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Silverman-Gavrila RV, Wilde A. Ran is required before metaphase for spindle assembly and chromosome alignment and after metaphase for chromosome segregation and spindle midbody organization. Mol Biol Cell 2006; 17:2069-80. [PMID: 16481399 PMCID: PMC1415283 DOI: 10.1091/mbc.e05-10-0991] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Ran pathway has been shown to have a role in spindle assembly. However, the extent of the role of the Ran pathway in mitosis in vivo is unclear. We report that perturbation of the Ran pathway disrupted multiple steps of mitosis in syncytial Drosophila embryos and uncovered new mitotic processes that are regulated by Ran. During the onset of mitosis, the Ran pathway is required for the production, organization, and targeting of centrosomally nucleated microtubules to chromosomes. However, the role of Ran is not restricted to microtubule organization, because Ran is also required for the alignment of chromosomes at the metaphase plate. In addition, the Ran pathway is required for postmetaphase events, including chromosome segregation and the assembly of the microtubule midbody. The Ran pathway mediates these mitotic events, in part, by facilitating the correct targeting of the kinase Aurora A and the kinesins KLP61F and KLP3A to spindles.
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52
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Nacerddine K, Lehembre F, Bhaumik M, Artus J, Cohen-Tannoudji M, Babinet C, Pandolfi PP, Dejean A. The SUMO pathway is essential for nuclear integrity and chromosome segregation in mice. Dev Cell 2006; 9:769-79. [PMID: 16326389 DOI: 10.1016/j.devcel.2005.10.007] [Citation(s) in RCA: 409] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 07/21/2005] [Accepted: 10/13/2005] [Indexed: 12/19/2022]
Abstract
Covalent modification by SUMO regulates a wide range of cellular processes, including transcription, cell cycle, and chromatin dynamics. To address the biological function of the SUMO pathway in mammals, we generated mice deficient for the SUMO E2-conjugating enzyme Ubc9. Ubc9-deficient embryos die at the early postimplantation stage. In culture, Ubc9 mutant blastocysts are viable, but fail to expand after 2 days and show apoptosis of the inner cell mass. Loss of Ubc9 leads to major chromosome condensation and segregation defects. Ubc9-deficient cells also show severe defects in nuclear organization, including nuclear envelope dysmorphy and disruption of nucleoli and PML nuclear bodies. Moreover, RanGAP1 fails to accumulate at the nuclear pore complex in mutant cells that show a collapse in Ran distribution. Together, these findings reveal a major role for Ubc9, and, by implication, for the SUMO pathway, in nuclear architecture and function, chromosome segregation, and embryonic viability in mammals.
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Affiliation(s)
- Karim Nacerddine
- Unité d'Organisation Nucléaire et Oncogénèse, INSERM U 579, Institut Pasteur, 75724 Paris Cedex 15, France
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53
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Hetzer MW, Walther TC, Mattaj IW. PUSHING THE ENVELOPE: Structure, Function, and Dynamics of the Nuclear Periphery. Annu Rev Cell Dev Biol 2005; 21:347-80. [PMID: 16212499 DOI: 10.1146/annurev.cellbio.21.090704.151152] [Citation(s) in RCA: 253] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The nuclear envelope (NE) is a highly specialized membrane that delineates the eukaryotic cell nucleus. It is composed of the inner and outer nuclear membranes, nuclear pore complexes (NPCs) and, in metazoa, the lamina. The NE not only regulates the trafficking of macromolecules between nucleoplasm and cytosol but also provides anchoring sites for chromatin and the cytoskeleton. Through these interactions, the NE helps position the nucleus within the cell and chromosomes within the nucleus, thereby regulating the expression of certain genes. The NE is not static, rather it is continuously remodeled during cell division. The most dramatic example of NE reorganization occurs during mitosis in metazoa when the NE undergoes a complete cycle of disassembly and reformation. Despite the importance of the NE for eukaryotic cell life, relatively little is known about its biogenesis or many of its functions. We thus are far from understanding the molecular etiology of a diverse group of NE-associated diseases.
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Affiliation(s)
- Martin W Hetzer
- Molecular and Cell Biology Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037, USA.
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54
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Ozlü N, Srayko M, Kinoshita K, Habermann B, O'toole ET, Müller-Reichert T, Schmalz N, Desai A, Hyman AA. An essential function of the C. elegans ortholog of TPX2 is to localize activated aurora A kinase to mitotic spindles. Dev Cell 2005; 9:237-48. [PMID: 16054030 DOI: 10.1016/j.devcel.2005.07.002] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2005] [Revised: 06/10/2005] [Accepted: 07/08/2005] [Indexed: 12/16/2022]
Abstract
In vertebrates, the microtubule binding protein TPX2 is required for meiotic and mitotic spindle assembly. TPX2 is also known to bind to and activate Aurora A kinase and target it to the spindle. However, the relationship between the TPX2-Aurora A interaction and the role of TPX2 in spindle assembly is unclear. Here, we identify TPXL-1, a C. elegans protein that is the first characterized invertebrate ortholog of TPX2. We demonstrate that an essential role of TPXL-1 during mitosis is to activate and target Aurora A to microtubules. Our data suggest that this targeting stabilizes microtubules connecting kinetochores to the spindle poles. Thus, activation and targeting of Aurora A appears to be an ancient and conserved function of TPX2 that plays a central role in mitotic spindle assembly.
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Affiliation(s)
- Nurhan Ozlü
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, Dresden 01307, Germany.
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55
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Cao YK, Zhong ZS, Chen DY, Zhang GX, Schatten H, Sun QY. Cell cycle-dependent localization and possible roles of the small GTPase Ran in mouse oocyte maturation, fertilization and early cleavage. Reproduction 2005; 130:431-40. [PMID: 16183861 DOI: 10.1530/rep.1.00391] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The small GTPase Ran controls numerous cellular processes of the mitotic cell cycle. In this experiment, we investigated the localization and possible roles of Ran during mouse oocyte meiotic maturation, fertilization and early cleavage by using confocal laser scanning microscopy, antibody microinjection and microtubule disturbance. The results showed that Ran was localized mainly in the nucleus (except for the nucleolus) in the oocyte, zygote and early embryo. At pro-metaphase of meiosis I, Ran distributed throughout the cell, but predominantly concentrated around the condensed chromosomes. During the completion of meiosis I and meiosis II, it concentrated to the meiotic spindle microtubules except for the midbody region. After sperm penetration, Ran dispersed with the extrusion of the second polar body and gradually concentrated in the male and female pronuclei thereafter. Ran was also observed to exist diffusely in the cytoplasm in prophase; it concentrated at the mitotic spindle, and migrated to the nucleus during early cleavage. Ran’s concentration around the spindle disappeared when microtubule assembly was inhibited by colchicine, while it was concentrated around the chromosomes after microtubule stabilization with taxol treatment. Ran did not display any role in cytokinesis during division when pseudo-cleavage of germinal vesicle-intact oocytes was induced. Anti-Ran antibody microinjection decreased the germinal vesicle breakdown and the first polar body extrusion, and distorted spindle organization and chromosome alignment. Our results indicate that Ran has a cell cycle-dependent localization and may have regulatory roles in cell cycle progression and microtubule organization in mouse oocytes, fertilized eggs and early embryos.
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Affiliation(s)
- Yun-Kao Cao
- State Key Laboratory of Reproductive Biology, Institute of Zoology, The Chinese Academy of Sciences, No. 25 Beisihuanxi Road, Beijing 100080, China
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56
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Srayko M, Kaya A, Stamford J, Hyman AA. Identification and Characterization of Factors Required for Microtubule Growth and Nucleation in the Early C. elegans Embryo. Dev Cell 2005; 9:223-36. [PMID: 16054029 DOI: 10.1016/j.devcel.2005.07.003] [Citation(s) in RCA: 178] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Revised: 06/10/2005] [Accepted: 07/08/2005] [Indexed: 11/19/2022]
Abstract
Microtubules (MTs) are dynamic polymers that undergo cell cycle and position-sensitive regulation of polymerization and depolymerization. Although many different factors that regulate MT dynamics have been described, to date there has been no systematic analysis of genes required for MT dynamics in a single system. Here, we use a transgenic EB1::GFP strain, which labels the growing plus ends of MTs, to analyze the growth rate, nucleation rate, and distribution of growing MTs in the Caenorhabditis elegans embryo. We also present the results from an RNAi screen of 40 genes previously implicated in MT-based processes. Our findings suggest that fast microtubule growth is dependent on the amount of free tubulin and the ZYG-9-TAC-1 complex. Robust MT nucleation by centrosomes requires AIR-1, SPD-2, SPD-5, and gamma-tubulin. However, we found that centrosomes do not nucleate MTs to saturation; rather, the depolymerizing kinesin-13 subfamily member KLP-7 is required to limit microtubule outgrowth from centrosomes.
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Affiliation(s)
- Martin Srayko
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany.
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57
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Abstract
The centrosome is the main MT organizing center in animal cells, and has traditionally been regarded as essential for organization of the bipolar spindle that facilitates chromosome segregation during mitosis. Centrosomes are associated with the poles of the mitotic spindle, and several cell types require these organelles for spindle formation. However, most plant cells and some female meiotic systems get along without this organelle, and centrosome-independent spindle assembly has now been identified within some centrosome containing cells. How can such observations, which point to mutually incompatible conclusions regarding the requirement of centrosomes in spindle formation, be interpreted? With emphasis on the functional role of centrosomes, this article summarizes the current models of spindle formation, and outlines how observations obtained from spindle assembly assays in vitro may reconcile conflicting opinions about the mechanism of spindle assembly. It is further described how Drosophila mutants are used to address the functional interrelationships between individual centrosomal proteins and spindle formation in vivo.
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Affiliation(s)
- Hanne Varmark
- Programme of Cell Biology and Biophysics, European Molecular Biology Laboratory, Meyerhofstrasse, D-69117 Heidelberg, Germany.
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58
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Abstract
Microtubules are dynamic polymers required for many aspects of eukaryotic cell function. The interphase microtubule network is essential for intracellular transport, organization, and cell polarization, whereas the mitotic spindle is required for chromosome segregation and cell division. Studies in different areas such as cell migration, mitosis, and asymmetric cell division have shown that Ran, Rho, and heterotrimeric G proteins regulate many aspects of microtubule functions. This review surveys how G protein-signaling coordinates microtubule polymerization and organization with specific cellular activities.
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Affiliation(s)
- Yixian Zheng
- Department of Embryology, Carnegie Institution of Washington and Howard Hughes Medical Institute, Baltimore, MD 21210, USA.
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59
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Abstract
Importin beta, once thought to be exclusively a nuclear transport receptor, is emerging as a global regulator of diverse cellular functions. Importin beta acts positively in multiple interphase roles: in nuclear import, as a chaperone for highly charged nuclear proteins, and as a potential motor adaptor for movement along microtubules. In contrast, importin beta plays a negative regulatory role in mitotic spindle assembly, centrosome dynamics, nuclear membrane formation, and nuclear pore assembly. In most of these, importin beta is counteracted by its regulator, Ran-GTP. In light of this, the recent discovery of Ran's involvement in spindle checkpoint control suggested a potential new arena for importin beta action, although it is also possible that one of importin beta's relatives, the karyopherin family of proteins, manages this checkpoint. Lastly, importin beta plays a role in transducing damage signals from the axons of injured neurons back to the cell body.
