1
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Wang K, Okada H, Wloka C, Bi E. Unraveling the mechanisms and evolution of a two-domain module in IQGAP proteins for controlling eukaryotic cytokinesis. Cell Rep 2023; 42:113510. [PMID: 38041816 PMCID: PMC10809011 DOI: 10.1016/j.celrep.2023.113510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 08/17/2023] [Accepted: 11/13/2023] [Indexed: 12/04/2023] Open
Abstract
The IQGAP family of proteins plays a crucial role in cytokinesis across diverse organisms, but the underlying mechanisms are not fully understood. In this study, we demonstrate that IQGAPs in budding yeast, fission yeast, and human cells use a two-domain module to regulate their localization as well as the assembly and disassembly of the actomyosin ring during cytokinesis. Strikingly, the calponin homology domains (CHDs) in these IQGAPs bind to distinct cellular F-actin structures with varying specificity, whereas the non-conserved domains immediately downstream of the CHDs in these IQGAPs all target the division site, but differ in timing, localization strength, and binding partners. We also demonstrate that human IQGAP3 acts in parallel to septins and myosin-IIs to mediate the role of anillin in cytokinesis. Collectively, our findings highlight the two-domain mechanism by which IQGAPs regulate cytokinesis in distantly related organisms as well as their evolutionary conservation and divergence.
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Affiliation(s)
- Kangji Wang
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6058, USA
| | - Hiroki Okada
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6058, USA
| | - Carsten Wloka
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6058, USA; Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, A Corporate Member of Freie Universität, Humboldt-University, The Berlin Institute of Health, Berlin, Germany
| | - Erfei Bi
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6058, USA.
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2
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Willet AH, Chen JS, Ren L, Gould KL. Membrane binding of endocytic myosin-1s is inhibited by a class of ankyrin repeat proteins. Mol Biol Cell 2023; 34:br17. [PMID: 37531259 PMCID: PMC10559312 DOI: 10.1091/mbc.e23-06-0233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 07/24/2023] [Accepted: 07/27/2023] [Indexed: 08/04/2023] Open
Abstract
Myosin-1s are monomeric actin-based motors that function at membranes. Myo1 is the single myosin-1 isoform in Schizosaccharomyces pombe that works redundantly with Wsp1-Vrp1 to activate the Arp2/3 complex for endocytosis. Here, we identified Ank1 as an uncharacterized cytoplasmic Myo1 binding partner. We found that in ank1Δ cells, Myo1 dramatically redistributed from endocytic patches to decorate the entire plasma membrane and endocytosis was defective. Biochemical analysis and structural predictions suggested that the Ank1 ankyrin repeats bind the Myo1 lever arm and the Ank1 acidic tail binds the Myo1 TH1 domain to prevent TH1-dependent Myo1 membrane binding. Indeed, Ank1 overexpression precluded Myo1 membrane localization and recombinant Ank1 reduced purified Myo1 liposome binding in vitro. Based on biochemical and cell biological analyses, we propose budding yeast Ank1 and human OSTF1 are functional Ank1 orthologs and that cytoplasmic sequestration by small ankyrin repeat proteins is a conserved mechanism regulating myosin-1s in endocytosis.
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Affiliation(s)
- Alaina H. Willet
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Jun-Song Chen
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Liping Ren
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Kathleen L. Gould
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
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3
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Willet AH, Chen JS, Ren L, Gould KL. Membrane binding of endocytic myosin-1s is inhibited by a class of ankyrin repeat proteins. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.26.538419. [PMID: 37163016 PMCID: PMC10168314 DOI: 10.1101/2023.04.26.538419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Myosin-1s are monomeric actin-based motors that function at membranes. Myo1 is the single myosin-1 isoform in Schizosaccharomyces pombe that works redundantly with Wsp1-Vrp1 to activate the Arp2/3 complex for endocytosis. Here, we identified Ank1 as an uncharacterized cytoplasmic Myo1 binding partner. We found that in ank1Δ cells, Myo1 dramatically redistributed from endocytic patches to decorate the entire plasma membrane and endocytosis was defective. Biochemical analysis and structural predictions suggested that the Ank1 ankyrin repeats bind the Myo1 lever arm and the Ank1 acidic tail binds the Myo1 TH1 domain to prevent TH1-dependent Myo1 membrane binding. Indeed, Ank1 over-expression precluded Myo1 membrane localization and recombinant Ank1 blocked purified Myo1 liposome binding in vitro. Based on biochemical and cell biology analyses, we propose budding yeast Ank1 and human OSTF1 are functional Ank1 orthologs and that cytoplasmic sequestration by small ankyrin repeat proteins is a conserved mechanism regulating myosin-1s in endocytosis. Summary Fission yeast long-tailed myosin-1 binds Ank1. Ank1 ankyrin repeats associate with the Myo1 lever arm and Ank1 acidic tail binds the Myo1 TH1 domain to inhibit Myo1 membrane binding. Ank1 orthologs exists in budding yeast (Ank1) and humans (OSTF1).
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Affiliation(s)
- Alaina H Willet
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Jun-Song Chen
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Liping Ren
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Kathleen L Gould
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
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4
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Hayakawa Y, Takaine M, Ngo KX, Imai T, Yamada MD, Behjat AB, Umeda K, Hirose K, Yurtsever A, Kodera N, Tokuraku K, Numata O, Fukuma T, Ando T, Nakano K, Uyeda TQ. Actin-binding domain of Rng2 sparsely bound on F-actin strongly inhibits actin movement on myosin II. Life Sci Alliance 2023; 6:e202201469. [PMID: 36288901 PMCID: PMC9610768 DOI: 10.26508/lsa.202201469] [Citation(s) in RCA: 2] [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: 03/31/2022] [Revised: 09/29/2022] [Accepted: 09/30/2022] [Indexed: 12/04/2022] Open
Abstract
We report a case in which sub-stoichiometric binding of an actin-binding protein has profound structural and functional consequences, providing an insight into the fundamental properties of actin regulation. Rng2 is an IQGAP contained in contractile rings in the fission yeast Schizosaccharomyces pombe Here, we used high-speed atomic force microscopy and electron microscopy and found that sub-stoichiometric binding of the calponin-homology actin-binding domain of Rng2 (Rng2CHD) induces global structural changes in skeletal muscle actin filaments, including shortening of the filament helical pitch. Sub-stoichiometric binding of Rng2CHD also reduced the affinity between actin filaments and muscle myosin II carrying ADP and strongly inhibited the motility of actin filaments on myosin II in vitro. On skeletal muscle myosin II-coated surfaces, Rng2CHD stopped the actin movements at a binding ratio of 11%. Rng2CHD also inhibited actin movements on myosin II of the amoeba Dictyostelium, but in this case, by detaching actin filaments from myosin II-coated surfaces. Thus, sparsely bound Rng2CHD induces apparently cooperative structural changes in actin filaments and inhibits force generation by actomyosin II.
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Affiliation(s)
- Yuuki Hayakawa
- Department of Physics, Faculty of Science and Engineering, Graduate School of Waseda University, Shinjuku, Japan
| | - Masak Takaine
- Department of Biology, Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba, Japan
| | - Kien Xuan Ngo
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Taiga Imai
- Department of Applied Sciences, Muroran Institute of Technology, Muroran, Japan
| | - Masafumi D Yamada
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
| | - Arash Badami Behjat
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Kenichi Umeda
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Keiko Hirose
- Department of Biology, Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba, Japan
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
| | - Ayhan Yurtsever
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Noriyuki Kodera
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Kiyotaka Tokuraku
- Department of Applied Sciences, Muroran Institute of Technology, Muroran, Japan
| | - Osamu Numata
- Department of Biology, Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba, Japan
| | - Takeshi Fukuma
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Toshio Ando
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, Japan
| | - Kentaro Nakano
- Department of Biology, Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba, Japan
| | - Taro Qp Uyeda
- Department of Physics, Faculty of Science and Engineering, Graduate School of Waseda University, Shinjuku, Japan
- Department of Biology, Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba, Japan
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
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5
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Mohapatra T, Dixit M. IQ Motif Containing GTPase Activating Proteins (IQGAPs), A-Kinase Anchoring Proteins (AKAPs) and Kinase Suppressor of Ras Proteins (KSRs) in Scaffolding Oncogenic Pathways and Their Therapeutic Potential. ACS OMEGA 2022; 7:45837-45848. [PMID: 36570181 PMCID: PMC9773950 DOI: 10.1021/acsomega.2c05505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Accepted: 11/18/2022] [Indexed: 06/17/2023]
Abstract
Scaffolding proteins colocalize interacting partners on their surface and facilitate complex formation. They have multiple domains and motifs, which provide binding sites for various molecules. This property of scaffolding proteins helps in the orderly transduction of signals. Abnormal signal transduction is frequently observed in cancers, which can also be attributed to the altered functionality of scaffolding proteins. IQ motif containing GTPase activating proteins (IQGAPs), kinase suppressor of Ras (KSR), and A-kinase anchoring proteins (AKAPs) tether oncogenic pathways RAS/RAF/MEK/ERK, PI3K/AKT, Hippo, Wnt, and CDC42/RAC to them. Scaffolding proteins are attractive drug targets as they are the controlling hub for multiple pathways and regulate crosstalk between them. The first part of this review describes the human scaffolding proteins known to play a role in oncogenesis, pathways altered by them, and the impact on oncogenic processes. The second part provides information on the therapeutic potential of scaffolding proteins and future possibilities. The information on the explored and unexplored areas of the therapeutic potential of scaffolding proteins will be equally helpful for biologists and chemists.
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Affiliation(s)
- Talina Mohapatra
- National
Institute of Science Education and Research, School of Biological Sciences, Bhubaneswar, Odisha 752050, India
- Homi
Bhabha National Institute, Training School
Complex, Anushaktinagar, Mumbai 400094, India
| | - Manjusha Dixit
- National
Institute of Science Education and Research, School of Biological Sciences, Bhubaneswar, Odisha 752050, India
- Homi
Bhabha National Institute, Training School
Complex, Anushaktinagar, Mumbai 400094, India
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6
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Opalko HE, Miller KE, Kim HS, Vargas-Garcia CA, Singh A, Keogh MC, Moseley JB. Arf6 anchors Cdr2 nodes at the cell cortex to control cell size at division. J Cell Biol 2022; 221:e202109152. [PMID: 34958661 PMCID: PMC8931934 DOI: 10.1083/jcb.202109152] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Revised: 11/12/2021] [Accepted: 12/02/2021] [Indexed: 12/25/2022] Open
Abstract
Fission yeast cells prevent mitotic entry until a threshold cell surface area is reached. The protein kinase Cdr2 contributes to this size control system by forming multiprotein nodes that inhibit Wee1 at the medial cell cortex. Cdr2 node anchoring at the cell cortex is not fully understood. Through a genomic screen, we identified the conserved GTPase Arf6 as a component of Cdr2 signaling. Cells lacking Arf6 failed to divide at a threshold surface area and instead shifted to volume-based divisions at increased overall size. Arf6 stably localized to Cdr2 nodes in its GTP-bound but not GDP-bound state, and its guanine nucleotide exchange factor (GEF), Syt22, was required for both Arf6 node localization and proper size at division. In arf6Δ mutants, Cdr2 nodes detached from the membrane and exhibited increased dynamics. These defects were enhanced when arf6Δ was combined with other node mutants. Our work identifies a regulated anchor for Cdr2 nodes that is required for cells to sense surface area.
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Affiliation(s)
- Hannah E. Opalko
- Department of Biochemistry and Cell Biology, the Geisel School of Medicine at Dartmouth, Hanover, NH
| | - Kristi E. Miller
- Department of Biochemistry and Cell Biology, the Geisel School of Medicine at Dartmouth, Hanover, NH
| | - Hyun-Soo Kim
- Department of Cell Biology, Albert Einstein College of Medicine, New York, NY
| | - Cesar Augusto Vargas-Garcia
- Grupo de Investigación en Sistemas Agropecuarios Sostenibles, Corporación Colombiana de Investigación Agropecuaria – AGROSAVIA, Bogotá, Colombia
| | - Abhyudai Singh
- Department of Electrical and Computer Engineering, University of Delaware, Newark, DE
| | | | - James B. Moseley
- Department of Biochemistry and Cell Biology, the Geisel School of Medicine at Dartmouth, Hanover, NH
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7
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Palani S, Ghosh S, Ivorra-Molla E, Clarke S, Suchenko A, Balasubramanian MK, Köster DV. Calponin-homology domain mediated bending of membrane-associated actin filaments. eLife 2021; 10:e61078. [PMID: 34269679 PMCID: PMC8315802 DOI: 10.7554/elife.61078] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Accepted: 07/15/2021] [Indexed: 11/13/2022] Open
Abstract
Actin filaments are central to numerous biological processes in all domains of life. Driven by the interplay with molecular motors, actin binding and actin modulating proteins, the actin cytoskeleton exhibits a variety of geometries. This includes structures with a curved geometry such as axon-stabilizing actin rings, actin cages around mitochondria and the cytokinetic actomyosin ring, which are generally assumed to be formed by short linear filaments held together by actin cross-linkers. However, whether individual actin filaments in these structures could be curved and how they may assume a curved geometry remains unknown. Here, we show that 'curly', a region from the IQGAP family of proteins from three different organisms, comprising the actin-binding calponin-homology domain and a C-terminal unstructured domain, stabilizes individual actin filaments in a curved geometry when anchored to lipid membranes. Although F-actin is semi-flexible with a persistence length of ~10 μm, binding of mobile curly within lipid membranes generates actin filament arcs and full rings of high curvature with radii below 1 μm. Higher rates of fully formed actin rings are observed in the presence of the actin-binding coiled-coil protein tropomyosin and when actin is directly polymerized on lipid membranes decorated with curly. Strikingly, curly induced actin filament rings contract upon the addition of muscle myosin II filaments and expression of curly in mammalian cells leads to highly curved actin structures in the cytoskeleton. Taken together, our work identifies a new mechanism to generate highly curved actin filaments, which opens a range of possibilities to control actin filament geometries, that can be used, for example, in designing synthetic cytoskeletal structures.
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Affiliation(s)
- Saravanan Palani
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
- Department of Biochemistry, Division of Biological Sciences, Indian Institute of ScienceBangaloreIndia
| | - Sayantika Ghosh
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
| | - Esther Ivorra-Molla
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
| | - Scott Clarke
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
| | - Andrejus Suchenko
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
| | - Mohan K Balasubramanian
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
| | - Darius Vasco Köster
- Centre for Mechanochemical Cell Biology and Warwick Medical School, Division of Biomedical SciencesCoventryUnited Kingdom
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8
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Magliozzi JO, Sears J, Cressey L, Brady M, Opalko HE, Kettenbach AN, Moseley JB. Fission yeast Pak1 phosphorylates anillin-like Mid1 for spatial control of cytokinesis. J Cell Biol 2021; 219:151784. [PMID: 32421151 PMCID: PMC7401808 DOI: 10.1083/jcb.201908017] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 03/09/2020] [Accepted: 04/28/2020] [Indexed: 12/17/2022] Open
Abstract
Protein kinases direct polarized growth by regulating the cytoskeleton in time and space and could play similar roles in cell division. We found that the Cdc42-activated polarity kinase Pak1 colocalizes with the assembling contractile actomyosin ring (CAR) and remains at the division site during septation. Mutations in pak1 led to defects in CAR assembly and genetic interactions with cytokinesis mutants. Through a phosphoproteomic screen, we identified novel Pak1 substrates that function in polarized growth and cytokinesis. For cytokinesis, we found that Pak1 regulates the localization of its substrates Mid1 and Cdc15 to the CAR. Mechanistically, Pak1 phosphorylates the Mid1 N-terminus to promote its association with cortical nodes that act as CAR precursors. Defects in Pak1-Mid1 signaling lead to misplaced and defective division planes, but these phenotypes can be rescued by synthetic tethering of Mid1 to cortical nodes. Our work defines a new signaling mechanism driven by a cell polarity kinase that promotes CAR assembly in the correct time and place.
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Affiliation(s)
- Joseph O Magliozzi
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH
| | - Jack Sears
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH.,Norris Cotton Cancer Center, The Geisel School of Medicine at Dartmouth, Lebanon, NH
| | - Lauren Cressey
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH.,Norris Cotton Cancer Center, The Geisel School of Medicine at Dartmouth, Lebanon, NH
| | - Marielle Brady
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH
| | - Hannah E Opalko
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH
| | - Arminja N Kettenbach
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH.,Norris Cotton Cancer Center, The Geisel School of Medicine at Dartmouth, Lebanon, NH
| | - James B Moseley
- Department of Biochemistry and Cell Biology, The Geisel School of Medicine at Dartmouth, Hanover, NH
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9
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Kamnev A, Palani S, Zambon P, Cheffings T, Burroughs N, Balasubramanian MK. Time-varying mobility and turnover of actomyosin ring components during cytokinesis in Schizosaccharomyces pombe. Mol Biol Cell 2021; 32:237-246. [PMID: 33326250 PMCID: PMC8098825 DOI: 10.1091/mbc.e20-09-0588] [Citation(s) in RCA: 6] [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: 09/15/2020] [Revised: 12/01/2020] [Accepted: 12/07/2020] [Indexed: 01/01/2023] Open
Abstract
Cytokinesis in many eukaryotes is dependent on a contractile actomyosin ring (AMR), composed of F-actin, myosin II, and other actin and myosin II regulators. Through fluorescence recovery after photobleaching experiments, many components of the AMR have been shown to be mobile and to undergo constant exchange with the cytosolic pools. However, how the mobility of its components changes at distinct stages of mitosis and cytokinesis has not been addressed. Here, we describe the mobility of eight Schizosaccharomyces pombe AMR proteins at different stages of mitosis and cytokinesis using an approach we have developed. We identified three classes of proteins, which showed 1) high (Ain1, Myo2, Myo51), 2) low (Rng2, Mid1, Myp2, Cdc12), and 3) cell cycle-dependent (Cdc15) mobile fractions. We observed that the F-BAR protein Cdc15 undergoes a 20-30% reduction in its mobile fraction after spindle breakdown and initiation of AMR contraction. Moreover, our data indicate that this change in Cdc15 mobility is dependent on the septation initiation network (SIN). Our work offers a novel strategy for estimating cell cycle-dependent mobile protein fractions in cellular structures and provides a valuable dataset, that is of interest to researchers working on cytokinesis.
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Affiliation(s)
- Anton Kamnev
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, and
| | - Saravanan Palani
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, and
| | - Paola Zambon
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, and
| | - Tom Cheffings
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, and
| | - Nigel Burroughs
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, and
- Department of Mathematics, University of Warwick, Coventry CV4 7AL, UK
| | - Mohan K. Balasubramanian
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, and
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10
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Cell cycle-dependent phosphorylation of IQGAP is involved in assembly and stability of the contractile ring in fission yeast. Biochem Biophys Res Commun 2020; 534:1026-1032. [PMID: 33131769 DOI: 10.1016/j.bbrc.2020.10.043] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2020] [Accepted: 10/19/2020] [Indexed: 11/20/2022]
Abstract
Cytokinesis is the final step in cell division and is driven by the constriction of the medial actomyosin-based contractile ring (CR) in many eukaryotic cells. In the fission yeast Schizosaccharomyces pombe, the IQGAP-like protein Rng2 is required for assembly and constriction of the CR, and specifically interacts with actin filaments (F-actin) in the CR after anaphase. However, the mechanism that timely activates Rng2 has not yet been elucidated. We herein tested the hypothesis that the cytokinetic function of Rng2 is regulated by phosphorylation by examining phenotypes of a series of non-phosphorylatable and phosphomimetic rng2 mutant strains. In phosphomimetic mutant cells, F-actin in the CR was unstable. Genetic analyses indicated that phosphorylated Rng2 was involved in CR assembly in cooperation with myosin-II, whereas the phosphomimetic mutation attenuated the localization of Rng2 to CR F-actin. The present results suggest that Rng2 is phosphorylated during CR assembly and then dephosphorylated, which enhances the interaction between Rng2 and CR F-actin to stabilize the ring, thereby ensuring secure cytokinesis.
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11
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Morita R, Nakano K, Shigeta Y, Harada R. Molecular Mechanism for the Actin-Binding Domain of α-Actinin Ain1 Elucidated by Molecular Dynamics Simulations and Mutagenesis Experiments. J Phys Chem B 2020; 124:8495-8503. [DOI: 10.1021/acs.jpcb.0c04623] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Rikuri Morita
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Kentaro Nakano
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
| | - Yasuteru Shigeta
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Ryuhei Harada
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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12
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Hill TW, Wendt KE, Jones DA, Williamson MH, Ugwu UJ, Rowland LB, Jackson-Hayes L. The Aspergillus nidulans IQGAP orthologue SepG is required for constriction of the contractile actomyosin ring. Fungal Genet Biol 2020; 144:103439. [PMID: 32768603 DOI: 10.1016/j.fgb.2020.103439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 07/14/2020] [Accepted: 07/28/2020] [Indexed: 10/23/2022]
Abstract
In this research we report that the sepG1 mutation in Aspergillus nidulans resides in gene AN9463, which is predicted to encode an IQGAP orthologue. The genetic lesion is predicted to result in a G-to-R substitution at residue 1637 of the 1737-residue protein in a highly conserved region of the RasGAP-C-terminal (RGCT) domain. When grown at restrictive temperature, strains expressing the sepGG1637R (sepG1) allele are aseptate, with reduced colony growth and aberrantly formed conidiophores. The aseptate condition can be replicated by deletion of AN9463 or by downregulating its expression via introduced promoters. The mutation does not prevent assembly of a cortical contractile actomyosin ring (CAR) at putative septation sites, but tight compaction of the rings is impaired and the rings fail to constrict. Both GFP::SepG wild type and the GFP-tagged product of the sepG1 allele localize to the CAR at both permissive and restrictive temperatures. Downregulation of myoB (encoding the A. nidulans type-II myosin heavy chain) does not prevent formation of SepG rings at septation sites, but filamentous actin is required for CAR localization of SepG and MyoB. We identify fourteen probable IQ-motifs (EF-hand protein binding sites) in the predicted SepG sequence. Two of the A. nidulans EF-hand proteins, myosin essential light chain (AnCdc4) and myosin regulatory light chain (MrlC), colocalize with SepG and MyoB at all stages of CAR formation and constriction. However, calmodulin (CamA) appears at septation sites only after the CAR has become fully compacted. When expression of sepG is downregulated, leaving MyoB as the sole IQ-motif protein in the pre-compaction CAR, both MrlC and AnCdc4 continue to associate with the forming CAR. When myoB expression is downregulated, leaving SepG as the sole IQ-motif protein in the CAR, AnCdc4 association with the forming CAR continues but MrlC fails to associate. This supports a model in which the IQ motifs of MyoB bind both MrlC and AnCdc4, while the IQ motifs of SepG bind only AnCdc4. Downregulation of either mrlC or Ancdc4 results in an aseptate phenotype, but has no effect on association of either SepG or MyoB with the CAR.
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Affiliation(s)
- Terry W Hill
- Department of Biology, Rhodes College, Memphis, TN 38112, USA; Biochemistry and Molecular Biology Program, Rhodes College, Memphis, TN 38112, USA.
| | - Kristen E Wendt
- Biochemistry and Molecular Biology Program, Rhodes College, Memphis, TN 38112, USA
| | - David A Jones
- Department of Chemistry, Rhodes College, Memphis, TN 38112, USA
| | - McLean H Williamson
- Biochemistry and Molecular Biology Program, Rhodes College, Memphis, TN 38112, USA
| | - Uchenna J Ugwu
- Division of Natural & Mathematic Sciences, LeMoyne-Owen College, Memphis, TN 38126, USA
| | - Lauren B Rowland
- Biochemistry and Molecular Biology Program, Rhodes College, Memphis, TN 38112, USA
| | - Loretta Jackson-Hayes
- Biochemistry and Molecular Biology Program, Rhodes College, Memphis, TN 38112, USA; Department of Chemistry, Rhodes College, Memphis, TN 38112, USA
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13
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The Correct Localization of Borealin in Midbody during Cytokinesis Depends on IQGAP1. BIOMED RESEARCH INTERNATIONAL 2020; 2020:6231697. [PMID: 32685508 PMCID: PMC7334785 DOI: 10.1155/2020/6231697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 05/31/2020] [Accepted: 06/08/2020] [Indexed: 11/17/2022]
Abstract
Borealin is a key component of chromosomal passenger complex, which is vital in cytokinesis. IQ domain-containing GTPase-activating protein 1 (IQGAP1) also participates in cytokinesis. The correlation between Borealin and IQGAP1 during cytokinesis is not yet clear. Here, we used mass spectrometry and endogenous coimmunoprecipitation experiments to investigate the interaction between IQGAP1 and Borealin. Results of the current study showed that Borealin interacted directly with IQGAP1 both in vitro and in vivo. Knockdown of IQGAP1 resulted in an abnormal location of Borealin in the midbody. Knocking down Borealin alone, IQGAP1 alone, or Borealin and IQGAP1 at the same time inhibited the completion of cytokinesis and formed multinucleated cells. Our results indicated that IQGAP1 interacts with Borealin during cytokinesis, and the correct localization of Borealin in the midbody during cytokinesis is determined by IQGAP1, and IQGAP1 may play an important role in regulating Borealin function in cytokinesis.
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14
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Morris Z, Sinha D, Poddar A, Morris B, Chen Q. Fission yeast TRP channel Pkd2p localizes to the cleavage furrow and regulates cell separation during cytokinesis. Mol Biol Cell 2019; 30:1791-1804. [PMID: 31116668 PMCID: PMC6727746 DOI: 10.1091/mbc.e18-04-0270] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Force plays a central role in separating daughter cells during cytokinesis, the last stage of cell division. However, the mechanism of force sensing during cytokinesis remains unknown. Here we discovered that Pkd2p, a putative force-sensing transient receptor potential channel, localizes to the cleavage furrow during cytokinesis of the fission yeast, Schizosaccharomyces pombe. Pkd2p, whose human homologues are associated with autosomal polycystic kidney disease, is an essential protein whose localization depends on the contractile ring and the secretory pathway. We identified and characterized a novel pkd2 mutant pkd2-81KD. The pkd2 mutant cells show signs of osmotic stress, including temporary shrinking, paused turnover of the cytoskeletal structures, and hyperactivated mitogen-activated protein kinase signaling. During cytokinesis, although the contractile ring constricts more rapidly in the pkd2 mutant than the wild-type cells (50% higher), the cell separation in the mutant is slower and often incomplete. These cytokinesis defects are also consistent with misregulated turgor pressure. Finally, the pkd2 mutant exhibits strong genetic interactions with two mutants of the septation initiation network pathway, a signaling cascade essential for cytokinesis. We propose that Pkd2p modulates osmotic homeostasis and is potentially a novel regulator of cytokinesis.
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Affiliation(s)
- Zachary Morris
- Department of Biological Sciences, University of Toledo, Toledo, OH 43606
| | - Debatrayee Sinha
- Department of Biological Sciences, University of Toledo, Toledo, OH 43606
| | - Abhishek Poddar
- Department of Biological Sciences, University of Toledo, Toledo, OH 43606
| | - Brittni Morris
- Department of Biological Sciences, University of Toledo, Toledo, OH 43606
| | - Qian Chen
- Department of Biological Sciences, University of Toledo, Toledo, OH 43606
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15
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Morita R, Takaine M, Numata O, Nakano K. Molecular dissection of the actin-binding ability of the fission yeast α-actinin, Ain1, in vitro and in vivo. J Biochem 2017; 162:93-102. [PMID: 28338873 DOI: 10.1093/jb/mvx008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 12/27/2016] [Indexed: 02/02/2023] Open
Abstract
A contractile ring (CR) is involved in cytokinesis in animal and yeast cells. Although several types of actin-bundling proteins associate with F-actin in the CR, their individual roles in the CR have not yet been elucidated in detail. Ain1 is the sole α-actinin homologue in the fission yeast Schizosaccharomyces pombe and specifically localizes to the CR with a high turnover rate. S. pombe cells lacking the ain1+ gene show defects in cytokinesis under stress conditions. We herein investigated the biochemical activity and cellular localization mechanisms of Ain1. Ain1 showed weaker affinity to F-actin in vitro than other actin-bundling proteins in S. pombe. We identified a mutation that presumably loosened the interaction between two calponin-homology domains constituting the single actin-binding domain (ABD) of Ain1, which strengthened the actin-binding activity of Ain1. This mutant protein induced a deformation in the ring shape of the CR. Neither a truncated protein consisting only of an N-terminal ABD nor a truncated protein lacking a C-terminal region containing an EF-hand motif localized to the CR, whereas the latter was involved in the bundling of F-actin in vitro. We herein propose detailed mechanisms for how each part of the molecule is involved in the proper cellular localization and function of Ain1.
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Affiliation(s)
- Rikuri Morita
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
| | - Masak Takaine
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
| | - Osamu Numata
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
| | - Kentaro Nakano
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
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16
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Abstract
Cytokinesis is essential for the survival of all organisms. It requires concerted functions of cell signaling, force production, exocytosis, and extracellular matrix remodeling. Due to the conservation in core components and mechanisms between fungal and animal cells, the budding yeast Saccharomyces cerevisiae has served as an attractive model for studying this fundamental process. In this review, we discuss the mechanics and regulation of distinct events of cytokinesis in budding yeast, including the assembly, constriction, and disassembly of the actomyosin ring, septum formation, abscission, and their spatiotemporal coordination. We also highlight the key concepts and questions that are common to animal and fungal cytokinesis.
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Affiliation(s)
- Yogini P Bhavsar-Jog
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Erfei Bi
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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17
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Rincon SA, Paoletti A. Molecular control of fission yeast cytokinesis. Semin Cell Dev Biol 2016; 53:28-38. [PMID: 26806637 DOI: 10.1016/j.semcdb.2016.01.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 01/06/2016] [Indexed: 12/29/2022]
Abstract
Cytokinesis gives rise to two independent daughter cells at the end of the cell division cycle. The fission yeast Schizosaccharomyces pombe has emerged as one of the most powerful systems to understand how cytokinesis is controlled molecularly. Like in most eukaryotes, fission yeast cytokinesis depends on an acto-myosin based contractile ring that assembles at the division site under the control of spatial cues that integrate information on cell geometry and the position of the mitotic apparatus. Cytokinetic events are also tightly coordinated with nuclear division by the cell cycle machinery. These spatial and temporal regulations ensure an equal cleavage of the cytoplasm and an accurate segregation of the genetic material in daughter cells. Although this model system has specificities, the basic mechanisms of contractile ring assembly and function deciphered in fission yeast are highly valuable to understand how cytokinesis is controlled in other organisms that rely on a contractile ring for cell division.
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Affiliation(s)
- Sergio A Rincon
- Institut Curie, Centre de Recherche, PSL Research University, F-75248 Paris, France; CNRS UMR144, F-75248 Paris, France
| | - Anne Paoletti
- Institut Curie, Centre de Recherche, PSL Research University, F-75248 Paris, France; CNRS UMR144, F-75248 Paris, France.
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18
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Lian ATY, Hains PG, Sarcevic B, Robinson PJ, Chircop M. IQGAP1 is associated with nuclear envelope reformation and completion of abscission. Cell Cycle 2015; 14:2058-74. [PMID: 25928398 DOI: 10.1080/15384101.2015.1044168] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The final stage of mitosis is cytokinesis, which results in 2 independent daughter cells. Cytokinesis has 2 phases: membrane ingression followed by membrane abscission. IQGAP1 is a scaffold protein that interacts with proteins implicated in mitosis, including F-actin, myosin and CaM. IQGAP1 in yeast recruits actin and myosin II filaments to the contractile ring for membrane ingression. In contrast, we show that mammalian IQGAP1 is not required for ingression, but coordinates nuclear pore complex (NPC) reassembly and completion of abscission. Depletion of IQGAP1 disrupts Nup98 and mAb414 nuclear envelope localization and delays abscission timing. IQGAP1 phosphorylation increases 15-fold upon mitotic entry at S86, S330 and T1434, with the latter site being targeted by CDK2/Cyclin A and CDK1/Cyclin A/B in vitro. Expressing the phospho-deficient mutant IQGAP1-S330A impairs NPC reassembly in cells undergoing abscission. Thus, mammalian IQGAP1 functions later in mitosis than its yeast counterpart to regulate nuclear pore assembly in a S330 phosphorylation-dependent manner during the abscission phase of cytokinesis.
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Affiliation(s)
- Audrey T Y Lian
- a Children's Medical Research Institute; The University of Sydney ; Westmead , New South Wales , Australia
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19
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Hedman AC, Smith JM, Sacks DB. The biology of IQGAP proteins: beyond the cytoskeleton. EMBO Rep 2015; 16:427-46. [PMID: 25722290 DOI: 10.15252/embr.201439834] [Citation(s) in RCA: 145] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Accepted: 01/07/2015] [Indexed: 01/02/2023] Open
Abstract
IQGAP scaffold proteins are evolutionarily conserved in eukaryotes and facilitate the formation of complexes that regulate cytoskeletal dynamics, intracellular signaling, and intercellular interactions. Fungal and mammalian IQGAPs are implicated in cytokinesis. IQGAP1, IQGAP2, and IQGAP3 have diverse roles in vertebrate physiology, operating in the kidney, nervous system, cardio-vascular system, pancreas, and lung. The functions of IQGAPs can be corrupted during oncogenesis and are usurped by microbial pathogens. Therefore, IQGAPs represent intriguing candidates for novel therapeutic agents. While modulation of the cytoskeletal architecture was initially thought to be the primary function of IQGAPs, it is now clear that they have roles beyond the cytoskeleton. This review describes contributions of IQGAPs to physiology at the organism level.
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Affiliation(s)
- Andrew C Hedman
- Department of Laboratory Medicine, National Institutes of Health, Bethesda, MD, USA
| | - Jessica M Smith
- Department of Laboratory Medicine, National Institutes of Health, Bethesda, MD, USA
| | - David B Sacks
- Department of Laboratory Medicine, National Institutes of Health, Bethesda, MD, USA
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20
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IQ-motif selectivity in human IQGAP2 and IQGAP3: binding of calmodulin and myosin essential light chain. Biosci Rep 2015; 31:371-9. [PMID: 21299499 PMCID: PMC3263943 DOI: 10.1042/bsr20100123] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The IQGAP [IQ-motif-containing GAP (GTPase-activating protein)] family members are eukaryotic proteins that act at the interface between cellular signalling and the cytoskeleton. As such they collect numerous inputs from a variety of signalling pathways. A key binding partner is the calcium-sensing protein CaM (calmodulin). This protein binds mainly through a series of IQ-motifs which are located towards the middle of the primary sequence of the IQGAPs. In some IQGAPs, these motifs also provide binding sites for CaM-like proteins such as myosin essential light chain and S100B. Using synthetic peptides and native gel electrophoresis, the binding properties of the IQ-motifs from human IQGAP2 and IQGAP3 have been mapped. The second and third IQ-motifs in IQGAP2 and all four of the IQ-motifs of IQGAP3 interacted with CaM in the presence of calcium ions. However, there were differences in the type of interaction: while some IQ-motifs were able to form complexes with CaM which were stable under the conditions of the experiment, others formed more transient interactions. The first IQ-motifs from IQGAP2 and IQGAP3 formed transient interactions with CaM in the absence of calcium and the first motif from IQGAP3 formed a transient interaction with the myosin essential light chain Mlc1sa. None of these IQ-motifs interacted with S100B. Molecular modelling suggested that all of the IQ-motifs, except the first one from IQGAP2 formed α-helices in solution. These results extend our knowledge of the selectivity of IQ-motifs for CaM and related proteins.
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21
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Adachi M, Kawasaki A, Nojima H, Nishida E, Tsukita S. Involvement of IQGAP family proteins in the regulation of mammalian cell cytokinesis. Genes Cells 2014; 19:803-20. [DOI: 10.1111/gtc.12179] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Accepted: 08/08/2014] [Indexed: 02/01/2023]
Affiliation(s)
- Makoto Adachi
- Department of Cell Biology; Graduate School of Medicine; Kyoto University; Sakyo-ku Kyoto 606-8501 Japan
| | - Asami Kawasaki
- Laboratory of Biological Science; Graduate School of Frontier Biosciences and Graduate School of Medicine; Osaka University; 1-3 Yamadaoka, Suita Osaka 565-0871 Japan
- Division of Molecular and Cellular Biology; Graduate School of Medical and Dental Sciences; Niigata University; Chuo-ku Niigata 951-8510 Japan
| | - Hisashi Nojima
- Laboratory of Biological Science; Graduate School of Frontier Biosciences and Graduate School of Medicine; Osaka University; 1-3 Yamadaoka, Suita Osaka 565-0871 Japan
- MRC National Institute for Medical Research; London NW7 1AA UK
| | - Eisuke Nishida
- Department of Cell and Developmental Biology; Graduate School of Biostudies; Kyoto University; Sakyo-ku Kyoto 606-8502 Japan
| | - Sachiko Tsukita
- Laboratory of Biological Science; Graduate School of Frontier Biosciences and Graduate School of Medicine; Osaka University; 1-3 Yamadaoka, Suita Osaka 565-0871 Japan
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22
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Tao EY, Calvert M, Balasubramanian MK. Rewiring Mid1p-independent medial division in fission yeast. Curr Biol 2014; 24:2181-2188. [PMID: 25176634 DOI: 10.1016/j.cub.2014.07.074] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Revised: 06/27/2014] [Accepted: 07/25/2014] [Indexed: 10/24/2022]
Abstract
Correct positioning of the cell division machinery is key to genome stability. Schizosaccharomyces pombe is an attractive organism to study cytokinesis as it, like higher eukaryotes, divides using a contractile actomyosin ring. In S. pombe, many actomyosin ring components assemble at the medial cortex into node-like structures before coalescing into a ring [1, 2]. Assembly of cytokinetic nodes requires Mid1p, which recruits IQGAP-related Rng2p to the division site, after which other node components accumulate at the division site in a characteristic sequence [3-6]. How cytokinetic nodes assemble, whether the order of assembly of ring components is important, and whether Mid1p solely participates in ring positioning are poorly understood. Here, we show that synthetic targeting of IQGAP-related Rng2p, formin-Cdc12p, and myosin II (Myo2p) restores medial division in mid1 mutants, suggesting that ring proteins need not assemble at the division site in an invariant order. Unlike in wild-type cells, actomyosin rings in cells rewired to divide medially in the absence of Mid1p assemble late in anaphase. Furthermore, the rewiring process affects the ability of the actomyosin ring to track the nucleus upon perturbation of nuclear position. Our work reveals the power of synthetic rewiring studies in deciphering roles performed by multifunctional proteins.
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Affiliation(s)
- Evelyn Yaqiong Tao
- Department of Biological Sciences, The National University of Singapore, 1 Research Link, Singapore 117604, Republic of Singapore
| | - Meredith Calvert
- Temasek Life Sciences Laboratory, 1 Research Link, Singapore 117604, Republic of Singapore
| | - Mohan K Balasubramanian
- Department of Biological Sciences, The National University of Singapore, 1 Research Link, Singapore 117604, Republic of Singapore; Temasek Life Sciences Laboratory, 1 Research Link, Singapore 117604, Republic of Singapore; Mechanobiology Institute, The National University of Singapore, 1 Research Link, Singapore 117604, Republic of Singapore; Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
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23
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Takaine M, Imada K, Numata O, Nakamura T, Nakano K. The meiosis-specific nuclear passenger protein is required for proper assembly of forespore membrane in fission yeast. J Cell Sci 2014; 127:4429-42. [PMID: 25146394 DOI: 10.1242/jcs.151738] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sporulation, gametogenesis in yeast, consists of meiotic nuclear division and spore morphogenesis. In the fission yeast Schizosaccharomyces pombe, the four haploid nuclei produced after meiosis II are encapsulated by the forespore membrane (FSM), which is newly synthesized from spindle pole bodies (SPBs) in the cytoplasm of the mother cell as spore precursors. Although the coordination between meiosis and FSM assembly is vital for proper sporulation, the underlying mechanism remains unclear. In the present study, we identified a new meiosis-specific protein Npg1, and found that it was involved in the efficient formation of spores and spore viability. The accumulation and organization of the FSM was compromised in npg1-null cells, leading to the error-prone envelopment of nuclei. Npg1 was first seen as internuclear dots and translocated to the SPBs before the FSM assembled. Genetic analysis revealed that Npg1 worked in conjunction with the FSM proteins Spo3 and Meu14. These results suggest a possible signaling link from the nucleus to the meiotic SPBs in order to associate the onset of FSM assembly with meiosis II, which ensures the successful partitioning of gametic nuclei.
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Affiliation(s)
- Masak Takaine
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Kazuki Imada
- Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Osamu Numata
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Taro Nakamura
- Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Kentaro Nakano
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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24
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Mishra M, Huang J, Balasubramanian MK. The yeast actin cytoskeleton. FEMS Microbiol Rev 2014; 38:213-27. [PMID: 24467403 DOI: 10.1111/1574-6976.12064] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 01/18/2014] [Accepted: 01/20/2014] [Indexed: 11/29/2022] Open
Abstract
The actin cytoskeleton is a complex network of dynamic polymers, which plays an important role in various fundamental cellular processes, including maintenance of cell shape, polarity, cell division, cell migration, endocytosis, vesicular trafficking, and mechanosensation. Precise spatiotemporal assembly and disassembly of actin structures is regulated by the coordinated activity of about 100 highly conserved accessory proteins, which nucleate, elongate, cross-link, and sever actin filaments. Both in vivo studies in a wide range of organisms from yeast to metazoans and in vitro studies of purified proteins have helped shape the current understanding of actin dynamics and function. Molecular genetics, genome-wide functional analysis, sophisticated real-time imaging, and ultrastructural studies in concert with biochemical analysis have made yeast an attractive model to understand the actin cytoskeleton, its molecular dynamics, and physiological function. Studies of the yeast actin cytoskeleton have contributed substantially in defining the universal mechanism regulating actin assembly and disassembly in eukaryotes. Here, we review some of the important insights generated by the study of actin cytoskeleton in two important yeast models the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe.
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Affiliation(s)
- Mithilesh Mishra
- Temasek Life Sciences Laboratory, National University of Singapore, Singapore
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25
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Takaine M, Numata O, Nakano K. Fission yeast IQGAP maintains F-actin-independent localization of myosin-II in the contractile ring. Genes Cells 2013; 19:161-76. [DOI: 10.1111/gtc.12120] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Accepted: 11/02/2013] [Indexed: 11/29/2022]
Affiliation(s)
- Masak Takaine
- Department of Biological Sciences; Graduate School of Life and Environmental Sciences; University of Tsukuba; 1-1-1 Tennohdai Tsukuba Ibaraki 305-8577 Japan
| | - Osamu Numata
- Department of Biological Sciences; Graduate School of Life and Environmental Sciences; University of Tsukuba; 1-1-1 Tennohdai Tsukuba Ibaraki 305-8577 Japan
| | - Kentaro Nakano
- Department of Biological Sciences; Graduate School of Life and Environmental Sciences; University of Tsukuba; 1-1-1 Tennohdai Tsukuba Ibaraki 305-8577 Japan
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26
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Zhu YH, Ye Y, Wu Z, Wu JQ. Cooperation between Rho-GEF Gef2 and its binding partner Nod1 in the regulation of fission yeast cytokinesis. Mol Biol Cell 2013; 24:3187-204. [PMID: 23966468 PMCID: PMC3806657 DOI: 10.1091/mbc.e13-06-0301] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Previous results showed that putative Rho-GEF Gef2 regulates division-site positioning during early cytokinesis in fission yeast. Here Nod1 is identified as a binding partner of Gef2. The two proteins form a complex to regulate division-site positioning and contractile-ring maintenance. In addition, Gef2 binds to GTPases Rho1, Rho4, and Rho5 in vitro. Cytokinesis is the last step of the cell-division cycle, which requires precise spatial and temporal regulation to ensure genetic stability. Rho guanine nucleotide exchange factors (Rho GEFs) and Rho GTPases are among the key regulators of cytokinesis. We previously found that putative Rho-GEF Gef2 coordinates with Polo kinase Plo1 to control the medial cortical localization of anillin-like protein Mid1 in fission yeast. Here we show that an adaptor protein, Nod1, colocalizes with Gef2 in the contractile ring and its precursor cortical nodes. Like gef2∆, nod1∆ has strong genetic interactions with various cytokinesis mutants involved in division-site positioning, suggesting a role of Nod1 in early cytokinesis. We find that Nod1 and Gef2 interact through the C-termini, which is important for their localization. The contractile-ring localization of Nod1 and Gef2 also depends on the interaction between Nod1 and the F-BAR protein Cdc15, where the Nod1/Gef2 complex plays a role in contractile-ring maintenance and affects the septation initiation network. Moreover, Gef2 binds to purified GTPases Rho1, Rho4, and Rho5 in vitro. Taken together, our data indicate that Nod1 and Gef2 function cooperatively in a protein complex to regulate fission yeast cytokinesis.
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Affiliation(s)
- Yi-Hua Zhu
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210 Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, OH 43210 Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210
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27
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Jacquemet G, Morgan MR, Byron A, Humphries JD, Choi CK, Chen CS, Caswell PT, Humphries MJ. Rac1 is deactivated at integrin activation sites through an IQGAP1-filamin-A-RacGAP1 pathway. J Cell Sci 2013; 126:4121-35. [PMID: 23843620 DOI: 10.1242/jcs.121988] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Cell migration makes a fundamental contribution to both normal physiology and disease pathogenesis. Integrin engagement with extracellular ligands spatially controls, via the cyclical activation and deactivation of the small GTPase Rac1, the dynamic membrane protrusion and cytoskeletal reorganization events that are required for directional migration. Although the pathways that control integrin-mediated Rac1 activation are reasonably well defined, the mechanisms that are responsible for switching off activity are poorly understood. Here, proteomic analysis of activated integrin-associated complexes suggests filamin-A and IQ-motif-containing GTPase-activating protein 1 (IQGAP1) as candidates that link β1 integrin to Rac1. siRNA-mediated knockdown of either filamin-A or IQGAP1 induced high, dysregulated Rac1 activity during cell spreading on fibronectin. Using immunoprecipitation and immunocytochemistry, filamin-A and IQGAP1 were shown to be part of a complex that is recruited to active β1 integrin. Mass spectrometric analysis of individual filamin-A, IQGAP1 and Rac1 pull-downs and biochemical analysis, identified RacGAP1 as a novel IQGAP1 binding partner. Further immunoprecipitation and immunocytochemistry analyses demonstrated that RacGAP1 is recruited to IQGAP1 and active β1 integrin, and that suppression of RacGAP1 expression triggered elevated Rac1 activity during spreading on fibronectin. Consistent with these findings, reduced expression of filamin-A, IQGAP1 or RacGAP1 triggered unconstrained membrane protrusion and disrupted directional cell migration on fibrillar extracellular matrices. These findings suggest a model whereby integrin engagement, followed by filamin-A, IQGAP1 and RacGAP1 recruitment, deactivates Rac1 to constrain its activity spatially and thereby coordinate directional cell migration.
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Affiliation(s)
- Guillaume Jacquemet
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
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28
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In vitro contraction of cytokinetic ring depends on myosin II but not on actin dynamics. Nat Cell Biol 2013; 15:853-9. [PMID: 23770677 DOI: 10.1038/ncb2781] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 05/09/2013] [Indexed: 01/17/2023]
Abstract
Cytokinesis in many eukaryotes involves the contraction of an actomyosin-based contractile ring. However, the detailed mechanism of contractile ring contraction is not fully understood. Here, we establish an experimental system to study contraction of the ring to completion in vitro. We show that the contractile ring of permeabilized fission yeast cells undergoes rapid contraction in an ATP- and myosin-II-dependent manner in the absence of other cytoplasmic constituents. Surprisingly, neither actin polymerization nor its disassembly is required for contraction of the contractile ring, although addition of exogenous actin-crosslinking proteins blocks ring contraction. Using contractile rings generated from fission yeast cytokinesis mutants, we show that not all proteins required for assembly of the ring are required for its contraction in vitro. Our work provides the beginnings of the definition of a minimal contraction-competent cytokinetic ring apparatus.
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29
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Tebbs IR, Pollard TD. Separate roles of IQGAP Rng2p in forming and constricting the Schizosaccharomyces pombe cytokinetic contractile ring. Mol Biol Cell 2013; 24:1904-17. [PMID: 23615450 PMCID: PMC3681696 DOI: 10.1091/mbc.e12-10-0775] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Rng2p is required for both the normal process of contractile ring formation from precursor nodes and an alternative mechanism by which rings form from strands of actin filaments, as well as for ring constriction. Systematic analysis of domain deletion mutants establishes how the four domains of Rng2p contribute to cytokinesis. Eukaryotic cells require IQGAP family multidomain adapter proteins for cytokinesis, but many questions remain about how IQGAPs contribute to the process. Here we show that fission yeast IQGAP Rng2p is required for both the normal process of contractile ring formation from precursor nodes and an alternative mechanism by which rings form from strands of actin filaments. Our work adds to previous studies suggesting a role for Rng2p in node and ring formation. We demonstrate that Rng2p is also required for normal ring constriction and septum formation. Systematic analysis of domain-deletion mutants established how the four domains of Rng2p contribute to cytokinesis. Contrary to a previous report, the actin-binding calponin homology domain of Rng2p is not required for viability, ring formation, or ring constriction. The IQ motifs are not required for ring formation but are important for ring constriction and septum formation. The GTPase-activating protein (GAP)–related domain is required for node-based ring formation. The Rng2p C-terminal domain is the only domain essential for viability. Our studies identified several distinct functions of Rng2 at multiple stages of cytokinesis.
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Affiliation(s)
- Irene R Tebbs
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103, USA
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30
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Lee IJ, Coffman VC, Wu JQ. Contractile-ring assembly in fission yeast cytokinesis: Recent advances and new perspectives. Cytoskeleton (Hoboken) 2012; 69:751-63. [PMID: 22887981 DOI: 10.1002/cm.21052] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 07/16/2012] [Indexed: 11/07/2022]
Abstract
The fission yeast Schizosaccharomyces pombe is an excellent model organism to study cytokinesis. Here, we review recent advances on contractile-ring assembly in fission yeast. First, we summarize the assembly of cytokinesis nodes, the precursors of a normal contractile ring. IQGAP Rng2 and myosin essential light chain Cdc4 are recruited by the anillin-like protein Mid1, followed by the addition of other cytokinesis node proteins. Mid1 localization on the plasma membrane is stabilized by interphase node proteins. Second, we discuss proteins and processes that contribute to the search, capture, pull, and release mechanism of contractile-ring assembly. Actin filaments nucleated by formin Cdc12, the motor activity of myosin-II, the stiffness of the actin network, and severing of actin filaments by cofilin all play essential roles in contractile-ring assembly. Finally, we discuss the Mid1-independent pathway for ring assembly, and the possible mechanisms underlying the ring maturation and constriction. Collectively, we provide an overview of the current understanding of contractile-ring assembly and uncover future directions in studying cytokinesis in fission yeast.
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Affiliation(s)
- I-Ju Lee
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, USA
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31
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Rincon SA, Paoletti A. Mid1/anillin and the spatial regulation of cytokinesis in fission yeast. Cytoskeleton (Hoboken) 2012; 69:764-77. [DOI: 10.1002/cm.21056] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Revised: 07/13/2012] [Accepted: 07/20/2012] [Indexed: 12/20/2022]
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32
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Raudaskoski M, Kothe E, Fowler TJ, Jung EM, Horton JS. Ras and Rho small G proteins: insights from the Schizophyllum commune genome sequence and comparisons to other fungi. Biotechnol Genet Eng Rev 2012; 28:61-100. [PMID: 22616482 DOI: 10.5661/bger-28-61] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Unlike in animal cells and yeasts, the Ras and Rho small G proteins and their regulators have not received extensive research attention in the case of the filamentous fungi. In an effort to begin to rectify this deficiency, the genome sequence of the basidiomycete mushroom Schizophyllum commune was searched for all known components of the Ras and Rho signalling pathways. The results of this study should provide an impetus for further detailed investigations into their role in polarized hyphal growth, sexual reproduction and fruiting body development. These processes have long been the targets for genetic and cell biological research in this fungus.
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Affiliation(s)
- Marjatta Raudaskoski
- Department of Biology, University of Turku, Biocity A, Tykistökatu 6A, FI-20520 Turku, Finland
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33
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Hsp90 interaction with Cdc2 and Plo1 kinases contributes to actomyosin ring condensation in fission yeast. Curr Genet 2012; 58:191-203. [DOI: 10.1007/s00294-012-0376-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 04/02/2012] [Accepted: 04/13/2012] [Indexed: 12/13/2022]
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34
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IQGAP Family Members in Yeast, Dictyostelium, and Mammalian Cells. Int J Cell Biol 2012; 2012:894817. [PMID: 22505937 PMCID: PMC3296274 DOI: 10.1155/2012/894817] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Revised: 10/06/2011] [Accepted: 10/23/2011] [Indexed: 01/04/2023] Open
Abstract
IQGAPs are a family of scaffolding proteins with multiple domains, named for the IQ motifs and GTPase activating protein (GAP) related domains. Despite their GAP homology, IQGAP proteins act as effectors for GTP-bound GTPases of the Ras superfamily and do not stimulate GTP hydrolysis. IQGAPs are found in eukaryotic cells from yeast to human, and localize to actin-containing structures such as lamellipodia, membrane ruffles, cell-cell adhesions, phagocytic cups, and the actomyosin ring formed during cytokinesis. Mammalian IQGAPs also act as scaffolds for signaling pathways. IQGAPs perform their myriad functions through association with a large number of proteins including filamentous actin (F-actin), GTPases, calcium-binding proteins, microtubule binding proteins, kinases, and receptors. The focus of this paper is on recent studies describing new binding partners, mechanisms of regulation, and biochemical and physiological functions of IQGAPs in yeast, amoeba, and mammalian cells.
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35
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Calvert MEK, Wright GD, Leong FY, Chiam KH, Chen Y, Jedd G, Balasubramanian MK. Myosin concentration underlies cell size-dependent scalability of actomyosin ring constriction. ACTA ACUST UNITED AC 2012; 195:799-813. [PMID: 22123864 PMCID: PMC3257563 DOI: 10.1083/jcb.201101055] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The rate of actomyosin ring constriction in cells of different sizes correlates with myosin motor concentration in Neurospora crassa cells, leading to increased division rates in larger cells during cytokinesis. In eukaryotes, cytokinesis is accomplished by an actomyosin-based contractile ring. Although in Caenorhabditis elegans embryos larger cells divide at a faster rate than smaller cells, it remains unknown whether a similar mode of scalability operates in other cells. We investigated cytokinesis in the filamentous fungus Neurospora crassa, which exhibits a wide range of hyphal circumferences. We found that N. crassa cells divide using an actomyosin ring and larger rings constricted faster than smaller rings. However, unlike in C. elegans, the total amount of myosin remained constant throughout constriction, and there was a size-dependent increase in the starting concentration of myosin in the ring. We predict that the increased number of ring-associated myosin motors in larger rings leads to the increased constriction rate. Accordingly, reduction or inhibition of ring-associated myosin slows down the rate of constriction. Because the mechanical characteristics of contractile rings are conserved, we predict that these findings will be relevant to actomyosin ring constriction in other cell types.
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Affiliation(s)
- Meredith E K Calvert
- Temasek Life Sciences Laboratory, The National University of Singapore, Singapore 117604.
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36
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Yan H, Balasubramanian MK. A Meiotic Actin Ring (MeiAR) Essential for Proper Sporulation in Fission Yeast. J Cell Sci 2012. [DOI: 10.1242/jcs.jcs091561] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Sporulation is a unique form of cytokinesis that occurs following meiosis II in many yeasts, during which four daughter cells (spores) are generated within a single mother cell. Here we characterize the role of F-actin in the process of sporulation in the fission yeast Schizosaccharomyces pombe. As shown previously, we find that F-actin assembles into 4 ring structures per ascus, referred to as the MeiAR (meiotic actin ring). The actin nucleators Arp2/3 and formin-For3 assemble into ring structures that overlap with Meu14, a protein known to assemble into the so-called leading edge, a ring structure that is known to guide forespore membrane assembly. Interestingly, F-actin makes rings that occupy a larger region behind the leading edge ring. Time-lapse microscopy showed that the MeiAR assembles near the spindle pole bodies and undergoes an expansion in diameter during the early stages of meiosis II, followed by closure in later stages of meiosis II. MeiAR closure completes the process of forespore membrane assembly. Loss of MeiAR leads to excessive assembly of forespore membranes with a deformed appearance. The rate of closure of the MeiAR is dictated by the function of the Septation Initiation Network (SIN). We conclude that the MeiAR ensures proper targeting of the membrane biogenesis machinery to the leading edge, thereby ensuring the formation of spherically shaped spores.
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37
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Pelikan-Conchaudron A, Le Clainche C, Didry D, Carlier MF. The IQGAP1 protein is a calmodulin-regulated barbed end capper of actin filaments: possible implications in its function in cell migration. J Biol Chem 2011; 286:35119-28. [PMID: 21730051 DOI: 10.1074/jbc.m111.258772] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
IQGAP1 is a large modular protein that displays multiple partnership and is thought to act as a scaffold in coupling cell signaling to the actin and microtubule cytoskeletons in cell migration, adhesion, and cytokinesis. However the molecular mechanisms underlying the activities of IQGAP1 are poorly understood in part because of its large size, poor solubility and lack of functional assays to challenge biochemical properties in various contexts. We have purified bacterially expressed recombinant human IQGAP1. The protein binds Cdc42, Rac1, and the CRIB domain of N-WASP in a calmodulin-sensitive fashion. We further show that in addition to bundling of filaments via a single N-terminal calponin-homology domain, IQGAP1 actually regulates actin assembly. It caps barbed ends, with a higher affinity for ADP-bound terminal subunits (K(B) = 4 nM). The barbed end capping activity is inhibited by calmodulin, consistent with calmodulin binding to IQGAP1 with a K(C) of 40 nm, both in the absence and presence of Ca(2+) ions. The barbed end capping activity resides in the C-terminal half of IQGAP1. It is possible that the capping activity of IQGAP1 accounts for its stimulation of cell migration. We further find that bacterially expressed recombinant IQGAP1 fragments easily co-purify with nucleic acids that turn out to activate N-WASP protein to branch filaments with Arp2/3 complex. The present results open perspectives for tackling the function of IQGAP1 in more complex reconstituted systems.
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Affiliation(s)
- Andrea Pelikan-Conchaudron
- Cytoskeleton Dynamics and Motility group, UPR 3289, Laboratoire d'Enzymologie et Biochimie Structurale, CNRS, 91198 Gif-sur-Yvette, France
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38
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Sammons MR, James ML, Clayton JE, Sladewski TE, Sirotkin V, Lord M. A calmodulin-related light chain from fission yeast that functions with myosin-I and PI 4-kinase. J Cell Sci 2011; 124:2466-77. [PMID: 21693583 DOI: 10.1242/jcs.067850] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Fission yeast myosin-I (Myo1p) not only associates with calmodulin, but also employs a second light chain called Cam2p. cam2Δ cells exhibit defects in cell polarity and growth consistent with a loss of Myo1p function. Loss of Cam2p leads to a reduction in Myo1p levels at endocytic patches and a 50% drop in the rates of Myo1p-driven actin filament motility. Thus, Cam2p plays a significant role in Myo1p function. However, further studies indicated the existence of an additional Cam2p-binding partner. Cam2p was still present at cortical patches in myo1Δ cells (or in myo1-IQ2 mutants, which lack an intact Cam2p-binding motif), whereas a cam2 null (cam2Δ) suppressed cytokinesis defects of an essential light chain (ELC) mutant known to be impaired in binding to PI 4-kinase (Pik1p). Binding studies revealed that Cam2p and the ELC compete for Pik1p. Cortical localization of Cam2p in the myo1Δ background relied on its association with Pik1p, whereas overexpression studies indicated that Cam2p, in turn, contributes to Pik1p function. The fact that the Myo1p-associated defects of a cam2Δ mutant are more potent than those of a myo1-IQ2 mutant suggests that myosin light chains can contribute to actomyosin function both directly and indirectly (via phospholipid synthesis at sites of polarized growth).
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Affiliation(s)
- Matthew R Sammons
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA.
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39
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Almonacid M, Celton-Morizur S, Jakubowski JL, Dingli F, Loew D, Mayeux A, Chen JS, Gould KL, Clifford DM, Paoletti A. Temporal control of contractile ring assembly by Plo1 regulation of myosin II recruitment by Mid1/anillin. Curr Biol 2011; 21:473-9. [PMID: 21376600 DOI: 10.1016/j.cub.2011.02.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 12/23/2010] [Accepted: 02/01/2011] [Indexed: 11/26/2022]
Abstract
In eukaryotes, cytokinesis generally involves an actomyosin ring, the contraction of which promotes daughter cell segregation. Assembly of the contractile ring is tightly controlled in space and time. In the fission yeast, contractile ring components are first organized by the anillin-like protein Mid1 into medial cortical nodes. These nodes then coalesce laterally into a functional contractile ring. Although Mid1 is present at the medial cortex throughout G2, recruitment of contractile ring components to nodes starts only at mitotic onset, indicating that this event is cell-cycle regulated. Polo kinases are key temporal coordinators of mitosis and cytokinesis, and the Polo-like kinase Plo1 is known to activate Mid1 nuclear export at mitotic onset, coupling division plane specification to nuclear position. Here we provide evidence that Plo1 also triggers the recruitment of contractile ring components into medial cortical nodes. Plo1 binds at least two independent sites on Mid1, including a consensus site phosphorylated by Cdc2. Plo1 phosphorylates several residues within the first 100 amino acids of Mid1, which directly interact with the IQGAP Rng2, and influences the timing of myosin II recruitment. Plo1 thereby facilitates contractile ring assembly at mitotic onset.
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40
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Padmanabhan A, Bakka K, Sevugan M, Naqvi N, D'souza V, Tang X, Mishra M, Balasubramanian M. IQGAP-Related Rng2p Organizes Cortical Nodes and Ensures Position of Cell Division in Fission Yeast. Curr Biol 2011; 21:467-72. [DOI: 10.1016/j.cub.2011.01.059] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Revised: 12/22/2010] [Accepted: 01/24/2011] [Indexed: 12/01/2022]
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41
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Goyal A, Takaine M, Simanis V, Nakano K. Dividing the spoils of growth and the cell cycle: The fission yeast as a model for the study of cytokinesis. Cytoskeleton (Hoboken) 2011; 68:69-88. [PMID: 21246752 PMCID: PMC3044818 DOI: 10.1002/cm.20500] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Revised: 12/15/2010] [Accepted: 12/20/2010] [Indexed: 12/12/2022]
Abstract
Cytokinesis is the final stage of the cell cycle, and ensures completion of both genome segregation and organelle distribution to the daughter cells. Cytokinesis requires the cell to solve a spatial problem (to divide in the correct place, orthogonally to the plane of chromosome segregation) and a temporal problem (to coordinate cytokinesis with mitosis). Defects in the spatiotemporal control of cytokinesis may cause cell death, or increase the risk of tumor formation [Fujiwara et al., 2005 (Fujiwara T, Bandi M, