1
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Shaulov L, Gruber R, Cohen I, Harel A. A dominant-negative form of POM121 binds chromatin and disrupts the two separate modes of nuclear pore assembly. J Cell Sci 2011; 124:3822-34. [PMID: 22100917 DOI: 10.1242/jcs.086660] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Nuclear pore complexes (NPCs) are formed during two separate stages of the metazoan cell cycle. They are assembled into the re-forming nuclear envelope (NE) at the exit from mitosis and into an intact, expanding NE during interphase. Here, we show that a soluble internal fragment of the membrane nucleoporin POM121 has a dominant-negative effect on both modes of assembly in a cell-free reconstitution system. The soluble POM121 fragment binds chromatin at sites that are distinct from ELYS-Nup107-160 'seeding' sites and prevents membrane enclosure and NPC formation. Importin-β negatively regulates chromatin binding by the POM121 fragment through a conserved NLS motif and is also shown to affect the recruitment of the endogenous membrane protein to chromatin in the full assembly system. When an intact NE is present before the addition of the dominant-negative fragment, NPCs are inserted into the NE but membrane expansion is inhibited. This results in densely packed NPCs with no intervening membrane patches, as visualized by scanning electron microscopy. We conclude that POM121 plays an important role in both modes of assembly and links nuclear membrane formation and expansion to nuclear pore biogenesis.
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Affiliation(s)
- Lihi Shaulov
- Department of Biology, Technion - Israel Institute of Technology, Haifa 32000, Israel
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2
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Tseng LC, Chen RH. Temporal control of nuclear envelope assembly by phosphorylation of lamin B receptor. Mol Biol Cell 2011; 22:3306-17. [PMID: 21795390 PMCID: PMC3172257 DOI: 10.1091/mbc.e11-03-0199] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Revised: 07/06/2011] [Accepted: 07/18/2011] [Indexed: 01/13/2023] Open
Abstract
The nuclear envelope of metazoans disassembles during mitosis and reforms in late anaphase after sister chromatids have well separated. The coordination of these mitotic events is important for genome stability, yet the temporal control of nuclear envelope reassembly is unknown. Although the steps of nuclear formation have been extensively studied in vitro using the reconstitution system from egg extracts, the temporal control can only be studied in vivo. Here, we use time-lapse microscopy to investigate this process in living HeLa cells. We demonstrate that Cdk1 activity prevents premature nuclear envelope assembly and that phosphorylation of the inner nuclear membrane protein lamin B receptor (LBR) by Cdk1 contributes to the temporal control. We further identify a region in the nucleoplasmic domain of LBR that inhibits premature chromatin binding of the protein. We propose that this inhibitory effect is partly mediated by Cdk1 phosphorylation. Furthermore, we show that the reduced chromatin-binding ability of LBR together with Aurora B activity contributes to nuclear envelope breakdown. Our studies reveal for the first time a mechanism that controls the timing of nuclear envelope reassembly through modification of an integral nuclear membrane protein.
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Affiliation(s)
- Li-Chuan Tseng
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan
| | - Rey-Huei Chen
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan
- Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan
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3
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Rafikova ER, Melikov K, Ramos C, Dye L, Chernomordik LV. Transmembrane protein-free membranes fuse into xenopus nuclear envelope and promote assembly of functional pores. J Biol Chem 2009; 284:29847-59. [PMID: 19696024 PMCID: PMC2785615 DOI: 10.1074/jbc.m109.044453] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 08/17/2009] [Indexed: 11/06/2022] Open
Abstract
Post-mitotic reassembly of nuclear envelope (NE) and the endoplasmic reticulum (ER) has been reconstituted in a cell-free system based on interphase Xenopus egg extract. To evaluate the relative contributions of cytosolic and transmembrane proteins in NE and ER assembly, we replaced a part of native membrane vesicles with ones either functionally impaired by trypsin or N-ethylmaleimide treatments or with protein-free liposomes. Although neither impaired membrane vesicles nor liposomes formed ER and nuclear membrane, they both supported assembly reactions by fusing with native membrane vesicles. At membrane concentrations insufficient to generate full-sized functional nuclei, addition of liposomes and their fusion with membrane vesicles resulted in an extensive expansion of NE, further chromatin decondensation, restoration of the functionality, and spatial distribution of the nuclear pore complexes (NPCs), and, absent newly delivered transmembrane proteins, an increase in NPC numbers. This rescue of the nuclear assembly by liposomes was inhibited by wheat germ agglutinin and thus required active nuclear transport, similarly to the assembly of full-sized functional NE with membrane vesicles. Mechanism of fusion between liposomes and between liposomes and membrane vesicles was investigated using lipid mixing assay. This fusion required interphase cytosol and, like fusion between native membrane vesicles, was inhibited by guanosine 5'-3-O-(thio)triphosphate, soluble N-ethylmaleimide-sensitive factor attachment protein, and N-ethylmaleimide. Our findings suggest that interphase cytosol contains proteins that mediate the fusion stage of ER and NE reassembly, emphasize an unexpected tolerance of nucleus assembly to changes in concentrations of transmembrane proteins, and reveal the existence of a feedback mechanism that couples NE expansion with NPC assembly.