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Affiliation(s)
- Amnon Harel
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California, San Diego, 9500 Gilman Drive, Room 2124A, Pacific Hall, La Jolla, CA 92093, USA
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60
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Abstract
Recent work has provided new insights into the mechanism of spindle assembly. Growing evidence supports a model in which the small GTPase Ran plays a central role in this process. Here, we examine the evidence for the existence of a RanGTP gradient around mitotic chromosomes and some controversial data on the role that chromosomes play in spindle assembly. We review the current knowledge on the Ran downstream targets for spindle assembly and we focus on the multiple roles of TPX2, one of the targets of RanGTP during cell division.
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Affiliation(s)
- Oliver J Gruss
- Cell Biology and Biophysics Program, European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg 69117, Germany.
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61
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Kerres A, Vietmeier-Decker C, Ortiz J, Karig I, Beuter C, Hegemann J, Lechner J, Fleig U. The fission yeast kinetochore component Spc7 associates with the EB1 family member Mal3 and is required for kinetochore-spindle association. Mol Biol Cell 2004; 15:5255-67. [PMID: 15371542 PMCID: PMC532008 DOI: 10.1091/mbc.e04-06-0443] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A critical aspect of mitosis is the interaction of the kinetochore with spindle microtubules. Fission yeast Mal3 is a member of the EB1 family of microtubule plus-end binding proteins, which have been implicated in this process. However, the Mal3 interaction partner at the kinetochore had not been identified. Here, we show that the mal3 mutant phenotype can be suppressed by the presence of extra Spc7, an essential kinetochore protein associated with the central centromere region. Mal3 and Spc7 interact physically as both proteins can be coimmunoprecipitated. Overexpression of a Spc7 variant severely compromises kinetochore-microtubule interaction, indicating that the Spc7 protein plays a role in this process. Spc7 function seems to be conserved because, Spc105, a Saccharomyces cerevisiae homolog of Spc7, identified by mass spectrometry as a component of the conserved Ndc80 complex, can rescue mal3 mutant strains.
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Affiliation(s)
- Anne Kerres
- Institut für Mikrobiologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
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62
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Shi WY, Skeath JB. The Drosophila RCC1 homolog, Bj1, regulates nucleocytoplasmic transport and neural differentiation during Drosophila development. Dev Biol 2004; 270:106-21. [PMID: 15136144 DOI: 10.1016/j.ydbio.2004.02.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2003] [Revised: 02/10/2004] [Accepted: 02/12/2004] [Indexed: 11/18/2022]
Abstract
The Bj1 gene encodes the Drosophila homolog of RCC1, the guanine-nucleotide exchange factor for RanGTPase. Here, we provide the first phenotypic characterization of a RCC1 homolog in a developmental model system. We identified Bj1 (dRCC1) in a genetic screen to identify mutations that alter central nervous system development. We find that zygotic dRCC1 mutant embryos exhibit specific defects in the development and differentiation of lateral CNS neurons although cell division and the cell cycle appear grossly normal. dRCC1 mutant nerve cords contain abnormally large cells with compartmentalized nuclei and exhibit increased transcription in the lateral CNS. As RCC1 is an important component of the nucleocytoplasmic transport machinery, we find that dRCC1 function is required for nuclear import of nuclear localization signal sequence (NLS)-carrying cargo molecules. Finally, we show that dRCC1 is required for cell proliferation and/or survival during germline, eye and wing development and that dRCC1 appears to facilitate apoptosis.
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Affiliation(s)
- Wei-Yang Shi
- Program in Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA
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63
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Shojaei F, Gallacher L, Bhatia M. Differential gene expression of human stem progenitor cells derived from early stages of in utero human hematopoiesis. Blood 2004; 103:2530-40. [PMID: 14656878 DOI: 10.1182/blood-2003-09-3209] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractHematopoietic stem progenitor cells (HSPCs) are highly enriched in a rare subset of Lin-CD34+CD38- cells. Independent of stage of human development, HSPC function segregates to the subset of Lin-CD34+CD38- cells. However, fetal-derived HSPCs demonstrate distinct self-renewal and differentiation capacities compared with their adult counterparts. Here, to characterize the molecular nature of fetal HSPCs, suppressive subtractive hybridization was used to compare gene expression of HSPCs isolated from fetal blood (FB-HSPCs) versus adult mobilized peripheral blood (MPB-HSPCs). We identified 97 differentially expressed genes that could be annotated into distinct groups that include transcription factors, cell cycle regulators, and genes involved in signal transduction. Candidate regulators, such as Lim only domain-2 (LMO2), nuclear factor–kappa B (NF-κB), tripartite motif 28 (Trim28), and N-myc protooncogene (MYCN), and a novel homeobox gene product were among transcripts that were found to be differentially expressed and could be associated with specific proliferation and differentiation properties unique to FB-HSPCs. Interestingly, the majority of genes associated with signal transduction belong to Ras pathway, highlighting the significance of Ras signaling in FB-HSPCs. Genes differentially expressed in FB-HSPCs versus adult MPB-HSPCs were verified using quantitative real-time polymerase chain reaction (Q-PCR). This approach also resulted in the identification of a transcript that is highly expressed in FB-HSPCs but not detectable in more differentiated Lin-CD34+CD38+ FB progenitors. Our investigation represents the first study to compare phenotypically similar, but functionally distinct, HSPC populations and to provide a gene profile of unique human HSPCs with higher proliferative capacity derived from early in utero human blood development.
