101
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Bezanilla M, Gladfelter AS, Kovar DR, Lee WL. Cytoskeletal dynamics: a view from the membrane. ACTA ACUST UNITED AC 2015; 209:329-37. [PMID: 25963816 PMCID: PMC4427793 DOI: 10.1083/jcb.201502062] [Citation(s) in RCA: 123] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Many aspects of cytoskeletal assembly and dynamics can be recapitulated in vitro; yet, how the cytoskeleton integrates signals in vivo across cellular membranes is far less understood. Recent work has demonstrated that the membrane alone, or through membrane-associated proteins, can effect dynamic changes to the cytoskeleton, thereby impacting cell physiology. Having identified mechanistic links between membranes and the actin, microtubule, and septin cytoskeletons, these studies highlight the membrane’s central role in coordinating these cytoskeletal systems to carry out essential processes, such as endocytosis, spindle positioning, and cellular compartmentalization.
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Affiliation(s)
- Magdalena Bezanilla
- Department of Biology, University of Massachusetts Amherst, Amherst, MA 01003
| | - Amy S Gladfelter
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology and Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637 Department of Molecular Genetics and Cell Biology and Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637
| | - Wei-Lih Lee
- Department of Biology, University of Massachusetts Amherst, Amherst, MA 01003
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102
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Abstract
Epithelia form intelligent, dynamic barriers between the external environment and an organism's interior. Intercellular cadherin-based adhesions adapt and respond to mechanical forces and cell density, while tight junctions flexibly control diffusion both within the plasma membrane and between adjacent cells. Epithelial integrity and homeostasis are of central importance to survival, and mechanisms have evolved to ensure these processes are maintained during growth and in response to damage. For instance, cell competition surveys the fitness of cells within epithelia and removes the less fit; extrusion or delamination can remove apoptotic or defective cells from the epithelial sheet and can restore homeostasis when an epithelial layer becomes too crowded; spindle orientation ensures two-dimensional growth in simple epithelia and controls stratification in complex epithelia; and transition to a mesenchymal phenotype enables active escape from an epithelial layer. This review will discuss these various mechanisms and consider how they are subverted in disease.
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Affiliation(s)
- Ian G Macara
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
| | - Richard Guyer
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Graham Richardson
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Yongliang Huo
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Syed M Ahmed
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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103
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Bizzotto S, Francis F. Morphological and functional aspects of progenitors perturbed in cortical malformations. Front Cell Neurosci 2015; 9:30. [PMID: 25729350 PMCID: PMC4325918 DOI: 10.3389/fncel.2015.00030] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Accepted: 01/18/2015] [Indexed: 11/13/2022] Open
Abstract
In this review, we discuss molecular and cellular mechanisms important for the function of neuronal progenitors during development, revealed by their perturbation in different cortical malformations. We focus on a class of neuronal progenitors, radial glial cells (RGCs), which are renowned for their unique morphological and behavioral characteristics, constituting a key element during the development of the mammalian cerebral cortex. We describe how the particular morphology of these cells is related to their roles in the orchestration of cortical development and their influence on other progenitor types and post-mitotic neurons. Important for disease mechanisms, we overview what is currently known about RGC cellular components, cytoskeletal mechanisms, signaling pathways and cell cycle characteristics, focusing on how defects lead to abnormal development and cortical malformation phenotypes. The multiple recent entry points from human genetics and animal models are contributing to our understanding of this important cell type. Combining data from phenotypes in the mouse reveals molecules which potentially act in common pathways. Going beyond this, we discuss future directions that may provide new data in this expanding area.
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Affiliation(s)
- Sara Bizzotto
- INSERM UMRS 839 Paris, France ; Sorbonne Universités, Université Pierre et Marie Curie Paris, France ; Institut du Fer à Moulin Paris, France
| | - Fiona Francis
- INSERM UMRS 839 Paris, France ; Sorbonne Universités, Université Pierre et Marie Curie Paris, France ; Institut du Fer à Moulin Paris, France
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104
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Brown NE, Goswami D, Branch MR, Ramineni S, Ortlund EA, Griffin PR, Hepler JR. Integration of G protein α (Gα) signaling by the regulator of G protein signaling 14 (RGS14). J Biol Chem 2015; 290:9037-49. [PMID: 25666614 DOI: 10.1074/jbc.m114.634329] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Indexed: 11/06/2022] Open
Abstract
RGS14 contains distinct binding sites for both active (GTP-bound) and inactive (GDP-bound) forms of Gα subunits. The N-terminal regulator of G protein signaling (RGS) domain binds active Gαi/o-GTP, whereas the C-terminal G protein regulatory (GPR) motif binds inactive Gαi1/3-GDP. The molecular basis for how RGS14 binds different activation states of Gα proteins to integrate G protein signaling is unknown. Here we explored the intramolecular communication between the GPR motif and the RGS domain upon G protein binding and examined whether RGS14 can functionally interact with two distinct forms of Gα subunits simultaneously. Using complementary cellular and biochemical approaches, we demonstrate that RGS14 forms a stable complex with inactive Gαi1-GDP at the plasma membrane and that free cytosolic RGS14 is recruited to the plasma membrane by activated Gαo-AlF4(-). Bioluminescence resonance energy transfer studies showed that RGS14 adopts different conformations in live cells when bound to Gα in different activation states. Hydrogen/deuterium exchange mass spectrometry revealed that RGS14 is a very dynamic protein that undergoes allosteric conformational changes when inactive Gαi1-GDP binds the GPR motif. Pure RGS14 forms a ternary complex with Gαo-AlF4(-) and an AlF4(-)-insensitive mutant (G42R) of Gαi1-GDP, as observed by size exclusion chromatography and differential hydrogen/deuterium exchange. Finally, a preformed RGS14·Gαi1-GDP complex exhibits full capacity to stimulate the GTPase activity of Gαo-GTP, demonstrating that RGS14 can functionally engage two distinct forms of Gα subunits simultaneously. Based on these findings, we propose a working model for how RGS14 integrates multiple G protein signals in host CA2 hippocampal neurons to modulate synaptic plasticity.
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Affiliation(s)
| | - Devrishi Goswami
- the Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458
| | | | | | - Eric A Ortlund
- Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322 and
| | - Patrick R Griffin
- the Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458
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105
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Takayanagi H, Yuzawa S, Sumimoto H. Structural basis for the recognition of the scaffold protein Frmpd4/Preso1 by the TPR domain of the adaptor protein LGN. Acta Crystallogr F Struct Biol Commun 2015; 71:175-83. [PMID: 25664792 PMCID: PMC4321472 DOI: 10.1107/s2053230x14028143] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2014] [Accepted: 12/26/2014] [Indexed: 12/19/2022] Open
Abstract
The adaptor protein LGN interacts via the N-terminal domain comprising eight tetratricopeptide-repeat (TPR) motifs with its partner proteins mInsc, NuMA, Frmpd1 and Frmpd4 in a mutually exclusive manner. Here, the crystal structure of the LGN TPR domain in complex with human Frmpd4 is described at 1.5 Å resolution. In the complex, the LGN-binding region of Frmpd4 (amino-acid residues 990-1011) adopts an extended structure that runs antiparallel to LGN along the concave surface of the superhelix formed by the TPR motifs. Comparison with the previously determined structures of the LGN-Frmpd1, LGN-mInsc and LGN-NuMA complexes reveals that these partner proteins interact with LGN TPR1-6 via a common core binding region with consensus sequence (E/Q)XEX4-5(E/D/Q)X1-2(K/R)X0-1(V/I). In contrast to Frmpd1, Frmpd4 makes additional contacts with LGN via regions N- and C-terminal to the core sequence. The N-terminal extension is replaced by a specific α-helix in mInsc, which drastically increases the direct contacts with LGN TPR7/8, consistent with the higher affinity of mInsc for LGN. A crystal structure of Frmpd4-bound LGN in an oxidized form is also reported, although oxidation does not appear to strongly affect the interaction with Frmpd4.
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Affiliation(s)
- Hiroki Takayanagi
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Satoru Yuzawa
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Hideki Sumimoto
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
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106
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Applebaum M, Kalcheim C. Mechanisms of myogenic specification and patterning. Results Probl Cell Differ 2015; 56:77-98. [PMID: 25344667 DOI: 10.1007/978-3-662-44608-9_4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Mesodermal somites are initially composed of columnar cells arranged as a pseudostratified epithelium that undergoes sequential and spatially restricted changes to generate the sclerotome and dermomyotome, intermediate structures that develop into vertebrae, striated muscles of the body and limbs, dermis, smooth muscle, and endothelial cells. Regional cues were elucidated that impart differential traits upon the originally multipotent progenitors. How do somite cells and their intermediate progenitors interpret these extrinsic cues and translate them into various levels and/or modalities of intracellular signaling that lead to differential gene expression profiles remains a significant challenge. So is the understanding of how differential fate specification relates to complex cellular migrations prefiguring the formation of body muscles and vertebrae. Research in the past years has largely transited from a descriptive phase in which the lineages of distinct somite-derived progenitors and their cellular movements were traced to a more mechanistic understanding of the local function of genes and regulatory networks underlying lineage segregation and tissue organization. In this chapter, we focus on some major advances addressing the segregation of lineages from the dermomyotome, while discussing both cellular as well as molecular mechanisms, where possible.
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Affiliation(s)
- Mordechai Applebaum
- Department of Medical Neurobiology, IMRIC and ELSC-Hebrew University-Hadassah Medical School, Jerusalem, 9101201, 12272, Israel,
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107
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Mukherjee S, Kong J, Brat DJ. Cancer stem cell division: when the rules of asymmetry are broken. Stem Cells Dev 2014; 24:405-16. [PMID: 25382732 DOI: 10.1089/scd.2014.0442] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Asymmetric division of stem cells is a highly conserved and tightly regulated process by which a single stem cell produces two daughter cells and simultaneously directs the differential fate of both: one retains its stem cell identity while the other becomes specialized and loses stem cell properties. Coordinating these events requires control over numerous intra- and extracellular biological processes and signaling networks. In the initial stages, critical events include the compartmentalization of fate determining proteins within the mother cell and their subsequent passage to the appropriate daughter cell. Disturbance of these events results in an altered dynamic of self-renewing and differentiation within the cell population, which is highly relevant to the growth and progression of cancer. Other critical events include proper asymmetric spindle assembly, extrinsic regulation through micro-environmental cues, and noncanonical signaling networks that impact cell division and fate determination. In this review, we discuss mechanisms that maintain the delicate balance of asymmetric cell division in normal tissues and describe the current understanding how some of these mechanisms are deregulated in cancer. The universe is asymmetric and I am persuaded that life, as it is known to us, is a direct result of the asymmetry of the universe or of its indirect consequences. The universe is asymmetric. -Louis Pasteur.
