maturation, and chromosome segregation. The microtubule-associated protein TPX2 controls spindle assembly and is the main AurkA regulator, contributing to AurkA activation, localisation, and stabilisation. Since their identification, AurkA and TPX2 have been described as being overexpressed in cancer, with a significant correlation with highly proliferative and aneuploid tumours. Despite the frequent occurrence of AurkA/TPX2 co-overexpression in cancer, the investigation of their involvement in tumorigenesis and cancer therapy resistance mostly arises from studies focusing only on one at the time. Here, we review the existing literature and discuss the mitotic phenotypes described under conditions of AurkA, TPX2, or AurkA/TPX2 overexpression, to build a picture that may help clarify their oncogenic potential through the induction of chromosome instability. We highlight the relevance of the AurkA/TPX2 complex as an oncogenic unit, based on which we discuss recent strategies under development that aim at disrupting the complex as a promising therapeutic perspective.
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Affiliation(s)
- Federica Polverino
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy
| | - Anna Mastrangelo
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy
| | - Giulia Guarguaglini
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy
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2
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Skinner MW, Simington CJ, López-Jiménez P, Baran KA, Xu J, Dayani Y, Pryzhkova MV, Page J, Gómez R, Holland AJ, Jordan PW. Spermatocytes have the capacity to segregate chromosomes despite centriole duplication failure. EMBO Rep 2024; 25:3373-3405. [PMID: 38943004 PMCID: PMC11316026 DOI: 10.1038/s44319-024-00187-6] [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: 12/12/2023] [Revised: 06/13/2024] [Accepted: 06/14/2024] [Indexed: 06/30/2024] Open
Abstract
Centrosomes are the canonical microtubule organizing centers (MTOCs) of most mammalian cells, including spermatocytes. Centrosomes comprise a centriole pair within a structurally ordered and dynamic pericentriolar matrix (PCM). Unlike in mitosis, where centrioles duplicate once per cycle, centrioles undergo two rounds of duplication during spermatogenesis. The first duplication is during early meiotic prophase I, and the second is during interkinesis. Using mouse mutants and chemical inhibition, we have blocked centriole duplication during spermatogenesis and determined that non-centrosomal MTOCs (ncMTOCs) can mediate chromosome segregation. This mechanism is different from the acentriolar MTOCs that form bipolar spindles in oocytes, which require PCM components, including gamma-tubulin and CEP192. From an in-depth analysis, we identified six microtubule-associated proteins, TPX2, KIF11, NuMA, and CAMSAP1-3, that localized to the non-centrosomal MTOC. These factors contribute to a mechanism that ensures bipolar MTOC formation and chromosome segregation during spermatogenesis when centriole duplication fails. However, despite the successful completion of meiosis and round spermatid formation, centriole inheritance and PLK4 function are required for normal spermiogenesis and flagella assembly, which are critical to ensure fertility.
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Affiliation(s)
- Marnie W Skinner
- Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - Carter J Simington
- Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA
| | - Pablo López-Jiménez
- Department of Biology, Autonomous University of Madrid, Madrid, Spain
- MRC Laboratory of Medical Sciences, London, W12 0NN, UK
| | - Kerstin A Baran
- Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA
| | - Jingwen Xu
- Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA
| | - Yaron Dayani
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
- The Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, USA
| | - Marina V Pryzhkova
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
- The Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, MD, USA
| | - Jesús Page
- Department of Biology, Autonomous University of Madrid, Madrid, Spain
| | - Rocío Gómez
- Department of Biology, Autonomous University of Madrid, Madrid, Spain
| | - Andrew J Holland
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Philip W Jordan
- Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
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3
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Prassanawar SS, Sarkar T, Panda D. CEP41, a ciliopathy-linked centrosomal protein, regulates microtubule assembly and cell proliferation. J Cell Sci 2024; 137:jcs261927. [PMID: 38841887 DOI: 10.1242/jcs.261927] [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: 12/22/2023] [Accepted: 05/29/2024] [Indexed: 06/07/2024] Open
Abstract
Centrosomal proteins play pivotal roles in orchestrating microtubule dynamics, and their dysregulation leads to disorders, including cancer and ciliopathies. Understanding the multifaceted roles of centrosomal proteins is vital to comprehend their involvement in disease development. Here, we report novel cellular functions of CEP41, a centrosomal and ciliary protein implicated in Joubert syndrome. We show that CEP41 is an essential microtubule-associated protein with microtubule-stabilizing activity. Purified CEP41 binds to preformed microtubules, promotes microtubule nucleation and suppresses microtubule disassembly. When overexpressed in cultured cells, CEP41 localizes to microtubules and promotes microtubule bundling. Conversely, shRNA-mediated knockdown of CEP41 disrupts the interphase microtubule network and delays microtubule reassembly, emphasizing its role in microtubule organization. Further, we demonstrate that the association of CEP41 with microtubules relies on its conserved rhodanese homology domain (RHOD) and the N-terminal region. Interestingly, a disease-causing mutation in the RHOD domain impairs CEP41-microtubule interaction. Moreover, depletion of CEP41 inhibits cell proliferation and disrupts cell cycle progression, suggesting its potential involvement in cell cycle regulation. These insights into the cellular functions of CEP41 hold promise for unraveling the impact of its mutations in ciliopathies.
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Affiliation(s)
- Shweta Shyam Prassanawar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Tuhin Sarkar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Dulal Panda
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
- National Institute of Pharmaceutical Education and Research, SAS Nagar, Punjab 160062, India
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4
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Perez-Bertoldi JM, Zhao Y, Thawani A, Yildiz A, Nogales E. Molecular interplay between HURP and Kif18A in mitotic spindle regulation. RESEARCH SQUARE 2024:rs.3.rs-4249615. [PMID: 38854046 PMCID: PMC11160874 DOI: 10.21203/rs.3.rs-4249615/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
During mitosis, microtubule dynamics are regulated to ensure proper alignment and segregation of chromosomes. The dynamics of kinetochore-attached microtubules are regulated by hepatoma-upregulated protein (HURP) and the mitotic kinesin-8 Kif18A, but the underlying mechanism remains elusive. Using single-molecule imaging in vitro, we demonstrate that Kif18A motility is regulated by HURP. While sparse decoration of HURP activates the motor, higher concentrations hinder processive motility. To shed light on this behavior, we determined the binding mode of HURP to microtubules using Cryo-EM. The structure reveals that one HURP motif spans laterally across β-tubulin, while a second motif binds between adjacent protofilaments. HURP partially overlaps with the microtubule-binding site of the Kif18A motor domain, indicating that excess HURP inhibits Kif18A motility by steric exclusion. We also observed that HURP and Kif18A function together to suppress dynamics of the microtubule plus-end, providing a mechanistic basis for how they collectively serve in spindle length control.
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Affiliation(s)
| | - Yuanchang Zhao
- Physics Department, University of California, Berkeley, CA, USA
| | - Akanksha Thawani
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
| | - Ahmet Yildiz
- Biophysics Graduate Group, University of California, Berkeley, CA, USA
- Physics Department, University of California, Berkeley, CA, USA
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
- Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Eva Nogales
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA
- Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- Howard Hughes Medical Institute, University of California, Berkeley, CA, USA
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5
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Sun S, Zhou J, Liu P. Liquid-liquid phase separation of microtubule-binding proteins in the regulation of spindle assembly. Cell Prolif 2024:e13649. [PMID: 38736355 DOI: 10.1111/cpr.13649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 03/19/2024] [Accepted: 04/15/2024] [Indexed: 05/14/2024] Open
Abstract
Cell division is a highly regulated process essential for the accurate segregation of chromosomes. Central to this process is the assembly of a bipolar mitotic spindle, a highly dynamic microtubule (MT)-based structure responsible for chromosome movement. The nucleation and dynamics of MTs are intricately regulated by MT-binding proteins. Over the recent years, various MT-binding proteins have been reported to undergo liquid-liquid phase separation, forming either single- or multi-component condensates on MTs. Herein, we provide a comprehensive summary of the phase separation characteristics of these proteins. We underscore their critical roles in MT nucleation, spindle assembly and kinetochore-MT attachment during the cell division process. Furthermore, we discuss the current challenges and various remaining unsolved problems, highlights the ongoing research efforts aimed at a deeper understanding of the role of the phase separation process during spindle assembly and orientation. Our review aims to contribute to the collective knowledge in this area and stimulate further investigations that will enhance our comprehension of the intricate mechanisms governing cell division.
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Affiliation(s)
- Shuang Sun
- Center for Cell Structure and Function, Shandong Provincial Key Laboratory of Animal Resistance Biology, Collaborative Innovation Center of Cell Biology in Universities of Shandong, Institute of Biomedical Sciences, College of Life Sciences, Shandong Normal University, Jinan, China
| | - Jun Zhou
- Center for Cell Structure and Function, Shandong Provincial Key Laboratory of Animal Resistance Biology, Collaborative Innovation Center of Cell Biology in Universities of Shandong, Institute of Biomedical Sciences, College of Life Sciences, Shandong Normal University, Jinan, China
- State Key Laboratory of Medicinal Chemical Biology, Haihe Laboratory of Cell Ecosystem, College of Life Sciences, Nankai University, Tianjin, China
| | - Peiwei Liu
- Center for Cell Structure and Function, Shandong Provincial Key Laboratory of Animal Resistance Biology, Collaborative Innovation Center of Cell Biology in Universities of Shandong, Institute of Biomedical Sciences, College of Life Sciences, Shandong Normal University, Jinan, China
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6
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Perez-Bertoldi JM, Zhao Y, Thawani A, Yildiz A, Nogales E. Molecular interplay between HURP and Kif18A in mitotic spindle regulation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.11.589088. [PMID: 38645125 PMCID: PMC11030443 DOI: 10.1101/2024.04.11.589088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
During mitosis, microtubule dynamics are regulated to ensure proper alignment and segregation of chromosomes. The dynamics of kinetochore-attached microtubules are regulated by hepatoma-upregulated protein (HURP) and the mitotic kinesin-8 Kif18A, but the underlying mechanism remains elusive. Using single-molecule imaging in vitro , we demonstrate that Kif18A motility is regulated by HURP. While sparse decoration of HURP activates the motor, higher concentrations hinder processive motility. To shed light on this behavior, we determined the binding mode of HURP to microtubules using Cryo-EM. The structure reveals that one HURP motif spans laterally across β-tubulin, while a second motif binds between adjacent protofilaments. HURP partially overlaps with the microtubule-binding site of the Kif18A motor domain, indicating that excess HURP inhibits Kif18A motility by steric exclusion. We also observed that HURP and Kif18A function together to suppress dynamics of the microtubule plus-end, providing a mechanistic basis for how they collectively serve in spindle length control.
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7
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Pena G, Rohrberg J, Goga A, Heald R. Changes in spindle morphology driven by TPX2 overexpression in MYC-driven breast cancer cells. MICROPUBLICATION BIOLOGY 2024; 2024:10.17912/micropub.biology.001182. [PMID: 38660563 PMCID: PMC11040394 DOI: 10.17912/micropub.biology.001182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Revised: 04/09/2024] [Accepted: 04/08/2024] [Indexed: 04/26/2024]
Abstract
The MYC oncogene was previously shown to induce mitotic spindle defects, chromosome instability, and reliance on the microtubule-associated protein TPX2 to survive, but how TPX2 levels affect spindle morphology in cancer cells has not previously been examined in detail. We show that breast cancer cell lines expressing high levels of MYC and TPX2 possess shorter spindles with increased TPX2 localization at spindle poles. A similar effect was observed in non-transformed human RPE-1 cells compared to a tumor cell line (HeLa) that overexpresses MYC . These results demonstrate that TPX2 alters spindle length and morphology in cancer cells, which may contribute their ability to divide despite MYC-induced mitotic stress.
