1
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Calvo IA, Sharma S, Paulo JA, Gulka AO, Boeszoermenyi A, Zhang J, Lombana JM, Palmieri CM, Laviolette LA, Arthanari H, Iliopoulos O, Gygi SP, Motamedi M. The fission yeast FLCN/FNIP complex augments TORC1 repression or activation in response to amino acid (AA) availability. iScience 2021; 24:103338. [PMID: 34805795 PMCID: PMC8590082 DOI: 10.1016/j.isci.2021.103338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 06/10/2021] [Accepted: 10/21/2021] [Indexed: 11/13/2022] Open
Abstract
The target of Rapamycin complex1 (TORC1) senses and integrates several environmental signals, including amino acid (AA) availability, to regulate cell growth. Folliculin (FLCN) is a tumor suppressor (TS) protein in renal cell carcinoma, which paradoxically activates TORC1 in response to AA supplementation. Few tractable systems for modeling FLCN as a TS are available. Here, we characterize the FLCN-containing complex in Schizosaccharomyces pombe (called BFC) and show that BFC augments TORC1 repression and activation in response to AA starvation and supplementation, respectively. BFC co-immunoprecipitates V-ATPase, a TORC1 modulator, and regulates its activity in an AA-dependent manner. BFC genetic and proteomic networks identify the conserved peptide transmembrane transporter Ptr2 and the phosphoribosylformylglycinamidine synthase Ade3 as new AA-dependent regulators of TORC1. Overall, these data ascribe an additional repressive function to Folliculin in TORC1 regulation and reveal S. pombe as an excellent system for modeling the AA-dependent, FLCN-mediated repression of TORC1 in eukaryotes.
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Affiliation(s)
- Isabel A. Calvo
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Shalini Sharma
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Joao A. Paulo
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Alexander O.D. Gulka
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Andras Boeszoermenyi
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
- Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Jingyu Zhang
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Jose M. Lombana
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Christina M. Palmieri
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Laura A. Laviolette
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
| | - Haribabu Arthanari
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
- Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Othon Iliopoulos
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
- Division of Hematology-Oncology, Department of Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Steven P. Gygi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Mo Motamedi
- Massachusetts General Hospital Center for Cancer Research and Department of Medicine Harvard Medical School, Charlestown, MA 02129, USA
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2
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Tanaka N, Kagami A, Hirai K, Suzuki S, Matsuura S, Fukunaga T, Tabuchi M, Takegawa K. The fission yeast gmn2 + gene encodes an ERD1 homologue of Saccharomyces cerevisiae required for protein glycosylation and retention of luminal endoplasmic reticulum proteins. J GEN APPL MICROBIOL 2021; 67:67-76. [PMID: 33536395 DOI: 10.2323/jgam.2020.07.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The gmn2 mutant of Schizosaccharomyces pombe has previously been shown to exhibit defects in protein glycosylation of N-linked oligosaccharides (Ballou, L. and Ballou, CE., Proc. Natl. Acad. Sci. USA, 92, 2790-2794 (1995)). Like most glycosylation-defective mutants, the S. pombe gmn2 mutant was found to be sensitive to hygromycin B, an aminoglycoside antibiotic. As a result of complementation analysis, the gmn2+ gene was found to be a single open reading frame that encodes a polypeptide of 373 amino acids consisting of multiple membrane-spanning regions. The Gmn2 protein shares sequence similarity with Kluyveromyces lactis and Saccharomyces cerevisiae Erd1 proteins, which are required for retention of luminal endoplasmic reticulum (ER) proteins. Although disruption of the gmn2+ gene is not lethal, the secreted glycoprotein showed a significant glycosylation defect with destabilization of the glycosyltransferase responsible for N-glycan elongation. It was also shown that a significant amount of BiP was missorted to the cell surface according to ADEL receptor destabilization. Fluorescent microscopy revealed that the functional Gmn2-EGFP fusion protein is mainly localized in the Golgi membrane. These results indicate that the Gmn2 protein is required for protein glycosylation and for retention of ER-resident proteins in S. pombe cells.
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Affiliation(s)
- Naotaka Tanaka
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University
| | - Akinari Kagami
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University
| | - Keisuke Hirai
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University
| | - Shotaro Suzuki
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University
| | - Shiori Matsuura
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University
| | - Takamasa Fukunaga
- Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University
| | - Mitsuaki Tabuchi
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University
| | - Kaoru Takegawa
- Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University
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3
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Knapp BD, Odermatt P, Rojas ER, Cheng W, He X, Huang KC, Chang F. Decoupling of Rates of Protein Synthesis from Cell Expansion Leads to Supergrowth. Cell Syst 2019; 9:434-445.e6. [PMID: 31706948 PMCID: PMC6911364 DOI: 10.1016/j.cels.2019.10.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2019] [Revised: 07/02/2019] [Accepted: 09/30/2019] [Indexed: 01/02/2023]
Abstract
Cell growth is a complex process in which cells synthesize cellular components while they increase in size. It is generally assumed that the rate of biosynthesis must somehow be coordinated with the rate of growth in order to maintain intracellular concentrations. However, little is known about potential feedback mechanisms that could achieve proteome homeostasis or the consequences when this homeostasis is perturbed. Here, we identify conditions in which fission yeast cells are prevented from volume expansion but nevertheless continue to synthesize biomass, leading to general accumulation of proteins and increased cytoplasmic density. Upon removal of these perturbations, this biomass accumulation drove cells to undergo a multi-generational period of "supergrowth" wherein rapid volume growth outpaced biosynthesis, returning proteome concentrations back to normal within hours. These findings demonstrate a mechanism for global proteome homeostasis based on modulation of volume growth and dilution.
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Affiliation(s)
- Benjamin D Knapp
- Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143, USA; Biophysics Program, Stanford University, Stanford, CA 94305, USA
| | - Pascal Odermatt
- Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143, USA; Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Enrique R Rojas
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Wenpeng Cheng
- Life Sciences Institute, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Xiangwei He
- Life Sciences Institute, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Kerwyn Casey Huang
- Biophysics Program, Stanford University, Stanford, CA 94305, USA; Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA; Chan Zuckerberg Biohub, San Francisco, CA 941586, USA.
| | - Fred Chang
- Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143, USA.
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4
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Kashiwazaki J, Yoneda Y, Mutoh T, Arai R, Yoshida M, Mabuchi I. A unique kinesin-like protein, Klp8, is involved in mitosis and cell morphology through microtubule stabilization. Cytoskeleton (Hoboken) 2019; 76:355-367. [PMID: 31276301 DOI: 10.1002/cm.21551] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 05/23/2019] [Accepted: 07/01/2019] [Indexed: 11/10/2022]
Abstract
Kinesins are microtubule (MT)-based motors involved in various cellular functions including intracellular transport of vesicles and organelles, and dynamics of chromosomes during cell division. The fission yeast Schizosaccharomyces pombe expresses nine kinesin-like proteins (klps). Klp8 is one of them and has not been characterized yet though it has been reported to localize at the division site. Here, we studied function and localization of Klp8 in S. pombe cells. The gene klp8+ was not essential for both viability and cytoskeletal organization. Klp8-YFP was concentrated as medial cortical dots during interphase, and organized into a ring at the division site during mitosis. The Klp8 ring seemed to be localized in the space between the actomyosin contractile ring and the plasma membrane. The Klp8 ring shrank as cytokinesis proceeded. In klp8-deleted (Δ) cells, the speed of spindle elongation during anaphase B was slowed down. Overproduction of Klp8 caused bent or elongated cells, in which MTs were abnormally elongated and less dynamic than those in normal cells. Deletion of klp8+ gene suppressed the delay in mitotic entry in blt1Δ cells. These results suggest that Klp8 is involved in mitosis and cell morphology through MT stabilization.
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Affiliation(s)
- Jun Kashiwazaki
- Department of Life Science, Gakushuin University, Tokyo, Japan
| | - Yumi Yoneda
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan
| | - Tadashi Mutoh
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan
| | - Ritsuko Arai
- Chemical Genetics Laboratory, RIKEN, Wako, Japan
| | - Minoru Yoshida
- Chemical Genetics Laboratory, RIKEN, Wako, Japan.,CREST Research Project, Japan Science and Technology Corporation, Wako, Japan
| | - Issei Mabuchi
- Department of Life Science, Gakushuin University, Tokyo, Japan.,Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan
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5
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Winters L, Ban I, Prelogović M, Kalinina I, Pavin N, Tolić IM. Pivoting of microtubules driven by minus-end-directed motors leads to spindle assembly. BMC Biol 2019; 17:42. [PMID: 31122217 PMCID: PMC6533735 DOI: 10.1186/s12915-019-0656-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 04/16/2019] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND At the beginning of mitosis, the cell forms a spindle made of microtubules and associated proteins to segregate chromosomes. An important part of spindle architecture is a set of antiparallel microtubule bundles connecting the spindle poles. A key question is how microtubules extending at arbitrary angles form an antiparallel interpolar bundle. RESULTS Here, we show in fission yeast that microtubules meet at an oblique angle and subsequently rotate into antiparallel alignment. Our live-cell imaging approach provides a direct observation of interpolar bundle formation. By combining experiments with theory, we show that microtubules from each pole search for those from the opposite pole by performing random angular movement. Upon contact, two microtubules slide sideways along each other in a directed manner towards the antiparallel configuration. We introduce the contour length of microtubules as a measure of activity of motors that drive microtubule sliding, which we used together with observation of Cut7/kinesin-5 motors and our theory to reveal the minus-end-directed motility of this motor in vivo. CONCLUSION Random rotational motion helps microtubules from the opposite poles to find each other and subsequent accumulation of motors allows them to generate forces that drive interpolar bundle formation.
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Affiliation(s)
- Lora Winters
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307, Dresden, Germany
| | - Ivana Ban
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000, Zagreb, Croatia
| | - Marcel Prelogović
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000, Zagreb, Croatia
| | - Iana Kalinina
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307, Dresden, Germany
| | - Nenad Pavin
- Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000, Zagreb, Croatia.
| | - Iva M Tolić
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307, Dresden, Germany.
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička cesta 54, 10000, Zagreb, Croatia.