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Affiliation(s)
- Elvira R. Rafikova
- From the Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892-1855
| | - Kamran Melikov
- From the Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892-1855
| | - Corinne Ramos
- the Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093-0347, and
| | - Louis Dye
- the Microscopy and Imaging Core, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892-1855
| | - Leonid V. Chernomordik
- From the Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892-1855
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4
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Abstract
During mitosis in metazoans, the nuclear envelope (NE) breaks down at prophase and reassembles at telophase. The regulation of NE assembly is essential to correct cell functioning. The complex issue of the regulation of NE formation remains to be solved. It is still uncertain that a single mechanism depicts NE formation during mitosis. The aim of this review is to address some of the cytological, biophysical, and molecular aspects of models of NE formation. Our emphasis is on the role of lipids and their modifying enzymes in envelope assembly. We consider how the NE can be used as a model in characterizing membrane dynamics during membrane fusion. Fusion mechanisms that give insight into the formation of the double membrane of the envelope are summarized. We speculate on the possible roles of phosphoinositides in membrane fusion and NE formation.
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Affiliation(s)
- Banafshé Larijani
- Lincoln's Inn Fields Laboratories, Cancer Research UK, London WC2A 3PX, UK.
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5
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Vollmar F, Hacker C, Zahedi RP, Sickmann A, Ewald A, Scheer U, Dabauvalle MC. Assembly of nuclear pore complexes mediated by major vault protein. J Cell Sci 2009; 122:780-6. [PMID: 19240118 DOI: 10.1242/jcs.039529] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
During interphase growth of eukaryotic cells, nuclear pore complexes (NPCs) are continuously incorporated into the intact nuclear envelope (NE) by mechanisms that are largely unknown. De novo formation of NPCs involves local fusion events between the inner and outer nuclear membrane, formation of a transcisternal membranous channel of defined diameter and the coordinated assembly of hundreds of nucleoporins into the characteristic NPC structure. Here we have used a cell-free system based on Xenopus egg extract, which allows the experimental separation of nuclear-membrane assembly and NPC formation. Nuclei surrounded by a closed double nuclear membrane, but devoid of NPCs, were first reconstituted from chromatin and a specific membrane fraction. Insertion of NPCs into the preformed pore-free nuclei required cytosol containing soluble nucleoporins or nucleoporin subcomplexes and, quite unexpectedly, major vault protein (MVP). MVP is the main component of vaults, which are ubiquitous barrel-shaped particles of enigmatic function. Our results implicate MVP, and thus also vaults, in NPC biogenesis and provide a functional explanation for the association of a fraction of vaults with the NE and specifically with NPCs in intact cells.
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Affiliation(s)
- Friederike Vollmar
- Division of Electron Microscopy, Biocenter, University of Würzburg, 97074 Würzburg, Germany
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6
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Anderson DJ, Hetzer MW. Shaping the endoplasmic reticulum into the nuclear envelope. J Cell Sci 2008; 121:137-42. [PMID: 18187447 DOI: 10.1242/jcs.005777] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The nuclear envelope (NE), a double membrane enclosing the nucleus of eukaryotic cells, controls the flow of information between the nucleoplasm and the cytoplasm and provides a scaffold for the organization of chromatin and the cytoskeleton. In dividing metazoan cells, the NE breaks down at the onset of mitosis and then reforms around segregated chromosomes to generate the daughter nuclei. Recent data from intact cells and cell-free nuclear assembly systems suggest that the endoplasmic reticulum (ER) is the source of membrane for NE assembly. At the end of mitosis, ER membrane tubules are targeted to chromatin via tubule ends and reorganized into flat nuclear membrane sheets by specific DNA-binding membrane proteins. In contrast to previous models, which proposed vesicle fusion to be the principal mechanism of NE formation, these new studies suggest that the nuclear membrane forms by the chromatin-mediated reshaping of the ER.