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Affiliation(s)
- Guadalupe Pena
- Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, United States
| | - Julia Rohrberg
- Medicine, University of California, San Francisco, San Francisco, California, United States
- Cell & Tissue Biology, University of California, San Francisco, San Francisco, California, United States
| | - Andrei Goga
- Medicine, University of California, San Francisco, San Francisco, California, United States
- Cell & Tissue Biology, University of California, San Francisco, San Francisco, California, United States
| | - Rebecca Heald
- Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, United States
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8
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Pena GE, Zhou X, Slevin L, Brownlee C, Heald R. Identification of a motif in TPX2 that regulates spindle architecture in Xenopus egg extracts. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.10.579770. [PMID: 38370704 PMCID: PMC10871311 DOI: 10.1101/2024.02.10.579770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
A bipolar spindle composed of microtubules and many associated proteins functions to segregate chromosomes during cell division in all eukaryotes, yet spindle size and architecture varies dramatically across different species and cell types. Targeting protein for Xklp2 (TPX2) is one candidate factor for modulating spindle microtubule organization through its roles in branching microtubule nucleation, activation of the mitotic kinase Aurora A, and association with the kinesin-5 (Eg5) motor. Here we identify a conserved nuclear localization sequence (NLS) motif, 123 KKLK 126 in X. laevis TPX2, which regulates astral microtubule formation and spindle pole morphology in Xenopus egg extracts. Addition of recombinant TPX2 with this sequence mutated to AALA dramatically increased spontaneous formation of microtubule asters and recruitment of phosphorylated Aurora A, pericentrin, and Eg5 to meiotic spindle poles. We propose that TPX2 is a linchpin spindle assembly factor whose regulation contributes to the recruitment and activation of multiple microtubule polymerizing and organizing proteins, generating distinct spindle architectures.
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9
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Zhu Z, Becam I, Tovey CA, Elfarkouchi A, Yen EC, Bernard F, Guichet A, Conduit PT. Multifaceted modes of γ-tubulin complex recruitment and microtubule nucleation at mitotic centrosomes. J Cell Biol 2023; 222:e202212043. [PMID: 37698931 PMCID: PMC10497398 DOI: 10.1083/jcb.202212043] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Revised: 05/18/2023] [Accepted: 07/24/2023] [Indexed: 09/14/2023] Open
Abstract
Microtubule nucleation is mediated by γ-tubulin ring complexes (γ-TuRCs). In most eukaryotes, a GCP4/5/4/6 "core" complex promotes γ-tubulin small complex (γ-TuSC) association to generate cytosolic γ-TuRCs. Unlike γ-TuSCs, however, this core complex is non-essential in various species and absent from budding yeasts. In Drosophila, Spindle defective-2 (Spd-2) and Centrosomin (Cnn) redundantly recruit γ-tubulin complexes to mitotic centrosomes. Here, we show that Spd-2 recruits γ-TuRCs formed via the GCP4/5/4/6 core, but Cnn can recruit γ-TuSCs directly via its well-conserved CM1 domain, similar to its homologs in budding yeast. When centrosomes fail to recruit γ-tubulin complexes, they still nucleate microtubules via the TOG domain protein Mini-spindles (Msps), but these microtubules have different dynamic properties. Our data, therefore, help explain the dispensability of the GCP4/5/4/6 core and highlight the robustness of centrosomes as microtubule organizing centers. They also suggest that the dynamic properties of microtubules are influenced by how they are nucleated.
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Affiliation(s)
- Zihan Zhu
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Isabelle Becam
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Corinne A. Tovey
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Abir Elfarkouchi
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Eugenie C. Yen
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Fred Bernard
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Antoine Guichet
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Paul T. Conduit
- Department of Zoology, University of Cambridge, Cambridge, UK
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
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10
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Didaskalou S, Efstathiou C, Galtsidis S, Kesisova I, Halavatyi A, Elmali T, Tsolou A, Girod A, Koffa M. HURP localization in metaphase is the result of a multi-step process requiring its phosphorylation at Ser627 residue. Front Cell Dev Biol 2023; 11:981425. [PMID: 37484914 PMCID: PMC10361663 DOI: 10.3389/fcell.2023.981425] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 06/20/2023] [Indexed: 07/25/2023] Open
Abstract
Faithful chromosome segregation during cell division requires accurate mitotic spindle formation. As mitosis occurs rapidly within the cell cycle, the proteins involved in mitotic spindle assembly undergo rapid changes, including their interactions with other proteins. The proper localization of the HURP protein on the kinetochore fibers, in close proximity to chromosomes, is crucial for ensuring accurate congression and segregation of chromosomes. In this study, we employ photoactivation and FRAP experiments to investigate the impact of alterations in microtubule flux and phosphorylation of HURP at the Ser627 residue on its dynamics. Furthermore, through immunoprecipitations assays, we demonstrate the interactions of HURP with various proteins, such as TPX2, Aurora A, Eg5, Dynein, Kif5B, and Importin β, in mammalian cells during mitosis. We also find that phosphorylation of HURP at Ser627 regulates its interaction with these partners during mitosis. Our findings suggest that HURP participates in at least two distinct complexes during metaphase to ensure its proper localization in close proximity to chromosomes, thereby promoting the bundling and stabilization of kinetochore fibers.
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Affiliation(s)
- Stylianos Didaskalou
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece
| | - Christos Efstathiou
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece
- Department of Life Sciences and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Sotirios Galtsidis
- Department of Life Sciences and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Ilοna Kesisova
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece
- Department of Life Sciences and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Aliaksandr Halavatyi
- Advanced Light Microscopy Facility, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Tountzai Elmali
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece
| | - Avgi Tsolou
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece
| | - Andreas Girod
- Department of Life Sciences and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Maria Koffa
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece
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11
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Guo C, Alfaro-Aco R, Zhang C, Russell RW, Petry S, Polenova T. Structural basis of protein condensation on microtubules underlying branching microtubule nucleation. Nat Commun 2023; 14:3682. [PMID: 37344496 PMCID: PMC10284871 DOI: 10.1038/s41467-023-39176-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 06/01/2023] [Indexed: 06/23/2023] Open
Abstract
Targeting protein for Xklp2 (TPX2) is a key factor that stimulates branching microtubule nucleation during cell division. Upon binding to microtubules (MTs), TPX2 forms condensates via liquid-liquid phase separation, which facilitates recruitment of microtubule nucleation factors and tubulin. We report the structure of the TPX2 C-terminal minimal active domain (TPX2α5-α7) on the microtubule lattice determined by magic-angle-spinning NMR. We demonstrate that TPX2α5-α7 forms a co-condensate with soluble tubulin on microtubules and binds to MTs between two adjacent protofilaments and at the intersection of four tubulin heterodimers. These interactions stabilize the microtubules and promote the recruitment of tubulin. Our results reveal that TPX2α5-α7 is disordered in solution and adopts a folded structure on MTs, indicating that TPX2α5-α7 undergoes structural changes from unfolded to folded states upon binding to microtubules. The aromatic residues form dense interactions in the core, which stabilize folding of TPX2α5-α7 on microtubules. This work informs on how the phase-separated TPX2α5-α7 behaves on microtubules and represents an atomic-level structural characterization of a protein that is involved in a condensate on cytoskeletal filaments.
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Affiliation(s)
- Changmiao Guo
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716, USA
| | - Raymundo Alfaro-Aco
- Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, USA
| | - Chunting Zhang
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716, USA
| | - Ryan W Russell
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716, USA
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ, 08544, USA.
| | - Tatyana Polenova
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716, USA.
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12
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Sobajima T, Kowalczyk KM, Skylakakis S, Hayward D, Fulcher LJ, Neary C, Batley C, Kurlekar S, Roberts E, Gruneberg U, Barr FA. PP6 regulation of Aurora A-TPX2 limits NDC80 phosphorylation and mitotic spindle size. J Cell Biol 2023; 222:e202205117. [PMID: 36897279 PMCID: PMC10041653 DOI: 10.1083/jcb.202205117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 11/22/2022] [Accepted: 02/10/2023] [Indexed: 03/11/2023] Open
Abstract
Amplification of the mitotic kinase Aurora A or loss of its regulator protein phosphatase 6 (PP6) have emerged as drivers of genome instability. Cells lacking PPP6C, the catalytic subunit of PP6, have amplified Aurora A activity, and as we show here, enlarged mitotic spindles which fail to hold chromosomes tightly together in anaphase, causing defective nuclear structure. Using functional genomics to shed light on the processes underpinning these changes, we discover synthetic lethality between PPP6C and the kinetochore protein NDC80. We find that NDC80 is phosphorylated on multiple N-terminal sites during spindle formation by Aurora A-TPX2, exclusively at checkpoint-silenced, microtubule-attached kinetochores. NDC80 phosphorylation persists until spindle disassembly in telophase, is increased in PPP6C knockout cells, and is Aurora B-independent. An Aurora-phosphorylation-deficient NDC80-9A mutant reduces spindle size and suppresses defective nuclear structure in PPP6C knockout cells. In regulating NDC80 phosphorylation by Aurora A-TPX2, PP6 plays an important role in mitotic spindle formation and size control and thus the fidelity of cell division.
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Affiliation(s)
| | | | | | - Daniel Hayward
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
- Randall Centre for Cell and Molecular Biophysics, King’s College London, London, UK
| | - Luke J. Fulcher
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Colette Neary
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Caleb Batley
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Samvid Kurlekar
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Emile Roberts
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Ulrike Gruneberg
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Francis A. Barr
- Department of Biochemistry, University of Oxford, Oxford, UK
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13
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Kraus J, Travis SM, King MR, Petry S. Augmin is a Ran-regulated spindle assembly factor. J Biol Chem 2023; 299:104736. [PMID: 37086784 DOI: 10.1016/j.jbc.2023.104736] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 04/03/2023] [Accepted: 04/05/2023] [Indexed: 04/24/2023] Open
Abstract
Mitotic spindles are composed of microtubules (MTs) that must nucleate at the right place and time. Ran regulates this process by directly controlling the release of spindle assembly factors (SAFs) from nucleocytoplasmic shuttle proteins importin-αβ and subsequently forms a biochemical gradient of SAFs localized around chromosomes. The majority of spindle MTs are generated by branching MT nucleation, which has been shown to require an eight-subunit protein complex known as augmin. InXenopus laevis, Ran can control branching through a canonical SAF, TPX2, which is non-essential in Drosophila melanogaster embryos and HeLa cells. Thus, how Ran regulates branching MT nucleation when TPX2 is not required remains unknown. Here, we use in vitro pulldowns and TIRF microscopy to show that augmin is a Ran-regulated SAF. We demonstrate that augmin directly interacts with both importin-α and importin-β through two nuclear localization sequences on the Haus8 subunit, which overlap with the MT binding site. Moreover, we show Ran controls localization of augmin to MTs in both Xenopus egg extract and in vitro. Our results demonstrate that RanGTP directly regulates augmin, which establishes a new way by which Ran controls branching MT nucleation and spindle assembly both in the absence and presence of TPX2.
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Affiliation(s)
- Jodi Kraus
- Department of Molecular Biology; Princeton University; Princeton, NJ, 08544; USA
| | - Sophie M Travis
- Department of Molecular Biology; Princeton University; Princeton, NJ, 08544; USA
| | - Matthew R King
- Department of Molecular Biology; Princeton University; Princeton, NJ, 08544; USA
| | - Sabine Petry
- Department of Molecular Biology; Princeton University; Princeton, NJ, 08544; USA.