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6
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Mehta K, Chacko LA, Chug MK, Jhunjhunwala S, Ananthanarayanan V. Association of mitochondria with microtubules inhibits mitochondrial fission by precluding assembly of the fission protein Dnm1. J Biol Chem 2019; 294:3385-3396. [PMID: 30602572 DOI: 10.1074/jbc.ra118.006799] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 12/27/2018] [Indexed: 11/06/2022] Open
Abstract
Mitochondria are organized as tubular networks in the cell and undergo fission and fusion. Although several of the molecular players involved in mediating mitochondrial dynamics have been identified, the precise cellular cues that initiate mitochondrial fission or fusion remain largely unknown. In fission yeast (Schizosaccharomyces pombe), mitochondria are organized along microtubule bundles. Here, we employed deletions of kinesin-like proteins to perturb microtubule dynamics and used high-resolution and time-lapse fluorescence microscopy, revealing that mitochondrial lengths mimic microtubule lengths. Furthermore, we determined that compared with WT cells, mutant cells with long microtubules exhibit fewer mitochondria, and mutant cells with short microtubules have an increased number of mitochondria because of reduced mitochondrial fission in the former and elevated fission in the latter. Correspondingly, upon onset of closed mitosis in fission yeast, wherein interphase microtubules assemble to form the spindle within the nucleus, we observed increased mitochondrial fission. We found that the consequent rise in the mitochondrial copy number is necessary to reduce partitioning errors during independent segregation of mitochondria between daughter cells. We also discovered that the association of mitochondria with microtubules physically impedes the assembly of the fission protein Dnm1 around mitochondria, resulting in inhibition of mitochondrial fission. Taken together, we demonstrate a mechanism for the regulation of mitochondrial fission that is dictated by the interaction between mitochondria and the microtubule cytoskeleton.
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Affiliation(s)
- Kritika Mehta
- From the Centre for BioSystems Science and Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Leeba Ann Chacko
- From the Centre for BioSystems Science and Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Manjyot Kaur Chug
- From the Centre for BioSystems Science and Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Siddharth Jhunjhunwala
- From the Centre for BioSystems Science and Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Vaishnavi Ananthanarayanan
- From the Centre for BioSystems Science and Engineering, Indian Institute of Science, Bangalore 560012, India
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7
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Davidson R, Pontasch JA, Wu JQ. Sbg1 Is a Novel Regulator for the Localization of the β-Glucan Synthase Bgs1 in Fission Yeast. PLoS One 2016; 11:e0167043. [PMID: 27898700 PMCID: PMC5127554 DOI: 10.1371/journal.pone.0167043] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2016] [Accepted: 11/08/2016] [Indexed: 02/03/2023] Open
Abstract
Glucan synthases synthesize glucans, complex polysaccharides that are the major components in fungal cell walls and division septa. Studying regulation of glucan synthases is important as they are essential for fungal cell survival and thus popular targets for anti-fungal drugs. Linear 1,3-β-glucan is the main component of primary septum and is synthesized by the conserved β-glucan synthase Bgs1 in fission yeast cytokinesis. It is known that Rho1 GTPase regulates Bgs1 catalytic activity and the F-BAR protein Cdc15 plays a role in Bgs1 delivery to the plasma membrane. Here we characterize a novel protein Sbg1 that is present in a complex with Bgs1 and regulates its protein levels and localization. Sbg1 is essential for contractile-ring constriction and septum formation during cytokinesis. Sbg1 and Bgs1 physically interact and are interdependent for localization to the plasma membrane. Bgs1 is less stable and/or mis-targeted to vacuoles in sbg1 mutants. Moreover, Sbg1 plays an earlier and more important role in Bgs1 trafficking and localization than Cdc15. Together, our data reveal a new mode of regulation for the essential β-glucan synthase Bgs1 by the novel protein Sbg1.
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Affiliation(s)
- Reshma Davidson
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - Josef A. Pontasch
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - Jian-Qiu Wu
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
- Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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8
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Wang N, Lee IJ, Rask G, Wu JQ. Roles of the TRAPP-II Complex and the Exocyst in Membrane Deposition during Fission Yeast Cytokinesis. PLoS Biol 2016; 14:e1002437. [PMID: 27082518 PMCID: PMC4833314 DOI: 10.1371/journal.pbio.1002437] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Accepted: 03/15/2016] [Indexed: 12/27/2022] Open
Abstract
The cleavage-furrow tip adjacent to the actomyosin contractile ring is believed to be the predominant site for plasma-membrane insertion through exocyst-tethered vesicles during cytokinesis. Here we found that most secretory vesicles are delivered by myosin-V on linear actin cables in fission yeast cytokinesis. Surprisingly, by tracking individual exocytic and endocytic events, we found that vesicles with new membrane are deposited to the cleavage furrow relatively evenly during contractile-ring constriction, but the rim of the cleavage furrow is the main site for endocytosis. Fusion of vesicles with the plasma membrane requires vesicle tethers. Our data suggest that the transport particle protein II (TRAPP-II) complex and Rab11 GTPase Ypt3 help to tether secretory vesicles or tubulovesicular structures along the cleavage furrow while the exocyst tethers vesicles at the rim of the division plane. We conclude that the exocyst and TRAPP-II complex have distinct localizations at the division site, but both are important for membrane expansion and exocytosis during cytokinesis. Two putative vesicle tethers—the exocyst and TRAPP-II complexes—localize differently at the division plane to ensure efficient plasma-membrane deposition along the whole cleavage furrow during cytokinesis in the fission yeast Schizosaccharomyces pombe. Cytokinesis partitions a mother cell into two daughter cells at the end of each cell-division cycle. A significant amount of new plasma membrane is needed at the cleavage furrow during cytokinesis in many cell types. Membrane expansion is achieved through the balance of exocytosis and endocytosis. It is poorly understood where and when the membrane is deposited and retrieved during cytokinesis. By tracking individual vesicles with high spatiotemporal resolution and using electron microscopy, we found that new membrane is deposited relatively evenly along the cleavage furrow in fission yeast, while the rim of the division plane is the predominant site for endocytosis. The secretory vesicles/compartments carrying new membrane are mainly delivered along formin-nucleated actin cables by myosin-V motors. Surprisingly, we find that both exocytosis and endocytosis at the division site are ramped up before contractile-ring constriction and last until daughter-cell separation. We discovered that two putative vesicle tethers, the exocyst and TRAPP-II complexes, localize to different sites at the cleavage furrow to promote tethering of different, yet overlapping, classes of secretory vesicles/compartments for exocytosis and new membrane deposition.
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Affiliation(s)
- Ning Wang
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - I-Ju Lee
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - Galen Rask
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - Jian-Qiu Wu
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
- Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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9
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Cranz-Mileva S, MacTaggart B, Russell J, Hitchcock-DeGregori SE. Evolutionarily conserved sites in yeast tropomyosin function in cell polarity, transport and contractile ring formation. Biol Open 2015; 4:1040-51. [PMID: 26187949 PMCID: PMC4542287 DOI: 10.1242/bio.012609] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Tropomyosin is a coiled-coil protein that binds and regulates actin filaments. The tropomyosin gene in Schizosaccharomyces pombe, cdc8, is required for formation of actin cables, contractile rings, and polar localization of actin patches. The roles of conserved residues were investigated in gene replacement mutants. The work validates an evolution-based approach to identify tropomyosin functions in living cells and sites of potential interactions with other proteins. A cdc8 mutant with near-normal actin affinity affects patch polarization and vacuole fusion, possibly by affecting Myo52p, a class V myosin, function. The presence of labile residual cell attachments suggests a delay in completion of cell division and redistribution of cell patches following cytokinesis. Another mutant with a mild phenotype is synthetic negative with GFP-fimbrin, inferring involvement of the mutated tropomyosin sites in interaction between the two proteins. Proteins that assemble in the contractile ring region before actin do so in a mutant cdc8 strain that cannot assemble condensed actin rings, yet some cells can divide. Of general significance, LifeAct-GFP negatively affects the actin cytoskeleton, indicating caution in its use as a biomarker for actin filaments.
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Affiliation(s)
- Susanne Cranz-Mileva
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Brittany MacTaggart
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Jacquelyn Russell
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Sarah E Hitchcock-DeGregori
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
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10
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Li T, Zheng F, Cheung M, Wang F, Fu C. Fission yeast mitochondria are distributed by dynamic microtubules in a motor-independent manner. Sci Rep 2015; 5:11023. [PMID: 26046468 PMCID: PMC4457142 DOI: 10.1038/srep11023] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Accepted: 04/27/2015] [Indexed: 12/21/2022] Open
Abstract
The cytoskeleton plays a critical role in regulating mitochondria distribution. Similar to axonal mitochondria, the fission yeast mitochondria are distributed by the microtubule cytoskeleton, but this is regulated by a motor-independent mechanism depending on the microtubule associated protein mmb1p as the absence of mmb1p causes mitochondria aggregation. In this study, using a series of chimeric proteins to control the subcellular localization and motility of mitochondria, we show that a chimeric molecule containing a microtubule binding domain and the mitochondria outer membrane protein tom22p can restore the normal interconnected mitochondria network in mmb1-deletion (mmb1∆) cells. In contrast, increasing the motility of mitochondria by using a chimeric molecule containing a kinesin motor domain and tom22p cannot rescue mitochondria aggregation defects in mmb1∆ cells. Intriguingly a chimeric molecule carrying an actin binding domain and tom22p results in mitochondria associated with actin filaments at the actomyosin ring during mitosis, leading to cytokinesis defects. These findings suggest that the passive motor-independent microtubule-based mechanism is the major contributor to mitochondria distribution in wild type fission yeast cells. Hence, we establish that attachment to microtubules, but not kinesin-dependent movement and the actin cytoskeleton, is required and crucial for proper mitochondria distribution in fission yeast.
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Affiliation(s)
- Tianpeng Li
- 1] Department of Biochemistry [2] HKU-Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen, China
| | - Fan Zheng
- 1] Department of Biochemistry [2] HKU-Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen, China
| | - Martin Cheung
- Department of Anatomy, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Fengsong Wang
- School of Life Sciences, Anhui Medical University, Hefei, Anhui 230032, China
| | - Chuanhai Fu
- 1] Department of Biochemistry [2] HKU-Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen, China
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11
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Arasada R, Pollard TD. Contractile ring stability in S. pombe depends on F-BAR protein Cdc15p and Bgs1p transport from the Golgi complex. Cell Rep 2014; 8:1533-44. [PMID: 25159149 DOI: 10.1016/j.celrep.2014.07.048] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Revised: 05/22/2014] [Accepted: 07/25/2014] [Indexed: 11/17/2022] Open
Abstract
Cdc15p is known to contribute to cytokinesis in fission yeast; however, the protein is not required to assemble the contractile ring of actin and myosin, but it helps to anchor the ring to the plasma membrane. Cdc15p has a lipid-binding F-BAR domain, suggesting that it provides a physical link between the plasma membrane and contractile ring proteins. However, we find that a more important function of Cdc15p during cytokinesis is to help deliver a transmembrane enzyme, Bgs1p (also called Cps1p), from the Golgi apparatus to the plasma membrane, where it appears to anchor the contractile ring. Bgs1p synthesizes the cell wall in the cleavage furrow, but its enzyme activity is not required to anchor the contractile ring. We estimate that ∼ 2,000 Bgs1p molecules are required to anchor the ring. Without Bgs1p anchors, contractile rings slide along the plasma membrane, a phenomenon that depends on an unconventional type II myosin called Myp2p.