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Affiliation(s)
- Subhas Mukherjee
- 1 Department of Pathology and Laboratory Medicine, Emory University , Atlanta, Georgia
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108
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Uversky VN. Unreported intrinsic disorder in proteins: Building connections to the literature on IDPs. INTRINSICALLY DISORDERED PROTEINS 2014; 2:e970499. [PMID: 28232880 PMCID: PMC5314882 DOI: 10.4161/21690693.2014.970499] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Accepted: 09/08/2014] [Indexed: 02/07/2023]
Abstract
This review opens a new series entitled “Unreported intrinsic disorder in proteins.” The goal of this series is to bring attention of researchers to an interesting phenomenon of missed (or overlooked, or ignored, or unreported) disorder. This series serves as a companion to “Digested Disorder” which provides a quarterly review of papers on intrinsically disordered proteins (IDPs) found by standard literature searches. The need for this alternative series results from the observation that there are numerous publications that describe IDPs (or hybrid proteins with ordered and disordered regions) yet fail to recognize many of the key discoveries and publications in the IDP field. By ignoring the body of work on IDPs, such publications often fail to relate their findings to prior discoveries or fail to explore the obvious implications of their work. Thus, the goal of this series is not only to review these very interesting and important papers, but also to point out how each paper relates to the IDP field and show how common tools in the IDP field can readily take the findings in new directions or provide a broader context for the reported findings.
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Affiliation(s)
- Vladimir N Uversky
- Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute; Morsani College of Medicine; University of South Florida; Tampa, FL USA; Institute for Biological Instrumentation; Russian Academy of Sciences; Pushchino, Russia; Biology Department; Faculty of Science; King Abdulaziz University; Jeddah, Kingdom of Saudi Arabia
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109
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Uppal T, Banerjee S, Sun Z, Verma SC, Robertson ES. KSHV LANA--the master regulator of KSHV latency. Viruses 2014; 6:4961-98. [PMID: 25514370 PMCID: PMC4276939 DOI: 10.3390/v6124961] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 12/03/2014] [Accepted: 12/05/2014] [Indexed: 12/16/2022] Open
Abstract
Kaposi's sarcoma associated herpesvirus (KSHV), like other human herpes viruses, establishes a biphasic life cycle referred to as dormant or latent, and productive or lytic phases. The latent phase is characterized by the persistence of viral episomes in a highly ordered chromatin structure and with the expression of a limited number of viral genes. Latency Associated Nuclear Antigen (LANA) is among the most abundantly expressed proteins during latency and is required for various nuclear functions including the recruitment of cellular machineries for viral DNA replication and segregation of the replicated genomes to daughter cells. LANA achieves these functions by recruiting cellular proteins including replication factors, chromatin modifying enzymes and cellular mitotic apparatus assembly. LANA directly binds to the terminal repeat region of the viral genome and associates with nucleosomal proteins to tether to the host chromosome. Binding of LANA to TR recruits the replication machinery, thereby initiating DNA replication within the TR. However, other regions of the viral genome can also initiate replication as determined by Single Molecule Analysis of the Replicated DNA (SMARD) approach. Recent, next generation sequence analysis of the viral transcriptome shows the expression of additional genes during latent phase. Here, we discuss the newly annotated latent genes and the role of major latent proteins in KSHV biology.
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Affiliation(s)
- Timsy Uppal
- Department of Microbiology and Immunology, University of Nevada, Reno, School of Medicine, 1664 N Virginia Street, MS 320, Reno, NV 89557, USA.
| | - Sagarika Banerjee
- Department of Microbiology and the Tumor Virology Program of the Abramson Cancer Center, Perelman School of Medicine at the University of Pennsylvania, 201E Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA.
| | - Zhiguo Sun
- Department of Microbiology and the Tumor Virology Program of the Abramson Cancer Center, Perelman School of Medicine at the University of Pennsylvania, 201E Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA.
| | - Subhash C Verma
- Department of Microbiology and Immunology, University of Nevada, Reno, School of Medicine, 1664 N Virginia Street, MS 320, Reno, NV 89557, USA.
| | - Erle S Robertson
- Department of Microbiology and the Tumor Virology Program of the Abramson Cancer Center, Perelman School of Medicine at the University of Pennsylvania, 201E Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA.
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110
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Tse MK, Morris CJ, Zhang M, Wong YH. Activator of G protein signaling 3 forms a complex with resistance to inhibitors of cholinesterase-8A without promoting nucleotide exchange on Gα(i3). Mol Cell Biochem 2014; 401:27-38. [PMID: 25480567 DOI: 10.1007/s11010-014-2289-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 11/26/2014] [Indexed: 01/04/2023]
Abstract
Activator of G protein signaling 3 (AGS3) is a guanine nucleotide dissociation inhibitor (GDI) which stabilizes the Gα(i/o) subunits as an AGS3/Gα(i/o)-GDP complex. It has recently been demonstrated in reconstitution experiments that the AGS3/Gα(i/o)-GDP complex may act as a substrate of resistance to inhibitors of cholinesterase 8A (Ric-8A), a guanine exchange factor (GEF) for heterotrimeric Gα proteins. Since the ability of Ric-8A to activate Gα(i/o) subunits that are bound to AGS3 in a cellular environment has not been confirmed, we thus examined the effect of Ric-8A on cAMP accumulation in HEK293 cells expressing different forms of AGS3 and Gα(i3). Co-immunoprecipitation assays indicate that full-length AGS3 and its N- and C-terminal truncated mutants can interact with Ric-8A in HEK293 cells. Yeast two-hybrid assay further confirmed that Ric-8A can directly bind to AGS3S, a short form of AGS3 which is endogenously expressed in heart. However, Ric-8A failed to facilitate Gα(i)-induced suppression of adenylyl cyclase, suggesting that it may not serve as a GEF for AGS3/Gα(i/o)-GDP complex in a cellular environment.
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Affiliation(s)
- Man K Tse
- Division of Life Science and the Biotechnology Research Institute, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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111
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Carvalho CA, Moreira S, Ventura G, Sunkel CE, Morais-de-Sá E. Aurora A triggers Lgl cortical release during symmetric division to control planar spindle orientation. Curr Biol 2014; 25:53-60. [PMID: 25484294 DOI: 10.1016/j.cub.2014.10.053] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 09/23/2014] [Accepted: 10/21/2014] [Indexed: 11/30/2022]
Abstract
Mitotic spindle orientation is essential to control cell-fate specification and epithelial architecture. The tumor suppressor Lgl localizes to the basolateral cortex of epithelial cells, where it acts together with Dlg and Scrib to organize apicobasal polarity. Dlg and Scrib also control planar spindle orientation, but how the organization of polarity complexes is adjusted to control symmetric division is largely unknown. Here, we show that the Dlg complex is remodeled during Drosophila follicular epithelium cell division, when Lgl is released to the cytoplasm. Lgl redistribution during epithelial mitosis is reminiscent of asymmetric cell division, where it is proposed that Aurora A promotes aPKC activation to control the localization of Lgl and cell-fate determinants. We show that Aurora A controls Lgl localization directly, triggering its cortical release at early prophase in both epithelial and S2 cells. This relies on double phosphorylation within the putative aPKC phosphorylation site, which is required and sufficient for Lgl cortical release during mitosis and can be achieved by a combination of aPKC and Aurora A activities. Cortical retention of Lgl disrupts planar spindle orientation, but only when Lgl mutants that can bind Dlg are expressed. Hence, our work reveals that Lgl mitotic cortical release is not specifically linked to the asymmetric segregation of fate determinants, and we propose that Aurora A activation breaks the Dlg/Lgl interaction to allow planar spindle orientation during symmetric division via the Pins (LGN)/Dlg pathway.
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Affiliation(s)
- Cátia A Carvalho
- Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Sofia Moreira
- Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Guilherme Ventura
- Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | - Cláudio E Sunkel
- Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal; Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, Rua de Jorge Viterbo Ferreira 228, 4050-313 Porto, Portugal
| | - Eurico Morais-de-Sá
- Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
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112
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Garcia JD, Dewey EB, Johnston CA. Dishevelled binds the Discs large 'Hook' domain to activate GukHolder-dependent spindle positioning in Drosophila. PLoS One 2014; 9:e114235. [PMID: 25461409 PMCID: PMC4252473 DOI: 10.1371/journal.pone.0114235] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Accepted: 11/05/2014] [Indexed: 11/19/2022] Open
Abstract
Communication between cortical cell polarity cues and the mitotic spindle ensures proper orientation of cell divisions within complex tissues. Defects in mitotic spindle positioning have been linked to various developmental disorders and have recently emerged as a potential contributor to tumorigenesis. Despite the importance of this process to human health, the molecular mechanisms that regulate spindle orientation are not fully understood. Moreover, it remains unclear how diverse cortical polarity complexes might cooperate to influence spindle positioning. We and others have demonstrated spindle orientation roles for Dishevelled (Dsh), a key regulator of planar cell polarity, and Discs large (Dlg), a conserved apico-basal cell polarity regulator, effects which were previously thought to operate within distinct molecular pathways. Here we identify a novel direct interaction between the Dsh-PDZ domain and the alternatively spliced “I3-insert” of the Dlg-Hook domain, thus establishing a potential convergent Dsh/Dlg pathway. Furthermore, we identify a Dlg sequence motif necessary for the Dsh interaction that shares homology to the site of Dsh binding in the Frizzled receptor. Expression of Dsh enhanced Dlg-mediated spindle positioning similar to deletion of the Hook domain. This Dsh-mediated activation was dependent on the Dlg-binding partner, GukHolder (GukH). These results suggest that Dsh binding may regulate core interdomain conformational dynamics previously described for Dlg. Together, our results identify Dlg as an effector of Dsh signaling and demonstrate a Dsh-mediated mechanism for the activation of Dlg/GukH-dependent spindle positioning. Cooperation between these two evolutionarily-conserved cell polarity pathways could have important implications to both the development and maintenance of tissue homeostasis in animals.