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14
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Travis SM, Mahon BP, Huang W, Ma M, Rale MJ, Kraus J, Taylor DJ, Zhang R, Petry S. Integrated model of the vertebrate augmin complex. Nat Commun 2023; 14:2072. [PMID: 37055408 PMCID: PMC10102177 DOI: 10.1038/s41467-023-37519-4] [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: 09/26/2022] [Accepted: 03/17/2023] [Indexed: 04/15/2023] Open
Abstract
Accurate segregation of chromosomes is required to maintain genome integrity during cell division. This feat is accomplished by the microtubule-based spindle. To build a spindle rapidly and with high fidelity, cells take advantage of branching microtubule nucleation, which rapidly amplifies microtubules during cell division. Branching microtubule nucleation relies on the hetero-octameric augmin complex, but lack of structure information about augmin has hindered understanding how it promotes branching. In this work, we combine cryo-electron microscopy, protein structural prediction, and visualization of fused bulky tags via negative stain electron microscopy to identify the location and orientation of each subunit within the augmin structure. Evolutionary analysis shows that augmin's structure is highly conserved across eukaryotes, and that augmin contains a previously unidentified microtubule binding site. Thus, our findings provide insight into the mechanism of branching microtubule nucleation.
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Affiliation(s)
- Sophie M Travis
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Brian P Mahon
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Department of Structural Biology, Bristol Myers Squibb, Princeton, NJ, USA
| | - Wei Huang
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA
| | - Meisheng Ma
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine, St. Louis, MO, USA
- Department of Histology and Embryology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Michael J Rale
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Jodi Kraus
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Derek J Taylor
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA
| | - Rui Zhang
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine, St. Louis, MO, USA.
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
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15
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Shrestha S, Ems-McClung SC, Hazelbaker MA, Yount AL, Shaw SL, Walczak CE. Importin α/β promote Kif18B microtubule association and enhance microtubule destabilization activity. Mol Biol Cell 2023; 34:ar30. [PMID: 36790918 PMCID: PMC10092650 DOI: 10.1091/mbc.e22-03-0113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023] Open
Abstract
Tight regulation of microtubule (MT) dynamics is necessary for proper spindle assembly and chromosome segregation. The MT destabilizing Kinesin-8, Kif18B, controls astral MT dynamics and spindle positioning. Kif18B interacts with importin α/β as well as with the plus-tip tracking protein EB1, but how these associations modulate Kif18B is not known. We mapped the key binding sites on Kif18B, made residue-specific mutations, and assessed their impact on Kif18B function. Blocking EB1 interaction disrupted Kif18B MT plus-end accumulation and inhibited its ability to control MT length on monopolar spindles in cells. Blocking importin α/β interaction disrupted Kif18B localization without affecting aster size. In vitro, importin α/β increased Kif18B MT association by increasing the on-rate and decreasing the off-rate from MTs, which stimulated MT destabilization. In contrast, EB1 promoted MT destabilization without increasing lattice binding in vitro, which suggests that EB1 and importin α/β have distinct roles in the regulation of Kif18B-mediated MT destabilization. We propose that importin α/β spatially modulate Kif18B association with MTs to facilitate its MT destabilization activity. Our results suggest that Ran regulation is important not only to control molecular motor function near chromatin but also to provide a spatial control mechanism to modulate MT binding of nuclear localization signal-containing spindle assembly factors.
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Affiliation(s)
- Sanjay Shrestha
- Medical Sciences, Indiana School of Medicine-Bloomington, Bloomington, IN 47405
| | | | - Mark A Hazelbaker
- Medical Sciences, Indiana School of Medicine-Bloomington, Bloomington, IN 47405
| | - Amber L Yount
- Medical Sciences, Indiana School of Medicine-Bloomington, Bloomington, IN 47405
| | - Sidney L Shaw
- Department of Biology, Indiana University, Bloomington, IN 47405
| | - Claire E Walczak
- Medical Sciences, Indiana School of Medicine-Bloomington, Bloomington, IN 47405
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16
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Effects of Ran-GTP/importin β inhibition on the meiotic division of porcine oocytes. Histochem Cell Biol 2022; 158:571-582. [PMID: 35930054 DOI: 10.1007/s00418-022-02134-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/27/2022] [Indexed: 12/13/2022]
Abstract
The Ran-GTP/importin β pathway has been implicated in a diverse array of mitotic functions in somatic mitosis; however, the possible meiotic roles of Ran-GTP/importin β in mammalian oocyte meiosis are still not fully understood. In the present study, importazole (IPZ), a small molecule inhibitor of the interaction between Ran and importin β was used to explore the potential meiotic roles of Ran-GTP/importin β in porcine oocytes undergoing meiosis. After IPZ treatment, the extrusion rate of the first polar body (PB1) was significantly decreased, and a higher proportion of the oocytes were arrested at the germinal vesicle breakdown (GVBD) stage. Moreover, IPZ treatment led to severe defects in metaphase I (MI) spindle assembly and chromosome alignment during the germinal vesicle (GV)-to-MI stage, as well as failure of metaphase II (MII) spindle reassembly and homologous chromosome segregation during the MI-to-MII stage. Notably, IPZ treatment decreased TPX2 expression and abnormal subcellular localization. Furthermore, the expression levels of aurora kinase A (AURKA) and transforming acidic coiled-coil 3 (TACC3) were significantly reduced after IPZ treatment. Collectively, these data indicate that the interaction of Ran-GTP and importin β is essential for proper spindle assembly and successful chromosome segregation during two consecutive meiotic divisions in porcine oocytes, and regulation of this complex might be related to its effect on the TPX2 signaling cascades.
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17
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Li H, Wang Y, Lin K, Venkadakrishnan VB, Bakht M, Shi W, Meng C, Zhang J, Tremble K, Liang X, Song JH, Feng X, Van V, Deng P, Burks JK, Aparicio A, Keyomarsi K, Chen J, Lu Y, Beltran H, Zhao D. CHD1 Promotes Sensitivity to Aurora Kinase Inhibitors by Suppressing Interaction of AURKA with Its Coactivator TPX2. Cancer Res 2022; 82:3088-3101. [PMID: 35771632 PMCID: PMC9444962 DOI: 10.1158/0008-5472.can-22-0631] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Revised: 04/27/2022] [Accepted: 06/22/2022] [Indexed: 02/03/2023]
Abstract
Clinical studies have shown that subsets of patients with cancer achieve a significant benefit from Aurora kinase inhibitors, suggesting an urgent need to identify biomarkers for predicting drug response. Chromodomain helicase DNA binding protein 1 (CHD1) is involved in chromatin remodeling, DNA repair, and transcriptional plasticity. Prior studies have demonstrated that CHD1 has distinct expression patterns in cancers with different molecular features, but its impact on drug responsiveness remains understudied. Here, we show that CHD1 promotes the susceptibility of prostate cancer cells to inhibitors targeting Aurora kinases, while depletion of CHD1 impairs their efficacy in vitro and in vivo. Pan-cancer drug sensitivity analyses revealed that high expression of CHD1 was associated with increased sensitivity to Aurora kinase A (AURKA) inhibitors. Mechanistically, KPNA2 served as a direct target of CHD1 and suppressed the interaction of AURKA with the coactivator TPX2, thereby rendering cancer cells more vulnerable to AURKA inhibitors. Consistent with previous research reporting that loss of PTEN elevates CHD1 levels, studies in a genetically engineered mouse model, patient-derived organoids, and patient samples showed that PTEN defects are associated with a better response to AURKA inhibition in advanced prostate cancer. These observations demonstrate that CHD1 plays an important role in modulating Aurora kinases and drug sensitivities, providing new insights into biomarker-driven therapies targeting Aurora kinases for future clinical studies. SIGNIFICANCE CHD1 plays a critical role in controlling AURKA activation and promoting Aurora kinase inhibitor sensitivity, providing a potential clinical biomarker to guide cancer treatment.
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Affiliation(s)
- Haoyan Li
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Yin Wang
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Kevin Lin
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | | | - Martin Bakht
- Division of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Wei Shi
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Chenling Meng
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Jie Zhang
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Kaitlyn Tremble
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
- Honors College, Baylor University, Waco, TX 76706, USA
| | - Xin Liang
- Department of Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Jian H. Song
- Department of Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Xu Feng
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Vivien Van
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Pingna Deng
- Department of Cancer Biology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Jared K. Burks
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Ana Aparicio
- Department of Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Khandan Keyomarsi
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Junjie Chen
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Yue Lu
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Himisha Beltran
- Division of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Di Zhao
- Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
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18
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Sami AB, Gatlin JC. Dynein-dependent collection of membranes defines the architecture and position of microtubule asters in isolated, geometrically confined volumes of cell-free extracts. Mol Biol Cell 2022; 33:br20. [PMID: 35976715 DOI: 10.1091/mbc.e22-03-0074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
It is well established that changes in the underlying architecture of the cell's microtubule network can affect organelle organization within the cytoplasm, but it remains unclear whether the spatial arrangement of organelles reciprocally influences the microtubule network. Here we use a combination of cell-free extracts and hydrogel microenclosures to characterize the relationship between membranes and microtubules during microtubule aster centration. We found that initially disperse ER membranes are collected by the aster and compacted near its nucleating center, all while the whole ensemble moves toward the geometric center of its confining enclosure. Once there, aster microtubules adopt a bullseye pattern with a high density annular ring of microtubules surrounding the compacted membrane core of lower microtubule density. Formation of this pattern was inhibited when dynein-dependent transport was perturbed or when membranes were depleted from the extracts. Asters in membrane-depleted extracts were able to move away from the most proximal wall but failed to center in cylindrical enclosures with diameters greater than or equal to 150 µm. Taken as whole, our data suggest that the dynein-dependent transport of membranes buttresses microtubules near the aster center and that this plays an important role in modulating aster architecture and position. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text].
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Affiliation(s)
| | - Jesse C Gatlin
- Department of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA.,Cell Division & Organization Group, Marine Biological Laboratory, Woods Hole, MA 02543, USA
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19
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Imasaki T, Kikkawa S, Niwa S, Saijo-Hamano Y, Shigematsu H, Aoyama K, Mitsuoka K, Shimizu T, Aoki M, Sakamoto A, Tomabechi Y, Sakai N, Shirouzu M, Taguchi S, Yamagishi Y, Setsu T, Sakihama Y, Nitta E, Takeichi M, Nitta R. CAMSAP2 organizes a γ-tubulin-independent microtubule nucleation centre through phase separation. eLife 2022; 11:77365. [PMID: 35762204 PMCID: PMC9239687 DOI: 10.7554/elife.77365] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 05/24/2022] [Indexed: 11/24/2022] Open
Abstract
Microtubules are dynamic polymers consisting of αβ-tubulin heterodimers. The initial polymerization process, called microtubule nucleation, occurs spontaneously via αβ-tubulin. Since a large energy barrier prevents microtubule nucleation in cells, the γ-tubulin ring complex is recruited to the centrosome to overcome the nucleation barrier. However, a considerable number of microtubules can polymerize independently of the centrosome in various cell types. Here, we present evidence that the minus-end-binding calmodulin-regulated spectrin-associated protein 2 (CAMSAP2) serves as a strong nucleator for microtubule formation by significantly reducing the nucleation barrier. CAMSAP2 co-condensates with αβ-tubulin via a phase separation process, producing plenty of nucleation intermediates. Microtubules then radiate from the co-condensates, resulting in aster-like structure formation. CAMSAP2 localizes at the co-condensates and decorates the radiating microtubule lattices to some extent. Taken together, these in vitro findings suggest that CAMSAP2 supports microtubule nucleation and growth by organizing a nucleation centre as well as by stabilizing microtubule intermediates and growing microtubules. Cells are able to hold their shape thanks to tube-like structures called microtubules that are made of hundreds of tubulin proteins. Microtubules are responsible for maintaining the uneven distribution of molecules throughout the cell, a phenomenon known as polarity that allows cells to differentiate into different types with various roles. A protein complex called the γ-tubulin ring complex (γ-TuRC) is necessary for microtubules to form. This protein helps bind the tubulin proteins together and stabilises microtubules. However, recent research has found that in highly polarized cells such as neurons, which have highly specialised regions, microtubules can form without γ-TuRC. Searching for the proteins that could be filling in for γ-TuRC in these cells some evidence has suggested that a group known as CAMSAPs may be involved, but it is not known how. To characterize the role of CAMSAPs, Imasaki, Kikkawa et al. studied how one of these proteins, CAMSAP2, interacts with tubulins. To do this, they reconstituted both CAMSAP2 and tubulins using recombinant biotechnology and mixed them in solution. These experiments showed that CAMSAP2 can help form microtubules by bringing together their constituent proteins so that they can bind to each other more easily. Once microtubules start to form, CAMSAP2 continues to bind to them, stabilizing them and enabling them to grow to full size. These results shed light on how polarity is established in cells such as neurons, muscle cells, and epithelial cells. Additionally, the ability to observe intermediate structures during microtubule formation can provide insights into the processes that these structures are involved in.
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Affiliation(s)
- Tsuyoshi Imasaki
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan.,JST, PRESTO, Saitama, Japan.,RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Satoshi Kikkawa
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Shinsuke Niwa
- Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
| | - Yumiko Saijo-Hamano
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Hideki Shigematsu
- RIKEN SPring-8 Center, Hyogo, Japan.,Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, Japan
| | - Kazuhiro Aoyama
- Materials and Structural Analysis, Thermo Fisher Scientific, Tokyo, Japan.,Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Osaka, Japan
| | - Kaoru Mitsuoka
- Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Osaka, Japan
| | - Takahiro Shimizu
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Mari Aoki
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Ayako Sakamoto
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Yuri Tomabechi
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Naoki Sakai
- RIKEN SPring-8 Center, Hyogo, Japan.,Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, Japan
| | - Mikako Shirouzu
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Shinya Taguchi
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Yosuke Yamagishi
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Tomiyoshi Setsu
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Yoshiaki Sakihama
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Eriko Nitta
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan
| | | | - Ryo Nitta
- Division of Structural Medicine and Anatomy, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan.,RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
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20
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Ozugergin I, Mastronardi K, Law C, Piekny A. Diverse mechanisms regulate contractile ring assembly for cytokinesis in the two-cell Caenorhabditis elegans embryo. J Cell Sci 2022; 135:jcs258921. [PMID: 35022791 PMCID: PMC10660071 DOI: 10.1242/jcs.258921] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Accepted: 12/29/2021] [Indexed: 11/20/2022] Open
Abstract
Cytokinesis occurs at the end of mitosis as a result of the ingression of a contractile ring that cleaves the daughter cells. The core machinery regulating this crucial process is conserved among metazoans. Multiple pathways control ring assembly, but their contribution in different cell types is not known. We found that in the Caenorhabditis elegans embryo, AB and P1 cells fated to be somatic tissue and germline, respectively, have different cytokinesis kinetics supported by distinct myosin levels and organization. Through perturbation of RhoA or polarity regulators and the generation of tetraploid strains, we found that ring assembly is controlled by multiple fate-dependent factors that include myosin levels, and mechanisms that respond to cell size. Active Ran coordinates ring position with the segregating chromatids in HeLa cells by forming an inverse gradient with importins that control the cortical recruitment of anillin. We found that the Ran pathway regulates anillin in AB cells but functions differently in P1 cells. We propose that ring assembly delays in P1 cells caused by low myosin and Ran signaling coordinate the timing of ring closure with their somatic neighbors. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Imge Ozugergin
- Department of Biology, Concordia University, Montreal, H4B 1R6, Canada
| | | | - Chris Law
- Department of Biology, Concordia University, Montreal, H4B 1R6, Canada
| | - Alisa Piekny
- Department of Biology, Concordia University, Montreal, H4B 1R6, Canada
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21
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Lacroix B, Dumont J. Spatial and Temporal Scaling of Microtubules and Mitotic Spindles. Cells 2022; 11:cells11020248. [PMID: 35053364 PMCID: PMC8774166 DOI: 10.3390/cells11020248] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 01/07/2022] [Accepted: 01/09/2022] [Indexed: 02/01/2023] Open
Abstract
During cell division, the mitotic spindle, a macromolecular structure primarily comprised of microtubules, drives chromosome alignment and partitioning between daughter cells. Mitotic spindles can sense cellular dimensions in order to adapt their length and mass to cell size. This scaling capacity is particularly remarkable during early embryo cleavage when cells divide rapidly in the absence of cell growth, thus leading to a reduction of cell volume at each division. Although mitotic spindle size scaling can occur over an order of magnitude in early embryos, in many species the duration of mitosis is relatively short, constant throughout early development and independent of cell size. Therefore, a key challenge for cells during embryo cleavage is not only to assemble a spindle of proper size, but also to do it in an appropriate time window which is compatible with embryo development. How spatial and temporal scaling of the mitotic spindle is achieved and coordinated with the duration of mitosis remains elusive. In this review, we will focus on the mechanisms that support mitotic spindle spatial and temporal scaling over a wide range of cell sizes and cellular contexts. We will present current models and propose alternative mechanisms allowing cells to spatially and temporally coordinate microtubule and mitotic spindle assembly.
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Affiliation(s)
- Benjamin Lacroix
- Centre de Recherche de Biologie Cellulaire de Montpellier (CRBM), CNRS UMR 5237, Université de Montpellier, 1919 Route de Mende, CEDEX 5, 34293 Montpellier, France
- Correspondence:
| | - Julien Dumont
- Université de Paris, CNRS, Institut Jacques Monod, F-75013 Paris, France;
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22
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Schneider I, de Ruijter-Villani M, Hossain MJ, Stout TA, Ellenberg J. Dual spindles assemble in bovine zygotes despite the presence of paternal centrosomes. J Cell Biol 2021; 220:e202010106. [PMID: 34550316 PMCID: PMC8563290 DOI: 10.1083/jcb.202010106] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 07/05/2021] [Accepted: 09/02/2021] [Indexed: 11/30/2022] Open
Abstract
The first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded, and instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In nonrodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether nonrodent zygotes assemble a single centrosomal spindle around both genomes or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in nonrodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.
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Affiliation(s)
- Isabell Schneider
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Marta de Ruijter-Villani
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands
- Division of Woman and Baby, University Medical Centre Utrecht, Utrecht, the Netherlands
| | - M. Julius Hossain
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Tom A.E. Stout
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands
| | - Jan Ellenberg
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
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23
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Safari MS, King MR, Brangwynne CP, Petry S. Interaction of spindle assembly factor TPX2 with importins-α/β inhibits protein phase separation. J Biol Chem 2021; 297:100998. [PMID: 34302807 PMCID: PMC8390506 DOI: 10.1016/j.jbc.2021.100998] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 07/12/2021] [Accepted: 07/20/2021] [Indexed: 12/30/2022] Open
Abstract
The microtubule-based mitotic spindle is responsible for equally partitioning the genome during each cell division, and its assembly is executed via several microtubule nucleation pathways. Targeting Protein for XKlp2 (TPX2) stimulates the branching microtubule nucleation pathway, where new microtubules are nucleated from preexisting ones within mitotic or meiotic spindles. TPX2, like other spindle assembly factors, is sequestered by binding to nuclear importins-α/β until the onset of mitosis, yet the molecular nature of this regulation remains unclear. Here we demonstrate that TPX2 interacts with importins-α/β with nanomolar affinity in a 1:1:1 monodispersed trimer. We also identify a new nuclear localization sequence in TPX2 that contributes to its high-affinity interaction with importin-α. In addition, we establish that TPX2 interacts with importin-β via dispersed, weak interactions. We show that interactions of both importin-α and -β with TPX2 inhibit its ability to undergo phase separation, which was recently shown to enhance the kinetics of branching microtubule nucleation. In summary, our study informs how importins regulate TPX2 to facilitate spindle assembly, and provides novel insight into the functional regulation of protein phase separation.
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Affiliation(s)
- Mohammad S Safari
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA
| | - Matthew R King
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA
| | - Clifford P Brangwynne
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey, USA; Howard Hughes Medical Institute, Princeton University, Princeton, New Jersey, USA
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA.
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24
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Abstract
As one of four filament types, microtubules are a core component of the cytoskeleton and are essential for cell function. Yet how microtubules are nucleated from their building blocks, the αβ-tubulin heterodimer, has remained a fundamental open question since the discovery of tubulin 50 years ago. Recent structural studies have shed light on how γ-tubulin and the γ-tubulin complex proteins (GCPs) GCP2 to GCP6 form the γ-tubulin ring complex (γ-TuRC). In parallel, functional and single-molecule studies have informed on how the γ-TuRC nucleates microtubules in real time, how this process is regulated in the cell and how it compares to other modes of nucleation. Another recent surprise has been the identification of a second essential nucleation factor, which turns out to be the well-characterized microtubule polymerase XMAP215 (also known as CKAP5, a homolog of chTOG, Stu2 and Alp14). This discovery helps to explain why the observed nucleation activity of the γ-TuRC in vitro is relatively low. Taken together, research in recent years has afforded important insight into how microtubules are made in the cell and provides a basis for an exciting era in the cytoskeleton field.
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Affiliation(s)
- Akanksha Thawani
- California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, Berkeley, CA 94720, USA
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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25
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Huang J, Liang Z, Guan C, Hua S, Jiang K. WDR62 regulates spindle dynamics as an adaptor protein between TPX2/Aurora A and katanin. J Cell Biol 2021; 220:212395. [PMID: 34137789 PMCID: PMC8240853 DOI: 10.1083/jcb.202007167] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Revised: 04/12/2021] [Accepted: 05/18/2021] [Indexed: 12/21/2022] Open
Abstract
WDR62 is a microcephaly-related, microtubule (MT)-associated protein (MAP) that localizes to the spindle pole and regulates spindle organization, but the underlying mechanisms remain elusive. Here, we show that WDR62 regulates spindle dynamics by recruiting katanin to the spindle pole and further reveal a TPX2–Aurora A–WDR62–katanin axis in cells. By combining cellular and in vitro experiments, we demonstrate that WDR62 shows preference for curved segments of dynamic GDP-MTs, as well as GMPCPP- and paclitaxel-stabilized MTs, suggesting that it recognizes extended MT lattice. Consistent with this property, WDR62 alone is inefficient in recruiting katanin to GDP-MTs, while WDR62 complexed with TPX2/Aurora A can potently promote katanin-mediated severing of GDP-MTs in vitro. In addition, the MT-binding affinity of WDR62 is autoinhibited through JNK phosphorylation-induced intramolecular interaction. We propose that WDR62 is an atypical MAP and functions as an adaptor protein between its recruiting factor TPX2/Aurora A and the effector katanin to orchestrate the regulation of spindle dynamics.