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Affiliation(s)
- Rajesh Arasada
- Department of Molecular Cellular and Developmental Biology, Yale University, P.O. Box 208103, New Haven, CT 06520-8103 USA
| | - Thomas D Pollard
- Department of Molecular Cellular and Developmental Biology, Yale University, P.O. Box 208103, New Haven, CT 06520-8103 USA; Department of Molecular Biophysics and Biochemistry, Yale University, P.O. Box 208103, New Haven, CT 06520-8103 USA; Department of Cell Biology, Yale University, P.O. Box 208103, New Haven, CT 06520-8103 USA.
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12
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Egea G, Serra-Peinado C, Salcedo-Sicilia L, Gutiérrez-Martínez E. Actin acting at the Golgi. Histochem Cell Biol 2013; 140:347-60. [PMID: 23807268 DOI: 10.1007/s00418-013-1115-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/03/2013] [Indexed: 01/08/2023]
Abstract
The organization, assembly and remodeling of the actin cytoskeleton provide force and tracks for a variety of (endo)membrane-associated events such as membrane trafficking. This review illustrates in different cellular models how actin and many of its numerous binding and regulatory proteins (actin and co-workers) participate in the structural organization of the Golgi apparatus and in trafficking-associated processes such as sorting, biogenesis and motion of Golgi-derived transport carriers.
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Affiliation(s)
- Gustavo Egea
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Universitat de Barcelona, C/Casanova, 143, 08036, Barcelona, Spain.
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13
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Cabrera R, Sha Z, Vadakkan TJ, Otero J, Kriegenburg F, Hartmann-Petersen R, Dickinson ME, Chang EC. Proteasome nuclear import mediated by Arc3 can influence efficient DNA damage repair and mitosis in Schizosaccharomyces pombe. Mol Biol Cell 2010; 21:3125-36. [PMID: 20668161 PMCID: PMC2938379 DOI: 10.1091/mbc.e10-06-0506] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Proteasomes must efficiently remove their substrates throughout the cells in a timely manner as many of these proteins can be toxic. This study shows that proteasomes can do so efficiently because they are highly mobile. Furthermore this study uncovers that proteasome mobility requires functional Arc3, a subunit of the Arp2/3 complex. Proteasomes must remove regulatory molecules and abnormal proteins throughout the cell, but how proteasomes can do so efficiently remains unclear. We have isolated a subunit of the Arp2/3 complex, Arc3, which binds proteasomes. When overexpressed, Arc3 rescues phenotypes associated with proteasome deficiencies; when its expression is repressed, proteasome deficiencies intensify. Arp2/3 is best known for regulating membrane dynamics and vesicular transport; thus, we performed photobleaching experiments and showed that proteasomes are readily imported into the nucleus but exit the nucleus slowly. Proteasome nuclear import is reduced when Arc3 is inactivated, leading to hypersensitivity to DNA damage and inefficient cyclin-B degradation, two events occurring in the nucleus. These data suggest that proteasomes display Arc3-dependent mobility in the cell, and mobile proteasomes can efficiently access substrates throughout the cell, allowing them to effectively regulate cell-compartment–specific activities.
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Affiliation(s)
- Rodrigo Cabrera
- Department of Molecular and Cellular Biology, Interdepartmental Program of Cell and Molecular Biology, and Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX 77030, USA
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14
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Otero JH, Suo J, Gordon C, Chang EC. Int6 and Moe1 interact with Cdc48 to regulate ERAD and proper chromosome segregation. Cell Cycle 2010; 9:147-61. [PMID: 20016281 DOI: 10.4161/cc.9.1.10312] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Int6/eIF3e is implicated in tumorigenesis, but its molecular functions remain unclear. We have studied its fission yeast homolog Yin6, reporting that it regulates proteolysis by controlling the assembly/localization of proteasomes, and binds directly to another conserved protein, Moe1. In the present study, we isolated Cdc48 as a Moe1-binding protein from a yeast two-hybrid screen, and confirmed biochemically that they form a stable complex in fission yeast. Overexpressing Moe1 or Yin6 partially rescued phenotypes of cdc48 mutants; conversely, overexpressing Cdc48 partially rescued phenotypes of moe1 or yin6 mutants. Mutants defective in both Cdc48 and the Yin6-Moe1 complex showed growth defects that were far more severe than either alone. These double mutants were severely deficient in endoplasmic reticulum associated degradation (ERAD), as they were hypersensitive to accumulation of misfolded proteins. In addition, their chromosomes showed frequent defects in spindle attachment and segregation--these mitotic defects correlated with Ase1 and Bir1/survivin mislocalization. These results suggest that Cdc48, Yin6 and Moe1 act in the same protein complex to concertedly control ERAD and chromosome segregation. Many of these properties are evolutionarily conserved in humans, since human Cdc48 rescued the lethality of the yeast cdc48Delta mutant, and Int6 and Moe1/eIF3d bind Cdc48 in human cells.
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Affiliation(s)
- Joel H Otero
- Interdepartmental Program in Cell and Molecular Biology, and Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX, USA
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15
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Das M, Chiron S, Verde F. Microtubule-dependent spatial organization of mitochondria in fission yeast. Methods Cell Biol 2010; 97:203-21. [PMID: 20719273 DOI: 10.1016/s0091-679x(10)97012-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The microtubule cytoskeleton has an important role in the control of mitochondrial distribution in higher eukaryotes. In humans, defects in axonal mitochondrial transport are linked to neurodegenerative diseases. This chapter highlights fission yeast Schizosaccharomyces pombe as a powerful genetic model system for the study of microtubule-dependent mitochondrial movement, dynamics and inheritance.
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Affiliation(s)
- Maitreyi Das
- Department of Molecular and Cellular Pharmacology (R-189), University of Miami Miller School of Medicine, Miami, Florida 33101, USA
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16
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Stoica C, Park J, Pare JM, Willows S, Hobman TC. The Kinesin motor protein Cut7 regulates biogenesis and function of Ago1-complexes. Traffic 2010; 11:25-36. [PMID: 19883398 DOI: 10.1111/j.1600-0854.2009.01000.x] [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] [Indexed: 11/29/2022]
Abstract
Argonaute proteins are the effectors of small RNA-dependent gene-silencing pathways. In the cytoplasm, they are incorporated into large mobile ribonucleoprotein (RNP) complexes that travel along microtubules. We used a genetic screen to identify the microtubule-associated motor that interacts with Ago1-containing RNPs. Here, we report that activity of the kinesin family member Cut7 is important for biogenesis and/or stability of Ago1-containing RNPs in the cytoplasm. Results from pulldown and coimmunoprecipitation assays indicate that Cut7 interacts with Ago1 as well as its two cognate binding proteins, Dcr1 and Rdp1. Loss of Cut7 activity was associated with increased levels of reverse centromeric transcripts, presumably because of a defect in post-transcriptional gene silencing. Overexpression of the Ago1-binding region of Cut7 resulted in loss of microscopic Ago1-containing RNPs. Together, these results suggest that microtubule motor proteins function in the biogenesis and function of gene-silencing machinery in the cytoplasm.
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Affiliation(s)
- Cezar Stoica
- Department of Cell Biology, University of Alberta, Edmonton, T6G 2H7, Canada
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17
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Mukaiyama H, Tohda H, Takegawa K. Overexpression of protein disulfide isomerases enhances secretion of recombinant human transferrin in Schizosaccharomyces pombe. Appl Microbiol Biotechnol 2009; 86:1135-43. [DOI: 10.1007/s00253-009-2393-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2009] [Revised: 11/26/2009] [Accepted: 11/28/2009] [Indexed: 01/20/2023]
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18
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Phospho-regulated interaction between kinesin-6 Klp9p and microtubule bundler Ase1p promotes spindle elongation. Dev Cell 2009; 17:257-67. [PMID: 19686686 DOI: 10.1016/j.devcel.2009.06.012] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2009] [Revised: 05/08/2009] [Accepted: 06/19/2009] [Indexed: 12/30/2022]
Abstract
The spindle midzone-composed of antiparallel microtubules, microtubule-associated proteins (MAPs), and motors-is the structure responsible for microtubule organization and sliding during anaphase B. In general, MAPs and motors stabilize the midzone and motors produce sliding. We show that fission yeast kinesin-6 motor klp9p binds to the microtubule antiparallel bundler ase1p at the midzone at anaphase B onset. This interaction depends upon the phosphorylation states of klp9p and ase1p. The cyclin-dependent kinase cdc2p phosphorylates and its antagonist phosphatase clp1p dephosphorylates klp9p and ase1p to control the position and timing of klp9p-ase1p interaction. Failure of klp9p-ase1p binding leads to decreased spindle elongation velocity. The ase1p-mediated recruitment of klp9p to the midzone accelerates pole separation, as suggested by computer simulation. Our findings indicate that a phosphorylation switch controls the spatial-temporal interactions of motors and MAPs for proper anaphase B, and suggest a mechanism whereby a specific motor-MAP conformation enables efficient microtubule sliding.
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19
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Gonzalez Y, Meerbrey K, Chong J, Torii Y, Padte NN, Sazer S. Nuclear shape, growth and integrity in the closed mitosis of fission yeast depend on the Ran-GTPase system, the spindle pole body and the endoplasmic reticulum. J Cell Sci 2009; 122:2464-72. [PMID: 19571115 DOI: 10.1242/jcs.049999] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The double lipid bilayer of the nuclear envelope (NE) remains intact during closed mitosis. In the fission yeast Schizosaccharomyces pombe, the intranuclear mitotic spindle has envelope-embedded spindle pole bodies (SPB) at its ends. As the spindle elongates and the nucleus divides symmetrically, nuclear volume remains constant but nuclear area rapidly increases by 26%. When Ran-GTPase function is compromised in S. pombe, nuclear division is strikingly asymmetrical and the newly synthesized SPB is preferentially associated with the smaller nucleus, indicative of a Ran-dependent SPB defect that interferes with symmetrical nuclear division. A second defect, which specifically influences the NE, results in breakage of the NE upon spindle elongation. This defect, but not asymmetric nuclear division, is partially rescued by slowing spindle elongation, stimulating endoplasmic reticulum (ER) proliferation or changing conformation of the ER membrane. We propose that redistribution of lipid within the ER-NE network is crucial for mitosis-specific NE changes in both open and closed mitosis.
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Affiliation(s)
- Yanira Gonzalez
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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20
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Codlin S, Mole SE. S. pombe btn1, the orthologue of the Batten disease gene CLN3, is required for vacuole protein sorting of Cpy1p and Golgi exit of Vps10p. J Cell Sci 2009; 122:1163-73. [PMID: 19299465 DOI: 10.1242/jcs.038323] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Batten disease is characterised by lysosomal dysfunction. The most common type of the disease is caused by mutations in the membrane protein CLN3, whose function is unknown. We show that the fission yeast orthologue Btn1p, previously implicated in vacuole function, is required for correct sorting of the vacuole hydrolase carboxypeptidase Y (Cpy1p). This is, in part, due to a defect in trafficking of Vps10p, the sorting receptor for Cpy1p, from the Golgi to the trans-Golgi network in btn1Delta cells. Our data also implicate btn1 in other Vps10-independent Cpy1-sorting pathways. Furthermore, btn1 affects the number, intracellular location and structure of Golgi compartments. We show that the prevacuole location of Btn1p is at the Golgi, because Btn1p colocalises predominantly with the Golgi marker Gms1p in compartments that are sensitive to Brefeldin A. Btn1p function might be linked to that of Vps34p, a phosphatidylinositol 3-kinase, because Btn1p acts as a multicopy suppressor of the severe Cpy1p vacuole protein-sorting defect of vps34Delta cells. Together, these results indicate an important role for Btn1p in the Golgi complex, which affects Golgi homeostasis and vacuole protein sorting. We propose a similar role for CLN3 in mammalian cells.
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Affiliation(s)
- Sandra Codlin
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK
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21
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Chiron S, Bobkova A, Zhou H, Yaffe MP. CLASP regulates mitochondrial distribution in Schizosaccharomyces pombe. ACTA ACUST UNITED AC 2008; 182:41-9. [PMID: 18606849 PMCID: PMC2447910 DOI: 10.1083/jcb.200712147] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Movement of mitochondria in Schizosaccharomyces pombe depends on their association with the dynamic, or plus ends, of microtubules, yet the molecular basis for this interaction is poorly understood. We identified mmd4 in a screen of temperature-sensitive S. pombe strains for aberrant mitochondrial morphology and distribution. Cells with the mmd4 mutation display mitochondrial aggregation near the cell ends at elevated temperatures, a phenotype similar to mitochondrial defects observed in wild-type cells after microtubule depolymerization. However, microtubule morphology and function appear normal in the mmd4 mutant. The mmd4 lesion maps to peg1+, which encodes a microtubule-associated protein with homology to cytoplasmic linker protein–associated proteins (mammalian microtubule plus end–binding proteins). Peg1p localizes to the plus end of microtubules and to mitochondria and is recovered with mitochondria during subcellular fractionation. This mitochondrial-associated fraction of Peg1p displays properties of a peripherally associated protein. Peg1p is the first identified microtubule plus end–binding protein required for mitochondrial distribution and likely functions as a molecular link between mitochondria and microtubules.
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Affiliation(s)
- Stéphane Chiron
- Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
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22
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Fischer R, Zekert N, Takeshita N. Polarized growth in fungi--interplay between the cytoskeleton, positional markers and membrane domains. Mol Microbiol 2008; 68:813-26. [PMID: 18399939 DOI: 10.1111/j.1365-2958.2008.06193.x] [Citation(s) in RCA: 146] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
One kind of the most extremely polarized cells in nature are the indefinitely growing hyphae of filamentous fungi. A continuous flow of secretion vesicles from the hyphal cell body to the growing hyphal tip is essential for cell wall and membrane extension. Because microtubules (MT) and actin, together with their corresponding motor proteins, are involved in the process, the arrangement of the cytoskeleton is a crucial step to establish and maintain polarity. In Saccharomyces cerevisiae and Schizosaccharomyces pombe, actin-mediated vesicle transportation is sufficient for polar cell extension, but in S. pombe, MTs are in addition required for the establishment of polarity. The MT cytoskeleton delivers the so-called cell-end marker proteins to the cell pole, which in turn polarize the actin cytoskeleton. Latest results suggest that this scenario may principally be conserved from S. pombe to filamentous fungi. In addition, in filamentous fungi, MTs could provide the tracks for long-distance vesicle movement. In this review, we will compare the interaction of the MT and the actin cytoskeleton and their relation to the cortex between yeasts and filamentous fungi. In addition, we will discuss the role of sterol-rich membrane domains in combination with cell-end marker proteins for polarity establishment.
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Affiliation(s)
- Reinhard Fischer
- Department of Applied Microbiology, University of Karlsruhe, Hertzstrasse 16, D-76187 Karlsruhe, Germany
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23
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Boldogh IR, Pon LA. Mitochondria on the move. Trends Cell Biol 2007; 17:502-10. [PMID: 17804238 DOI: 10.1016/j.tcb.2007.07.008] [Citation(s) in RCA: 196] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Revised: 07/01/2007] [Accepted: 07/24/2007] [Indexed: 12/21/2022]
Abstract
Interactions of mitochondria with the cytoskeleton are crucial for normal mitochondrial function and for localization of the organelle at its sites of action within cells. Early studies revealed a role for microtubule motors in mitochondrial motility in neurons and other cell types. Here, we describe advances in our understanding of mitochondrial movement and distribution. Specifically, we review recent studies on proteins that mediate or regulate the interaction between motor molecules and the organelle, motor-independent mechanisms for mitochondrial motility, anchorage of mitochondria at cortical sites within cells and links between mitochondria-cytoskeleton interactions and mitochondrial plasticity.
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Affiliation(s)
- Istvan R Boldogh
- Department of Anatomy and Cell Biology, Columbia University, College of Physicians and Surgeons, 1130 St. Nicholas Avenue, Room 311B, New York, NY 10032, USA
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24
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Höög JL, Schwartz C, Noon AT, O'Toole ET, Mastronarde DN, McIntosh JR, Antony C. Organization of interphase microtubules in fission yeast analyzed by electron tomography. Dev Cell 2007; 12:349-61. [PMID: 17336902 DOI: 10.1016/j.devcel.2007.01.020] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2006] [Revised: 12/08/2006] [Accepted: 01/24/2007] [Indexed: 11/26/2022]
Abstract
Polarized cells, such as neuronal, epithelial, and fungal cells, all display a specialized organization of their microtubules (MTs). The interphase MT cytoskeleton of the rod-shaped fission yeast, Schizosaccharomyces pombe, has been extensively described by fluorescence microscopy. Here, we describe a large-scale, electron tomography investigation of S. pombe, including a 3D reconstruction of a complete eukaryotic cell volume at sufficient resolution to show both how many MTs there are in a bundle and their detailed architecture. Most cytoplasmic MTs are open at one end and capped at the other, providing evidence about their polarity. Electron-dense bridges between the MTs themselves and between MTs and the nuclear envelope were frequently observed. Finally, we have investigated structure/function relationships between MTs and both mitochondria and vesicles. Our analysis shows that electron tomography of well-preserved cells is ideally suited for describing fine ultrastructural details that were not visible with previous techniques.
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Affiliation(s)
- Johanna L Höög
- European Molecular Biology Laboratory, Cell Biology and Biophysics Program, D-69117 Heidelberg, Germany
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25
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Onken B, Wiener H, Philips MR, Chang EC. Compartmentalized signaling of Ras in fission yeast. Proc Natl Acad Sci U S A 2006; 103:9045-50. [PMID: 16754851 PMCID: PMC1482563 DOI: 10.1073/pnas.0603318103] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Compartment-specific Ras signaling is an emerging paradigm that may explain the multiplex outputs from a single GTPase. The fission yeast, Schizosaccharomyces pombe, affords a simple system in which to study Ras signaling because it has a single Ras protein, Ras1, that regulates two distinct pathways: one that controls mating through a Byr2-mitogen-activated protein kinase cascade and one that signals through Scd1-Cdc42 to maintain elongated cell morphology. We generated Ras1 mutants that are restricted to either the endomembrane or the plasma membrane. Protein binding studies showed that each could interact with the effectors of both pathways. However, when examined in ras1 null cells, endomembrane-restricted Ras1 supported morphology but not mating, and, conversely, plasma membrane-restricted Ras1 supported mating but did not signal to Scd1-Cdc42. These observations provide a striking demonstration of compartment-specific Ras signaling and indicate that spatial specificity in the Ras pathway is evolutionarily conserved.
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Affiliation(s)
- Brian Onken
- *Department of Molecular and Cell Biology, The Breast Center, Baylor College of Medicine, 1 Baylor Plaza, BCM 600, Houston, TX 77030; and
| | - Heidi Wiener
- Department of Medicine, Cell Biology, and Pharmacology, New York University School of Medicine, 550 1st Avenue, New York, NY 10016
| | - Mark R. Philips
- Department of Medicine, Cell Biology, and Pharmacology, New York University School of Medicine, 550 1st Avenue, New York, NY 10016
- To whom correspondence may be addressed. E-mail:
or
| | - Eric C. Chang
- *Department of Molecular and Cell Biology, The Breast Center, Baylor College of Medicine, 1 Baylor Plaza, BCM 600, Houston, TX 77030; and
- To whom correspondence may be addressed. E-mail:
or
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26
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Yoshida SH, Nakamura T, Shimoda C. The cation-transporting P-type ATPase Cta4 is required for assembly of the forespore membrane in fission yeast. Genes Genet Syst 2006; 80:317-24. [PMID: 16394583 DOI: 10.1266/ggs.80.317] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
A novel sporulation-deficient mutant, sev4-L5, was isolated in a genetic screen of a collection of temperature-sensitive mutants of Schizosaccharomyces pombe. The wild-type sev4 gene was identified as cta4+, which encodes a putative cation-transporting P-type ATPase. The sev4-L5 allele harbored a single missense mutation that caused replacement of Gly615 with a glutamate at the putative ATP-binding site. Similar to cta4-null mutants, sev4-L5 exhibited defects in growth at high and low temperatures, and sensitivity to high and extremely low concentrations of Ca2+. The cta4+ mRNA level was considerably enhanced during meiosis. When sev4-L5 cells were incubated in sporulation medium at the permissive temperature, meiotic nuclear divisions proceeded with normal kinetics, but spores were not formed. Structural alteration of the spindle pole body, which is prerequisite to construction of the forespore membrane in wild type, was incomplete. Consequently, formation of the forespore membrane was severely impaired. These observations show that perturbation of Ca2+ homeostasis by mutation of cta4/sev4 blocks sporulation mainly by interfering with forespore membrane assembly.