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Affiliation(s)
- Joshua D. Garcia
- Department of Biology, University of New Mexico, Albuquerque, New Mexico, United States of America
| | - Evan B. Dewey
- Department of Biology, University of New Mexico, Albuquerque, New Mexico, United States of America
| | - Christopher A. Johnston
- Department of Biology, University of New Mexico, Albuquerque, New Mexico, United States of America
- * E-mail:
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113
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Nam HJ, Naylor RM, van Deursen JM. Centrosome dynamics as a source of chromosomal instability. Trends Cell Biol 2014; 25:65-73. [PMID: 25455111 DOI: 10.1016/j.tcb.2014.10.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2014] [Revised: 10/14/2014] [Accepted: 10/15/2014] [Indexed: 01/03/2023]
Abstract
Accurate segregation of duplicated chromosomes between two daughter cells depends on bipolar spindle formation, a metaphase state in which sister kinetochores are attached to microtubules emanating from opposite spindle poles. To ensure bi-orientation, cells possess surveillance systems that safeguard against microtubule-kinetochore attachment defects, including the spindle assembly checkpoint and the error correction machinery. However, recent developments have identified centrosome dynamics--that is, centrosome disjunction and poleward movement of duplicated centrosomes--as a central target for deregulation of bi-orientation in cancer cells. In this review, we discuss novel insights into the mechanisms that underlie centrosome dynamics and discuss how these mechanisms are perturbed in cancer cells to drive chromosome mis-segregation and advance neoplastic transformation.
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Affiliation(s)
- Hyun-Ja Nam
- Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN, USA
| | - Ryan M Naylor
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN, USA
| | - Jan M van Deursen
- Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN, USA; Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN, USA.
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114
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Machicoane M, de Frutos CA, Fink J, Rocancourt M, Lombardi Y, Garel S, Piel M, Echard A. SLK-dependent activation of ERMs controls LGN-NuMA localization and spindle orientation. ACTA ACUST UNITED AC 2014; 205:791-9. [PMID: 24958772 PMCID: PMC4068135 DOI: 10.1083/jcb.201401049] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ERM activation by SLK kinase promotes polarized association at the mitotic cortex of LGN and NuMA, a necessary step in proper spindle orientation. Mitotic spindle orientation relies on a complex dialog between the spindle microtubules and the cell cortex, in which F-actin has been recently implicated. Here, we report that the membrane–actin linkers ezrin/radixin/moesin (ERMs) are strongly and directly activated by the Ste20-like kinase at mitotic entry in mammalian cells. Using microfabricated adhesive substrates to control the axis of cell division, we found that the activation of ERMs plays a key role in guiding the orientation of the mitotic spindle. Accordingly, impairing ERM activation in apical progenitors of the mouse embryonic neocortex severely disturbed spindle orientation in vivo. At the molecular level, ERM activation promotes the polarized association at the mitotic cortex of leucine-glycine-asparagine repeat protein (LGN) and nuclear mitotic apparatus (NuMA) protein, two essential factors for spindle orientation. We propose that activated ERMs, together with Gαi, are critical for the correct localization of LGN–NuMA force generator complexes and hence for proper spindle orientation.
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Affiliation(s)
- Mickael Machicoane
- Membrane Traffic and Cell Division Laboratory, Institut Pasteur, 75015 Paris, France Centre National de la Recherche Scientifique URA2582, 75015 Paris, France Sorbonne Universités, Université Pierre et Marie Curie, Université Paris 06, Institut de formation doctorale, 75252 Paris, France
| | - Cristina A de Frutos
- Institut de Biologie de L'Ecole Normale Supérieure, Ecole Normale Supérieure, 75005 Paris, France Institut National de la Santé et de la Recherche Médicale, U1024, Centre National de la Recherche Scientifique UMR8197, 75005 Paris, France
| | - Jenny Fink
- Systems Cell Biology of Cell Polarity and Cell Division Laboratory, Institut Curie, 75005 Paris, France Centre National de la Recherche Scientifique UMR144, 75005 Paris, France
| | - Murielle Rocancourt
- Membrane Traffic and Cell Division Laboratory, Institut Pasteur, 75015 Paris, France Centre National de la Recherche Scientifique URA2582, 75015 Paris, France
| | - Yannis Lombardi
- Membrane Traffic and Cell Division Laboratory, Institut Pasteur, 75015 Paris, France Centre National de la Recherche Scientifique URA2582, 75015 Paris, France
| | - Sonia Garel
- Institut de Biologie de L'Ecole Normale Supérieure, Ecole Normale Supérieure, 75005 Paris, France Institut National de la Santé et de la Recherche Médicale, U1024, Centre National de la Recherche Scientifique UMR8197, 75005 Paris, France
| | - Matthieu Piel
- Systems Cell Biology of Cell Polarity and Cell Division Laboratory, Institut Curie, 75005 Paris, France Centre National de la Recherche Scientifique UMR144, 75005 Paris, France
| | - Arnaud Echard
- Membrane Traffic and Cell Division Laboratory, Institut Pasteur, 75015 Paris, France Centre National de la Recherche Scientifique URA2582, 75015 Paris, France
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115
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Williams SE, Ratliff LA, Postiglione MP, Knoblich JA, Fuchs E. Par3-mInsc and Gαi3 cooperate to promote oriented epidermal cell divisions through LGN. Nat Cell Biol 2014; 16:758-69. [PMID: 25016959 DOI: 10.1038/ncb3001] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 05/30/2014] [Indexed: 12/14/2022]
Abstract
Asymmetric cell divisions allow stem cells to balance proliferation and differentiation. During embryogenesis, murine epidermis expands rapidly from a single layer of unspecified basal layer progenitors to a stratified, differentiated epithelium. Morphogenesis involves perpendicular (asymmetric) divisions and the spindle orientation protein LGN, but little is known about how the apical localization of LGN is regulated. Here, we combine conventional genetics and lentiviral-mediated in vivo RNAi to explore the functions of the LGN-interacting proteins Par3, mInsc and Gαi3. Whereas loss of each gene alone leads to randomized division angles, combined loss of Gnai3 and mInsc causes a phenotype of mostly planar divisions, akin to loss of LGN. These findings lend experimental support for the hitherto untested model that Par3-mInsc and Gαi3 act cooperatively to polarize LGN and promote perpendicular divisions. Finally, we uncover a developmental switch between delamination-driven early stratification and spindle-orientation-dependent differentiation that occurs around E15, revealing a two-step mechanism underlying epidermal maturation.
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Affiliation(s)
- Scott E Williams
- 1] Howard Hughes Medical Institute, Laboratory of Mammalian Cell Biology &Development, The Rockefeller University, 1230 York Avenue, Box 300, New York, New York 10065, USA [2] Department of Pathology &Laboratory Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | - Lyndsay A Ratliff
- Department of Pathology &Laboratory Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | - Maria Pia Postiglione
- 1] Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Dr. Bohrgasse 3, 1030 Vienna, Austria [2]
| | - Juergen A Knoblich
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Dr. Bohrgasse 3, 1030 Vienna, Austria
| | - Elaine Fuchs
- Howard Hughes Medical Institute, Laboratory of Mammalian Cell Biology &Development, The Rockefeller University, 1230 York Avenue, Box 300, New York, New York 10065, USA
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116
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Kotak S, Busso C, Gönczy P. NuMA interacts with phosphoinositides and links the mitotic spindle with the plasma membrane. EMBO J 2014; 33:1815-30. [PMID: 24996901 DOI: 10.15252/embj.201488147] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The positioning and the elongation of the mitotic spindle must be carefully regulated. In human cells, the evolutionary conserved proteins LGN/Gαi1-3 anchor the coiled-coil protein NuMA and dynein to the cell cortex during metaphase, thus ensuring proper spindle positioning. The mechanisms governing cortical localization of NuMA and dynein during anaphase remain more elusive. Here, we report that LGN/Gαi1-3 are dispensable for NuMA-dependent cortical dynein enrichment during anaphase. We further establish that NuMA is excluded from the equatorial region of the cell cortex in a manner that depends on the centralspindlin components CYK4 and MKLP1. Importantly, we reveal that NuMA can directly associate with PtdInsP (PIP) and PtdInsP2 (PIP2) phosphoinositides in vitro. Furthermore, chemical or enzymatic depletion of PIP/PIP2 prevents NuMA cortical localization during mitosis, and conversely, increasing PIP2 levels augments mitotic cortical NuMA. Overall, our study uncovers a novel function for plasma membrane phospholipids in governing cortical NuMA distribution and thus the proper execution of mitosis.
