1
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Kralt A, Wojtynek M, Fischer JS, Agote-Aran A, Mancini R, Dultz E, Noor E, Uliana F, Tatarek-Nossol M, Antonin W, Onischenko E, Medalia O, Weis K. An amphipathic helix in Brl1 is required for nuclear pore complex biogenesis in S. cerevisiae. eLife 2022; 11:78385. [PMID: 36000978 PMCID: PMC9402233 DOI: 10.7554/elife.78385] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 08/03/2022] [Indexed: 12/28/2022] Open
Abstract
The nuclear pore complex (NPC) is the central portal for macromolecular exchange between the nucleus and cytoplasm. In all eukaryotes, NPCs assemble into an intact nuclear envelope (NE) during interphase, but the process of NPC biogenesis remains poorly characterized. Furthermore, little is known about how NPC assembly leads to the fusion of the outer and inner NE, and no factors have been identified that could trigger this event. Here, we characterize the transmembrane protein Brl1 as an NPC assembly factor required for NE fusion in budding yeast. Brl1 preferentially associates with NPC assembly intermediates and its depletion halts NPC biogenesis, leading to NE herniations that contain inner and outer ring nucleoporins but lack the cytoplasmic export platform. Furthermore, we identify an essential amphipathic helix in the luminal domain of Brl1 that mediates interactions with lipid bilayers. Mutations in this amphipathic helix lead to NPC assembly defects, and cryo-electron tomography analyses reveal multilayered herniations of the inner nuclear membrane with NPC-like structures at the neck, indicating a failure in NE fusion. Taken together, our results identify a role for Brl1 in NPC assembly and suggest a function of its amphipathic helix in mediating the fusion of the inner and outer nuclear membranes.
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Affiliation(s)
- Annemarie Kralt
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Matthias Wojtynek
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland.,Department of Biochemistry, University of Zurich, Zürich, Switzerland
| | - Jonas S Fischer
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Arantxa Agote-Aran
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Roberta Mancini
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Elisa Dultz
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Elad Noor
- Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Federico Uliana
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Marianna Tatarek-Nossol
- Institute of Biochemistry and Molecular Cell Biology, Medical School, RWTH Aachen University, Aachen, Germany
| | - Wolfram Antonin
- Institute of Biochemistry and Molecular Cell Biology, Medical School, RWTH Aachen University, Aachen, Germany
| | - Evgeny Onischenko
- Department of Biological Sciences, University of Bergen, Bergen, Norway
| | - Ohad Medalia
- Department of Biochemistry, University of Zurich, Zürich, Switzerland
| | - Karsten Weis
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
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2
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The Nuclear Pore Complex: Birth, Life, and Death of a Cellular Behemoth. Cells 2022; 11:cells11091456. [PMID: 35563762 PMCID: PMC9100368 DOI: 10.3390/cells11091456] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 04/22/2022] [Accepted: 04/23/2022] [Indexed: 02/01/2023] Open
Abstract
Nuclear pore complexes (NPCs) are the only transport channels that cross the nuclear envelope. Constructed from ~500–1000 nucleoporin proteins each, they are among the largest macromolecular assemblies in eukaryotic cells. Thanks to advances in structural analysis approaches, the construction principles and architecture of the NPC have recently been revealed at submolecular resolution. Although the overall structure and inventory of nucleoporins are conserved, NPCs exhibit significant compositional and functional plasticity even within single cells and surprising variability in their assembly pathways. Once assembled, NPCs remain seemingly unexchangeable in post-mitotic cells. There are a number of as yet unresolved questions about how the versatility of NPC assembly and composition is established, how cells monitor the functional state of NPCs or how they could be renewed. Here, we review current progress in our understanding of the key aspects of NPC architecture and lifecycle.
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3
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Vitale J, Khan A, Neuner A, Schiebel E. A perinuclear α-helix with amphipathic features in Brl1 promotes NPC assembly. Mol Biol Cell 2022; 33:ar35. [PMID: 35293775 PMCID: PMC9282021 DOI: 10.1091/mbc.e21-12-0616] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
How nuclear pore complexes (NPC) assemble in the intact nuclear envelope (NE) is only rudimentarily understood. Nucleoporins accumulate at the inner NE (INM), deform this membrane towards the outer nuclear membrane (ONM) and eventually INM and ONM fuse by an unclear mechanism. In budding yeast, the integral membrane protein Brl1 that transiently associates with NPC assembly intermediates is involved in INM/ONM fusion during NPC assembly but leaving the molecular mechanism open. AlphaFold predictions indicate that Brl1-like proteins carry as common motifs an α-helix with amphipathic features (AαH) and a disulfide-stabilized anti-parallel helix bundle (DAH) in the perinuclear space. Mutants with defective AαH (brl1F391E, brl1F391P, brl1L402E) impair the essential function of BRL1. Overexpression of brl1F391E promotes formation of INM and ONM enclosed petal-like structures that carry nucleoporins at their base suggesting that they are derived from an NPC assembly attempt with failed INM/ONM fusion. Accordingly, brl1F391E expression triggers mis-localisation of Nup159 and Nup42 and to a lesser extent Nsp1 that localize on the cytoplasmic face of the NPC. The DAH also contributes to the function of Brl1 and AαH has functions independent of DAH. We propose that AαH and DAH in Brl1 promote INM/ONM fusion during NPC assembly.
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Affiliation(s)
- Jlenia Vitale
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Deutsches Krebsforschungszentrum (DKFZ)-ZMBH Allianz, Universität Heidelberg, 69120 Heidelberg, Germany.,Heidelberg Biosciences International Graduate School (HBIGS), Universität Heidelberg, 69120 Heidelberg, Germany
| | - Azqa Khan
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Deutsches Krebsforschungszentrum (DKFZ)-ZMBH Allianz, Universität Heidelberg, 69120 Heidelberg, Germany.,Heidelberg Biosciences International Graduate School (HBIGS), Universität Heidelberg, 69120 Heidelberg, Germany
| | - Annett Neuner
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Deutsches Krebsforschungszentrum (DKFZ)-ZMBH Allianz, Universität Heidelberg, 69120 Heidelberg, Germany
| | - Elmar Schiebel
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Deutsches Krebsforschungszentrum (DKFZ)-ZMBH Allianz, Universität Heidelberg, 69120 Heidelberg, Germany
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4
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Zhang W, Khan A, Vitale J, Neuner A, Rink K, Lüchtenborg C, Brügger B, Söllner TH, Schiebel E. A short perinuclear amphipathic α-helix in Apq12 promotes nuclear pore complex biogenesis. Open Biol 2021; 11:210250. [PMID: 34814743 PMCID: PMC8611336 DOI: 10.1098/rsob.210250] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The integral membrane protein Apq12 is an important nuclear envelope (NE)/endoplasmic reticulum (ER) modulator that cooperates with the nuclear pore complex (NPC) biogenesis factors Brl1 and Brr6. How Apq12 executes these functions is unknown. Here, we identified a short amphipathic α-helix (AαH) in Apq12 that links the two transmembrane domains in the perinuclear space and has liposome-binding properties. Cells expressing an APQ12 (apq12-ah) version in which AαH is disrupted show NPC biogenesis and NE integrity defects, without impacting Apq12-ah topology or NE/ER localization. Overexpression of APQ12 but not apq12-ah triggers striking over-proliferation of the outer nuclear membrane (ONM)/ER and promotes accumulation of phosphatidic acid (PA) at the NE. Apq12 and Apq12-ah both associate with NPC biogenesis intermediates and removal of AαH increases both Brl1 levels and the interaction between Brl1 and Brr6. We conclude that the short amphipathic α-helix of Apq12 regulates the function of Brl1 and Brr6 and promotes PA accumulation at the NE possibly during NPC biogenesis.