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Affiliation(s)
- Junjie Huang
- The State Key Laboratory Breeding Base of Basic Science of Stomatology and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China.,Frontier Science Center for Immunology and Metabolism, Medical Research Institute, Wuhan University, Wuhan, China
| | - Zhuobi Liang
- The State Key Laboratory Breeding Base of Basic Science of Stomatology and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China.,Frontier Science Center for Immunology and Metabolism, Medical Research Institute, Wuhan University, Wuhan, China
| | - Cuirong Guan
- The State Key Laboratory Breeding Base of Basic Science of Stomatology and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China.,Frontier Science Center for Immunology and Metabolism, Medical Research Institute, Wuhan University, Wuhan, China
| | - Shasha Hua
- The State Key Laboratory Breeding Base of Basic Science of Stomatology and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China.,Frontier Science Center for Immunology and Metabolism, Medical Research Institute, Wuhan University, Wuhan, China
| | - Kai Jiang
- The State Key Laboratory Breeding Base of Basic Science of Stomatology and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China.,Frontier Science Center for Immunology and Metabolism, Medical Research Institute, Wuhan University, Wuhan, China
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26
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Nord MS, Bernis C, Carmona S, Garland DC, Travesa A, Forbes DJ. Exportins can inhibit major mitotic assembly events in vitro: membrane fusion, nuclear pore formation, and spindle assembly. Nucleus 2021; 11:178-193. [PMID: 32762441 PMCID: PMC7540616 DOI: 10.1080/19491034.2020.1798093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Xenopus egg extracts are a powerful in vitro tool for studying complex biological processes, including nuclear reconstitution, nuclear membrane and pore assembly, and spindle assembly. Extracts have been further used to demonstrate a moonlighting regulatory role for nuclear import receptors or importins on these cell cycle assembly events. Here we show that exportins can also play a role in these events. Addition of Crm1, Exportin-t, or Exportin-5 decreased nuclear pore assembly in vitro. RanQ69L-GTP, a constitutively active form of RanGTP, ameliorated inhibition. Both Crm1 and Exportin-t inhibited fusion of nuclear membranes, again counteracted by RanQ69L-GTP. In mitotic extracts, Crm1 and Exportin-t negatively impacted spindle assembly. Pulldowns from the extracts using Crm1- or Exportin-t-beads revealed nucleoporins known to be essential for both nuclear pore and spindle assembly, with RanQ69L-GTP decreasing a subset of these target interactions. This study suggests a model where exportins, like importins, can regulate major mitotic assembly events.
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Affiliation(s)
- Matthew S Nord
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California-San Diego , La Jolla, CA, USA
| | - Cyril Bernis
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California-San Diego , La Jolla, CA, USA
| | - Sarah Carmona
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California-San Diego , La Jolla, CA, USA
| | - Dennis C Garland
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California-San Diego , La Jolla, CA, USA
| | - Anna Travesa
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California-San Diego , La Jolla, CA, USA
| | - Douglass J Forbes
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California-San Diego , La Jolla, CA, USA
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27
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Lai KY, Rizzato M, Aydin I, Villalonga-Planells R, Drexler HCA, Schelhaas M. A Ran-binding protein facilitates nuclear import of human papillomavirus type 16. PLoS Pathog 2021; 17:e1009580. [PMID: 33974675 PMCID: PMC8139508 DOI: 10.1371/journal.ppat.1009580] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 05/21/2021] [Accepted: 04/23/2021] [Indexed: 01/01/2023] Open
Abstract
Human papillomaviruses (HPVs) utilize an atypical mode of nuclear import during cell entry. Residing in the Golgi apparatus until mitosis onset, a subviral complex composed of the minor capsid protein L2 and viral DNA (L2/vDNA) is imported into the nucleus after nuclear envelope breakdown by associating with mitotic chromatin. In this complex, L2 plays a crucial role in the interactions with cellular factors that enable delivery and ultimately tethering of the viral genome to mitotic chromatin. To date, the cellular proteins facilitating these steps remain unknown. Here, we addressed which cellular proteins may be required for this process. Using label-free mass spectrometry, biochemical assays, microscopy, and functional virological assays, we discovered that L2 engages a hitherto unknown protein complex of Ran-binding protein 10 (RanBP10), karyopherin alpha2 (KPNA2), and dynein light chain DYNLT3 to facilitate transport towards mitotic chromatin. Thus, our study not only identifies novel cellular interactors and mechanism that facilitate a poorly understood step in HPV entry, but also a novel cellular transport complex. Human papillomaviruses (HPVs) cause proliferative lesions such as benign warts or malignant invasive cancers. Like other DNA viruses, HPV has to deliver its genome to the nucleus for viral genome transcription and replication. After initial attachment, HPVs are endocytosed to be eventually directed to the trans-Golgi-network (TGN) by intracellular trafficking, where they reside until cell division. Mitosis onset enables access of the virus to cellular chromatin after nuclear envelope breakdown. Tethering of the virus to mitotic chromatin ensures nuclear delivery upon reformation of the nuclear envelope after mitosis. Our previous work showed that the minor capsid protein L2 facilitates nuclear delivery. However, the detailed mechanism, namely, how HPV trafficks from cytosol to the nuclear space, is barely understood. Here, we identified for the first time cellular proteins that interacted with L2 for nuclear import. Mechanistically, the proteins formed a hitherto unknown cellular transport complex that interacted with L2 to direct the virus to mitotic chromosomes by microtubular transport. Our findings provided not only evidence for a transport mechanism of a poorly understood step of HPV entry, but also discovered a novel cellular transport complex.
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Affiliation(s)
- Kun-Yi Lai
- Institute of Cellular Virology, Westphalian Wilhelms-University of Münster, Münster, Germany
- Interfaculty Centre ‘Cells in Motion’ (CiM), Westphalian Wilhelms-University of Münster, Münster, Germany
| | - Matteo Rizzato
- Institute of Cellular Virology, Westphalian Wilhelms-University of Münster, Münster, Germany
| | - Inci Aydin
- Institute of Cellular Virology, Westphalian Wilhelms-University of Münster, Münster, Germany
| | | | - Hannes C. A. Drexler
- Biomolecular Mass Spectrometry Unit, Max Planck Institute for Molecular Biomedicine, Münster, Germany
| | - Mario Schelhaas
- Institute of Cellular Virology, Westphalian Wilhelms-University of Münster, Münster, Germany
- Interfaculty Centre ‘Cells in Motion’ (CiM), Westphalian Wilhelms-University of Münster, Münster, Germany
- * E-mail:
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28
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Smertenko A, Clare SJ, Effertz K, Parish A, Ross A, Schmidt S. A guide to plant TPX2-like and WAVE-DAMPENED2-like proteins. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:1034-1045. [PMID: 33130902 PMCID: PMC8502432 DOI: 10.1093/jxb/eraa513] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Accepted: 10/27/2020] [Indexed: 05/31/2023]
Abstract
TPX2 proteins were first identified in vertebrates as a key mitotic spindle assembly factor. Subsequent studies demonstrated that TPX2 is an intricate protein, with functionally and structurally distinct domains and motifs including Aurora kinase-binding, importin-binding, central microtubule-binding, and C-terminal TPX2 conserved domain, among others. The first plant TPX2-like protein, WAVE-DAMPENED2, was identified in Arabidopsis as a dominant mutation responsible for reducing the waviness of roots grown on slanted agar plates. Each plant genome encodes at least one 'canonical' protein with all TPX2 domains and a family of proteins (20 in Arabidopsis) that diversified to contain only some of the domains. Although all plant TPX2-family proteins to date bind microtubules, they function in distinct processes such as cell division, regulation of hypocotyl cell elongation by hormones and light signals, vascular development, or abiotic stress tolerance. Consequently, their expression patterns, regulation, and functions have diverged considerably. Here we summarize the current body of knowledge surrounding plant TPX2-family proteins.
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Affiliation(s)
- Andrei Smertenko
- Plant Molecular Sciences Graduate Program, Washington State University, Pullman, WA, USA
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Shaun J Clare
- Plant Molecular Sciences Graduate Program, Washington State University, Pullman, WA, USA
- Department of Crop and Soil Sciences, Washington State University, Pullman, WA, USA
| | - Karl Effertz
- Plant Molecular Sciences Graduate Program, Washington State University, Pullman, WA, USA
- Department of Crop and Soil Sciences, Washington State University, Pullman, WA, USA
| | - Alyssa Parish
- Plant Molecular Sciences Graduate Program, Washington State University, Pullman, WA, USA
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Austin Ross
- Plant Molecular Sciences Graduate Program, Washington State University, Pullman, WA, USA
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Sharol Schmidt
- Plant Molecular Sciences Graduate Program, Washington State University, Pullman, WA, USA
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
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29
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Ayukawa R, Iwata S, Imai H, Kamimura S, Hayashi M, Ngo KX, Minoura I, Uchimura S, Makino T, Shirouzu M, Shigematsu H, Sekimoto K, Gigant B, Muto E. GTP-dependent formation of straight tubulin oligomers leads to microtubule nucleation. J Cell Biol 2021; 220:211760. [PMID: 33544140 PMCID: PMC7871348 DOI: 10.1083/jcb.202007033] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 11/23/2020] [Accepted: 01/04/2021] [Indexed: 12/22/2022] Open
Abstract
Nucleation of microtubules (MTs) is essential for cellular activities, but its mechanism is unknown because of the difficulty involved in capturing rare stochastic events in the early stage of polymerization. Here, combining rapid flush negative stain electron microscopy (EM) and kinetic analysis, we demonstrate that the formation of straight oligomers of critical size is essential for nucleation. Both GDP and GTP tubulin form single-stranded oligomers with a broad range of curvatures, but upon nucleation, the curvature distribution of GTP oligomers is shifted to produce a minor population of straight oligomers. With tubulin having the Y222F mutation in the β subunit, the proportion of straight oligomers increases and nucleation accelerates. Our results support a model in which GTP binding generates a minor population of straight oligomers compatible with lateral association and further growth to MTs. This study suggests that cellular factors involved in nucleation promote it via stabilization of straight oligomers.
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Affiliation(s)
- Rie Ayukawa
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Seigo Iwata
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Hiroshi Imai
- Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, Tokyo, Japan
| | - Shinji Kamimura
- Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, Tokyo, Japan
| | - Masahito Hayashi
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Kien Xuan Ngo
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Itsushi Minoura
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Seiichi Uchimura
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Tsukasa Makino
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
| | - Mikako Shirouzu
- Laboratory for Protein Functional and Structural Biology, RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Hideki Shigematsu
- Laboratory for Protein Functional and Structural Biology, RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Ken Sekimoto
- Matière et Systèmes Complexes (MSC), CNRS UMR 7057, Université de Paris, Paris, France.,Gulliver, CNRS UMR 7083, ESPCI Paris and Université Paris Sciences et Lettres, Paris, France
| | - Benoît Gigant
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette, France
| | - Etsuko Muto
- Laboratory for Molecular Biophysics, RIKEN Center for Brain Science, Saitama, Japan
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30
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Ohi R, Strothman C, Zanic M. Impact of the 'tubulin economy' on the formation and function of the microtubule cytoskeleton. Curr Opin Cell Biol 2021; 68:81-89. [PMID: 33160109 PMCID: PMC7925340 DOI: 10.1016/j.ceb.2020.09.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/25/2020] [Accepted: 09/28/2020] [Indexed: 12/19/2022]
Abstract
The microtubule cytoskeleton is assembled from a finite pool of α,β-tubulin, the size of which is controlled by an autoregulation mechanism. Cells also tightly regulate the architecture and dynamic behavior of microtubule arrays. Here, we discuss progress in our understanding of how tubulin autoregulation is achieved and highlight work showing that tubulin, in its unassembled state, is relevant for regulating the formation and organization of microtubules. Emerging evidence suggests that tubulin regulates microtubule-associated proteins and kinesin motors that are critical for microtubule nucleation, dynamics, and function. These relationships create feedback loops that connect the tubulin assembly cycle to the organization and dynamics of microtubule networks. We term this concept the 'tubulin economy', which emphasizes the idea that tubulin is a resource that can be deployed for the immediate purpose of creating polymers, or alternatively as a signaling molecule that has more far-reaching consequences for the organization of microtubule arrays.
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Affiliation(s)
- Ryoma Ohi
- Department of Cell and Developmental Biology, University of Michigan, USA.
| | - Claire Strothman
- Department of Cell and Developmental Biology, Vanderbilt University, USA
| | - Marija Zanic
- Department of Cell and Developmental Biology, Vanderbilt University, USA; Department of Biomolecular and Chemical Engineering, Department of Biochemistry, Vanderbilt University, USA.
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31
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Chang CC, Hsia KC. More than a zip code: global modulation of cellular function by nuclear localization signals. FEBS J 2020; 288:5569-5585. [PMID: 33296547 DOI: 10.1111/febs.15659] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Revised: 12/03/2020] [Accepted: 12/07/2020] [Indexed: 12/27/2022]
Abstract
Extensive structural and functional studies have been carried out in the field of nucleocytoplasmic transport. Nuclear transport factors, such as Importin-α/-β, recognize nuclear localization signals (NLSs) on cargo, and together with the small GTPase Ran, facilitate their nuclear localization. However, it is now emerging that binding of nuclear transport factors to NLSs not only mediates nuclear transport but also contributes to a variety of cellular functions in eukaryotes. Here, we describe recent advances that reveal how NLSs facilitate diverse cellular functions beyond nuclear transport activity. We review separately NLS-mediated regulatory mechanisms at different levels of biological organization, including (a) assembly of higher-order structures; (b) cellular organelle dynamics; and (c) modulation of cellular stress responses and viral infections. Finally, we provide mechanistic insights into how NLSs can regulate such a broad range of functions via their structural and biochemical properties.
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Affiliation(s)
- Chih-Chia Chang
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Kuo-Chiang Hsia
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.,Institute of Biochemistry and Molecular Biology, College of Life Sciences, National Yang-Ming University, Taipei, Taiwan
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32
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Ong JY, Torres JZ. Phase Separation in Cell Division. Mol Cell 2020; 80:9-20. [PMID: 32860741 DOI: 10.1016/j.molcel.2020.08.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Revised: 07/10/2020] [Accepted: 08/07/2020] [Indexed: 02/08/2023]
Abstract
Cell division requires the assembly and organization of a microtubule spindle for the proper separation of chromosomes in mitosis and meiosis. Phase separation is an emerging paradigm for understanding spatial and temporal regulation of a variety of cellular processes, including cell division. Phase-separated condensates have been recently discovered at many structures during cell division as a possible mechanism for properly localizing, organizing, and activating proteins involved in cell division. Here, we review how these condensates play roles in regulating microtubule density and organization and spindle assembly and function and in activating some of the key players in cell division. We conclude with perspectives on areas of future research for this exciting and rapidly advancing field.
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Affiliation(s)
- Joseph Y Ong
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Jorge Z Torres
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095, USA; Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA; Jonsson Comprehensive Cancer Center, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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33
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Consolati T, Locke J, Roostalu J, Chen ZA, Gannon J, Asthana J, Lim WM, Martino F, Cvetkovic MA, Rappsilber J, Costa A, Surrey T. Microtubule Nucleation Properties of Single Human γTuRCs Explained by Their Cryo-EM Structure. Dev Cell 2020; 53:603-617.e8. [PMID: 32433913 PMCID: PMC7280788 DOI: 10.1016/j.devcel.2020.04.019] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 03/21/2020] [Accepted: 04/27/2020] [Indexed: 12/13/2022]
Abstract
The γ-tubulin ring complex (γTuRC) is the major microtubule nucleator in cells. The mechanism of its regulation is not understood. We purified human γTuRC and measured its nucleation properties in a total internal reflection fluorescence (TIRF) microscopy-based real-time nucleation assay. We find that γTuRC stably caps the minus ends of microtubules that it nucleates stochastically. Nucleation is inefficient compared with microtubule elongation. The 4 Å resolution cryoelectron microscopy (cryo-EM) structure of γTuRC, combined with crosslinking mass spectrometry analysis, reveals an asymmetric conformation with only part of the complex in a "closed" conformation matching the microtubule geometry. Actin in the core of the complex, and MZT2 at the outer perimeter of the closed part of γTuRC appear to stabilize the closed conformation. The opposite side of γTuRC is in an "open," nucleation-incompetent conformation, leading to a structural asymmetry explaining the low nucleation efficiency of purified human γTuRC. Our data suggest possible regulatory mechanisms for microtubule nucleation by γTuRC closure.
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Affiliation(s)
- Tanja Consolati
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK; Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology (BIST), Dr Aiguader 88, 08003 Barcelona, Spain
| | - Julia Locke
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | | | - Zhuo Angel Chen
- Bioanalytics, Institute of Biotechnology, Technische Universität Berlin, Berlin, Germany; Wellcome Centre for Cell Biology, University of Edinburgh, Edinburgh, UK
| | - Julian Gannon
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Jayant Asthana
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK; Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology (BIST), Dr Aiguader 88, 08003 Barcelona, Spain
| | - Wei Ming Lim
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK; Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology (BIST), Dr Aiguader 88, 08003 Barcelona, Spain
| | | | | | - Juri Rappsilber
- Bioanalytics, Institute of Biotechnology, Technische Universität Berlin, Berlin, Germany; Wellcome Centre for Cell Biology, University of Edinburgh, Edinburgh, UK
| | - Alessandro Costa
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK.
| | - Thomas Surrey
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK; Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology (BIST), Dr Aiguader 88, 08003 Barcelona, Spain; ICREA, Passeig de Lluis Companys 23, 08010 Barcelona, Spain.
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34
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Dvořák Tomaštíková E, Rutten T, Dvořák P, Tugai A, Ptošková K, Petrovská B, van Damme D, Houben A, Doležel J, Demidov D. Functional Divergence of Microtubule-Associated TPX2 Family Members in Arabidopsis thaliana. Int J Mol Sci 2020; 21:ijms21062183. [PMID: 32235723 PMCID: PMC7139753 DOI: 10.3390/ijms21062183] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 03/18/2020] [Accepted: 03/19/2020] [Indexed: 01/21/2023] Open
Abstract
TPX2 (Targeting Protein for Xklp2) is an evolutionary conserved microtubule-associated protein important for microtubule nucleation and mitotic spindle assembly. The protein was described as an activator of the mitotic kinase Aurora A in humans and the Arabidopsis AURORA1 (AUR1) kinase. In contrast to animal genomes that encode only one TPX2 gene, higher plant genomes encode a family with several TPX2-LIKE gene members (TPXL). TPXL genes of Arabidopsis can be divided into two groups. Group A proteins (TPXL2, 3, 4, and 8) contain Aurora binding and TPX2_importin domains, while group B proteins (TPXL1, 5, 6, and 7) harbor an Xklp2 domain. Canonical TPX2 contains all the above-mentioned domains. We confirmed using in vitro kinase assays that the group A proteins contain a functional Aurora kinase binding domain. Transient expression of Arabidopsis TPX2-like proteins in Nicotiana benthamiana revealed preferential localization to microtubules and nuclei. Co-expression of AUR1 together with TPX2-like proteins changed the localization of AUR1, indicating that these proteins serve as targeting factors for Aurora kinases. Taken together, we visualize the various localizations of the TPX2-LIKE family in Arabidopsis as a proxy to their functional divergence and provide evidence of their role in the targeted regulation of AUR1 kinase activity.
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Affiliation(s)
- Eva Dvořák Tomaštíková
- Institute of Experimental Botany of the Czech Academy of Sciences, Centre of the Region Hana for Biotechnological and Agricultural Research, Šlechtitelů 31, CZ-77900 Olomouc, Czech Republic; (K.P.); (B.P.); (J.D.)
- Correspondence: (E.D.T.); (D.D.); Tel.: +420-585-238-725 (E.D.T.); +49-394825-733 (D.D.)
| | - Twan Rutten
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Corrensstrasse 3, 06466 Seeland, Germany; (T.R.); (A.T.); (A.H.)
| | - Petr Dvořák
- Department of Botany, Faculty of Science, Palacký University Olomouc, Šlechtitelů 27, CZ-78371 Olomouc, Czech Republic;
| | - Alisa Tugai
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Corrensstrasse 3, 06466 Seeland, Germany; (T.R.); (A.T.); (A.H.)
| | - Klara Ptošková
- Institute of Experimental Botany of the Czech Academy of Sciences, Centre of the Region Hana for Biotechnological and Agricultural Research, Šlechtitelů 31, CZ-77900 Olomouc, Czech Republic; (K.P.); (B.P.); (J.D.)
| | - Beáta Petrovská
- Institute of Experimental Botany of the Czech Academy of Sciences, Centre of the Region Hana for Biotechnological and Agricultural Research, Šlechtitelů 31, CZ-77900 Olomouc, Czech Republic; (K.P.); (B.P.); (J.D.)
| | - Daniel van Damme
- Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium;
- Center for Plant Systems Biology, VIB, 9052 Ghent, Belgium
| | - Andreas Houben
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Corrensstrasse 3, 06466 Seeland, Germany; (T.R.); (A.T.); (A.H.)
| | - Jaroslav Doležel
- Institute of Experimental Botany of the Czech Academy of Sciences, Centre of the Region Hana for Biotechnological and Agricultural Research, Šlechtitelů 31, CZ-77900 Olomouc, Czech Republic; (K.P.); (B.P.); (J.D.)
| | - Dmitri Demidov
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Corrensstrasse 3, 06466 Seeland, Germany; (T.R.); (A.T.); (A.H.)
- Correspondence: (E.D.T.); (D.D.); Tel.: +420-585-238-725 (E.D.T.); +49-394825-733 (D.D.)
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Abstract
The Ran pathway has a well-described function in nucleocytoplasmic transport, where active Ran dissociates importin/karyopherin-bound cargo containing a nuclear localization signal (NLS) in the nucleus. As cells enter mitosis, the nuclear envelope breaks down and a gradient of active Ran forms where levels are highest near chromatin. This gradient plays a crucial role in regulating mitotic spindle assembly, where active Ran binds to and releases importins from NLS-containing spindle assembly factors. An emerging theme is that the Ran gradient also regulates the actomyosin cortex for processes including polar body extrusion during meiosis, and cytokinesis. For these events, active Ran could play an inhibitory role, where importin-binding may help promote or stabilize a conformation or interaction that favours the recruitment and function of cortical regulators. For either spindle assembly or cortical polarity, the gradient of active Ran determines the extent of importin-binding, the effects of which could vary for different proteins.
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Affiliation(s)
- Imge Ozugergin
- Department of Biology, Concordia University, Montreal, QC, Canada
| | - Alisa Piekny
- Department of Biology, Concordia University, Montreal, QC, Canada
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36
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Naso FD, Sterbini V, Crecca E, Asteriti IA, Russo AD, Giubettini M, Cundari E, Lindon C, Rosa A, Guarguaglini G. Excess TPX2 Interferes with Microtubule Disassembly and Nuclei Reformation at Mitotic Exit. Cells 2020; 9:E374. [PMID: 32041138 PMCID: PMC7072206 DOI: 10.3390/cells9020374] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 01/24/2020] [Accepted: 01/29/2020] [Indexed: 12/15/2022] Open
Abstract
The microtubule-associated protein TPX2 is a key mitotic regulator that contributes through distinct pathways to spindle assembly. A well-characterised function of TPX2 is the activation, stabilisation and spindle localisation of the Aurora-A kinase. High levels of TPX2 are reported in tumours and the effects of its overexpression have been investigated in cancer cell lines, while little is known in non-transformed cells. Here we studied TPX2 overexpression in hTERT RPE-1 cells, using either the full length TPX2 or a truncated form unable to bind Aurora-A, to identify effects that are dependent-or independent-on its interaction with the kinase. We observe significant defects in mitotic spindle assembly and progression through mitosis that are more severe when overexpressed TPX2 is able to interact with Aurora-A. Furthermore, we describe a peculiar, and Aurora-A-interaction-independent, phenotype in telophase cells, with aberrantly stable microtubules interfering with nuclear reconstitution and the assembly of a continuous lamin B1 network, resulting in daughter cells displaying doughnut-shaped nuclei. Our results using non-transformed cells thus reveal a previously uncharacterised consequence of abnormally high TPX2 levels on the correct microtubule cytoskeleton remodelling and G1 nuclei reformation, at the mitosis-to-interphase transition.
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Affiliation(s)
- Francesco D. Naso
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
| | - Valentina Sterbini
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
| | - Elena Crecca
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
| | - Italia A. Asteriti
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
| | - Alessandra D. Russo
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
| | - Maria Giubettini
- CrestOptics S.p.A., Via di Torre Rossa 66, 00165 Rome, Italy;
- Center for Life Nano Science, Istituto Italiano di Tecnologia, Viale Regina Elena 291, 00161 Rome, Italy;
| | - Enrico Cundari
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
| | - Catherine Lindon
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK;
| | - Alessandro Rosa
- Center for Life Nano Science, Istituto Italiano di Tecnologia, Viale Regina Elena 291, 00161 Rome, Italy;
- Department of Biology and Biotechnology “C. Darwin”, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Giulia Guarguaglini
- Institute of Molecular Biology and Pathology, National Research Council of Italy, c/o Sapienza University of Rome, Via degli Apuli 4, 00185 Rome, Italy; (F.D.N.); (V.S.); (E.C.); (I.A.A.); (A.D.R.); (E.C.)
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37
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Microtubules in Influenza Virus Entry and Egress. Viruses 2020; 12:v12010117. [PMID: 31963544 PMCID: PMC7020094 DOI: 10.3390/v12010117] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 01/10/2020] [Accepted: 01/14/2020] [Indexed: 12/14/2022] Open
Abstract
Influenza viruses are respiratory pathogens that represent a significant threat to public health, despite the large-scale implementation of vaccination programs. It is necessary to understand the detailed and complex interactions between influenza virus and its host cells in order to identify successful strategies for therapeutic intervention. During viral entry, the cellular microenvironment presents invading pathogens with a series of obstacles that must be overcome to infect permissive cells. Influenza hijacks numerous host cell proteins and associated biological pathways during its journey into the cell, responding to environmental cues in order to successfully replicate. The cellular cytoskeleton and its constituent microtubules represent a heavily exploited network during viral infection. Cytoskeletal filaments provide a dynamic scaffold for subcellular viral trafficking, as well as virus-host interactions with cellular machineries that are essential for efficient uncoating, replication, and egress. In addition, influenza virus infection results in structural changes in the microtubule network, which itself has consequences for viral replication. Microtubules, their functional roles in normal cell biology, and their exploitation by influenza viruses will be the focus of this review.
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38
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King MR, Petry S. Phase separation of TPX2 enhances and spatially coordinates microtubule nucleation. Nat Commun 2020; 11:270. [PMID: 31937751 PMCID: PMC6959270 DOI: 10.1038/s41467-019-14087-0] [Citation(s) in RCA: 121] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 12/10/2019] [Indexed: 12/14/2022] Open
Abstract
Phase separation of substrates and effectors is proposed to enhance biological reaction rates and efficiency. Targeting protein for Xklp2 (TPX2) is an effector of branching microtubule nucleation in spindles and functions with the substrate tubulin by an unknown mechanism. Here we show that TPX2 phase separates into a co-condensate with tubulin, which mediates microtubule nucleation in vitro and in isolated cytosol. TPX2-tubulin co-condensation preferentially occurs on pre-existing microtubules, the site of branching microtubule nucleation, at the endogenous and physiologically relevant concentration of TPX2. Truncation and chimera versions of TPX2 suggest that TPX2-tubulin co-condensation enhances the efficiency of TPX2-mediated branching microtubule nucleation. Finally, the known inhibitor of TPX2, the importin-α/β heterodimer, regulates TPX2 condensation in vitro and, consequently, branching microtubule nucleation activity in isolated cytosol. Our study demonstrates how regulated phase separation can simultaneously enhance reaction efficiency and spatially coordinate microtubule nucleation, which may facilitate rapid and accurate spindle formation.
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Affiliation(s)
- Matthew R King
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, 08544, USA
- Department of Biomedical Engineering, Washington University, Brauer Hall, One Brookings Drive, Saint Louis, Missouri, 63130, USA
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, 08544, USA.
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39
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Guo L, Mohd KS, Ren H, Xin G, Jiang Q, Clarke PR, Zhang C. Phosphorylation of importin-α1 by CDK1-cyclin B1 controls mitotic spindle assembly. J Cell Sci 2019; 132:jcs232314. [PMID: 31434716 PMCID: PMC6765185 DOI: 10.1242/jcs.232314] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Accepted: 08/09/2019] [Indexed: 12/22/2022] Open
Abstract
Importin-α serves as an adaptor linking importin-β to proteins carrying a nuclear localization sequence (NLS). During interphase, this interaction enables nuclear protein import, while in mitosis it regulates spindle assembly factors (SAFs) and controls microtubule nucleation, stabilization and spindle function. Here, we show that human importin-α1 is regulated during the cell cycle and is phosphorylated at two sites (threonine 9 and serine 62) during mitosis by the major mitotic protein kinase CDK1-cyclin B. Mutational analysis indicates that the mitotic phosphorylation of importin-α1 inhibits its binding to importin-β and promotes the release of TPX2 and KIFC1, which are then targeted like importin-β to the spindle. Loss of importin-α1 or expression of a non-phosphorylated mutant of importin-α1 results in the formation of shortened spindles with reduced microtubule density and induces a prolonged metaphase, whereas phosphorylation-mimicking mutants are functional in mitosis. We propose that phosphorylation of importin-α1 is a general mechanism for the spatial and temporal control of mitotic spindle assembly by CDK1-cyclin B1 that acts through the release of SAFs such as TPX2 and KIFC1 from inhibitory complexes that restrict spindle assembly.
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Affiliation(s)
- Li Guo
- The MOE Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China
| | - Khamsah Suryati Mohd
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
| | - He Ren
- The MOE Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China
| | - Guangwei Xin
- The MOE Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China
| | - Qing Jiang
- The MOE Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China
| | - Paul R Clarke
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
- The University of Queensland Diamantina Institute, The University of Queensland, Woolloongabba, Brisbane, QLD 4102, Australia
| | - Chuanmao Zhang
- The MOE Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China
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40
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Vargas-Hurtado D, Brault JB, Piolot T, Leconte L, Da Silva N, Pennetier C, Baffet A, Marthiens V, Basto R. Differences in Mitotic Spindle Architecture in Mammalian Neural Stem Cells Influence Mitotic Accuracy during Brain Development. Curr Biol 2019; 29:2993-3005.e9. [DOI: 10.1016/j.cub.2019.07.061] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Revised: 05/31/2019] [Accepted: 07/19/2019] [Indexed: 12/16/2022]
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41
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Schmidt S, Smertenko A. Identification and characterization of the land-plant-specific microtubule nucleation factor MACET4. J Cell Sci 2019; 132:jcs232819. [PMID: 31076517 DOI: 10.1242/jcs.232819] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 05/01/2019] [Indexed: 12/23/2022] Open
Abstract
Here, we show that the embryophyte (land-plant)-specific protein MACERATOR4 (MACET4) binds microtubules in vitro and in vivo, promotes microtubule polymerization at sub-critical tubulin concentrations, decreases the lag phase in microtubule bulk polymerization assays, and colocalizes with microtubule nucleation sites. Furthermore, we find that MACET4 forms oligomers that induce aster formation in vitro in a manner that is similar to aster formation mediated by centrosomes and TPX2. MACET4 is expressed during cell division and accumulates at the microtubule nucleation regions of the plant-specific cytokinetic microtubule array, the phragmoplast. We found that MACET4 localizes to the preprophase band and the cortical division zone, but not the spindle. MACET4 appears as cytoplasmic foci in vivo and forms octamers in vitro Transient expression in tobacco leaf pavement cells results in labeling of shrinking plus- and minus-ends. MACET4 facilitates microtubule depolymerization by increasing the frequency of catastrophes in vivo and by suppressing rescues in vitro Microtubules formed in the presence of MACET4 in vitro are shorter, most likely due to the depletion of the free tubulin pool. Accordingly, MACET4 knockdown results in longer phragmoplasts. We conclude that the direct activity of MACET4 is in promoting microtubule nucleation.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Sharol Schmidt
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Andrei Smertenko
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
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42
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Potential involvement of RITA in the activation of Aurora A at spindle poles during mitosis. Oncogene 2019; 38:4199-4214. [PMID: 30705408 DOI: 10.1038/s41388-019-0716-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 11/27/2018] [Accepted: 12/14/2018] [Indexed: 12/22/2022]
Abstract
The mitotic kinase Aurora A is crucial for various mitotic events. Its activation has been intensively investigated and is not yet completely understood. RITA, the RBP-J interacting and tubulin-associated protein, has been shown to modulate microtubule dynamics in mitosis. We asked if RITA could be related to the activation of Aurora A. We show here that RITA is colocalized with Aurora A and its activator TPX2 at spindle poles during mitosis. FLAG-RITA is precipitated with the complex of Aurora A, TPX2 and tubulin. Depletion of RITA increases exclusively active Aurora A and TPX2 at spindle poles in diverse cancer cell lines and in RITA knockout mouse embryonic fibroblasts. The enhanced active Aurora A, its substrate p-TACC3 and TPX2 are restored by adding back of RITA but not its Δtub mutant with an impaired tubulin-binding capability, indicating that RITA's role as Aurora A's modulator is mediated through its interaction with tubulin. Also, the mitotic failures in cells depleted of RITA are rescued by the inhibition of Aurora A. RITA itself does not directly interfere with the catalytic activity of Aurora A, instead, affects the microtubule binding of its activator TPX2. Moreover, Aurora A's activation correlates with microtubule stabilization induced by the microtubule stabilizer paclitaxel, implicating that stabilized microtubules caused by RITA depletion could also account for increased active Aurora A. Our data suggest a potential role for RITA in the activation of Aurora A at spindle poles by modulating the microtubule binding of TPX2 and the microtubule stability during mitosis.
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43
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Pintard L, Bowerman B. Mitotic Cell Division in Caenorhabditis elegans. Genetics 2019; 211:35-73. [PMID: 30626640 PMCID: PMC6325691 DOI: 10.1534/genetics.118.301367] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 10/24/2018] [Indexed: 11/18/2022] Open
Abstract
Mitotic cell divisions increase cell number while faithfully distributing the replicated genome at each division. The Caenorhabditis elegans embryo is a powerful model for eukaryotic cell division. Nearly all of the genes that regulate cell division in C. elegans are conserved across metazoan species, including humans. The C. elegans pathways tend to be streamlined, facilitating dissection of the more redundant human pathways. Here, we summarize the virtues of C. elegans as a model system and review our current understanding of centriole duplication, the acquisition of pericentriolar material by centrioles to form centrosomes, the assembly of kinetochores and the mitotic spindle, chromosome segregation, and cytokinesis.
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Affiliation(s)
- Lionel Pintard
- Equipe labellisée Ligue contre le Cancer, Institut Jacques Monod, Team Cell Cycle and Development UMR7592, Centre National de la Recherche Scientifique - Université Paris Diderot, Sorbonne Paris Cité, 75013 Paris, France
| | - Bruce Bowerman
- Institute of Molecular Biology, University of Oregon, Eugene, OR 97403
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44
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Elliott A, Shaw SL. Microtubule Array Patterns Have a Common Underlying Architecture in Hypocotyl Cells. PLANT PHYSIOLOGY 2018; 176:307-325. [PMID: 28894021 PMCID: PMC5761787 DOI: 10.1104/pp.17.01112] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 09/07/2017] [Indexed: 05/08/2023]
Abstract
Microtubules at the plant cell cortex influence cell shape by patterning the deposition of cell wall materials. The elongated cells of the hypocotyl create a variety of microtubule array patterns with differing degrees of polymer coalignment and orientation to the cell's growth axis. To gain insight into the mechanisms driving array organization, we investigated the underlying microtubule array architecture in light-grown epidermal cells with explicit reference to array pattern. We discovered that all nontransverse patterns share a common underlying array architecture, having a core unimodal peak of coaligned microtubules in a split bipolarized arrangement. The growing microtubule plus ends extend toward the cell's apex and base with a region of antiparallel microtubule overlap at the cell's midzone. This core coalignment continuously shifts between ±30° from the cell's longitudinal growth axis, forming a continuum of longitudinal and oblique arrays. Transverse arrays exhibit the same unimodal core coalignment but form local domains of microtubules polymerizing in the same direction rather than a split bipolarized architecture. Quantitative imaging experiments and analysis of katanin mutants showed that the longitudinal arrays are created from microtubules originating on the outer periclinal cell face, pointing to a cell-directed, rather than self-organizing, mechanism for specifying the major array pattern classes in the hypocotyl cell.
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Affiliation(s)
- Andrew Elliott
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47405
| | - Sidney L Shaw
- Department of Biology, Indiana University, Bloomington, Indiana 47405
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45
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Eibes S, Gallisà-Suñé N, Rosas-Salvans M, Martínez-Delgado P, Vernos I, Roig J. Nek9 Phosphorylation Defines a New Role for TPX2 in Eg5-Dependent Centrosome Separation before Nuclear Envelope Breakdown. Curr Biol 2017; 28:121-129.e4. [PMID: 29276125 DOI: 10.1016/j.cub.2017.11.046] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Revised: 10/31/2017] [Accepted: 11/21/2017] [Indexed: 11/18/2022]
Abstract
Centrosomes [1, 2] play a central role during spindle assembly in most animal cells [3]. In early mitosis, they organize two symmetrical microtubule arrays that upon separation define the two poles of the forming spindle. Centrosome separation is tightly regulated [4, 5], occurring through partially redundant mechanisms that rely on the action of microtubule-based dynein and kinesin motors and the actomyosin system [6]. While centrosomes can separate in prophase or in prometaphase after nuclear envelope breakdown (NEBD), prophase centrosome separation optimizes spindle assembly and minimizes the occurrence of abnormal chromosome attachments that could end in aneuploidy [7, 8]. Prophase centrosome separation relies on the activity of Eg5/KIF11, a mitotic kinesin [9] that accumulates around centrosomes in early mitosis under the control of CDK1 and the Nek9/Nek6/7 kinase module [10-17]. Here, we show that Eg5 localization and centrosome separation in prophase depend on the nuclear microtubule-associated protein TPX2 [18], a pool of which localizes to the centrosomes before NEBD. This localization involves RHAMM/HMMR [19] and the kinase Nek9 [20], which phosphorylates TPX2 nuclear localization signal (NLS) preventing its interaction with importin and nuclear import. The pool of centrosomal TPX2 in prophase has a critical role for both microtubule aster organization and Eg5 localization, and thereby for centrosome separation. Our results uncover an unsuspected role for TPX2 before NEBD and define a novel regulatory mechanism for centrosome separation in prophase. They furthermore suggest NLS phosphorylation as a novel regulatory mechanism for spindle assembly factors controlled by the importin/Ran system.
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Affiliation(s)
- Susana Eibes
- Molecular Biology Institute of Barcelona (IBMB-CSIC) and Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Barcelona 08028, Spain
| | - Núria Gallisà-Suñé
- Molecular Biology Institute of Barcelona (IBMB-CSIC) and Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Barcelona 08028, Spain
| | - Miquel Rosas-Salvans
- Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona 08003, Spain; Universitat Pompeu Fabra (UPF), Barcelona 08003, Spain
| | - Paula Martínez-Delgado
- Molecular Biology Institute of Barcelona (IBMB-CSIC) and Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Barcelona 08028, Spain
| | - Isabelle Vernos
- Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona 08003, Spain; Universitat Pompeu Fabra (UPF), Barcelona 08003, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona 08010, Spain
| | - Joan Roig
- Molecular Biology Institute of Barcelona (IBMB-CSIC) and Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Barcelona 08028, Spain.
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46
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Zhang R, Roostalu J, Surrey T, Nogales E. Structural insight into TPX2-stimulated microtubule assembly. eLife 2017; 6. [PMID: 29120325 PMCID: PMC5679754 DOI: 10.7554/elife.30959] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 10/29/2017] [Indexed: 11/13/2022] Open
Abstract
During mitosis and meiosis, microtubule (MT) assembly is locally upregulated by the chromatin-dependent Ran-GTP pathway. One of its key targets is the MT-associated spindle assembly factor TPX2. The molecular mechanism of how TPX2 stimulates MT assembly remains unknown because structural information about the interaction of TPX2 with MTs is lacking. Here, we determine the cryo-electron microscopy structure of a central region of TPX2 bound to the MT surface. TPX2 uses two flexibly linked elements ('ridge' and 'wedge') in a novel interaction mode to simultaneously bind across longitudinal and lateral tubulin interfaces. These MT-interacting elements overlap with the binding site of importins on TPX2. Fluorescence microscopy-based in vitro reconstitution assays reveal that this interaction mode is critical for MT binding and facilitates MT nucleation. Together, our results suggest a molecular mechanism of how the Ran-GTP gradient can regulate TPX2-dependent MT formation.
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Affiliation(s)
- Rui Zhang
- Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States
| | | | | | - Eva Nogales
- Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States.,Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
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47
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Chang CC, Huang TL, Shimamoto Y, Tsai SY, Hsia KC. Regulation of mitotic spindle assembly factor NuMA by Importin-β. J Cell Biol 2017; 216:3453-3462. [PMID: 28939615 PMCID: PMC5674899 DOI: 10.1083/jcb.201705168] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 07/14/2017] [Accepted: 08/22/2017] [Indexed: 01/13/2023] Open
Abstract
Ran-guanosine triphosphatase orchestrates mitotic spindle assembly by modulation of the interaction between Importin-α/-β and spindle assembly factors (SAFs). The inhibition of SAFs performed by importins needs to be done without much sequestration from abundant nuclear localization signal (NLS) -containing proteins. However, the molecular mechanisms that determine NLS-binding selectivity and that inhibit activity of Importin-β-regulated SAFs (e.g., nuclear mitotic apparatus protein [NuMA]) remain undefined. Here, we present a crystal structure of the Importin-α-NuMA C terminus complex showing a novel binding pattern that accounts for selective NLS recognition. We demonstrate that, in the presence of Importin-α, Importin-β inhibits the microtubule-binding function of NuMA. Further, we have identified a high-affinity microtubule-binding region that lies carboxyl-terminal to the NLS, which is sterically masked by Importin-β on being bound by Importin-α. Our study provides mechanistic evidence of how Importin-α/-β regulates the NuMA functioning required for assembly of higher-order microtubule structures, further illuminating how Ran-governed transport factors regulate diverse SAFs and accommodate various cell demands.
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Affiliation(s)
- Chih-Chia Chang
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Tzu-Lun Huang
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Yuta Shimamoto
- Center for Frontier Research, National Institute of Genetics, Shizuoka, Japan
| | - Su-Yi Tsai
- Department of Life Science, National Taiwan University, Taipei, Taiwan
| | - Kuo-Chiang Hsia
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan .,Institute of Biochemistry and Molecular Biology, College of Life Sciences, National Yang-Ming University, Taipei, Taiwan
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48
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Programmed Self-Assembly of a Biochemical and Magnetic Scaffold to Trigger and Manipulate Microtubule Structures. Sci Rep 2017; 7:11344. [PMID: 28900114 PMCID: PMC5595911 DOI: 10.1038/s41598-017-10297-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 08/07/2017] [Indexed: 11/25/2022] Open
Abstract
Artificial bio-based scaffolds offer broad applications in bioinspired chemistry, nanomedicine, and material science. One current challenge is to understand how the programmed self-assembly of biomolecules at the nanometre level can dictate the emergence of new functional properties at the mesoscopic scale. Here we report a general approach to design genetically encoded protein-based scaffolds with modular biochemical and magnetic functions. By combining chemically induced dimerization strategies and biomineralisation, we engineered ferritin nanocages to nucleate and manipulate microtubule structures upon magnetic actuation. Triggering the self-assembly of engineered ferritins into micrometric scaffolds mimics the function of centrosomes, the microtubule organizing centres of cells, and provides unique magnetic and self-organizing properties. We anticipate that our approach could be transposed to control various biological processes and extend to broader applications in biotechnology or material chemistry.
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49
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Roostalu J, Surrey T. Microtubule nucleation: beyond the template. Nat Rev Mol Cell Biol 2017; 18:702-710. [PMID: 28831203 DOI: 10.1038/nrm.2017.75] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Microtubules are cytoskeletal filaments central to a wide range of essential cellular functions in eukaryotic cells. Consequently, cells need to exert tight control over when, where and how many microtubules are being made. Whereas the regulation of microtubule dynamics is well studied, the molecular mechanisms of microtubule nucleation are still poorly understood. Next to the established master template of nucleation, the γ-tubulin ring complex, other microtubule-associated proteins that affect microtubule dynamic properties have recently been found to contribute to nucleation. It has begun to emerge that the nucleation efficiency is controlled not only by template activity but also by, either additionally or alternatively, the stabilization of the nascent microtubule 'nucleus'. This suggests a simple conceptual framework for the mechanisms regulating microtubule nucleation in cells.
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Affiliation(s)
| | - Thomas Surrey
- The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
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Alfaro-Aco R, Thawani A, Petry S. Structural analysis of the role of TPX2 in branching microtubule nucleation. J Cell Biol 2017; 216:983-997. [PMID: 28264915 PMCID: PMC5379942 DOI: 10.1083/jcb.201607060] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2016] [Revised: 11/03/2016] [Accepted: 01/09/2017] [Indexed: 12/14/2022] Open
Abstract
TPX2 is required for microtubule nucleation in mitosis, but the mechanism underlying its function is unclear. Alfaro-Aco et al. analyze the domains of TPX2 necessary for its activity and identify the minimal region required for branching microtubule nucleation. The mitotic spindle consists of microtubules (MTs), which are nucleated by the γ-tubulin ring complex (γ-TuRC). How the γ-TuRC gets activated at the right time and location remains elusive. Recently, it was uncovered that MTs nucleate from preexisting MTs within the mitotic spindle, which requires the protein TPX2, but the mechanism basis for TPX2 action is unknown. Here, we investigate the role of TPX2 in branching MT nucleation. We establish the domain organization of Xenopus laevis TPX2 and define the minimal TPX2 version that stimulates branching MT nucleation, which we find is unrelated to TPX2’s ability to nucleate MTs in vitro. Several domains of TPX2 contribute to its MT-binding and bundling activities. However, the property necessary for TPX2 to induce branching MT nucleation is contained within newly identified γ-TuRC nucleation activator motifs. Separation-of-function mutations leave the binding of TPX2 to γ-TuRC intact, whereas branching MT nucleation is abolished, suggesting that TPX2 may activate γ-TuRC to promote branching MT nucleation.
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Affiliation(s)
| | - Akanksha Thawani
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544
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