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Affiliation(s)
- Sachin Kotak
- School of Life Sciences, Swiss Institute for Experimental Cancer Research (ISREC), Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Coralie Busso
- School of Life Sciences, Swiss Institute for Experimental Cancer Research (ISREC), Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
| | - Pierre Gönczy
- School of Life Sciences, Swiss Institute for Experimental Cancer Research (ISREC), Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
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117
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Mora-Bermúdez F, Matsuzaki F, Huttner WB. Specific polar subpopulations of astral microtubules control spindle orientation and symmetric neural stem cell division. eLife 2014; 3. [PMID: 24996848 PMCID: PMC4112548 DOI: 10.7554/elife.02875] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Accepted: 07/03/2014] [Indexed: 12/13/2022] Open
Abstract
Mitotic spindle orientation is crucial for symmetric vs asymmetric cell division and depends on astral microtubules. Here, we show that distinct subpopulations of astral microtubules exist, which have differential functions in regulating spindle orientation and division symmetry. Specifically, in polarized stem cells of developing mouse neocortex, astral microtubules reaching the apical and basal cell cortex, but not those reaching the central cell cortex, are more abundant in symmetrically than asymmetrically dividing cells and reduce spindle orientation variability. This promotes symmetric divisions by maintaining an apico-basal cleavage plane. The greater abundance of apical/basal astrals depends on a higher concentration, at the basal cell cortex, of LGN, a known spindle-cell cortex linker. Furthermore, newly developed specific microtubule perturbations that selectively decrease apical/basal astrals recapitulate the symmetric-to-asymmetric division switch and suffice to increase neurogenesis in vivo. Thus, our study identifies a novel link between cell polarity, astral microtubules, and spindle orientation in morphogenesis. DOI:http://dx.doi.org/10.7554/eLife.02875.001 A stem cell can divide in two ways. Either it can split symmetrically into two identical daughter stem cells, or it can split asymmetrically into a stem cell and a specialist cell. The structure that forms inside the dividing cell to separate pairs of chromosomes—called the mitotic spindle—also partitions the molecules that determine what kind of cell each daughter cell will become. The mitotic spindle is made up of protein microtubules. Astral microtubules connect the spindle to a structure found at the inner face of the cell membrane called the cell cortex. This helps the spindle to orient itself correctly and control the plane of cell division. This is particularly important in cells that are different at their top and bottom, like polarized neural stem cells. To divide symmetrically, these cells need to split vertically from top to bottom. Then, to divide asymmetrically they tilt the cell division plane off-vertical. Classical studies on neuroblasts from the fruit fly Drosophila have shown that a big, 90° reorientation, from vertical to horizontal underlies this change. However, in the primary stem cells of the mammalian brain, subtle off-vertical tilting suffices for asymmetric divisions to occur. This tilting must be finely regulated: if not, neurodevelopmental disorders, such as microcephaly and lissencephaly, may arise. Mora-Bermúdez et al. investigated how mammalian cortical stem cells control such subtle spindle orientation changes by taking images of developing brain tissue from genetically modified mice. These show that not all astral microtubules affect whether the spindle reorients, as was previously thought. Instead, only those connecting the spindle to the cell cortex at the top and bottom of the cell—the apical/basal astrals—are involved. A decrease in the number of apical/basal astrals enables the spindle to undergo small reorientations. Mora-Bermúdez et al. therefore propose a model in which the spindle becomes less strongly anchored when the number of apical/basal astrals is reduced. This makes the spindle easier to tilt, allowing neural stem cells to undergo asymmetric divisions to produce neurons. The decrease in the number of apical/basal astrals appears to be caused by a reduction in the amount of a molecule that is known to help link the microtubules to the cell cortex. This reduction occurs only in the cortex at the top of the cell. Mora-Bermúdez et al. were also able to manipulate this process by adding very low doses of a microtubule inhibitor called nocodazole, which reduced the number of only the apical/basal astrals, increasing the ability of the spindle to reorient. DOI:http://dx.doi.org/10.7554/eLife.02875.002
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Affiliation(s)
| | | | - Wieland B Huttner
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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118
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Raaijmakers JA, Medema RH. Function and regulation of dynein in mitotic chromosome segregation. Chromosoma 2014; 123:407-22. [PMID: 24871939 DOI: 10.1007/s00412-014-0468-7] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Revised: 05/08/2014] [Accepted: 05/09/2014] [Indexed: 12/23/2022]
Abstract
Cytoplasmic dynein is a large minus-end-directed microtubule motor complex, involved in many different cellular processes including intracellular trafficking, organelle positioning, and microtubule organization. Furthermore, dynein plays essential roles during cell division where it is implicated in multiple processes including centrosome separation, chromosome movements, spindle organization, spindle positioning, and mitotic checkpoint silencing. How is a single motor able to fulfill this large array of functions and how are these activities temporally and spatially regulated? The answer lies in the unique composition of the dynein motor and in the interactions it makes with multiple regulatory proteins that define the time and place where dynein becomes active. Here, we will focus on the different mitotic processes that dynein is involved in, and how its regulatory proteins act to support dynein. Although dynein is highly conserved amongst eukaryotes (with the exception of plants), there is significant variability in the cellular processes that depend on dynein in different species. In this review, we concentrate on the functions of cytoplasmic dynein in mammals but will also refer to data obtained in other model organisms that have contributed to our understanding of dynein function in higher eukaryotes.
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Affiliation(s)
- J A Raaijmakers
- Department of Cell Biology and Cancer Genomics Center, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, Netherlands
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119
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Abstract
Self-organization of dynamic microtubules via interactions with associated motors plays a critical role in spindle formation. The microtubule-based mechanisms underlying other aspects of cellular morphogenesis, such as the formation and development of protrusions from neuronal cells is less well understood. In a recent study, we investigated the molecular mechanism that underlies the massive reorganization of microtubules induced in non-neuronal cells by expression of the neuronal microtubule stabilizer MAP2c. In that study we directly observed cortical dynein complexes and how they affect the dynamic behavior of motile microtubules in living cells. We found that stationary dynein complexes transiently associate with motile microtubules near the cell cortex and that their rapid turnover facilitates efficient microtubule transport. Here, we discuss our findings in the larger context of cellular morphogenesis with specific focus on self-organizing principles from which cellular shape patterns such as the thin protrusions of neurons can emerge.
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Affiliation(s)
- Leif Dehmelt
- Department of Systemic Cell Biology; Max Planck Institute of Molecular Physiology; Dortmund, Germany; Fakultät für Chemie und Chemische Biologie; Dortmund University of Technology; Dortmund, Germany
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120
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Zigman M, Laumann-Lipp N, Titus T, Postlethwait J, Moens CB. Hoxb1b controls oriented cell division, cell shape and microtubule dynamics in neural tube morphogenesis. Development 2014; 141:639-49. [PMID: 24449840 PMCID: PMC3899817 DOI: 10.1242/dev.098731] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Hox genes are classically ascribed to function in patterning the anterior-posterior axis of bilaterian animals; however, their role in directing molecular mechanisms underlying morphogenesis at the cellular level remains largely unstudied. We unveil a non-classical role for the zebrafish hoxb1b gene, which shares ancestral functions with mammalian Hoxa1, in controlling progenitor cell shape and oriented cell division during zebrafish anterior hindbrain neural tube morphogenesis. This is likely distinct from its role in cell fate acquisition and segment boundary formation. We show that, without affecting major components of apico-basal or planar cell polarity, Hoxb1b regulates mitotic spindle rotation during the oriented neural keel symmetric mitoses that are required for normal neural tube lumen formation in the zebrafish. This function correlates with a non-cell-autonomous requirement for Hoxb1b in regulating microtubule plus-end dynamics in progenitor cells in interphase. We propose that Hox genes can influence global tissue morphogenesis by control of microtubule dynamics in individual cells in vivo.
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Affiliation(s)
- Mihaela Zigman
- Centre for Organismal Studies (COS), University of Heidelberg, Im Neuenheimer Feld 329, 69120 Heidelberg, Germany
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121
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Rewiring cell polarity signaling in cancer. Oncogene 2014; 34:939-50. [PMID: 24632617 DOI: 10.1038/onc.2014.59] [Citation(s) in RCA: 125] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 02/07/2014] [Accepted: 02/11/2014] [Indexed: 02/08/2023]
Abstract
Disrupted cell polarity is a feature of epithelial cancers. The Crumbs, Par and Scribble polarity complexes function to specify and maintain apical and basolateral membrane domains, which are essential to organize intracellular signaling pathways that maintain epithelial homeostasis. Disruption of apical-basal polarity proteins facilitates rewiring of oncogene and tumor suppressor signaling pathways to deregulate proliferation, apoptosis, invasion and metastasis. Moreover, apical-basal polarity integrates intracellular signaling with the microenvironment by regulating metabolic signaling, extracellular matrix remodeling and tissue level organization. In this review, we discuss recent advances in our understanding of how polarity proteins regulate diverse signaling pathways throughout cancer progression from initiation to metastasis.
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122
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Bañón-Rodríguez I, Gálvez-Santisteban M, Vergarajauregui S, Bosch M, Borreguero-Pascual A, Martín-Belmonte F. EGFR controls IQGAP basolateral membrane localization and mitotic spindle orientation during epithelial morphogenesis. EMBO J 2014; 33:129-45. [PMID: 24421325 DOI: 10.1002/embj.201385946] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Establishing the correct orientation of the mitotic spindle is an essential step in epithelial cell division in order to ensure that epithelial tubules form correctly during organ development and regeneration. While recent findings have identified some of the molecular mechanisms that underlie spindle orientation, many aspects of this process remain poorly understood. Here, we have used the 3D-MDCK model system to demonstrate a key role for a newly identified protein complex formed by IQGAP1 and the epithelial growth factor receptor (EGFR) in controlling the orientation of the mitotic spindle. IQGAP1 is a scaffolding protein that regulates many cellular pathways, from cell-cell adhesion to microtubule organization, and its localization in the basolateral membrane ensures correct spindle orientation. Through its IQ motifs, IQGAP1 binds to EGFR, which is responsible for maintaining IQGAP1 in the basolateral membrane domain. Silencing IQGAP1, or disrupting the basolateral localization of either IQGAP1 or EGFR, results in a non-polarized distribution of NuMA, mitotic spindle misorientation and defects in single lumen formation.
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Affiliation(s)
- Inmaculada Bañón-Rodríguez
- Centro de Biología Molecular Severo Ochoa Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
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123
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Tame MA, Raaijmakers JA, van den Broek B, Lindqvist A, Jalink K, Medema RH. Astral microtubules control redistribution of dynein at the cell cortex to facilitate spindle positioning. Cell Cycle 2014; 13:1162-70. [PMID: 24553118 PMCID: PMC4013166 DOI: 10.4161/cc.28031] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Cytoplasmic dynein is recruited to the cell cortex in early mitosis, where it can generate pulling forces on astral microtubules to position the mitotic spindle. Recent work has shown that dynein displays a dynamic asymmetric cortical localization, and that dynein recruitment is negatively regulated by spindle pole-proximity. This results in oscillating dynein recruitment to opposite sides of the cortex to center the mitotic spindle. However, although the centrosome-derived signal that promotes displacement of dynein has been identified, it is currently unknown how dynein is re-recruited to the cortex once it has been displaced. Here we show that re-recruitment of cortical dynein requires astral microtubules. We find that microtubules are necessary for the sustained localized enrichment of dynein at the cortex. Furthermore, we show that stabilization of astral microtubules causes spindle misorientation, followed by mispositioning of dynein at the cortex. Thus, our results demonstrate the importance of astral microtubules in the dynamic regulation of cortical dynein recruitment in mitosis.
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Affiliation(s)
- Mihoko A Tame
- Division of Cell Biology; The Netherlands Cancer Institute; Amsterdam, The Netherlands
| | - Jonne A Raaijmakers
- Division of Cell Biology; The Netherlands Cancer Institute; Amsterdam, The Netherlands
| | - Bram van den Broek
- Division of Cell Biology; The Netherlands Cancer Institute; Amsterdam, The Netherlands
| | - Arne Lindqvist
- Department of Cell and Molecular Biology; Karolinska Institutet; Stockholm, Sweden
| | - Kees Jalink
- Division of Cell Biology; The Netherlands Cancer Institute; Amsterdam, The Netherlands
| | - René H Medema
- Division of Cell Biology; The Netherlands Cancer Institute; Amsterdam, The Netherlands
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124
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Boularan C, Kamenyeva O, Cho H, Kehrl JH. Resistance to inhibitors of cholinesterase (Ric)-8A and Gαi contribute to cytokinesis abscission by controlling vacuolar protein-sorting (Vps)34 activity. PLoS One 2014; 9:e86680. [PMID: 24466196 PMCID: PMC3897744 DOI: 10.1371/journal.pone.0086680] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/12/2013] [Indexed: 11/18/2022] Open
Abstract
Resistance to inhibitors of cholinesterase (Ric)-8A is a guanine nucleotide exchange factor for Gαi, Gαq, and Gα12/13, which is implicated in cell signaling and as a molecular chaperone required for the initial association of nascent Gα subunits with cellular membranes. Ric-8A, Gαi subunits, and their regulators are localized at the midbody prior to abscission and linked to the final stages of cell division. Here, we identify a molecular mechanism by which Ric-8A affects cytokinesis and abscission by controlling Vps34 activity. We showed that Ric-8A protein expression is post-transcriptionally controlled during the cell cycle reaching its maximum levels at mitosis. A FRET biosensor created to measure conformational changes in Ric-8A by FLIM (Fluorescence Lifetime Imaging Microscopy) revealed that Ric-8A was in a close-state during mitosis and particularly so at cytokinesis. Lowering Ric-8A expression delayed the abscission time of dividing cells, which correlated with increased intercellular bridge length and multinucleation. During cytokinesis, Ric-8A co-localized with Vps34 at the midbody along with Gαi and LGN, where these proteins functioned to regulate Vps34 phosphatidylinositol 3-kinase activity.
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Affiliation(s)
- Cedric Boularan
- B-cell Molecular Immunology Section, Laboratory of Immunoregulation, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Olena Kamenyeva
- B-cell Molecular Immunology Section, Laboratory of Immunoregulation, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Hyeseon Cho
- B-cell Molecular Immunology Section, Laboratory of Immunoregulation, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - John H. Kehrl
- B-cell Molecular Immunology Section, Laboratory of Immunoregulation, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
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125
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Chatterjee SJ, McCaffrey L. Emerging role of cell polarity proteins in breast cancer progression and metastasis. BREAST CANCER-TARGETS AND THERAPY 2014; 6:15-27. [PMID: 24648766 PMCID: PMC3929326 DOI: 10.2147/bctt.s43764] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Breast cancer is a heterogeneous group of diseases that frequently exhibits loss of growth control, and disrupted tissue organization and differentiation. Several recent studies indicate that apical–basal polarity provides a tumor-suppressive function, and that disrupting polarity proteins affects many stages of breast cancer progression from initiation through metastasis. In this review we highlight some of the recent advances in our understanding of the molecular mechanisms by which loss of apical–basal polarity deregulates apoptosis, proliferation, and promotes invasion and metastasis in breast cancer.
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Affiliation(s)
- Sudipa June Chatterjee
- Rosalind and Morris Goodman Cancer Centre, Department of Oncology, McGill University, Montreal, QC, Canada
| | - Luke McCaffrey
- Rosalind and Morris Goodman Cancer Centre, Department of Oncology, McGill University, Montreal, QC, Canada
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126
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Ahmed SM, Angers S. Emerging non-canonical functions for heterotrimeric G proteins in cellular signaling. J Recept Signal Transduct Res 2013; 33:177-83. [PMID: 23721574 DOI: 10.3109/10799893.2013.795972] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Classically heterotrimeric G proteins have been described as the principal signal transducing machinery for G-protein-coupled receptors. Receptor activation catalyzes nucleotide exchange on the Gα protein, enabling Gα-GTP and Gβγ-subunits to engage intracellular effectors to generate various cellular effects such as second messenger production or regulation of ion channel conductivity. Recent genetic and proteomic screens have identified novel heterotrimeric G-protein-interacting proteins and expanded their functional roles. This review highlights some examples of recently identified interacting proteins and summarizes how they functionally connect heterotrimeric G proteins to previously underappreciated cellular roles.
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Affiliation(s)
- Syed M Ahmed
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, ON, Canada
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127
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Zheng Z, Wan Q, Meixiong G, Du Q. Cell cycle-regulated membrane binding of NuMA contributes to efficient anaphase chromosome separation. Mol Biol Cell 2013; 25:606-19. [PMID: 24371089 PMCID: PMC3937087 DOI: 10.1091/mbc.e13-08-0474] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The mitotic apparatus protein NuMA has an intrinsic membrane-targeting mechanism that is regulated by CDK1-mediated phosphorylation, underlies anaphase-specific cortical accumulation of dynein, and contributes to chromosome separation. Accurate and efficient separation of sister chromatids during anaphase is critical for faithful cell division. It has been proposed that cortical dynein–generated pulling forces on astral microtubules contribute to anaphase spindle elongation and chromosome separation. In mammalian cells, however, definitive evidence for the involvement of cortical dynein in chromosome separation is missing. It is believed that dynein is recruited and anchored at the cell cortex during mitosis by the α subunit of heterotrimeric G protein (Gα)/mammalian homologue of Drosophila Partner of Inscuteable/nuclear mitotic apparatus (NuMA) ternary complex. Here we uncover a Gα/LGN-independent lipid- and membrane-binding domain at the C-terminus of NuMA. We show that the membrane binding of NuMA is cell cycle regulated—it is inhibited during prophase and metaphase by cyclin-dependent kinase 1 (CDK1)–mediated phosphorylation and only occurs after anaphase onset when CDK1 activity is down-regulated. Further studies indicate that cell cycle–regulated membrane association of NuMA underlies anaphase-specific enhancement of cortical NuMA and dynein. By replacing endogenous NuMA with membrane-binding-deficient NuMA, we can specifically reduce the cortical accumulation of NuMA and dynein during anaphase and demonstrate that cortical NuMA and dynein contribute to efficient chromosome separation in mammalian cells.
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Affiliation(s)
- Zhen Zheng
- Institute of Molecular Medicine and Genetics, Georgia Regents University, Augusta, GA 30912 Department of Neurology, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912 Lakeside High School, Evans, GA 30809
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128
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Par1b induces asymmetric inheritance of plasma membrane domains via LGN-dependent mitotic spindle orientation in proliferating hepatocytes. PLoS Biol 2013; 11:e1001739. [PMID: 24358023 PMCID: PMC3866089 DOI: 10.1371/journal.pbio.1001739] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Accepted: 11/05/2013] [Indexed: 01/06/2023] Open
Abstract
Proliferating hepatocytes in the liver show an atypical, asymmetric mode of cell division, which is coordinated by Par1b and LGN and may explain the unique tissue architecture of the liver. The development and maintenance of polarized epithelial tissue requires a tightly controlled orientation of mitotic cell division relative to the apical polarity axis. Hepatocytes display a unique polarized architecture. We demonstrate that mitotic hepatocytes asymmetrically segregate their apical plasma membrane domain to the nascent daughter cells. The non-polarized nascent daughter cell can form a de novo apical domain with its new neighbor. This asymmetric segregation of apical domains is facilitated by a geometrically distinct “apicolateral” subdomain of the lateral surface present in hepatocytes. The polarity protein partitioning-defective 1/microtubule-affinity regulating kinase 2 (Par1b/MARK2) translates this positional landmark to cortical polarity by promoting the apicolateral accumulation of Leu-Gly-Asn repeat-enriched protein (LGN) and the capture of nuclear mitotic apparatus protein (NuMA)–positive astral microtubules to orientate the mitotic spindle. Proliferating hepatocytes thus display an asymmetric inheritance of their apical domains via a mechanism that involves Par1b and LGN, which we postulate serves the unique tissue architecture of the developing liver parenchyma. The development and maintenance of the polarized epithelial architecture and function of organs that form tubular “lumen” structures is important for normal physiology and, when deregulated, gives rise to disease. Recent studies have highlighted the importance of a strict coordination of the orientation of mitotic divisions relative to an internal axis of asymmetry in proliferating epithelial cells during this process. Hepatocytes are the predominant epithelial cells of the liver. Hepatocytes display a unique lumen-forming architecture and cellular asymmetry, but the molecular basis for this special polarized architecture is not well understood. Our study now reveals an unexpected mode of plasma membrane domain inheritance that is coupled to a cellular axis of asymmetry in proliferating mammalian hepatocytes. We show that mitotic hepatocytes asymmetrically segregate their apical plasma membrane (the membrane facing the lumen structure) along with the lumen to their daughter cells. We demonstrate that the coordinated action of two proteins, Par1b and LGN, constitutes a fundamental part of the underlying molecular mechanism. This coupling of cell division and polarity in hepatocytes is distinct from that established in other epithelial cell types. These findings are important for understanding the unique polarized tissue architecture in the developing liver.
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129
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A molecular blueprint at the apical surface establishes planar asymmetry in cochlear hair cells. Dev Cell 2013; 27:88-102. [PMID: 24135232 DOI: 10.1016/j.devcel.2013.09.011] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 08/29/2013] [Accepted: 09/13/2013] [Indexed: 11/22/2022]
Abstract
Sound perception relies on the planar polarization of the mechanosensory hair cell apex, which develops a V-shaped stereocilia bundle pointing toward an eccentric kinocilium. It remains unknown how intrinsically asymmetric bundles arise and are concomitantly oriented in the tissue. We report here that mInsc, LGN, and Gαi proteins, which classically regulate mitotic spindle orientation, are polarized in a lateral microvilli-free region, or "bare zone," at the apical hair cell surface. By creating and extending the bare zone, these proteins trigger a relocalization of the eccentric kinocilium midway toward the cell center. aPKC is restrained medially by mInsc/LGN/Gαi, resulting in compartmentalization of the apical surface that imparts the V-shaped distribution of stereocilia and brings the asymmetric bundle in register with the relocalized kinocilium. Gαi is additionally required for lateral orientation of cochlear hair cells, providing a possible mechanism to couple the emergence of asymmetric stereocilia bundles with planar cell polarity.
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130
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Collins E, Mann BJ, Wadsworth P. Eg5 restricts anaphase B spindle elongation in mammalian cells. Cytoskeleton (Hoboken) 2013; 71:136-44. [PMID: 24285623 DOI: 10.1002/cm.21158] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Revised: 10/29/2013] [Accepted: 11/11/2013] [Indexed: 01/31/2023]
Abstract
During anaphase, overlapping antiparallel microtubules in the spindle interzone elongate and contribute to chromosome segregation. Kinesin-5 family members are required for spindle elongation in some cells, but in other cases they restrict elongation acting like a brake. To determine how kinesin-5 contributes to spindle elongation in mammalian cells, we treated LLC-Pk1 epithelial cells with small molecule inhibitors of the mammalian kinesin-5, Eg5, at anaphase onset and measured the rate and extent of spindle pole separation using multidimensional tracking of centrosomes in cells expressing GFP-γ-tubulin. Centrosome separation was biphasic, with an initial fast phase followed by a slower phase. Treatment with the small molecule inhibitor, STLC, which weakens the interaction of Eg5 with microtubules, resulted in an increase in the rate of centrosome separation. Conversely, treatment with FCPT, which induces a rigor-like interaction of Eg5 with microtubules, reduced the rate of spindle elongation. In control cells, GFP-Eg5 was localized to spindle microtubules and accumulated in the interzone as anaphase progressed. Spindle fluorescence of GFP-Eg5 was decreased following treatment with STLC and increased in cells treated with FCPT. In anaphase cells, cortical dynein increases and rocking motion of spindle poles was detected consistent with the possibility that dynein mediates spindle elongation. In summary, our results demonstrate that Eg5 is not required for spindle elongation, and in fact, restricts the rate of spindle elongation in mammalian cells.
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Affiliation(s)
- Elizabeth Collins
- Department of Biology University of Massachusetts Amherst, Amherst, Massachusetts
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131
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Blumer JB, Lanier SM. Activators of G protein signaling exhibit broad functionality and define a distinct core signaling triad. Mol Pharmacol 2013; 85:388-96. [PMID: 24302560 DOI: 10.1124/mol.113.090068] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Activators of G protein signaling (AGS), initially discovered in the search for receptor-independent activators of G protein signaling, define a broad panel of biologic regulators that influence signal transfer from receptor to G-protein, guanine nucleotide binding and hydrolysis, G protein subunit interactions, and/or serve as alternative binding partners for Gα and Gβγ independently of the classic heterotrimeric Gαβγ. AGS proteins generally fall into three groups based upon their interaction with and regulation of G protein subunits: group I, guanine nucleotide exchange factors (GEF); group II, guanine nucleotide dissociation inhibitors; and group III, entities that bind to Gβγ. Group I AGS proteins can engage all subclasses of G proteins, whereas group II AGS proteins primarily engage the Gi/Go/transducin family of G proteins. A fourth group of AGS proteins with selectivity for Gα16 may be defined by the Mitf-Tfe family of transcription factors. Groups I-III may act in concert, generating a core signaling triad analogous to the core triad for heterotrimeric G proteins (GEF + G proteins + effector). These two core triads may function independently of each other or actually cross-integrate for additional signal processing. AGS proteins have broad functional roles, and their discovery has advanced new concepts in signal processing, cell and tissue biology, receptor pharmacology, and system adaptation, providing unexpected platforms for therapeutic and diagnostic development.
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Affiliation(s)
- Joe B Blumer
- Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston, South Carolina
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132
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Lu MS, Prehoda KE. A NudE/14-3-3 pathway coordinates dynein and the kinesin Khc73 to position the mitotic spindle. Dev Cell 2013; 26:369-80. [PMID: 23987511 DOI: 10.1016/j.devcel.2013.07.021] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Revised: 07/07/2013] [Accepted: 07/29/2013] [Indexed: 12/11/2022]
Abstract
Mitotic spindle position is controlled by interactions of cortical molecular motors with astral microtubules. In animal cells, Partner of Inscuteable (Pins) acts at the cortex to coordinate the activity of Dynein and Kinesin-73 (Khc73; KIF13B in mammals) to orient the spindle. Though the two motors move in opposite directions, their synergistic activity is required for robust Pins-mediated spindle orientation. Here, we identify a physical connection between Dynein and Khc73 that mediates cooperative spindle positioning. Khc73's motor and MBS domains link Pins to microtubule plus ends, while its stalk domain is necessary for Dynein activation and precise positioning of the spindle. A motif in the stalk domain binds, in a phospho-dependent manner, 14-3-3ζ, which dimerizes with 14-3-3ε. The 14-3-3ζ/ε heterodimer binds the Dynein adaptor NudE to complete the Dynein connection. The Khc73 stalk/14-3-3/NudE pathway defines a physical connection that coordinates the activities of multiple motor proteins to precisely position the spindle.
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Affiliation(s)
- Michelle S Lu
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
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133
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Mazel T, Biesemann A, Krejczy M, Nowald J, Müller O, Dehmelt L. Direct observation of microtubule pushing by cortical dynein in living cells. Mol Biol Cell 2013; 25:95-106. [PMID: 24173713 PMCID: PMC3873897 DOI: 10.1091/mbc.e13-07-0376] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Single-molecule speckle microscopy and computational modeling reveal the relation between cortical dynein complex dynamics and microtubule behavior in mammalian cells. Experimentally observed rapid turnover of dynein complexes at the cell cortex facilitates their search to efficiently capture and push microtubules with leading plus ends. Microtubules are under the influence of forces mediated by cytoplasmic dynein motors associated with the cell cortex. If such microtubules are free to move, they are rapidly transported inside cells. Here we directly observe fluorescent protein–labeled cortical dynein speckles and motile microtubules. We find that several dynein complex subunits, including the heavy chain, the intermediate chain, and the associated dynactin subunit Dctn1 (also known as p150glued) form spatially resolved, dynamic speckles at the cell cortex, which are preferentially associated with microtubules. Measurements of bleaching and dissociation kinetics at the cell cortex reveal that these speckles often contain multiple labeled dynein heavy-chain molecules and turn over rapidly within seconds. The dynamic behavior of microtubules, such as directional movement, bending, or rotation, is influenced by association with dynein speckles, suggesting a direct physical and functional interaction. Our results support a model in which rapid turnover of cell cortex–associated dynein complexes facilitates their search to efficiently capture and push microtubules directionally with leading plus ends.
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Affiliation(s)
- Tomáš Mazel
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, and Fakultät Chemie, Chemische Biologie, Dortmund University of Technology, 44227 Dortmund, Germany
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134
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Toughiri R, Li X, Du Q, Bieberich CJ. Phosphorylation of NuMA by Aurora-A kinase in PC-3 prostate cancer cells affects proliferation, survival, and interphase NuMA localization. J Cell Biochem 2013; 114:823-30. [PMID: 23097092 DOI: 10.1002/jcb.24421] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Accepted: 10/08/2012] [Indexed: 11/08/2022]
Abstract
Aurora-A is a serine/threonine kinase that has oncogenic properties in vivo. The expression and kinase activity of Aurora-A are up-regulated in multiple malignancies. Aurora-A is a key regulator of mitosis that localizes to the centrosome from the G2 phase through mitotic exit and regulates mitotic spindle formation as well as centrosome separation. Overexpression of Aurora-A in multiple malignancies has been linked to higher tumor grade and poor prognosis through mechanisms that remain to be defined. Using an unbiased proteomics approach, we identified the protein nuclear mitotic apparatus (NuMA) as a robust substrate of Aurora-A kinase. Using a small molecule Aurora-A inhibitor in conjunction with a reverse in-gel kinase assay (RIKA), we demonstrate that NuMA becomes hypo-phosphorylated in vivo upon Aurora-A inhibition. Using an alanine substitution strategy, we identified multiple Aurora-A phospho-acceptor sites in the C-terminal tail of NuMA. Functional analyses demonstrate that mutation of three of these phospho-acceptor sites significantly diminished cell proliferation. In addition, alanine mutation at these sites significantly increased the rate of apoptosis. Using confocal immunofluorescence microscopy, we show that the NuMA T1804A mutant mis-localizes to the cytoplasm in interphase nuclei in a punctate pattern. The identification of Aurora-A phosphorylation sites in NuMA that are important for cell cycle progression and apoptosis provides new insights into Aurora-A function.
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Affiliation(s)
- Raheleh Toughiri
- Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA
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135
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Bergstralh DT, Haack T, St Johnston D. Epithelial polarity and spindle orientation: intersecting pathways. Philos Trans R Soc Lond B Biol Sci 2013; 368:20130291. [PMID: 24062590 PMCID: PMC3785970 DOI: 10.1098/rstb.2013.0291] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
During asymmetric stem cell divisions, the mitotic spindle must be correctly oriented and positioned with respect to the axis of cell polarity to ensure that cell fate determinants are appropriately segregated into only one daughter cell. By contrast, epithelial cells divide symmetrically and orient their mitotic spindles perpendicular to the main apical–basal polarity axis, so that both daughter cells remain within the epithelium. Work in the past 20 years has defined a core ternary complex consisting of Pins, Mud and Gαi that participates in spindle orientation in both asymmetric and symmetric divisions. As additional factors that interact with this complex continue to be identified, a theme has emerged: there is substantial overlap between the mechanisms that orient the spindle and those that establish and maintain apical–basal polarity in epithelial cells. In this review, we examine several factors implicated in both processes, namely Canoe, Bazooka, aPKC and Discs large, and consider the implications of this work on how the spindle is oriented during epithelial cell divisions.
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Affiliation(s)
- Dan T Bergstralh
- The Gurdon Institute and the Department of Genetics, University of Cambridge, , Tennis Court Road, Cambridge CB2 1QN, UK
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136
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Schappi JM, Krbanjevic A, Rasenick MM. Tubulin, actin and heterotrimeric G proteins: coordination of signaling and structure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:674-81. [PMID: 24071592 DOI: 10.1016/j.bbamem.2013.08.026] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Revised: 08/19/2013] [Accepted: 08/26/2013] [Indexed: 01/17/2023]
Abstract
G proteins mediate signals from membrane G protein coupled receptors to the cell interior, evoking significant regulation of cell physiology. The cytoskeleton contributes to cell morphology, motility, division, and transport functions. This review will discuss the interplay between heterotrimeric G protein signaling and elements of the cytoskeleton. Also described and discussed will be the interplay between tubulin and G proteins that results in atypical modulation of signaling pathways and cytoskeletal dynamics. This will be extended to describe how tubulin and G proteins act in concert to influence various aspects of cellular behavior. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters.This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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Affiliation(s)
- Jeffrey M Schappi
- Department of Physiology and Biophysics, University Of Illinois, Chicago, IL 60612, USA
| | - Aleksandar Krbanjevic
- Department of Physiology and Biophysics, University Of Illinois, Chicago, IL 60612, USA; Jesse Brown VAMC, Chicago, IL 60612, USA
| | - Mark M Rasenick
- Department of Physiology and Biophysics, University Of Illinois, Chicago, IL 60612, USA; Department of Psychiatry, University Of Illinois, Chicago, IL 60612, USA.
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137
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Abstract
Asymmetric cell divisions (ACDs) result in two unequal daughter cells and are a hallmark of stem cells. ACDs can be achieved either by asymmetric partitioning of proteins and organelles or by asymmetric cell fate acquisition due to the microenvironment in which the daughters are placed. Increasing evidence suggests that in the mammalian epidermis, both of these processes occur. During embryonic epidermal development, changes occur in the orientation of the mitotic spindle in relation to the underlying basement membrane. These changes are guided by conserved molecular machinery that is operative in lower eukaryotes and dictates asymmetric partitioning of proteins during cell divisions. That said, the shift in spindle alignment also determines whether a division will be parallel or perpendicular to the basement membrane, and this in turn provides a differential microenvironment for the resulting daughter cells. Here, we review how oriented divisions of progenitors contribute to the development and stratification of the epidermis.
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Affiliation(s)
- Anita Kulukian
- Laboratory of Mammalian Cell Biology and Development, Howard Hughes Medical Institute, The Rockefeller University, , New York, NY 10065, USA
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138
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Hofler C, Koelle MR. The G protein regulator AGS-3 allows C. elegans to alter behaviors in response to food deprivation. WORM 2013; 1:56-60. [PMID: 24058824 PMCID: PMC3670173 DOI: 10.4161/worm.19042] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Behavioral responses to food deprivation are a fundamental aspect of nervous system function in all animals. In humans, these behavioral responses prevent dieting from being an effective remedy for obesity. Several signaling molecules in the mammalian brain act through G proteins of the Gαi/o family to mediate responses to food restriction. The mechanisms for neural response to food deprivation may be conserved across species, allowing the power of genetic model organisms to generate insights relevant to the problem of human obesity. In a recent study, we found that C. elegans uses Gαo signaling to mediate a number of behavioral changes that occur after food deprivation. Food deprivation causes biochemical changes in the G Protein Regulator (GPR) domain protein AGS-3 and AGS-3, together with the guanine nucleotide exchange factor RIC-8, activates Gαo signaling to alter food-seeking behavior. These proteins are all conserved in the human brain. Thus the study of behavioral responses to food deprivation in C. elegans may reveal the details of conserved molecular mechanisms underlying neural responses to food deprivation.
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139
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Moon HM, Youn YH, Pemble H, Yingling J, Wittmann T, Wynshaw-Boris A. LIS1 controls mitosis and mitotic spindle organization via the LIS1-NDEL1-dynein complex. Hum Mol Genet 2013; 23:449-66. [PMID: 24030547 DOI: 10.1093/hmg/ddt436] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Heterozygous LIS1 mutations are responsible for the human neuronal migration disorder lissencephaly. Mitotic functions of LIS1 have been suggested from many organisms throughout evolution. However, the cellular functions of LIS1 at distinct intracellular compartments such as the centrosome and the cell cortex have not been well defined especially during mitotic cell division. Here, we used detailed cellular approaches and time-lapse live cell imaging of mitosis from Lis1 mutant mouse embryonic fibroblasts to reveal critical roles of LIS1 in mitotic spindle regulation. We found that LIS1 is required for the tight control of chromosome congression and segregation to dictate kinetochore-microtubule (MT) interactions and anaphase progression. In addition, LIS1 is essential for the establishment of mitotic spindle pole integrity by maintaining normal centrosome number. Moreover, LIS1 plays crucial roles in mitotic spindle orientation by increasing the density of astral MT plus-end movements toward the cell cortex, which enhances cortical targeting of LIS1-dynein complex. Overexpression of NDEL1-dynein and MT stabilization rescues spindle orientation defects in Lis1 mutants, demonstrating that mouse LIS1 acts via the LIS1-NDEL1-dynein complex to regulate astral MT plus-ends dynamics and establish proper contacts of MTs with the cell cortex to ensure precise cell division.
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Affiliation(s)
- Hyang Mi Moon
- Department of Pediatrics, Institute for Human Genetics
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140
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Kotak S, Gönczy P. Mechanisms of spindle positioning: cortical force generators in the limelight. Curr Opin Cell Biol 2013; 25:741-8. [PMID: 23958212 DOI: 10.1016/j.ceb.2013.07.008] [Citation(s) in RCA: 138] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Revised: 07/09/2013] [Accepted: 07/15/2013] [Indexed: 01/04/2023]
Abstract
Correct positioning of the spindle governs placement of the cytokinesis furrow and thus plays a crucial role in the partitioning of fate determinants and the disposition of daughter cells in a tissue. Converging evidence indicates that spindle positioning is often dictated by interactions between the plus-end of astral microtubules that emanate from the spindle poles and an evolutionary conserved cortical machinery that serves to pull on them. At the heart of this machinery lies a ternary complex (LIN-5/GPR-1/2/Gα in Caenorhabditis elegans and NuMA/LGN/Gαi in Homo sapiens) that promotes the presence of the motor protein dynein at the cell cortex. In this review, we discuss how the above components contribute to spindle positioning and how the underlying mechanisms are precisely regulated to ensure the proper execution of this crucial process in metazoan organisms.
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Affiliation(s)
- Sachin Kotak
- Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Swiss Federal Institute of Technology (EPFL), Lausanne CH-1005, Switzerland
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141
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Ezan J, Lasvaux L, Gezer A, Novakovic A, May-Simera H, Belotti E, Lhoumeau AC, Birnbaumer L, Beer-Hammer S, Borg JP, Le Bivic A, Nürnberg B, Sans N, Montcouquiol M. Primary cilium migration depends on G-protein signalling control of subapical cytoskeleton. Nat Cell Biol 2013; 15:1107-15. [PMID: 23934215 DOI: 10.1038/ncb2819] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 07/03/2013] [Indexed: 01/06/2023]
Abstract
In ciliated mammalian cells, the precise migration of the primary cilium at the apical surface of the cells, also referred to as translational polarity, defines planar cell polarity (PCP) in very early stages. Recent research has revealed a co-dependence between planar polarization of some cell types and cilium positioning at the surface of cells. This important role of the primary cilium in mammalian cells is in contrast with its absence from Drosophila melanogaster PCP establishment. Here, we show that deletion of GTP-binding protein alpha-i subunit 3 (Gαi3) and mammalian Partner of inscuteable (mPins) disrupts the migration of the kinocilium at the surface of cochlear hair cells and affects hair bundle orientation and shape. Inhibition of G-protein function in vitro leads to kinocilium migration defects, PCP phenotype and abnormal hair bundle morphology. We show that Gαi3/mPins are expressed in an apical and distal asymmetrical domain, which is opposite and complementary to an aPKC/Par-3/Par-6b expression domain, and non-overlapping with the core PCP protein Vangl2. Thus G-protein-dependent signalling controls the migration of the cilium cell autonomously, whereas core PCP signalling controls long-range tissue PCP.
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Affiliation(s)
- Jerome Ezan
- 1] INSERM, Planar Polarity and Plasticity Group, Neurocentre Magendie, 33077 Bordeaux, France [2] Université Bordeaux, Neurocentre Magendie, Bordeaux 33077, France
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142
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Kotak S, Busso C, Gönczy P. NuMA phosphorylation by CDK1 couples mitotic progression with cortical dynein function. EMBO J 2013; 32:2517-29. [PMID: 23921553 DOI: 10.1038/emboj.2013.172] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Accepted: 07/15/2013] [Indexed: 12/19/2022] Open
Abstract
Spindle positioning and spindle elongation are critical for proper cell division. In human cells, an evolutionary conserved ternary complex (NuMA/LGN/Gαi) anchors dynein at the cortex during metaphase, thus ensuring correct spindle positioning. Whether this complex contributes to anaphase spindle elongation is not known. More generally, the mechanisms coupling mitotic progression with spindle behaviour remain elusive. Here, we uncover that levels of cortical dynein markedly increase during anaphase in a NuMA-dependent manner. We demonstrate that during metaphase, CDK1-mediated phosphorylation at T2055 negatively regulates NuMA cortical localization and that this phosphorylation is counteracted by PPP2CA phosphatase activity. We establish that this tug of war is essential for proper levels of cortical dynein and thus spindle positioning during metaphase. Moreover, we find that upon CDK1 inactivation in anaphase, the rise in dephosphorylated NuMA at the cell cortex leads to cortical dynein enrichment, and thus to robust spindle elongation. Our findings uncover a mechanism whereby the status of NuMA phosphorylation coordinates mitotic progression with proper spindle function.
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Affiliation(s)
- Sachin Kotak
- Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland
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143
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Mapelli M, Gonzalez C. On the inscrutable role of Inscuteable: structural basis and functional implications for the competitive binding of NuMA and Inscuteable to LGN. Open Biol 2013; 2:120102. [PMID: 22977735 PMCID: PMC3438535 DOI: 10.1098/rsob.120102] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Accepted: 07/20/2012] [Indexed: 11/12/2022] Open
Abstract
Alignment of the mitotic spindle to the cellular polarity axis is a prerequisite for asymmetric cell divisions. The protein network coordinating the spindle position with cortical polarity includes the molecular machinery pulling on astral microtubules, which is assembled on conserved NuMA:LGN:Gαi complexes, the polarity proteins Par3:Par6:aPKC and an adaptor molecule known as Inscuteable (Insc). To date, all these components were assumed to enter a macromolecular complex localized at polarity sites in mitosis. However, recent structural studies revealed the Insc and NuMA are mutually exclusive interactors of LGN, implying that the molecular mechanism of spindle coupling to polarity is more sophisticated than has been believed to date.
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Affiliation(s)
- Marina Mapelli
- Department of Experimental Oncology, European Institute of Oncology, Via Adamello 16, 20139 Milan, Italy.
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144
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Abstract
Accurate positioning of the mitotic spindle is critical to ensure proper distribution of chromosomes during cell division. The small GTPase Ran, which regulates a variety of processes throughout the cell cycle, including interphase nucleocytoplasmic transport and mitotic spindle assembly, was recently shown to also control spindle alignment. Ran is required for the correct cortical localization of LGN and nuclear-mitotic apparatus protein (NuMA), proteins that generate pulling forces on astral microtubules (MTs) through cytoplasmic dynein. Here we use importazole, a small-molecule inhibitor of RanGTP/importin-β function, to study the role of Ran in spindle positioning in human cells. We find that importazole treatment results in defects in astral MT dynamics, as well as in mislocalization of LGN and NuMA, leading to misoriented spindles. Of interest, importazole-induced spindle-centering defects can be rescued by nocodazole treatment, which depolymerizes astral MTs, or by overexpression of CLASP1, which does not restore proper LGN and NuMA localization but stabilizes astral MT interactions with the cortex. Together our data suggest a model for mitotic spindle positioning in which RanGTP and CLASP1 cooperate to align the spindle along the long axis of the dividing cell.
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Affiliation(s)
- Stephen L Bird
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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145
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Lu MS, Johnston CA. Molecular pathways regulating mitotic spindle orientation in animal cells. Development 2013; 140:1843-56. [PMID: 23571210 DOI: 10.1242/dev.087627] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Orientation of the cell division axis is essential for the correct development and maintenance of tissue morphology, both for symmetric cell divisions and for the asymmetric distribution of fate determinants during, for example, stem cell divisions. Oriented cell division depends on the positioning of the mitotic spindle relative to an axis of polarity. Recent studies have illuminated an expanding list of spindle orientation regulators, and a molecular model for how cells couple cortical polarity with spindle positioning has begun to emerge. Here, we review both the well-established spindle orientation pathways and recently identified regulators, focusing on how communication between the cell cortex and the spindle is achieved, to provide a contemporary view of how positioning of the mitotic spindle occurs.
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Affiliation(s)
- Michelle S Lu
- Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA
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146
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Berends CWH, Muñoz J, Portegijs V, Schmidt R, Grigoriev I, Boxem M, Akhmanova A, Heck AJR, van den Heuvel S. F-actin asymmetry and the endoplasmic reticulum-associated TCC-1 protein contribute to stereotypic spindle movements in the Caenorhabditis elegans embryo. Mol Biol Cell 2013; 24:2201-15. [PMID: 23699393 PMCID: PMC3708726 DOI: 10.1091/mbc.e13-02-0076] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The position of the spindle apparatus determines the plane of cell cleavage and, therefore, the size and position of daughter cells, as well as the decision between symmetric and asymmetric cell division. We show that asymmetry in cortical actin and, remarkably, an endoplasmic reticulum–localized protein contribute to proper spindle positioning in the Caenorhabditis elegans embryo. The microtubule spindle apparatus dictates the plane of cell cleavage in animal cells. During development, dividing cells control the position of the spindle to determine the size, location, and fate of daughter cells. Spindle positioning depends on pulling forces that act between the cell periphery and astral microtubules. This involves dynein recruitment to the cell cortex by a heterotrimeric G-protein α subunit in complex with a TPR-GoLoco motif protein (GPR-1/2, Pins, LGN) and coiled-coil protein (LIN-5, Mud, NuMA). In this study, we searched for additional factors that contribute to spindle positioning in the one-cell Caenorhabditis elegans embryo. We show that cortical actin is not needed for Gα–GPR–LIN-5 localization and pulling force generation. Instead, actin accumulation in the anterior actually reduces pulling forces, possibly by increasing cortical rigidity. Examining membrane-associated proteins that copurified with GOA-1 Gα, we found that the transmembrane and coiled-coil domain protein 1 (TCC-1) contributes to proper spindle movements. TCC-1 localizes to the endoplasmic reticulum membrane and interacts with UNC-116 kinesin-1 heavy chain in yeast two-hybrid assays. RNA interference of tcc-1 and unc-116 causes similar defects in meiotic spindle positioning, supporting the concept of TCC-1 acting with kinesin-1 in vivo. These results emphasize the contribution of membrane-associated and cortical proteins other than Gα–GPR–LIN-5 in balancing the pulling forces that position the spindle during asymmetric cell division.
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147
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Pan Z, Zhu J, Shang Y, Wei Z, Jia M, Xia C, Wen W, Wang W, Zhang M. An autoinhibited conformation of LGN reveals a distinct interaction mode between GoLoco motifs and TPR motifs. Structure 2013; 21:1007-17. [PMID: 23665171 DOI: 10.1016/j.str.2013.04.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 03/11/2013] [Accepted: 04/05/2013] [Indexed: 10/26/2022]
Abstract
LGN plays essential roles in asymmetric cell divisions via its N-terminal TPR-motif-mediated binding to mInsc and NuMA. This scaffolding activity requires the release of the autoinhibited conformation of LGN by binding of Gα(i) to its C-terminal GoLoco (GL) motifs. The interaction between the GL and TPR motifs of LGN represents a distinct GL/target binding mode with an unknown mechanism. Here, we show that two consecutive GL motifs of LGN form a minimal TPR-motif-binding unit. GL12 and GL34 bind to TPR0-3 and TPR4-7, respectively. The crystal structure of a truncated LGN reveals that GL34 forms a pair of parallel α helices and binds to the concave surface of TPR4-7, thereby preventing LGN from binding to other targets. Importantly, the GLs bind to TPR motifs with a mode distinct from that observed in the GL/Gα(i)·GDP complexes. Our results also indicate that multiple and orphan GL motif proteins likely respond to G proteins with distinct mechanisms.
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Affiliation(s)
- Zhu Pan
- Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry and Institutes of Biomedical Sciences, Fudan University, Shanghai, China
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148
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Interaction of NuMA protein with the kinesin Eg5: its possible role in bipolar spindle assembly and chromosome alignment. Biochem J 2013; 451:195-204. [DOI: 10.1042/bj20121447] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Bipolar spindle assembly in mitotic cells is a prerequisite to ensure correct alignment of chromosomes for their segregation to each daughter cell; spindle microtubules are tethered at plus ends to chromosomes and focused at minus ends to either of the two spindle poles. NuMA (nuclear mitotic apparatus protein) is present solely in the nucleus in interphase cells, but relocalizes during mitosis to the spindle poles to play a crucial role in spindle assembly via focusing spindle microtubules to each pole. In the present study we show that the kinesin-5 family motor Eg5 is a protein that directly interacts with NuMA, using a proteomics approach and various binding assays both in vivo and in vitro. During mitosis Eg5 appears to interact with NuMA in the vicinity of the spindle poles, whereas the interaction does not occur in interphase cells, where Eg5 is distributed throughout the cytoplasm but NuMA exclusively localizes to the nucleus. Slight, but significant, depletion of Eg5 in HeLa cells by RNA interference results in formation of less-focused spindle poles with misaligned chromosomes in metaphase; these phenotypes are similar to those induced by depletion of NuMA. Since NuMA is less accumulated at the spindle poles in Eg5-depleted cells, Eg5 probably contributes to spindle assembly via regulating NuMA localization. Furthermore, depletion of cytoplasmic dynein induces mislocalization of NuMA and phenotypes similar to those observed in NuMA-depleted cells, without affecting Eg5 localization to the spindles. Thus dynein appears to control NuMA function in conjunction with Eg5.
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149
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Zhu M, Settele F, Kotak S, Sanchez-Pulido L, Ehret L, Ponting CP, Gönczy P, Hoffmann I. MISP is a novel Plk1 substrate required for proper spindle orientation and mitotic progression. J Cell Biol 2013; 200:773-87. [PMID: 23509069 PMCID: PMC3601349 DOI: 10.1083/jcb.201207050] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 02/13/2013] [Indexed: 02/04/2023] Open
Abstract
Precise positioning of the mitotic spindle determines the correct cell division axis and is crucial for organism development. Spindle positioning is mediated through a cortical machinery by capturing astral microtubules, thereby generating pushing/pulling forces at the cell cortex. However, the molecular link between these two structures remains elusive. Here we describe a previously uncharacterized protein, MISP (C19orf21), as a substrate of Plk1 that is required for correct mitotic spindle positioning. MISP is an actin-associated protein throughout the cell cycle. MISP depletion led to an impaired metaphase-to-anaphase transition, which depended on phosphorylation by Plk1. Loss of MISP induced mitotic defects including spindle misorientation accompanied by shortened astral microtubules. Furthermore, we find that MISP formed a complex with and regulated the cortical distribution of the +TIP binding protein p150(glued), a subunit of the dynein-dynactin complex. We propose that Plk1 phosphorylates MISP, thus stabilizing cortical and astral microtubule attachments required for proper mitotic spindle positioning.
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Affiliation(s)
- Mei Zhu
- Cell Cycle Control and Carcinogenesis, German Cancer Research Center, DKFZ, D-69120 Heidelberg, Germany
| | - Florian Settele
- Cell Cycle Control and Carcinogenesis, German Cancer Research Center, DKFZ, D-69120 Heidelberg, Germany
| | - Sachin Kotak
- School of Life Sciences, Swiss Federal Institute of Technology (EPFL), Swiss Institute for Experimental Cancer Research (ISREC), CH-1015 Lausanne, Switzerland
| | - Luis Sanchez-Pulido
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, England, UK
| | - Lena Ehret
- Cell Cycle Control and Carcinogenesis, German Cancer Research Center, DKFZ, D-69120 Heidelberg, Germany
| | - Chris P. Ponting
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, England, UK
| | - Pierre Gönczy
- School of Life Sciences, Swiss Federal Institute of Technology (EPFL), Swiss Institute for Experimental Cancer Research (ISREC), CH-1015 Lausanne, Switzerland
| | - Ingrid Hoffmann
- Cell Cycle Control and Carcinogenesis, German Cancer Research Center, DKFZ, D-69120 Heidelberg, Germany
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150
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Kotak S, Busso C, Gönczy P. Cortical dynein is critical for proper spindle positioning in human cells. ACTA ACUST UNITED AC 2013; 199:97-110. [PMID: 23027904 PMCID: PMC3461507 DOI: 10.1083/jcb.201203166] [Citation(s) in RCA: 168] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Dynein is anchored at the plasma membrane by a ternary complex comprising NuMA–LGN–Gα and thus ensures correct spindle positioning Correct spindle positioning is fundamental for proper cell division during development and in stem cell lineages. Dynein and an evolutionarily conserved ternary complex (nuclear mitotic apparatus protein [NuMA]–LGN–Gα in human cells and LIN-5–GPR-1/2–Gα in Caenorhabditis elegans) are required for correct spindle positioning, but their relationship remains incompletely understood. By analyzing fixed specimens and conducting live-imaging experiments, we uncovered that appropriate levels of ternary complex components are critical for dynein-dependent spindle positioning in HeLa cells and C. elegans embryos. Moreover, using mutant versions of Gα in both systems, we established that dynein acts at the membrane to direct spindle positioning. Importantly, we identified a region within NuMA that mediates association with dynein. By using this region to target dynein to the plasma membrane, we demonstrated that the mere presence of dynein at that location is sufficient to direct spindle positioning in HeLa cells. Overall, we propose a model in which the ternary complex serves to anchor dynein at the plasma membrane to ensure correct spindle positioning.
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Affiliation(s)
- Sachin Kotak
- Swiss Institute for Experimental Cancer Research, School of Life Sciences, Swiss Federal Institute of Technology Lausanne, Lausanne CH-1015, Switzerland
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