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Affiliation(s)
- Farbod Shojaei
- Robarts Research Institute, Stem Cell Biology and Regenerative Medicine, London, ON, Canada
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64
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Affiliation(s)
- Richard Wozniak
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada T6R 2A4
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65
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Gruenbaum Y, Goldman RD, Meyuhas R, Mills E, Margalit A, Fridkin A, Dayani Y, Prokocimer M, Enosh A. The nuclear lamina and its functions in the nucleus. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 226:1-62. [PMID: 12921235 DOI: 10.1016/s0074-7696(03)01001-5] [Citation(s) in RCA: 173] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The nuclear lamina is a structure near the inner nuclear membrane and the peripheral chromatin. It is composed of lamins, which are also present in the nuclear interior, and lamin-associated proteins. The increasing number of proteins that interact with lamins and the compound interactions between these proteins and chromatin-associated proteins make the nuclear lamina a highly complex but also a very exciting structure. The nuclear lamina is an essential component of metazoan cells. It is involved in most nuclear activities including DNA replication, RNA transcription, nuclear and chromatin organization, cell cycle regulation, cell development and differentiation, nuclear migration, and apoptosis. Specific mutations in nuclear lamina genes cause a wide range of heritable human diseases. These diseases include Emery-Dreifuss muscular dystrophy, limb girdle muscular dystrophy, dilated cardiomyopathy (DCM) with conduction system disease, familial partial lipodystrophy (FPLD), autosomal recessive axonal neuropathy (Charcot-Marie-Tooth disorder type 2, CMT2), mandibuloacral dysplasia (MAD), Hutchison Gilford Progeria syndrome (HGS), Greenberg Skeletal Dysplasia, and Pelger-Huet anomaly (PHA). Genetic analyses in Caenorhabditis elegans, Drosophila, and mice show new insights into the functions of the nuclear lamina, and recent structural analyses have begun to unravel the molecular structure and assembly of lamins and their associated proteins.
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Affiliation(s)
- Yosef Gruenbaum
- Department of Genetics, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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66
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Hachet V, Köcher T, Wilm M, Mattaj IW. Importin alpha associates with membranes and participates in nuclear envelope assembly in vitro. EMBO J 2004; 23:1526-35. [PMID: 15014441 PMCID: PMC391064 DOI: 10.1038/sj.emboj.7600154] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2003] [Accepted: 02/11/2004] [Indexed: 11/09/2022] Open
Abstract
Importin alpha is well known as an adaptor that functions with Importin beta in the nuclear import of proteins containing specific nuclear localization signals (NLSs). We show here that either an excess or a lack of Importin alpha blocks nuclear envelope (NE) assembly in vitro, and our data suggest that soluble Importin alpha functions in NE assembly in conjunction with NLS-containing partner proteins. Surprisingly, a significant proportion of Importin alpha is found to fractionate with Xenopus egg membranes. We demonstrate that membrane association of Importin alpha is regulated by phosphorylation. Using mutant forms of Importin alpha that either do not bind membranes or are not released from them by phosphorylation, we provide evidence that membrane-associated Importin alpha is required for NE formation. Unlike other functions of Importin alpha, this membrane-associated activity does not require interaction with NLS proteins.
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Affiliation(s)
- Virginie Hachet
- European Molecular Biology Laboratory, Meyerhofstrasse, Heidelberg, Germany
| | - Thomas Köcher
- European Molecular Biology Laboratory, Meyerhofstrasse, Heidelberg, Germany
| | - Matthias Wilm
- European Molecular Biology Laboratory, Meyerhofstrasse, Heidelberg, Germany
| | - Iain W Mattaj
- European Molecular Biology Laboratory, Meyerhofstrasse, Heidelberg, Germany
- Gene Expression Programme, European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany. Tel.: +49 6221 387 393; Fax: +49 6221 387 518; E-mail:
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67
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Eichenlaub-Ritter U, Vogt E, Yin H, Gosden R. Spindles, mitochondria and redox potential in ageing oocytes. Reprod Biomed Online 2004; 8:45-58. [PMID: 14759287 DOI: 10.1016/s1472-6483(10)60497-x] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Studies of human oocytes obtained from women of advanced reproductive age revealed that spindles are frequently aberrant, with chromosomes sometimes failing to align properly at the equator during meiosis I and II. Chromosomal analyses of donated and spare human oocytes and cytogenetic and molecular studies on the origin of trisomies collectively suggest that errors in chromosome segregation during oogenesis increase with advancing maternal age and as the menopause approaches. Disturbances in the fidelity of chromosome segregation, especially at anaphase I, leading to aneuploidy are prime causes of reduced developmental competence of embryos in assisted reproduction, as well as being responsible for the genesis of genetic disease. This review provides an overview of spindle formation and chromosome behaviour in mammalian oocytes. Evidence of a link between abnormal mitochondrial function in oocytes and somatic follicular cells, and finally disturbances in chromosome cohesion and segregation, and cell cycle control in aged mammalian oocytes, are also discussed.
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Affiliation(s)
- U Eichenlaub-Ritter
- Institute of Gene Technology/Microbiology, Faculty of Biology, University of Bielefeld, D-33501 Bielefeld, Germany.
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68
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Abstract
With the rapid development of sequencing technologies in the past decade, many eukaryotic genomes have been resolved at the primary sequence level. However, organization of the genome within nuclei and the principles that govern such properties remain largely unclear. Optimization of fluorescence probe-based hybridization technologies combined with new advances in the instrumentation for microscopy has steadily yielded more structural information on chromosome organization in eukaryote model systems. These studies provide static snapshots of the detailed organization of chromatin. More recently, the successful application of a chromatin tagging strategy utilizing auto fluorescent fusion proteins opened a new era of chromatin studies in which the dynamic organization of the genome can be tracked in near real time. This review focuses on these new approaches to studying chromatin organization and dynamics in plants, and on future prospects in unraveling the basic principle of chromosome organization.
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Affiliation(s)
- Eric Lam
- Biotech Center for Agriculture and the Environment, Department of Plant Science, Rutgers the State University of New Jersey, New Brunswick, New Jersey 08901, USA.
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69
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Segbert C, Barkus R, Powers J, Strome S, Saxton WM, Bossinger O. KLP-18, a Klp2 kinesin, is required for assembly of acentrosomal meiotic spindles in Caenorhabditis elegans. Mol Biol Cell 2003; 14:4458-69. [PMID: 12937278 PMCID: PMC266765 DOI: 10.1091/mbc.e03-05-0283] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The proper segregation of chromosomes during meiosis or mitosis requires the assembly of well organized spindles. In many organisms, meiotic spindles lack centrosomes. The formation of such acentrosomal spindles seems to involve first assembly or capture of microtubules (MTs) in a random pattern around the meiotic chromosomes and then parallel bundling and bipolar organization by the action of MT motors and other proteins. Here, we describe the structure, distribution, and function of KLP-18, a Caenorhabditis elegans Klp2 kinesin. Previous reports of Klp2 kinesins agree that it concentrates in spindles, but do not provide a clear view of its function. During prometaphase, metaphase, and anaphase, KLP-18 concentrates toward the poles in both meiotic and mitotic spindles. Depletion of KLP-18 by RNA-mediated interference prevents parallel bundling/bipolar organization of the MTs that accumulate around female meiotic chromosomes. Hence, meiotic chromosome segregation fails, leading to haploid or aneuploid embryos. Subsequent assembly and function of centrosomal mitotic spindles is normal except when aberrant maternal chromatin is present. This suggests that although KLP-18 is critical for organizing chromosome-derived MTs into a parallel bipolar spindle, the order inherent in centrosome-derived astral MT arrays greatly reduces or eliminates the need for KLP-18 organizing activity in mitotic spindles.
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Affiliation(s)
- Christoph Segbert
- Institut für Genetik, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
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70
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Ems-McClung SC, Zheng Y, Walczak CE. Importin alpha/beta and Ran-GTP regulate XCTK2 microtubule binding through a bipartite nuclear localization signal. Mol Biol Cell 2003; 15:46-57. [PMID: 13679510 PMCID: PMC307526 DOI: 10.1091/mbc.e03-07-0454] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The small GTPase Ran is essential for spindle assembly. Ran is proposed to act through its nuclear import receptors importin alpha and/or importin beta to control the sequestration of proteins necessary for spindle assembly. To date, the molecular mechanisms by which the Ran pathway functions remain unclear. Using purified proteins, we have reconstituted Ran-regulated microtubule binding of the C-terminal kinesin XCTK2, a kinesin important for spindle assembly. We show that the tail of XCTK2 binds to microtubules and that this binding is inhibited in the presence of importin alpha and beta (alpha/beta) and restored by addition of Ran-GTP. The bipartite nuclear localization signal (NLS) in the tail of XCTK2 is essential to this process, because mutation of the NLS abolishes importin alpha/beta-mediated regulation of XCTK2 microtubule binding. Our data show that importin alpha/beta directly regulates the activity of XCTK2 and that one of the molecular mechanisms of Ran-regulated spindle assembly is identical to that used in classical NLS-driven nuclear transport.
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71
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Walther TC, Askjaer P, Gentzel M, Habermann A, Griffiths G, Wilm M, Mattaj IW, Hetzer M. RanGTP mediates nuclear pore complex assembly. Nature 2003; 424:689-94. [PMID: 12894213 DOI: 10.1038/nature01898] [Citation(s) in RCA: 174] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2003] [Accepted: 07/10/2003] [Indexed: 11/09/2022]
Abstract
In metazoa, the nuclear envelope breaks down and reforms during each cell cycle. Nuclear pore complexes (NPCs), which serve as channels for transport between the nucleus and cytoplasm, assemble into the reforming nuclear envelope in a sequential process involving association of a subset of NPC proteins, nucleoporins, with chromatin followed by the formation of a closed nuclear envelope fenestrated by NPCs. How chromatin recruitment of nucleoporins and NPC assembly are regulated is unknown. Here we demonstrate that RanGTP production is required to dissociate nucleoporins Nup107, Nup153 and Nup358 from Importin beta, to target them to chromatin and to induce association between separate NPC subcomplexes. Additionally, either an excess of RanGTP or removal of Importin beta induces formation of NPC-containing membrane structures--annulate lamellae--both in vitro in the absence of chromatin and in vivo. Annulate lamellae formation is strongly and specifically inhibited by an excess of Importin beta. The data demonstrate that RanGTP triggers distinct steps of NPC assembly, and suggest a mechanism for the spatial restriction of NPC assembly to the surface of chromatin.
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Affiliation(s)
- Tobias C Walther
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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72
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Schatz CA, Santarella R, Hoenger A, Karsenti E, Mattaj IW, Gruss OJ, Carazo-Salas RE. Importin alpha-regulated nucleation of microtubules by TPX2. EMBO J 2003; 22:2060-70. [PMID: 12727873 PMCID: PMC156067 DOI: 10.1093/emboj/cdg195] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The importin alpha-regulated microtubule-associated protein TPX2 is known to be critical for meiotic and mitotic spindle formation in vertebrates, but its detailed mechanism of action and regulation is not understood. Here, the site of interaction on TPX2 for importin alpha is mapped. A TPX2 mutant that cannot bind importin alpha is constitutively active in the induction of microtubule-containing aster-like structures in Xenopus egg extract, demonstrating that no other importin alpha or RanGTPase target is required to mediate microtubule assembly in this system. Further, recombinant TPX2 is shown to induce the formation and bundling of microtubules in dilute solutions of pure tubulin. In this purified system, importin alpha prevents TPX2-induced microtubule formation, but not TPX2-tubulin interaction or microtubule bundling. This demonstrates that TPX2 has more than one mode of interaction with tubulin and that only one of these types of interaction is abolished by importin alpha. The data suggest that the critical early function in spindle formation regulated by importin alpha is TPX2-mediated microtubule nucleation.
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Affiliation(s)
- Christoph A Schatz
- European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
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73
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Braunwarth A, Fromont-Racine M, Legrain P, Bischoff FR, Gerstberger T, Hurt E, Kunzler M. Identification and characterization of a novel RanGTP-binding protein in the yeast Saccharomyces cerevisiae. J Biol Chem 2003; 278:15397-405. [PMID: 12578832 DOI: 10.1074/jbc.m210630200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The small Ras-like GTPase Ran plays an essential role in the transport of macromolecules in and out of the nucleus and has been implicated in spindle (1,2 ) and nuclear envelope formation (3,4 ) during mitosis in higher eukaryotes. We identified Saccharomyces cerevisiae open reading frame YGL164c encoding a novel RanGTP-binding protein, termed Yrb30p. The protein competes with yeast RanBP1 (Yrb1p) for binding to the GTP-bound form of yeast Ran (Gsp1p) and is, like Yrb1p, able to form trimeric complexes with RanGTP and some of the karyopherins. In contrast to Yrb1p, Yrb30p does not coactivate but inhibits RanGAP1(Rna1p)-mediated GTP hydrolysis on Ran, like the karyopherins. At steady state, Yrb30p localizes exclusively to the cytoplasm, but the presence of a functional nuclear export signal and the localization of truncated forms of Yrb30p suggest that the protein shuttles between nucleus and cytoplasm and is exported via two alternative pathways, dependent on the nuclear export receptor Xpo1p/Crm1p and on RanGTP binding. Whereas overproduction of the full-length protein and complete deletion of the open reading frame reveal no obvious phenotype, overproduction of C-terminally truncated forms of the protein inhibits yeast vegetative growth. Based on these results and the exclusive conservation of the protein in the fungal kingdom, we hypothesize that Yrb30p represents a novel modulator of the Ran GTPase switch related to fungal lifestyle.
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Affiliation(s)
- Andreas Braunwarth
- Biochemie-Zentrum Heidelberg, Ruprecht-Karls-Universität, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
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74
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Lutz W, Frank EM, Craig TA, Thompson R, Venters RA, Kojetin D, Cavanagh J, Kumar R. Calbindin D28K interacts with Ran-binding protein M: identification of interacting domains by NMR spectroscopy. Biochem Biophys Res Commun 2003; 303:1186-92. [PMID: 12684061 DOI: 10.1016/s0006-291x(03)00499-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Calbindin D(28K) is an EF-hand containing protein that plays a vital role in neurological function. We now show that calcium-loaded calbindin D(28K) interacts with Ran-binding protein M, a protein known to play a role in microtubule function. Using NMR methods, we show that a peptide, LASIKNR, derived from Ran-binding protein M, interacts with several regions of the calcium-loaded protein including the amino terminus and two other regions that exhibit conformational exchange on the NMR timescale. We suggest that the interaction between calbindin D(28K) and Ran-binding protein M may be important in calbindin D(28K) function.
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Affiliation(s)
- Ward Lutz
- Department of Biochemistry, Research Center, Mayo Clinic and Foundation, 200 First Street SW, Rochester, MN 55905, USA
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75
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Abstract
Here, we report the first evidence that the Ran GTPase cycle is required for nuclear pore complex (NPC) assembly. Using a genetic approach, factors required for NPC assembly were identified in Saccharomyces cerevisiae. Four mutant complementation groups were characterized that correspond to respective mutations in genes encoding Ran (gsp1), and essential Ran regulatory factors Ran GTPase-activating protein (rna1), Ran guanine nucleotide exchange factor (prp20), and the RanGDP import factor (ntf2). All the mutants showed temperature-dependent mislocalization of green fluorescence protein (GFP)-tagged nucleoporins (nups) and the pore-membrane protein Pom152. A decrease in GFP fluorescence associated with the nuclear envelope was observed along with an increase in the diffuse, cytoplasmic signal with GFP foci. The defects did not affect the stability of existing NPCs, and nup mislocalization was dependent on de novo protein synthesis and continued cell growth. Electron microscopy analysis revealed striking membrane perturbations and the accumulation of vesicles in arrested mutants. Using both biochemical fractionation and immunoelectron microscopy methods, these vesicles were shown to contain nups. We propose a model wherein a Ran-mediated vesicular fusion step is required for NPC assembly into intact nuclear envelopes.
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Affiliation(s)
- Kathryn J Ryan
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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76
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Abstract
Macromolecular transport between the cytoplasm and the nucleus occurs through the nuclear pore complex (NPC) and is mediated by multiple families of soluble transport factors. All these transport factors share the ability to translocate across the NPC through specific interactions with components of the nuclear pore. This review highlights advances in our understanding of the structure and function of the NPC and the shuttling transport receptors involved in nuclear transport. It discusses recently proposed models for the translocation of receptor-cargo complexes through the NPC channel and reviews how the small GTPase Ran functions as a positional marker of the genome to regulate multiple important aspects of the eukaryotic cell cycle.
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Affiliation(s)
- Karsten Weis
- Department of Molecular and Cell Biology, Division of Cell and Developmental Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
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77
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Budde PP, Heald R. Centrosomes and Kinetochores, Who Needs 'Em? The Role of Noncentromeric Chromatin in Spindle Assembly. Curr Top Dev Biol 2003; 56:85-113. [PMID: 14584727 DOI: 10.1016/s0070-2153(03)01008-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Priya Prakash Budde
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
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78
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Askjaer P, Galy V, Hannak E, Mattaj IW. Ran GTPase cycle and importins alpha and beta are essential for spindle formation and nuclear envelope assembly in living Caenorhabditis elegans embryos. Mol Biol Cell 2002; 13:4355-70. [PMID: 12475958 PMCID: PMC138639 DOI: 10.1091/mbc.e02-06-0346] [Citation(s) in RCA: 139] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The small GTPase Ran has been found to play pivotal roles in several aspects of cell function. We have investigated the role of the Ran GTPase cycle in spindle formation and nuclear envelope assembly in dividing Caenorhabditis elegans embryos in real time. We found that Ran and its cofactors RanBP2, RanGAP, and RCC1 are all essential for reformation of the nuclear envelope after cell division. Reducing the expression of any of these components of the Ran GTPase cycle by RNAi leads to strong extranuclear clustering of integral nuclear envelope proteins and nucleoporins. Ran, RanBP2, and RanGAP are also required for building a mitotic spindle, whereas astral microtubules are normal in the absence of these proteins. RCC1(RNAi) embryos have similar abnormalities in the initial phase of spindle formation but eventually recover to form a bipolar spindle. Irregular chromatin structures and chromatin bridges due to spindle failure were frequently observed in embryos where the Ran cycle was perturbed. In addition, connection between the centrosomes and the male pronucleus, and thus centrosome positioning, depends upon the Ran cycle components. Finally, we have demonstrated that both IMA-2 and IMB-1, the homologues of vertebrate importin alpha and beta, are essential for both spindle assembly and nuclear formation in early embryos.
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Affiliation(s)
- Peter Askjaer
- European Molecular Biology Laboratory, 69117 Heidelberg, Germany
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79
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Hinkle B, Slepchenko B, Rolls MM, Walther TC, Stein PA, Mehlmann LM, Ellenberg J, Terasaki M. Chromosomal association of Ran during meiotic and mitotic divisions. J Cell Sci 2002; 115:4685-93. [PMID: 12415012 DOI: 10.1242/jcs.00136] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Recent studies in Xenopus egg extracts indicate that the small G protein Ran has a central role in spindle assembly and nuclear envelope reformation. We determined Ran localization and dynamics in cells during M phase. By immunofluorescence, Ran is accumulated on the chromosomes of meiosis-II-arrested Xenopus eggs. In living cells, fluorescently labeled Ran associated with the chromosomes in Xenopus and remained associated during anaphase when eggs were artificially activated. Fluorescent Ran associated with chromosomes in mouse eggs, during meiotic maturation and early embryonic divisions in starfish, and to a lesser degree during mitosis of a cultured mammalian cell line. Chromosomal Ran undergoes constant flux. From photobleach experiments in immature starfish oocytes, chromosomal Ran has a k(off) of approximately 0.06 second(-1), and binding analysis suggests that there is a single major site. The chromosomal interactions may serve to keep Ran-GTP in the vicinity of the chromosomes for spindle assembly and nuclear envelope reformation.
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Affiliation(s)
- Beth Hinkle
- Department of Physiology, University of Connecticut Health Center, Farmington, CT 06032, USA
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80
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Zhang C, Goldberg MW, Moore WJ, Allen TD, Clarke PR. Concentration of Ran on chromatin induces decondensation, nuclear envelope formation and nuclear pore complex assembly. Eur J Cell Biol 2002; 81:623-33. [PMID: 12494999 DOI: 10.1078/0171-9335-00288] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nuclear envelope (NE) formation can be studied in a cell-free system made from Xenopus eggs. In this system, NE formation involves the small GTPase Ran. Ran associates with chromatin early in nuclear assembly and concentration of Ran on inert beads is sufficient to induce NE formation. Here, we show that Ran binds to chromatin prior to NE formation and recruits RCC1, the nucleotide exchange factor that generates Ran-GTP. In extracts prepared by high-speed centrifugation, increased concentrations of Ran are sufficient to induce chromatin decondensation and NE assembly. Using field emission in-lens scanning electron microscopy (FEISEM), we show that Ran promotes the formation of smoothed membranes and the assembly of nuclear pore complexes (NPCs). In contrast, RanT24N, a mutant that fails to bind GTP and inhibits RCC1, does not support efficient NE assembly, whereas RanQ69L, a mutant locked in a GTP-bound state, permits some membrane vesicle recruitment to chromatin, but inhibits vesicle fusion and NPC assembly. Thus, binding of Ran to chromatin, followed by local generation of Ran-GTP and GTP hydrolysis by Ran, induces chromatin decondensation, membrane vesicle recruitment, membrane formation and NPC assembly. We propose that the biological activity of Ran is determined by its targeting to structures such as chromatin as well as its guanine nucleotide bound state.
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Affiliation(s)
- Chuanmao Zhang
- Biomedical Research Centre, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland, UK
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81
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Gruss OJ, Wittmann M, Yokoyama H, Pepperkok R, Kufer T, Silljé H, Karsenti E, Mattaj IW, Vernos I. Chromosome-induced microtubule assembly mediated by TPX2 is required for spindle formation in HeLa cells. Nat Cell Biol 2002; 4:871-9. [PMID: 12389033 DOI: 10.1038/ncb870] [Citation(s) in RCA: 248] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2002] [Revised: 08/07/2002] [Accepted: 08/26/2002] [Indexed: 11/09/2022]
Abstract
In Xenopus laevis egg extracts, TPX2 is required for the Ran-GTP-dependent assembly of microtubules around chromosomes. Here we show that interfering with the function of the human homologue of TPX2 in HeLa cells causes defects in microtubule organization during mitosis. Suppressing the expression of human TPX2 by RNA interference leads to the formation of two microtubule asters that do not interact and do not form a spindle. Our results suggest that in vivo, even in the presence of duplicated centrosomes, spindle formation requires the function of TPX2 to generate a stable bipolar spindle with overlapping antiparallel microtubule arrays. This indicates that chromosome-induced microtubule production is a general requirement for the formation of functional spindles in animal cells.
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82
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Moore W, Zhang C, Clarke PR. Targeting of RCC1 to chromosomes is required for proper mitotic spindle assembly in human cells. Curr Biol 2002; 12:1442-7. [PMID: 12194828 DOI: 10.1016/s0960-9822(02)01076-x] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ran GTPase is involved in several aspects of nuclear structure and function, including nucleocytoplasmic transport and nuclear envelope formation. Experiments using Xenopus egg extracts have shown that generation of Ran-GTP by the guanine nucleotide exchange factor RCC1 also plays roles in mitotic spindle assembly. Here, we have examined the localization and function of RCC1 in mitotic human cells. We show that RCC1, either the endogenous protein or that expressed as a fusion with green fluorescent protein (GFP), is localized predominantly to chromosomes in mitotic cells. This localization requires an N-terminal lysine-rich region that also contains a nuclear localization signal and is enhanced by interaction with Ran. Either mislocalization of GFP-RCC1 by removal of the N-terminal region or the expression of dominant Ran mutants that perturb the GTP/GDP cycle causes defects in mitotic spindle morphology, including misalignment of chromosomes and abnormal numbers of spindle poles. These results indicate that the generation of Ran-GTP in the vicinity of chromosomes by RCC1 is important for the fidelity of mitotic spindle assembly in human cells. Defects in this system may result in abnormal chromosome segregation and genomic instability, which are characteristic of many cancer cells.
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Affiliation(s)
- William Moore
- Biomedical Research Centre, University of Dundee, Level 5, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland, United Kingdom
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83
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Abstract
The small GTPase Ran has roles in multiple cellular processes, including nuclear transport, mitotic spindle assembly, the regulation of cell cycle progression and nuclear assembly. The past year has seen a remarkable unification of these different roles with respect to the effectors and mechanisms through which they function. Our emergent understanding of Ran suggests that it plays a central role in spatial and temporal organization of the vertebrate cell.
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Affiliation(s)
- Mary Dasso
- Laboratory of Gene Regulation and Development, NICHD/NIH, Bethesda, MD 20892-5431, USA.
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84
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Trieselmann N, Wilde A. Ran localizes around the microtubule spindle in vivo during mitosis in Drosophila embryos. Curr Biol 2002; 12:1124-9. [PMID: 12121620 DOI: 10.1016/s0960-9822(02)00934-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The GTPase Ran regulates multiple cellular functions throughout the cell cycle, including nucleocytoplasmic transport, nuclear membrane assembly, and spindle assembly. Ran mediates spindle assembly by affecting multiple spindle assembly pathways: microtubule dynamics, microtubule motor activity, and spindle pole assembly. Ran is predicted to facilitate spindle assembly by remaining in the GTP-bound state around the chromatin in mitosis. Here, we directly test the central tenet of this hypothesis in vivo by determining the cellular localization of Ran pathway components in Drosophila embryos. We find that, during mitosis, RCC1, the nucleotide exchange factor for Ran, is associated with chromatin, while Ran and RanL43E, an allele locked in the GTP-bound state, localize around the spindle. In contrast, nuclear proteins redistribute throughout the embryo upon nuclear envelope breakdown (NEB). Thus, in vivo RanGTP has the correct spatial localization within the cell to modulate spindle assembly.
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Affiliation(s)
- Nadia Trieselmann
- Department of Medical Genetics and Microbiology, University of Toronto, 1 King's College Circle, Ontario M5S 1A8, Canada
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85
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Hetzer M, Gruss OJ, Mattaj IW. The Ran GTPase as a marker of chromosome position in spindle formation and nuclear envelope assembly. Nat Cell Biol 2002; 4:E177-84. [PMID: 12105431 DOI: 10.1038/ncb0702-e177] [Citation(s) in RCA: 179] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The small GTPase Ran is a key regulator of nucleocytoplasmic transport during interphase. The asymmetric distribution of the GTP-bound form of Ran across the nuclear envelope--that is, large quantities in the nucleus compared with small quantities in the cytoplasm--determines the directionality of many nuclear transport processes. Recent findings that Ran also functions in spindle formation and nuclear envelope assembly during mitosis suggest that Ran has a general role in chromatin-centred processes. Ran functions in these events as a signal for chromosome position.
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Affiliation(s)
- Martin Hetzer
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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