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Affiliation(s)
- Wanlu Zhang
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Azqa Khan
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Jlenia Vitale
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Annett Neuner
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Kerstin Rink
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Christian Lüchtenborg
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Britta Brügger
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Thomas H. Söllner
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Elmar Schiebel
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
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5
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Zhang W, Neuner A, Rüthnick D, Sachsenheimer T, Lüchtenborg C, Brügger B, Schiebel E. Brr6 and Brl1 locate to nuclear pore complex assembly sites to promote their biogenesis. J Cell Biol 2018; 217:877-894. [PMID: 29439116 PMCID: PMC5839787 DOI: 10.1083/jcb.201706024] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 11/21/2017] [Accepted: 01/10/2018] [Indexed: 12/30/2022] Open
Abstract
The conserved paralogous Brr6 and Brl1 promote NPC biogenesis in an unclear manner. Here, Zhang et al. show that both transmembrane proteins transiently associate with NPC assembly intermediates and directly promote NPC biogenesis. The paralogous Brr6 and Brl1 are conserved integral membrane proteins of the nuclear envelope (NE) with an unclear role in nuclear pore complex (NPC) biogenesis. Here, we analyzed double-degron mutants of Brr6/Brl1 to understand this function. Depletion of Brr6 and Brl1 caused defects in NPC biogenesis, whereas the already assembled NPCs remained unaffected. This NPC biogenesis defect was not accompanied by a change in lipid composition. However, Brl1 interacted with Ndc1 and Nup188 by immunoprecipitation, and with transmembrane and outer and inner ring NPC components by split yellow fluorescent protein analysis, indicating a direct role in NPC biogenesis. Consistently, we found that Brr6 and Brl1 associated with a subpopulation of NPCs and emerging NPC assembly sites. Moreover, BRL1 overexpression affected NE morphology without a change in lipid composition and completely suppressed the nuclear pore biogenesis defect of nup116Δ and gle2Δ cells. We propose that Brr6 and Brl1 transiently associate with NPC assembly sites where they promote NPC biogenesis.
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Affiliation(s)
- Wanlu Zhang
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany
| | - Annett Neuner
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany
| | - Diana Rüthnick
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany
| | | | | | - Britta Brügger
- Heidelberg University Biochemistry Center, Heidelberg, Germany
| | - Elmar Schiebel
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Heidelberg, Germany
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6
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Cavanaugh AM, Jaspersen SL. Big Lessons from Little Yeast: Budding and Fission Yeast Centrosome Structure, Duplication, and Function. Annu Rev Genet 2017; 51:361-383. [PMID: 28934593 DOI: 10.1146/annurev-genet-120116-024733] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Centrosomes are a functionally conserved feature of eukaryotic cells that play an important role in cell division. The conserved γ-tubulin complex organizes spindle and astral microtubules, which, in turn, separate replicated chromosomes accurately into daughter cells. Like DNA, centrosomes are duplicated once each cell cycle. Although in some cell types it is possible for cell division to occur in the absence of centrosomes, these divisions typically result in defects in chromosome number and stability. In single-celled organisms such as fungi, centrosomes [known as spindle pole bodies (SPBs)] are essential for cell division. SPBs also must be inserted into the membrane because fungi undergo a closed mitosis in which the nuclear envelope (NE) remains intact. This poorly understood process involves events similar or identical to those needed for de novo nuclear pore complex assembly. Here, we review how analysis of fungal SPBs has advanced our understanding of centrosomes and NE events.
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Affiliation(s)
- Ann M Cavanaugh
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA;
| | - Sue L Jaspersen
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA; .,Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
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7
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Paul B, Montpetit B. Altered RNA processing and export lead to retention of mRNAs near transcription sites and nuclear pore complexes or within the nucleolus. Mol Biol Cell 2016; 27:2742-56. [PMID: 27385342 PMCID: PMC5007094 DOI: 10.1091/mbc.e16-04-0244] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 06/29/2016] [Indexed: 01/17/2023] Open
Abstract
In a screen of >1000 essential gene mutants in Saccharomyces cerevisiae, 26 mutants are found that directly or indirectly affect mRNA processing and/or mRNA export. Single-molecule FISH data show that the majority of these mutants retain mRNAs at discrete locations within the nucleus, which include the nucleolus. Many protein factors are required for mRNA biogenesis and nuclear export, which are central to the eukaryotic gene expression program. It is unclear, however, whether all factors have been identified. Here we report on a screen of >1000 essential gene mutants in Saccharomyces cerevisiae for defects in mRNA processing and export, identifying 26 mutants with defects in this process. Single-molecule FISH data showed that the majority of these mutants accumulated mRNA within specific regions of the nucleus, which included 1) mRNAs within the nucleolus when nucleocytoplasmic transport, rRNA biogenesis, or RNA processing and surveillance was disrupted, 2) the buildup of mRNAs near transcription sites in 3′-end processing and chromosome segregation mutants, and 3) transcripts being enriched near nuclear pore complexes when components of the mRNA export machinery were mutated. These data show that alterations to various nuclear processes lead to the retention of mRNAs at discrete locations within the nucleus.
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Affiliation(s)
- Biplab Paul
- Department of Cell Biology, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ben Montpetit
- Department of Cell Biology, University of Alberta, Edmonton, AB T6G 2H7, Canada
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8
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Liu G, Yong MYJ, Yurieva M, Srinivasan KG, Liu J, Lim JSY, Poidinger M, Wright GD, Zolezzi F, Choi H, Pavelka N, Rancati G. Gene Essentiality Is a Quantitative Property Linked to Cellular Evolvability. Cell 2015; 163:1388-99. [PMID: 26627736 DOI: 10.1016/j.cell.2015.10.069] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 08/01/2015] [Accepted: 10/20/2015] [Indexed: 11/24/2022]
Abstract
Gene essentiality is typically determined by assessing the viability of the corresponding mutant cells, but this definition fails to account for the ability of cells to adaptively evolve to genetic perturbations. Here, we performed a stringent screen to assess the degree to which Saccharomyces cerevisiae cells can survive the deletion of ~1,000 individual "essential" genes and found that ~9% of these genetic perturbations could in fact be overcome by adaptive evolution. Our analyses uncovered a genome-wide gradient of gene essentiality, with certain essential cellular functions being more "evolvable" than others. Ploidy changes were prevalent among the evolved mutant strains, and aneuploidy of a specific chromosome was adaptive for a class of evolvable nucleoporin mutants. These data justify a quantitative redefinition of gene essentiality that incorporates both viability and evolvability of the corresponding mutant cells and will enable selection of therapeutic targets associated with lower risk of emergence of drug resistance.
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Affiliation(s)
- Gaowen Liu
- Institute of Medical Biology (IMB), Agency for Science, Technology and Research (A(∗)STAR), Singapore 138648, Singapore; School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - Mei Yun Jacy Yong
- Institute of Medical Biology (IMB), Agency for Science, Technology and Research (A(∗)STAR), Singapore 138648, Singapore
| | - Marina Yurieva
- Singapore Immunology Network (SIgN), A(∗)STAR, Singapore 138648, Singapore
| | | | - Jaron Liu
- Institute of Medical Biology (IMB), Agency for Science, Technology and Research (A(∗)STAR), Singapore 138648, Singapore
| | - John Soon Yew Lim
- Institute of Medical Biology (IMB), Agency for Science, Technology and Research (A(∗)STAR), Singapore 138648, Singapore
| | - Michael Poidinger
- Singapore Immunology Network (SIgN), A(∗)STAR, Singapore 138648, Singapore
| | - Graham Daniel Wright
- Institute of Medical Biology (IMB), Agency for Science, Technology and Research (A(∗)STAR), Singapore 138648, Singapore
| | - Francesca Zolezzi
- Singapore Immunology Network (SIgN), A(∗)STAR, Singapore 138648, Singapore
| | - Hyungwon Choi
- Saw Swee Hock School of Public Health, National University of Singapore (NUS) and National University Health System, Singapore 117549, Singapore
| | - Norman Pavelka
- Singapore Immunology Network (SIgN), A(∗)STAR, Singapore 138648, Singapore.
| | - Giulia Rancati
- Institute of Medical Biology (IMB), Agency for Science, Technology and Research (A(∗)STAR), Singapore 138648, Singapore; School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore.
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9
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Yeast Integral Membrane Proteins Apq12, Brl1, and Brr6 Form a Complex Important for Regulation of Membrane Homeostasis and Nuclear Pore Complex Biogenesis. EUKARYOTIC CELL 2015; 14:1217-27. [PMID: 26432634 DOI: 10.1128/ec.00101-15] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 10/01/2015] [Indexed: 11/20/2022]
Abstract
Proper functioning of intracellular membranes is critical for many cellular processes. A key feature of membranes is their ability to adapt to changes in environmental conditions by adjusting their composition so as to maintain constant biophysical properties, including fluidity and flexibility. Similar changes in the biophysical properties of membranes likely occur when intracellular processes, such as vesicle formation and fusion, require dramatic changes in membrane curvature. Similar modifications must also be made when nuclear pore complexes (NPCs) are constructed within the existing nuclear membrane, as occurs during interphase in all eukaryotes. Here we report on the role of the essential nuclear envelope/endoplasmic reticulum (NE/ER) protein Brl1 in regulating the membrane composition of the NE/ER. We show that Brl1 and two other proteins characterized previously-Brr6, which is closely related to Brl1, and Apq12-function together and are required for lipid homeostasis. All three transmembrane proteins are localized to the NE and can be coprecipitated. As has been shown for mutations affecting Brr6 and Apq12, mutations in Brl1 lead to defects in lipid metabolism, increased sensitivity to drugs that inhibit enzymes involved in lipid synthesis, and strong genetic interactions with mutations affecting lipid metabolism. Mutations affecting Brl1 or Brr6 or the absence of Apq12 leads to hyperfluid membranes, because mutant cells are hypersensitive to agents that increase membrane fluidity. We suggest that the defects in nuclear pore complex biogenesis and mRNA export seen in these mutants are consequences of defects in maintaining the biophysical properties of the NE.
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10
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Smoyer CJ, Jaspersen SL. Breaking down the wall: the nuclear envelope during mitosis. Curr Opin Cell Biol 2013; 26:1-9. [PMID: 24529240 DOI: 10.1016/j.ceb.2013.08.002] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 08/13/2013] [Accepted: 08/13/2013] [Indexed: 11/28/2022]
Abstract
A defining feature of eukaryotic cells is the nucleus, which houses the genome inside the nuclear envelope (NE): a double lipid bilayer that separates the nuclear and cytoplasmic materials. Although the NE is commonly viewed as a barrier that is overcome only by embedded nuclear pore complexes (NPCs) that facilitate nuclear-cytoplasmic trafficking, recent work in a wide range of eukaryotes reveals that the NE is a dynamic organelle that is modified each time the cell divides to ultimately establish two functional daughter nuclei. Here, we review how studies of divergent mitotic strategies have helped elucidate common properties of NE biology that allow it to function throughout the cell cycle.
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Affiliation(s)
- Christine J Smoyer
- Stowers Institute for Medical Research, Kansas City, MO 64110, United States
| | - Sue L Jaspersen
- Stowers Institute for Medical Research, Kansas City, MO 64110, United States; Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, United States.
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11
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Schneiter R, Cole CN. Integrating complex functions: coordination of nuclear pore complex assembly and membrane expansion of the nuclear envelope requires a family of integral membrane proteins. Nucleus 2012; 1:387-92. [PMID: 21326820 DOI: 10.4161/nucl.1.5.12333] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Revised: 04/14/2010] [Accepted: 04/23/2010] [Indexed: 11/19/2022] Open
Abstract
The nuclear envelope harbors numerous large proteinaceous channels, the nuclear pore complexes (NPCs), through which macromolecular exchange between the cytosol and the nucleoplasm occurs. This double-membrane nuclear envelope is continuous with the endoplasmic reticulum and thus functionally connected to such diverse processes as vesicular transport, protein maturation and lipid synthesis. Recent results obtained from studies in Saccharomyces cerevisiae indicate that assembly of the nuclear pore complex is functionally dependent upon maintenance of lipid homeostasis of the ER membrane. Previous work from one of our laboratories has revealed that an integral membrane protein Apq12 is important for the assembly of functional nuclear pores. Cells lacking APQ12 are viable but cannot grow at low temperatures, have aberrant NPCs and a defect in mRNA export. Remarkably, these defects in NPC assembly can be overcome by supplementing cells with a membrane fluidizing agent, benzyl alcohol, suggesting that Apq12 impacts the flexibility of the nuclear membrane, possibly by adjusting its lipid composition when cells are shifted to a reduced temperature. Our new study now expands these findings and reveals that an essential membrane protein, Brr6, shares at least partially overlapping functions with Apq12 and is also required for assembly of functional NPCs. A third nuclear envelope membrane protein, Brl1, is related to Brr6, and is also required for NPC assembly. Because maintenance of membrane homeostasis is essential for cellular survival, the fact that these three proteins are conserved in fungi that undergo closed mitoses, but are not found in metazoans or plants, may indicate that their functions are performed by proteins unrelated at the primary sequence level to Brr6, Brl1 and Apq12 in cells that disassemble their nuclear envelopes during mitosis.
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Affiliation(s)
- Roger Schneiter
- Division of Biochemistry, Department of Medicine, University of Fribourg, Fribourg, Switzerland.
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12
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Jaspersen SL, Ghosh S. Nuclear envelope insertion of spindle pole bodies and nuclear pore complexes. Nucleus 2012; 3:226-36. [PMID: 22572959 PMCID: PMC3414398 DOI: 10.4161/nucl.20148] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The defining feature of eukaryotic cells is the double lipid bilayer of the nuclear envelope (NE) that serves as a physical barrier separating the genome from the cytosol. Nuclear pore complexes (NPCs) are embedded in the NE to facilitate transport of proteins and other macromolecules into and out of the nucleus. In fungi and early embryos where the NE does not completely breakdown during mitosis, microtubule-organizing centers such as the spindle pole body (SPB) must also be inserted into the NE to facilitate organization of the mitotic spindle. Several recent papers have shed light on the mechanism by which SPB complexes are inserted into the NE. An unexpected link between the SPB and NPCs suggests that assembly of these NE complexes is tightly coordinated. We review the findings of these reports in light of our current knowledge of SPB, NPC and NE structure, assembly and function.
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Affiliation(s)
- Sue L Jaspersen
- Stowers Institute for Medical Research, Kansas City, MO, USA.
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13
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Tamm T, Grallert A, Grossman EPS, Alvarez-Tabares I, Stevens FE, Hagan IM. Brr6 drives the Schizosaccharomyces pombe spindle pole body nuclear envelope insertion/extrusion cycle. ACTA ACUST UNITED AC 2012; 195:467-84. [PMID: 22042620 PMCID: PMC3206342 DOI: 10.1083/jcb.201106076] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Insertion into and release of the cytoplasmic domain of the Schizosaccharomyces pombe spindle pole body from a nuclear envelope fenestra during mitosis requires Brr6. The fission yeast interphase spindle pole body (SPB) is a bipartite structure in which a bulky cytoplasmic domain is separated from a nuclear component by the nuclear envelope. During mitosis, the SPB is incorporated into a fenestra that forms within the envelope during mitotic commitment. Closure of this fenestra during anaphase B/mitotic exit returns the cytoplasmic component to the cytoplasmic face of an intact interphase nuclear envelope. Here we show that Brr6 is transiently recruited to SPBs at both SPB insertion and extrusion. Brr6 is required for both SPB insertion and nuclear envelope integrity during anaphase B/mitotic exit. Genetic interactions with apq12 and defective sterol assimilation suggest that Brr6 may alter envelope composition at SPBs to promote SPB insertion and extrusion. The restriction of the Brr6 domain to eukaryotes that use a polar fenestra in an otherwise closed mitosis suggests a conserved role in fenestration to enable a single microtubule organizing center to nucleate both cytoplasmic and nuclear microtubules on opposing sides of the nuclear envelope.
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Affiliation(s)
- Tiina Tamm
- Cancer Research UK Cell Division Group, Paterson Institute for Cancer Research, Manchester M20 4BX, England, UK
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14
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Doucet CM, Hetzer MW. Nuclear pore biogenesis into an intact nuclear envelope. Chromosoma 2010; 119:469-77. [DOI: 10.1007/s00412-010-0289-2] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2010] [Revised: 07/15/2010] [Accepted: 07/19/2010] [Indexed: 10/19/2022]
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Hodge CA, Choudhary V, Wolyniak MJ, Scarcelli JJ, Schneiter R, Cole CN. Integral membrane proteins Brr6 and Apq12 link assembly of the nuclear pore complex to lipid homeostasis in the endoplasmic reticulum. J Cell Sci 2010; 123:141-51. [PMID: 20016074 DOI: 10.1242/jcs.055046] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Cells of Saccharomyces cerevisiae lacking Apq12, a nuclear envelope (NE)-endoplasmic reticulum (ER) integral membrane protein, are defective in assembly of nuclear pore complexes (NPCs), possibly because of defects in regulating membrane fluidity. We identified BRR6, which encodes an essential integral membrane protein of the NE-ER, as a dosage suppressor of apq12 Delta. Cells carrying the temperature-sensitive brr6-1 allele have been shown to have defects in nucleoporin localization, mRNA metabolism and nuclear transport. Electron microscopy revealed that brr6-1 cells have gross NE abnormalities and proliferation of the ER. brr6-1 cells were hypersensitive to compounds that affect membrane biophysical properties and to inhibitors of lipid biosynthetic pathways, and displayed strong genetic interactions with genes encoding non-essential lipid biosynthetic enzymes. Strikingly, brr6-1 cells accumulated, in or near the NE, elevated levels of the two classes of neutral lipids, steryl esters and triacylglycerols, and over-accumulated sterols when they were provided exogenously. Although neutral lipid synthesis is dispensable in wild-type cells, viability of brr6-1 cells was fully dependent on neutral lipid production. These data indicate that Brr6 has an essential function in regulating lipid homeostasis in the NE-ER, thereby impacting NPC formation and nucleocytoplasmic transport.
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Affiliation(s)
- Christine A Hodge
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA
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Functional characterization of Pneumocystis carinii brl1 by transspecies complementation analysis. EUKARYOTIC CELL 2007; 6:2448-52. [PMID: 17993570 DOI: 10.1128/ec.00321-07] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Pneumocystis jirovecii is a fungus which causes severe opportunistic infections in immunocompromised humans. The brl1 gene of P. carinii infecting rats was identified and characterized by using bioinformatics in conjunction with functional complementation in Saccharomyces cerevisiae and Schizosaccharomyces pombe. The ectopic expression of this gene rescues null alleles of essential nuclear membrane proteins of the Brr6/Brl1 family in both yeasts.
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Sugimoto H, Kusumi K, Noguchi K, Yano M, Yoshimura A, Iba K. The rice nuclear gene, VIRESCENT 2, is essential for chloroplast development and encodes a novel type of guanylate kinase targeted to plastids and mitochondria. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2007; 52:512-27. [PMID: 17727616 DOI: 10.1111/j.1365-313x.2007.03251.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Guanylate kinase (GK) is a critical enzyme in guanine nucleotide metabolism pathways, catalyzing the phosphorylation of (d)GMP to (d)GDP. Here we show that a novel gene, VIRESCENT 2 (V2), encodes a new type of GK (designated pt/mtGK) that is localized in plastids and mitochondria. We initially identified the V2 gene by positional cloning of the rice v2 mutant. The v2 mutant is temperature-sensitive and develops chlorotic leaves at restrictive temperatures. The v2 mutation causes inhibition of chloroplast differentiation; in particular, it disrupts the chloroplast translation machinery during early leaf development [Sugimoto et al. (2004)Plant Cell Physiol. 45, 985]. In the bacterial and animal species studied to date, GK is localized in the cytoplasm and participates in maintenance of the guanine nucleotide pools required for many fundamental cellular processes. Phenotypic analysis of rice seedlings with RNAi knockdown of cytosolic GK (designated cGK) showed that cGK is indispensable for the growth and development of plants, but not for chloroplast development. Thus, rice has two types of GK, as does Arabidopsis, suggesting that higher plants have two types of GK. Our results suggest that, of the two types of GK, only pt/mtGK is essential for chloroplast differentiation.
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Affiliation(s)
- Hiroki Sugimoto
- Department of Biological Sciences, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan
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