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Affiliation(s)
- Shu-Hei Yoshida
- Department of Biology, Graduate School of Science, Osaka City University, Sugimoto, Japan
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27
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Nakashima A, Hasegawa T, Mori S, Ueno M, Tanaka S, Ushimaru T, Sato S, Uritani M. A starvation-specific serine protease gene, isp6 +, is involved in both autophagy and sexual development in Schizosaccharomyces pombe. Curr Genet 2006; 49:403-13. [PMID: 16550352 DOI: 10.1007/s00294-006-0067-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2005] [Revised: 02/23/2006] [Accepted: 02/25/2006] [Indexed: 11/26/2022]
Abstract
Schizosaccharomyces pombe isp6(+) gene encodes a vacuolar serine protease, which is specifically induced during nitrogen starvation. An isp6-disruption mutant, isp6Delta, grew normally under normal conditions but was defective in large-scale protein degradation during nitrogen starvation, a hallmark of autophagy. Vacuoles are the organelles for such drastic protein degradation but those of isp6Delta were apparently aberrant. isp6Delta was infertile under nitrogen source-free conditions with poor expression of ste11(+), a gene critical for sexual development. A protein kinase A-disruption mutant, pka1Delta, is prone to sexual development because expression of ste11(+) is derepressed. However, isp6Deltapka1Delta still showed defects in ste11(+) expression and sexual development under nitrogen source-free conditions. isp6Delta and isp6Deltapka1Delta were able to initiate sexual development to produce spores when only a small amount of a nitrogen source was present. Pat1 protein kinase negatively controls meiosis, and a temperature-sensitive mutant of pat1, pat1-114, initiates meiosis irrespective of ploidy at the restrictive temperature. However, isp6Deltapat1-114 did not start meiosis under nitrogen source-free conditions even at the restrictive temperature. These observations suggest that isp6(+) contributes to sexual development by providing a nitrogen source through autophagy.
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Affiliation(s)
- Akio Nakashima
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Oya, 422-8539, Shizuoka, Japan
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28
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Gachet Y, Codlin S, Hyams JS, Mole SE. btn1, theSchizosaccharomyces pombehomologue of the human Batten disease geneCLN3, regulates vacuole homeostasis. J Cell Sci 2005; 118:5525-36. [PMID: 16291725 DOI: 10.1242/jcs.02656] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have cloned the Schizosaccharomyces pombe homologue of the human Batten disease gene, CLN3. This gene, btn1, encodes a predicted transmembrane protein that is 30% identical and 48% similar to its human counterpart. Cells deleted for btn1 were viable but had enlarged and more alkaline vacuoles. Conversely overexpression of Btn1p reduced both vacuole diameter and pH. Thus Btn1p regulates vacuole homeostasis. The vacuolar defects of btn1Δ cells were rescued by heterologous expression of CLN3, proving that Btn1p and CLN3 are functional homologues. The disease severity of Batten disease-causing mutations (G187A, E295K and V330F), when expressed in btn1 appeared to correlate with their effect on vacuolar pH, suggesting that elevated lysosomal pH contributes to the disease process. In fission yeast, both Btn1p and CLN3 trafficked to the vacuole membrane via early endocytic and pre-vacuolar compartments, and localisation of Btn1p to the vacuole membrane was dependent on the Ras GTPase Ypt7p. Importantly, vacuoles in cells deleted for both ypt7 and btn1 were larger and more alkaline than those of cells deleted for ypt7 alone, indicating that Btn1p has a functional role prior to reaching the vacuole. Consistently, btn1 and vma1, the gene encoding subunit A of the V1 portion of vATPase, showed conditional synthetic lethality, and in cells deleted for vma1 (a subunit of the vacuolar ATPase) Btn1p was essential for septum deposition during cytokinesis.
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Affiliation(s)
- Yannick Gachet
- Department of Biology, University College London, Gower Street, London, WC1E 6BT, UK
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29
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Gachet Y, Hyams JS. Endocytosis in fission yeast is spatially associated with the actin cytoskeleton during polarised cell growth and cytokinesis. J Cell Sci 2005; 118:4231-42. [PMID: 16141239 DOI: 10.1242/jcs.02530] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the fission yeast, Schizosaccharomyces pombe, uptake of the fluorescent styryl dye FM4-64 via the endocytic pathway to the vacuole was localised to the poles of growing, interphase cells and to the cell equator during cell division, regions of cell wall deposition that are rich in actin. When the pattern of growth or the plane of cytokinesis was altered, the relationship between the actin cytoskeleton and the site of endocytosis was maintained. Transfer of the label to the vacuolar membrane was dependent upon the Rab GTPase Ypt7 and, hence, vesicle fusion. Endocytic vesicles transiently colocalised with actin patches and endocytosis was inhibited in mutants that affected actin patch integrity and by the actin inhibitor latrunculin A. Concentrations of latrunculin that removed actin cables but left patches unaffected had no effect on endocytosis at the poles, but abolished endocytosis at the cell equator. Equatorial, but not polar, endocytosis was also inhibited in cells lacking the formin For3 (which have selectively destabilised actin cables), in mutants of the exocyst complex and in cells treated with brefeldin A. Differential effects on endocytosis at the cell poles and equator were also observed in the actin mutant cps8 and the Arp2/3 complex mutant arp2. The redirection of endocytosis from the cell poles to the cell equator in M phase coincided with the anaphase separation of sister chromatids and was abolished in the septation initiation network (SIN) mutants cdc7, sid1 and sid2, demonstrating that the spatial reorganisation of the endocytic pathway in the S. pombe cell cycle requires a functional SIN pathway. We conclude that endocytosis in fission yeast has two distinct components, both of which are actin-based, but which are mechanistically distinct, as well as being spatially and temporally separated in the S. pombe cell cycle.
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Affiliation(s)
- Yannick Gachet
- Department of Biology, University College London, Gower Street, London WC1E 6BT, UK
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30
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Schuchardt I, Assmann D, Thines E, Schuberth C, Steinberg G. Myosin-V, Kinesin-1, and Kinesin-3 cooperate in hyphal growth of the fungus Ustilago maydis. Mol Biol Cell 2005; 16:5191-201. [PMID: 16120650 PMCID: PMC1266418 DOI: 10.1091/mbc.e05-04-0272] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Long-distance transport is crucial for polar-growing cells, such as neurons and fungal hyphae. Kinesins and myosins participate in this process, but their functional interplay is poorly understood. Here, we investigate the role of kinesin motors in hyphal growth of the plant pathogen Ustilago maydis. Although the microtubule plus-ends are directed to the hyphal tip, of all 10 kinesins analyzed, only conventional kinesin (Kinesin-1) and Unc104/Kif1A-like kinesin (Kinesin-3) were up-regulated in hyphae and they are essential for extended hyphal growth. deltakin1 and deltakin3 mutant hyphae grew irregular and remained short, but they were still able to grow polarized. No additional phenotype was detected in deltakin1rkin3 double mutants, but polarity was lost in deltamyo5rkin1 and deltamyo5rkin3 mutant cells, suggesting that kinesins and class V myosin cooperate in hyphal growth. Consistent with such a role in secretion, fusion proteins of green fluorescent protein and Kinesin-1, Myosin-V, and Kinesin-3 accumulate in the apex of hyphae, a region where secretory vesicles cluster to form the fungal Spitzenkörper. Quantitative assays revealed a role of Kin3 in secretion of acid phosphatase, whereas Kin1 was not involved. Our data demonstrate that just two kinesins and at least one myosin support hyphal growth.
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Affiliation(s)
- Isabel Schuchardt
- Max-Planck-Institut für Terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, D-35043 Marburg, Germany
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31
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Sanchez-Perez I, Renwick SJ, Crawley K, Karig I, Buck V, Meadows JC, Franco-Sanchez A, Fleig U, Toda T, Millar JBA. The DASH complex and Klp5/Klp6 kinesin coordinate bipolar chromosome attachment in fission yeast. EMBO J 2005; 24:2931-43. [PMID: 16079915 PMCID: PMC1187944 DOI: 10.1038/sj.emboj.7600761] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2004] [Accepted: 07/11/2005] [Indexed: 11/08/2022] Open
Abstract
We identified a truncated allele of dam1 as a multicopy suppressor of the sensitivity of cdc13-117 (cyclin B) and mal3-1 (EB-1) cells to thiabendazole, a microtubule poison. We find that Dam1 binds to the plus end of spindle microtubules and kinetochores as cells enter mitosis and this is dependent on other components of the fission yeast DASH complex, including Ask1, Duo1, Spc34 and Dad1. By contrast, Dad1 remains bound to kinetochores throughout the cell cycle and its association is dependent on the Mis6 and Mal2, but not Mis12, Nuf2 or Cnp1, kinetochore proteins. In cells lacking Dam1, or other components of the DASH complex, anaphase is delayed due to activation of the spindle assembly checkpoint and lagging sister chromatids are frequently observed and occasionally sister chromatid pairs segregate to the same spindle pole. We find that the mitotic centromere-associated Klp5/Klp6 kinesin complex is essential in cells lacking components of the DASH complex. Cells lacking both Dam1 and Klp5 undergo a first cell cycle arrest in mitosis due to a failure to establish bipolar chromosome attachment.
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Affiliation(s)
| | - Steven J Renwick
- Division of Yeast Genetics, National Institute for Medical Research, London, UK
| | - Karen Crawley
- Laboratory of Cell Regulation, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, London, UK
| | - Inga Karig
- Institut für Mikrobiologie, Heinrich-Heine-Universitat Düsseldorf, Düsseldorf, Germany
| | - Vicky Buck
- Division of Yeast Genetics, National Institute for Medical Research, London, UK
| | - John C Meadows
- Division of Yeast Genetics, National Institute for Medical Research, London, UK
| | | | - Ursula Fleig
- Institut für Mikrobiologie, Heinrich-Heine-Universitat Düsseldorf, Düsseldorf, Germany
| | - Takashi Toda
- Laboratory of Cell Regulation, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, London, UK
| | - Jonathan B A Millar
- Division of Yeast Genetics, National Institute for Medical Research, London, UK
- Division of Yeast Genetics, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK. Tel.: +44 208 816 2367; Fax: +44 208 816 2523; E-mail:
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32
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Rhee DK, Cho BA, Kim HB. ATP-binding motifs play key roles in Krp1p, kinesin-related protein 1, function for bi-polar growth control in fission yeast. Biochem Biophys Res Commun 2005; 331:658-68. [PMID: 15850809 DOI: 10.1016/j.bbrc.2005.03.207] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Indexed: 11/16/2022]
Abstract
Kinesin is a microtubule-based motor protein with various functions related to the cell growth and division. It has been reported that Krp1p, kinesin-related protein 1, which belongs to the kinesin heavy chain superfamily, localizes on microtubules and may play an important role in cytokinesis. However, the function of Krp1p has not been fully elucidated. In this study, we overexpressed an intact form and three different mutant forms of Krp1p in fission yeast constructed by site-directed mutagenesis in two ATP-binding motifs or by truncation of the leucine zipper-like motif (LZiP). We observed hyper-extended microtubules and the aberrant nuclear shape in Krp1p-overexpressed fission yeast. As a functional consequence, a point mutation of ATP-binding domain 1 (G89E) in Krp1p reversed the effect of Krp1p overexpression in fission yeast, whereas the specific mutation in ATP-binding domain 2 (G238E) resulted in the altered cell polarity. Additionally, truncation of the leucine zipper-like domain (LZiP) at the C-terminal of Krp1p showed a normal nuclear division. Taken together, we suggest that krp1p is involved in regulation of cell-polarized growth through ATP-binding motifs in fission yeast.
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Affiliation(s)
- Dong Keun Rhee
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Republic of Korea
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33
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Carazo-Salas RE, Antony C, Nurse P. The Kinesin Klp2 Mediates Polarization of Interphase Microtubules in Fission Yeast. Science 2005; 309:297-300. [PMID: 16002618 DOI: 10.1126/science.1113465] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Fission yeast (Schizosaccharomyces pombe) cells grow longitudinally in a manner dependent on a polarized distribution of their interphase microtubules. We found that this distribution required sliding of microtubules toward the cell center along preexisting microtubules. This sliding was mediated by the minus end-directed kinesin motor Klp2, which helped microtubules to become properly organized with plus ends predominantly oriented toward the cell ends and minus ends toward the cell center. Thus, interphase microtubules in the fission yeast require motor activities for their proper organization.
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Affiliation(s)
- Rafael E Carazo-Salas
- Cell Cycle Laboratory, 44 Lincoln's Inn Fields, Cancer Research UK, London Research Institute, WC2A 1PX, UK.
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34
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Castagnetti S, Behrens R, Nurse P. End4/Sla2 is involved in establishment of a new growth zone inSchizosaccharomyces pombe. J Cell Sci 2005; 118:1843-50. [PMID: 15827087 DOI: 10.1242/jcs.02311] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The rod-shaped Schizosaccharomyces pombe cell grows in a polarized fashion from opposing ends. Correct positioning of the growth zones is directed by the polarity marker Tea1 located at the cell ends where actin patches accumulate and cell growth takes place. We show that the S. pombe homologue of Saccharomyces cerevisiae SLA2, a protein involved in cortical actin organization and endocytosis, provides a link between the polarity marker and the growth machinery. In wild-type fission yeast cells, this homologue End4/Sla2 is enriched at cell ends during interphase and localizes to a medial ring at cell division, mirroring the actin localization pattern throughout the cell cycle. Proper localization relies on membrane trafficking and is independent of both the actin and microtubule cytoskeletons. End4/Sla2 is required for the establishment of new polarised growth zones, and deletion of its C-terminal talin-like domain prevents the establishment of a new growth zone after cell fission. We propose that End4/Sla2 acts downstream of the polarity marker Tea1 and is implicated in the recruitment of the actin cytoskeleton to bring about polarised cell growth.
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Affiliation(s)
- Stefania Castagnetti
- Cell Cycle Lab Cancer Research UK, 44 Lincoln's Inn Field, London, WC2A 3PX, UK.
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35
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Fuchs F, Westermann B. Role of Unc104/KIF1-related motor proteins in mitochondrial transport in Neurospora crassa. Mol Biol Cell 2004; 16:153-61. [PMID: 15483054 PMCID: PMC539160 DOI: 10.1091/mbc.e04-05-0413] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Eukaryotic cells use diverse cytoskeleton-dependent machineries to control inheritance and intracellular positioning of mitochondria. In particular, microtubules play a major role in mitochondrial motility in the filamentous fungus Neurospora crassa and in mammalian cells. We examined the role of two novel Unc104/KIF1-related members of the kinesin family, Nkin2 and Nkin3, in mitochondrial motility in Neurospora. The Nkin2 protein is required for mitochondrial interactions with microtubules in vitro. Mutant hyphae lacking Nkin2 show mitochondrial motility defects in vivo early after germination of conidiospores. Nkin3, a member of a unique fungal-specific subgroup of small Unc104/KIF1-related proteins, is not associated with mitochondria in wild-type cells. However, it is highly expressed and recruited to mitochondria in Deltankin-2 mutants. Mitochondria lacking Nkin2 require Nkin3 for binding to microtubules in vitro, and mitochondrial motility defects in Deltankin-2 mutants disappear with up-regulation of Nkin3 in vivo. We propose that mitochondrial transport is mediated by Nkin2 in Neurospora, and organelle motility defects in Deltankin-2 mutants are rescued by Nkin3. Apparently, a highly versatile complement of organelle motors allows the cell to efficiently respond to exogenous challenges, a process that might also account for the great variety of different mitochondrial transport systems that have evolved in eukaryotic cells.
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Affiliation(s)
- Florian Fuchs
- Institut für Physiologische Chemie, Universität München, 81377 München, Germany
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36
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Cortés JCG, Katoh-Fukui R, Moto K, Ribas JC, Ishiguro J. Schizosaccharomyces pombe Pmr1p is essential for cell wall integrity and is required for polarized cell growth and cytokinesis. EUKARYOTIC CELL 2004; 3:1124-35. [PMID: 15470240 PMCID: PMC522595 DOI: 10.1128/ec.3.5.1124-1135.2004] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2004] [Accepted: 06/22/2004] [Indexed: 11/20/2022]
Abstract
The cps5-138 fission yeast mutant shows an abnormal lemon-like morphology at 28 degrees C in minimal medium and a lethal thermosensitive phenotype at 37 degrees C. Cell growth is completely inhibited at 28 degrees C in a Ca2+-free medium, in which the wild type is capable of growing normally. Under these conditions, actin patches become randomly distributed throughout the cell, and defects in septum formation and subsequent cytokinesis appear. The mutant cell is hypersensitive to the cell wall-digesting enzymatic complex Novozym234 even under permissive conditions. The gene SPBC31E1.02c, which complements all the mutant phenotypes described above, was cloned and codes for the Ca2+-ATPase homologue Pmr1p. The gene is not essential under optimal growth conditions but is required under conditions of low Ca2+ (<0.1 mM) or high temperature (>35 degrees C). The green fluorescent protein-tagged Cps5 proteins, which are expressed under physiological conditions (an integrated single copy with its own promoter in the cps5Delta strain), display a localization pattern typical of endoplasmic reticulum proteins. Biochemical analyses show that 1,3-beta-D-glucan synthase activity in the mutant is decreased to nearly half that of the wild type and that the mutant cell wall contains no detectable galactomannan when the cells are exposed to a Ca2+-free medium. The mutant acid phosphatase has an increased electrophoretic mobility, suggesting that incomplete protein glycosylation takes place in the mutant cells. These results indicate that S. pombe Pmr1p is essential for the maintenance of cell wall integrity and cytokinesis, possibly by allowing protein glycosylation and the polarized actin distribution to take place normally. Disruption and complementation analyses suggest that Pmr1p shares its function with a vacuolar Ca2+-ATPase homologue, Pmc1p (SPAPB2B4.04c), to prevent lethal activation of calcineurin for cell growth.
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Affiliation(s)
- Juan Carlos G Cortés
- Department of Biology, Faculty of Science and Engineering, Konan University, Okamoto 8-9-1, Kobe 658-8501, Japan.
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37
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Weir BA, Yaffe MP. Mmd1p, a novel, conserved protein essential for normal mitochondrial morphology and distribution in the fission yeast Schizosaccharomyces pombe. Mol Biol Cell 2004; 15:1656-65. [PMID: 14767070 PMCID: PMC379264 DOI: 10.1091/mbc.e03-06-0371] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The mmd1 mutation causes temperature-sensitive growth and defects in mitochondrial morphology and distribution in the fission yeast Schizosaccharomyces pombe. In mutant cells, mitochondria aggregate at the two cell ends, with increased aggregation at elevated temperatures. Microtubules, which mediate mitochondrial positioning in fission yeast, seem normal in mmd1 cells at permissive temperature and after several hours at the nonpermissive temperature but display aberrant organization after prolonged periods at 37 degrees C. Additionally, cells harboring both mmd1 and ban5-4, a temperature-sensitive allele of alpha2-tubulin, display synthetic defects in growth and mitochondrial distribution. The mmd1 mutation maps to an open reading frame encoding a novel 35.7-kDa protein. The Mmd1p sequence features repeating EZ-HEAT motifs and displays high conservation with uncharacterized homologues found in a variety of organisms. Saccharomyces cerevisiae cells depleted for their MMD1 homologue show increased sensitivity to the antimicrotubule drug benomyl, and the S. cerevisiae gene complemented the S. pombe mutation. Mmd1p was localized to the cytosol. Mmd1p is the first identified component required for the alignment of mitochondria along microtubules in fission yeast.
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Affiliation(s)
- Barbara A Weir
- University of California, San Diego, Division of Biological Sciences, Section of Cell and Developmental Biology, La Jolla, California 92093, USA
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38
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Abstract
The origin of eukaryotes is one of the major challenges of evolutionary cell biology. Other than the endosymbiotic origin of mitochondria and chloroplasts, the steps leading to eukaryotic endomembranes and endoskeleton are poorly understood. Ras-family small GTPases are key regulators of cytoskeleton dynamics, vesicular trafficking and nuclear function. They are specific for eukaryotes and their expansion probably traces the evolution of core eukaryote features. The phylogeny of small GTPases suggests that the first endomembranes to evolve during eukaryote evolution had secretory, and not phagocytic, function. Based on the reconstruction of putative roles for ancestral small GTPases, a hypothetical scenario on the origins of the first endomembranes, the nucleus, and phagocytosis is presented.
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Affiliation(s)
- Gáspár Jékely
- European Molecular Biology Laboratory, Developmental Biology, Meyerhofstrasse 1., 69117 Heidelberg, Germany.
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39
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Yaffe MP, Stuurman N, Vale RD. Mitochondrial positioning in fission yeast is driven by association with dynamic microtubules and mitotic spindle poles. Proc Natl Acad Sci U S A 2003; 100:11424-8. [PMID: 12972644 PMCID: PMC208773 DOI: 10.1073/pnas.1534703100] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Microtubules mediate mitochondrial distribution in the yeast Schizosaccharomyces pombe and many higher eukaryotic cells. In higher eukaryotes, kinesin motor proteins have been shown to transport mitochondria along microtubules, but the nature of the mitochondria-microtubule interactions in S. pombe has not been explored. By time lapse, total internal reflection fluorescence microscopy, or spinning-disk confocal microscopy, mitochondria appeared to be both tethered to ends and bound laterally along the sides of microtubules. Mitochondrial tubules extended and retracted when attached to the tips of elongating or shortening microtubules, respectively, but translocation along established microtubules was never observed. Mitochondria that were not associated with microtubules were largely immobile until they were "captured" by a growing microtubule. In mitotic cells, a portion of the mitochondria was tethered to the spindle-pole bodies and moved to the cellular ends during spindle elongation. This association may be important for organelle inheritance during cell division. Thus, in contrast to kinesin-mediated transport used by higher eukaryotes, mitochondrial motility and distribution in fission yeast are driven largely by microtubule polymerization and the elongation of the mitotic spindle.
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Affiliation(s)
- Michael P Yaffe
- Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California at San Diego, La Jolla, CA 92093, USA
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40
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Schoch CL, Aist JR, Yoder OC, Gillian Turgeon B. A complete inventory of fungal kinesins in representative filamentous ascomycetes. Fungal Genet Biol 2003; 39:1-15. [PMID: 12742059 DOI: 10.1016/s1087-1845(03)00022-7] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Complete inventories of kinesins from three pathogenic filamentous ascomycetes, Botryotinia fuckeliana, Cochliobolus heterostrophus, and Gibberella moniliformis, are described. These protein sequences were compared with those of the filamentous saprophyte, Neurospora crassa and the two yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. Data mining and phylogenetic analysis of the motor domain yielded a constant set of 10 kinesins in the filamentous fungal species, compared with a smaller set in S. cerevisiae and S. pombe. The filamentous fungal kinesins fell into nine subfamilies when compared with well-characterized kinesins from other eukaryotes. A few putative kinesins (one in B. fuckeliana and two in C. heterostrophus) could not be defined as functional, due to unorthodox organization and lack of experimental data. The broad representation of filamentous fungal kinesins across most of the known subfamilies and the ease of gene manipulation make fungi ideal models for functional and evolutionary investigation of these proteins.
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Affiliation(s)
- Conrad L Schoch
- Department of Plant Pathology, 334 Plant Science Building, Cornell University, Ithaca, NY 14853, USA
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41
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Nakamura-Kubo M, Nakamura T, Hirata A, Shimoda C. The fission yeast spo14+ gene encoding a functional homologue of budding yeast Sec12 is required for the development of forespore membranes. Mol Biol Cell 2003; 14:1109-24. [PMID: 12631727 PMCID: PMC151583 DOI: 10.1091/mbc.e02-08-0504] [Citation(s) in RCA: 45] [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 Schizosaccharomyces pombe spo14-B221 mutant was originally isolated as a sporulation-deficient mutant. However, the spo14(+) gene is essential for cell viability and growth. spo14(+) is identical to the previously characterized stl1(+) gene encoding a putative homologue of Saccharomyces cerevisiae Sec12, which is essential for protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus. In the spo14 mutant cells, ER-like membranes were accumulated beneath the plasma membrane and the ER/Golgi shuttling protein Rer1 remained in the ER. Sec12 is a guanine nucleotide exchange factor for the Sar1 GTPase. Overproduction of psr1(+) coding for an S. pombe Sar1 homologue suppressed both the sporulation defect of spo14-B221 and cold-sensitive growth of newly isolated spo14-6 and spo14-7 mutants. These results indicate that Spo14 is involved in early steps of the protein secretory pathway. The spo14-B221 allele carries a single nucleotide change in the branch point consensus of the fifth intron, which reduces the abundance of the spo14 mRNA. During meiosis II, the forespore membrane was initiated near spindle pole bodies; however, subsequent extension of the membrane was arrested before its closure into a sac. We conclude that Spo14 is responsible for the assembly of the forespore membrane by supplying membrane vesicles.
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Affiliation(s)
- Michiko Nakamura-Kubo
- Department of Biology, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Japan
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42
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Routhier EL, Donover PS, Prendergast GC. hob1+, the fission yeast homolog of Bin1, is dispensable for endocytosis or actin organization, but required for the response to starvation or genotoxic stress. Oncogene 2003; 22:637-48. [PMID: 12569356 DOI: 10.1038/sj.onc.1206162] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BAR (Bin/Amphiphysin/Rvs) adapter proteins have been suggested to regulate endocytosis, actin organization, apoptosis, and transcription, but their precise roles are obscure. There are at least five mammalian genes that encode BAR adapter proteins, including the evolutionarily conserved and ubiquitously expressed Bin1/Amphiphysin-II and Bin3 genes. Bin1 holds special interest as certain splice isoforms localize to the nucleus, interact with the c-Abl and c-Myc oncoproteins, and display tumor suppressor properties. To obtain functional insights, we embarked upon a genetic analysis of the two BAR adapter proteins expressed in the fission yeast Schizosaccharomyces pombe. In a previous work, a role in actin organization and cytokinesis was identified for the Bin3 homolog hob3+. In this study, a role in stress signaling was defined for the Bin1 homolog, hob1+. Notably, hob1+ was dispensable for endocytosis, actin organization, or osmotic sensitivity. Instead, mutation of hob1+ led to slight cell elongation and faulty cell cycle arrest upon nutrient starvation. These defects were complemented by Bin1, but not by Amphiphysin-I, arguing that these genes have distinct functions despite their structural similarity. hob1 delta mutant cells were also hypersensitive to genotoxic stress. This was not related to a faulty checkpoint response, but mutation in the checkpoint gene rad3(+) further exacerbated the sensitivity of hob1 delta mutant cells. Interestingly, mutation of the cell cycle regulator wee1+ partially relieved the sensitivity defect, suggesting that hob1+ may influence the efficiency of DNA repair or checkpoint release after DNA damage. Genetic and biochemical evidence indicated that hob3+ is epistatic to hob1+ in the response to genotoxic stress. Our findings indicate that the Bin1 homolog hob1+ participates in DNA damage signaling and they suggest a novel role for BAR adapter proteins in stress response processes.
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Affiliation(s)
- Eric L Routhier
- Cancer Research Group, The DuPont Pharmaceuticals Company, Glenolden, PA 19036, USA
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43
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Wang H, Tang X, Liu J, Trautmann S, Balasundaram D, McCollum D, Balasubramanian MK. The multiprotein exocyst complex is essential for cell separation in Schizosaccharomyces pombe. Mol Biol Cell 2002; 13:515-29. [PMID: 11854409 PMCID: PMC65646 DOI: 10.1091/mbc.01-11-0542] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2001] [Revised: 10/27/2001] [Accepted: 11/14/2001] [Indexed: 11/11/2022] Open
Abstract
Schizosaccharomyces pombe cells divide by medial fission through the use of an actomyosin-based contractile ring. A mulitlayered division septum is assembled in concert with ring constriction. Finally, cleavage of the inner layer of the division septum results in the liberation of daughter cells. Although numerous studies have focused on actomyosin ring and division septum assembly, little information is available on the mechanism of cell separation. Here we describe a mutant, sec8-1, that is defective in cell separation but not in other aspects of cytokinesis. sec8-1 mutants accumulate about 100-nm vesicles and have reduced secretion of acid phosphatase, suggesting that they are defective in exocytosis. Sec8p is a component of the exocyst complex. Using biochemical methods, we show that Sec8p physically interacts with other members of the exocyst complex, including Sec6p, Sec10p, and Exo70p. These exocyst proteins localize to regions of active exocytosis-at the growing ends of interphase cells and in the medial region of cells undergoing cytokinesis-in an F-actin-dependent and exocytosis-independent manner. Analysis of a number of mutations in various exocyst components has established that these components are essential for cell viability. Interestingly, all exocyst mutants analyzed appear to be able to elongate and to assemble division septa but are defective for cell separation. We therefore propose that the fission yeast exocyst is involved in targeting of enzymes responsible for septum cleavage. We further propose that cell elongation and division septum assembly can continue with minimal levels of exocyst function.
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Affiliation(s)
- Hongyan Wang
- The Institute of Molecular Agrobiology, The National University of Singapore, Singapore 117604, Republic of Singapore
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44
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West RR, Malmstrom T, Troxell CL, McIntosh JR. Two related kinesins, klp5+ and klp6+, foster microtubule disassembly and are required for meiosis in fission yeast. Mol Biol Cell 2001; 12:3919-32. [PMID: 11739790 PMCID: PMC60765 DOI: 10.1091/mbc.12.12.3919] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The kinesin superfamily of microtubule motor proteins is important in many cellular processes, including mitosis and meiosis, vesicle transport, and the establishment and maintenance of cell polarity. We have characterized two related kinesins in fission yeast, klp5+ and klp6+,, that are amino-terminal motors of the KIP3 subfamily. Analysis of null mutants demonstrates that neither klp5+ nor klp6+, individually or together, is essential for vegetative growth, although these mutants have altered microtubule behavior. klp5Delta and klp6Delta are resistant to high concentrations of the microtubule poison thiabendazole and have abnormally long cytoplasmic microtubules that can curl around the ends of the cell. This phenotype is greatly enhanced in the cell cycle mutant cdc25-22, leading to a bent, asymmetric cell morphology as cells elongate during cell cycle arrest. Klp5p-GFP and Klp6p-GFP both localize to cytoplasmic microtubules throughout the cell cycle and to spindles in mitosis, but their localizations are not interdependent. During the meiotic phase of the life cycle, both of these kinesins are essential. Spore viability is low in homozygous crosses of either null mutant. Heterozygous crosses of klp5Delta with klp6Delta have an intermediate viability, suggesting cooperation between these proteins in meiosis.
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Affiliation(s)
- R R West
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
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45
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Bruneau N, Nganga A, Bendayan M, Lombardo D. Transcytosis of pancreatic bile salt-dependent lipase through human Int407 intestinal cells. Exp Cell Res 2001; 271:94-108. [PMID: 11697886 DOI: 10.1006/excr.2001.5361] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In previous studies, we have shown that the bile-salt-dependent-lipase (BSDL), secreted by pancreatic acinar cells and secreted into the duodenal lumen, can be transcytosed through intestinal cells up to the lamina propria. In this study, we used an in vitro system to provide insights into the apical to basolateral transport of BSDL, across the intestinal barrier. The Int407 human epithelial cell line, grown under conditions that optimize polarity, was used as a tight epithelium model. We attempted to delineate uptake mechanisms and the transcytotic pathway followed by this pancreatic enzyme within the intestinal Int407 cells, which do not produce BSDL. When added to the apical reservoir of Transwell-grown Int407 cells, BSDL was shown to first interact with the apical membrane. Further, BSDL forms clusters that are internalized via clathrin-coated pits. Following endocytosis, BSDL is directed to a nocodazole- and colchicin-sensitive multivesicular compartment. Interestingly, this protein transits through the Golgi apparatus, where it was found to colocalize with the KDEL retrieval-receptor. Finally, enzymatically active intact BSDL was released at the basolateral membrane level. This is the first demonstration for an apical-to-basolateral transcytotic pathway of a secreted pancreatic digestive enzyme through polarized intestinal cells.
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Affiliation(s)
- N Bruneau
- Unité de Recherche de Physiopathologie des cellules épithéliales, INSERM U-559, Marseilles, France
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46
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Troxell CL, Sweezy MA, West RR, Reed KD, Carson BD, Pidoux AL, Cande WZ, McIntosh JR. pkl1(+)and klp2(+): Two kinesins of the Kar3 subfamily in fission yeast perform different functions in both mitosis and meiosis. Mol Biol Cell 2001; 12:3476-88. [PMID: 11694582 PMCID: PMC60269 DOI: 10.1091/mbc.12.11.3476] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2001] [Revised: 07/25/2001] [Accepted: 08/29/2001] [Indexed: 11/11/2022] Open
Abstract
We have identified Klp2p, a new kinesin-like protein (KLP) of the KAR3 subfamily in fission yeast. The motor domain of this protein is 61% identical and 71% similar to Pkl1p, another fission yeast KAR3 protein, yet the two enzymes are different in behavior and function. Pkl1p is nuclear throughout the cell cycle, whereas Klp2p is cytoplasmic during interphase. During mitosis Klp2p enters the nucleus where it forms about six chromatin-associated dots. In metaphase-arrested cells these migrate back and forth across the nucleus. During early anaphase they segregate with the chromosomes into two sets of about three, fade, and are replaced by other dots that form on the spindle interzone. Neither klp2(+) nor pkl1(+) is essential, and the double deletion is also wild type for both vegetative and sexual reproduction. Each deletion rescues different alleles of cut7(ts), a KLP that contributes to spindle formation and elongation. When either or both deletions are combined with a dynein deletion, vegetative growth is normal, but sexual reproduction fails: klp2 Delta,dhc1-d1 in karyogamy, pkl1 Delta,dhc1-d1 in multiple phases of meiosis, and the triple deletion in both. Deletion of Klp2p elongates a metaphase-arrested spindle, but pkl1 Delta shortens it. The anaphase spindle of klp2 Delta becomes longer than the cell, leading it to curl around the cell's ends. Apparently, Klp2p promotes spindle disassembly and contributes to the behavior of mitotic chromosomes.
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Affiliation(s)
- C L Troxell
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
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47
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Mulvihill DP, Pollard PJ, Win TZ, Hyams JS. Myosin V-mediated vacuole distribution and fusion in fission yeast. Curr Biol 2001; 11:1124-7. [PMID: 11509236 DOI: 10.1016/s0960-9822(01)00322-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The class V myosins are actin-based motors that move a variety of cellular cargoes [1]. In budding yeast, their activity includes the relocation of a portion of the vacuole from the mother cell to the bud [2, 3]. Fission yeast cells contain numerous (approximately 80) small vacuoles. When S. pombe cells are placed in water, vacuoles fuse in response to osmotic stress [4]. Fission yeast possess two type V myosin genes, myo51(+) and myo52(+) [5]. In a myo51Delta strain, vacuoles were distributed throughout the cell, and mean vacuole diameter was identical to that seen in wild-type cells. When myo51Delta and wild-type cells were placed in water, vacuoles enlarged by fusion. In myo52Delta cells, by contrast, vacuoles were smaller and mostly clustered around the nucleus, and fusion in water was largely inhibited. When cells containing GFP-Myo52 were placed in water, Myo52 was seen to redistribute from the cell poles to the surface of the fusing vacuoles. Vacuole fusion in fission yeast was inhibited by the microtubule drug thiabendazole (TBZ) but not by the actin inhibitor latrunculin B. This is the first demonstration of the involvement of a type V myosin, possibly via an interaction with microtubules, in homotypic membrane fusion.
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Affiliation(s)
- D P Mulvihill
- Department of Biology, University College London, Gower Street, WC1E 6BT, London, United Kingdom
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48
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Routhier EL, Burn TC, Abbaszade I, Summers M, Albright CF, Prendergast GC. Human BIN3 complements the F-actin localization defects caused by loss of Hob3p, the fission yeast homolog of Rvs161p. J Biol Chem 2001; 276:21670-7. [PMID: 11274158 DOI: 10.1074/jbc.m101096200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The BAR adaptor proteins encoded by the RVS167 and RVS161 genes from Saccharomyces cerevisiae form a complex that regulates actin, endocytosis, and viability following starvation or osmotic stress. In this study, we identified a human homolog of RVS161, termed BIN3 (bridging integrator-3), and a Schizosaccharomyces pombe homolog of RVS161, termed hob3+ (homolog of Bin3). In human tissues, the BIN3 gene was expressed ubiquitously except for brain. S. pombe cells lacking Hob3p were often multinucleate and characterized by increased amounts of calcofluor-stained material and mislocalized F-actin. For example, while wild-type cells localized F-actin to cell ends during interphase, hob3Delta mutants had F-actin patches distributed randomly around the cell. In addition, medial F-actin rings were rarely found in hob3Delta mutants. Notably, in contrast to S. cerevisiae rvs161Delta mutants, hob3Delta mutants showed no measurable defects in endocytosis or response to osmotic stress, yet hob3+ complemented the osmosensitivity of a rvs161Delta mutant. BIN3 failed to rescue the osmosensitivity of rvs161Delta, but the actin localization defects of hob3Delta mutants were completely rescued by BIN3 and partially rescued by RVS161. These findings suggest that hob3+ and BIN3 regulate F-actin localization, like RVS161, but that other roles for this gene have diverged somewhat during evolution.
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Affiliation(s)
- E L Routhier
- Cancer Research Group, DuPont Pharmaceuticals Company, Glenolden Laboratory, Glenolden, Pennsylvania 19036, USA
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49
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Tanaka N, Takegawa K. Functional characterization of Gms1p/UDP-galactose transporter in Schizosaccharomyces pombe. Yeast 2001; 18:745-57. [PMID: 11378902 DOI: 10.1002/yea.725] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Galactosylation of glycoproteins in the fission yeast Schizosaccharomyces pombe requires the transport of UDP-galactose as substrate for the galactosyltransferase into the lumen of the Golgi apparatus, which is achieved by the UDP-galactose transporter. We isolated a mutant (gms1) that is deficient in galactosylation of cell surface glycoproteins in Sz.pombe, and found that the gms1(+) gene encodes a UDP-galactose transporter. In the prediction of secondary structure of the Gms1 protein, an eight-membrane-spanning structure was obtained. Fluorescent microscopy revealed the functional Gms1-GFP fusion protein to be stably localized at the Golgi membrane. Sequencing analysis of the coding region of Gms1p derived from galactosylation-defective mutants identified a single amino acid mutation (A102T or A258E) located within the putative transmembrane region, helix 2 or helix 7, respectively. The mutagenized Gms1(A102T or A258E)p exhibited loss of UDP-galactose transport activity but no change in the localization to the Golgi membrane. The C-terminal truncated Gms1p mutants demonstrated that the C-terminal hydrophilic region was dispensable for targeting and function as UDP-galactose transporter at the Golgi membrane. We suggest that the putative eighth (the most C-terminus-proximal) transmembrane helix of Gms1p is critical to targeting from ER to the Golgi membrane.
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Affiliation(s)
- N Tanaka
- Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan
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50
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Tran PT, Marsh L, Doye V, Inoué S, Chang F. A mechanism for nuclear positioning in fission yeast based on microtubule pushing. J Cell Biol 2001; 153:397-411. [PMID: 11309419 PMCID: PMC2169469 DOI: 10.1083/jcb.153.2.397] [Citation(s) in RCA: 371] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
The correct positioning of the nucleus is often important in defining the spatial organization of the cell, for example, in determining the cell division plane. In interphase Schizosaccharomyces pombe cells, the nucleus is positioned in the middle of the cylindrical cell in an active microtubule (MT)-dependent process. Here, we used green fluorescent protein markers to examine the dynamics of MTs, spindle pole body, and the nuclear envelope in living cells. We find that interphase MTs are organized in three to four antiparallel MT bundles arranged along the long axis of the cell, with MT plus ends facing both the cell tips and minus ends near the middle of the cell. The MT bundles are organized from medial MT-organizing centers that may function as nuclear attachment sites. When MTs grow to the cell tips, they exert transient forces produced by plus end MT polymerization that push the nucleus. After an average of 1.5 min of growth at the cell tip, MT plus ends exhibit catastrophe and shrink back to the nuclear region before growing back to the cell tip. Computer modeling suggests that a balance of these pushing MT forces can provide a mechanism to position the nucleus at the middle of the cell.
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Affiliation(s)
- P T Tran
- Department of Microbiology, Columbia University, New York, New York 10032, USA.
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