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Affiliation(s)
- Daniel J Anderson
- Salk Institute for Biological Studies, Molecular and Cell Biology Laboratory, 10010 N. Torrey Pines Road, La Jolla, CA 92037, USA
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7
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Hirano Y, Takahashi H, Kumeta M, Hizume K, Hirai Y, Otsuka S, Yoshimura SH, Takeyasu K. Nuclear architecture and chromatin dynamics revealed by atomic force microscopy in combination with biochemistry and cell biology. Pflugers Arch 2008; 456:139-53. [PMID: 18172599 DOI: 10.1007/s00424-007-0431-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2007] [Revised: 11/29/2007] [Accepted: 12/10/2007] [Indexed: 10/22/2022]
Abstract
The recent technical development of atomic force microscopy (AFM) has made nano-biology of the nucleus an attractive and promising field. In this paper, we will review our current understanding of nuclear architecture and dynamics from the structural point of view. Especially, special emphases will be given to: (1) How to approach the nuclear architectures by means of new techniques using AFM, (2) the importance of the physical property of DNA in the construction of the higher-order structures, (3) the significance and implication of the linker and core histones and the nuclear matrix/scaffold proteins for the chromatin dynamics, (4) the nuclear proteins that contribute to the formation of the inner nuclear architecture. Spatio-temporal analyses using AFM, in combination with biochemical and cell biological approaches, will play important roles in the nano-biology of the nucleus, as most of nuclear structures and events occur in nanometer, piconewton and millisecond order. The new applications of AFM, such as recognition imaging, fast-scanning imaging, and a variety of modified cantilevers, are expected to be powerful techniques to reveal the nanostructure of the nucleus.
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Affiliation(s)
- Yasuhiro Hirano
- Kyoto University Graduate School of Biostudies, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan
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8
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Larijani B, Poccia D. Protein and lipid signaling in membrane fusion: nuclear envelope assembly. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/sita.200600128] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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9
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Miyachi K, Hosaka H, Nakamura N, Miyakawa H, Mimori T, Shibata M, Matsushima S, Chinoh H, Horigome T, Hankins RW, Zhang M, Fritzler MJ. Anti-p97/VCP antibodies: an autoantibody marker for a subset of primary biliary cirrhosis patients with milder disease? Scand J Immunol 2006; 63:376-82. [PMID: 16640662 DOI: 10.1111/j.1365-3083.2006.01747.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We previously reported that 12.5% of primary biliary cirrhosis (PBC) sera reacted with a 95 kDa cytosol protein (p95c) that was subsequently identified as a p97/valosin-containing protein (VCP). The clinical features and course of the six anti-p97/VCP-positive PBC patients with Scheuer's stage 1 and 2 liver biopsies were monitored for an average of 15 years. This group was compared with 50 PBC patients that did not have detectable anti-VCP. Autoantibodies to a full-length recombinant p97/VCP were assayed by immunoprecipitation. All six PBC patients with anti-VCP had antibodies to the mitochondrial pyruvate dehydrogenase complex-E2 antigen as measured by an addressable laser bead immunoassay. The first was a male with no evidence of liver failure that died of cerebral infarction at the age of 85. The second was a 73-year-old female with Hashimoto's thyroiditis who has remained clinically stable without ursodeoxycolic acid (UDCA) treatment. Although the third had no HCV antibodies, he developed hepatocellular carcinoma at the age of 76 and died of renal failure at 78. The fourth was a 50-year-old female who remained clinically stable during follow-up and the fifth with Hashimoto's thyroiditis and stable liver function following UCDA treatment. The sixth was a male patient presenting a mild clinical course. The clinical course of these patients was in contrast to the 50 comparison group PBC patients who did not have anti-p97/VCP. As the six PBC patients with anti-p97/VCP antibodies had slowly progressive liver disease and no mortality related to autoimmune liver disease, our observations suggest that this autoantibody might be an indicator of a favourable prognosis.
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Affiliation(s)
- K Miyachi
- First Diagnostic Division, Health Sciences Research Institute, Inc., Yokohama, Japan.
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10
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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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11
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Miyachi K, Hirano Y, Horigome T, Mimori T, Miyakawa H, Onozuka Y, Shibata M, Hirakata M, Suwa A, Hosaka H, Matsushima S, Komatsu T, Matsushima H, Hankins RW, Fritzler MJ. Autoantibodies from primary biliary cirrhosis patients with anti-p95c antibodies bind to recombinant p97/VCP and inhibit in vitro nuclear envelope assembly. Clin Exp Immunol 2004; 136:568-73. [PMID: 15147362 PMCID: PMC1809050 DOI: 10.1111/j.1365-2249.2004.02456.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
We have reported previously that p95c, a novel 95-kDa cytosolic protein, was the target of autoantibodies in sera of patients with autoimmune hepatic diseases. We studied 30 sera that were shown previously to immunoprecipitate a 95 kDa protein from [(35)S]-methionine-labelled HeLa lysates and had a specific precipitin band in immunodiffusion. Thirteen sera were available to test the ability of p95c antibodies to inhibit nuclear envelope assembly in an in vitro assay in which confocal fluorescence microscopy was also used to identify the stages at which nuclear assembly was inhibited. The percentage inhibition of nuclear envelope assembly of the 13 sera ranged from 7% to 99% and nuclear envelope assembly and the swelling of nucleus was inhibited at several stages. The percentage inhibition of nuclear assembly was correlated with the titre of anti-p95c as determined by immunodiffusion. To confirm the identity of this autoantigen, we used a full-length cDNA of the p97/valosin-containing protein (VCP) to produce a radiolabelled recombinant protein that was then used in an immunoprecipitation (IP) assay. Our study demonstrated that 12 of the 13 (93%) human sera with antibodies to p95c immunoprecipitated recombinant p97/VCP. Because p95c and p97 have similar molecular masses and cell localization, and because the majority of sera bind recombinant p97/VCP and anti-p95c antibodies inhibit nuclear assembly, this is compelling evidence that p95c and p97/VCP are identical.
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Affiliation(s)
- K Miyachi
- Health Sciences Research Institute, Yokohama, Kanagawa, Japan.
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12
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Liu J, Prunuske AJ, Fager AM, Ullman KS. The COPI complex functions in nuclear envelope breakdown and is recruited by the nucleoporin Nup153. Dev Cell 2003; 5:487-98. [PMID: 12967567 DOI: 10.1016/s1534-5807(03)00262-4] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Nuclear envelope breakdown is a critical step in the cell cycle of higher eukaryotes. Although integral membrane proteins associated with the nuclear membrane have been observed to disperse into the endoplasmic reticulum at mitosis, the mechanisms involved in this reorganization remain to be fully elucidated. Here, using Xenopus extracts, we report a role for the COPI coatomer complex in nuclear envelope breakdown, implicating vesiculation as an important step. We have found that a nuclear pore protein, Nup153, plays a critical role in directing COPI to the nuclear membrane at mitosis and that this event provides feedback to other aspects of nuclear disassembly. These results provide insight into how key steps in nuclear division are orchestrated.
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Affiliation(s)
- Jin Liu
- Department of Oncological Sciences, Huntsman Cancer Institute, 2000 Circle of Hope, University of Utah, Salt Lake City, UT 84112, USA
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13
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Nakagawa T, Hirano Y, Inomata A, Yokota S, Miyachi K, Kaneda M, Umeda M, Furukawa K, Omata S, Horigome T. Participation of a fusogenic protein, glyceraldehyde-3-phosphate dehydrogenase, in nuclear membrane assembly. J Biol Chem 2003; 278:20395-404. [PMID: 12651855 DOI: 10.1074/jbc.m210824200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We found an autoimmune serum, K199, that strongly suppresses nuclear membrane assembly in a cell-free system involving a Xenopus egg extract. Four different antibodies that suppress nuclear assembly were affinity-purified from the serum using Xenopus egg cytosol proteins. Three proteins recognized by these antibodies were identified by partial amino acid sequencing to be glyceraldehyde-3-phosphate dehydrogenase (GAPDH), fructose-1,6-bisphosphate aldolase, and the regulator of chromatin condensation 1. GAPDH is known to be a fusogenic protein. To verify the participation of GAPDH in nuclear membrane fusion, authentic antibodies against human and rat GAPDH were applied, and strong suppression of nuclear assembly at the nuclear membrane fusion step was observed. The nuclear assembly activity suppressed by antibodies was recovered on the addition of purified chicken GAPDH. A peptide with the sequence of amino acid residues 70-94 of GAPDH, which inhibits GAPDH-induced phospholipid vesicle fusion, inhibited nuclear assembly at the nuclear membrane fusion step. We propose that GAPDH plays a crucial role in the membrane fusion step in nuclear assembly in a Xenopus egg extract cell-free system.
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Affiliation(s)
- Tomoaki Nakagawa
- Course of Functional Biology, Graduate School of Science and Technology, Niigata University, Igarashi-2, Japan
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14
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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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15
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Beaudouin J, Gerlich D, Daigle N, Eils R, Ellenberg J. Nuclear envelope breakdown proceeds by microtubule-induced tearing of the lamina. Cell 2002; 108:83-96. [PMID: 11792323 DOI: 10.1016/s0092-8674(01)00627-4] [Citation(s) in RCA: 338] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mechanism of nuclear envelope breakdown (NEBD) was investigated in live cells. Early spindle microtubules caused folds and invaginations in the NE up to one hour prior to NEBD, creating mechanical tension in the nuclear lamina. The first gap in the NE appeared before lamin B depolymerization, at the site of maximal tension, by a tearing mechanism. Gap formation relaxed this tension and dramatically accelerated the rate of chromosome condensation. The hole produced in the NE then rapidly expanded over the nuclear surface. NE fragments remaining on chromosomes were removed toward the centrosomes in a microtubule-dependent manner, suggesting a mechanism mediated by a minus-end-directed motor.
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Affiliation(s)
- Joël Beaudouin
- Gene Expression and Cell Biology/Biophysics Programmes, European Molecular Biology Laboratory, D-69117. Heidelberg, Germany
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16
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Hetzer M, Meyer HH, Walther TC, Bilbao-Cortes D, Warren G, Mattaj IW. Distinct AAA-ATPase p97 complexes function in discrete steps of nuclear assembly. Nat Cell Biol 2001; 3:1086-91. [PMID: 11781570 DOI: 10.1038/ncb1201-1086] [Citation(s) in RCA: 268] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although nuclear envelope (NE) assembly is known to require the GTPase Ran, the membrane fusion machinery involved is uncharacterized. NE assembly involves formation of a reticular network on chromatin, fusion of this network into a closed NE and subsequent expansion. Here we show that p97, an AAA-ATPase previously implicated in fusion of Golgi and transitional endoplasmic reticulum (ER) membranes together with the adaptor p47, has two discrete functions in NE assembly. Formation of a closed NE requires the p97-Ufd1-Npl4 complex, not previously implicated in membrane fusion. Subsequent NE growth involves a p97-p47 complex. This study provides the first insights into the molecular mechanisms and specificity of fusion events involved in NE formation.
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Affiliation(s)
- M Hetzer
- European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
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17
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Ewald A, Zünkler C, Lourim D, Dabauvalle MC. Microtubule-dependent assembly of the nuclear envelope in Xenopus laevis egg extract. Eur J Cell Biol 2001; 80:678-91. [PMID: 11824787 DOI: 10.1078/0171-9335-00207] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Microtubules take part in several mechanisms of intracellular motility, including organelle transport and mitosis. We have studied the ability of Xenopus egg extract to support nuclear membrane and pore complex formation when microtubule dynamics are manipulated. In this report we show that the formation of a nuclear envelope surrounding sperm chromatin requires polymerized microtubules. We have observed that microtubule-depolymerizing reagents, and AS-2, a known inhibitor of the microtubule motor protein kinesin, do not inhibit the formation of a double nuclear membrane. However these double membranes contain no morphologically identifiable nuclear pore complexes and do not support the accumulation of karyophilic proteins. In contrast, the assembly of annulate lamellae, cytoplasmic structures containing a subset of pore complex proteins, was not affected. Our data show that not only polymerized microtubules, but also the microtubule motor protein kinesin, are involved in the formation of the nuclear envelope. These results support the conclusion that multiple nuclear envelope-forming mitotic vesicle populations exist, that microtubules play an essential and selective role in the transport of nuclear envelope-forming vesicle population(s), and that separate mechanisms are involved in nuclear envelope and annulate lamellae formation.
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Affiliation(s)
- A Ewald
- Department of Cell and Developmental Biology, Theodor-Boveri-Institute, University of Würzburg, Germany
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18
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Abstract
Communication between the nucleus and cytoplasm occurs through large macromolecular structures, the nuclear pores. Quantitative scanning transmission electron microscopy has estimated the mass of a nuclear pore to be 60 million Daltons in yeast and 120 million Daltons in vertebrates. The past two years were noteworthy in that they saw: 1) the purification of both the yeast and vertebrate nuclear pores, 2) the initial description of routes through the pore for specific transport receptors, 3) glimpses of intranuclear organization imposed by the nuclear pores and envelope and 4) the revelation of new and pivotal roles for the small GTPase Ran not only in nuclear import but in spindle assembly and nuclear membrane fusion.
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Affiliation(s)
- S K Vasu
- Section of Cell and Developmental Biology, Division of Biology, University of California San Diego, La Jolla, CA 92093-0347, USA
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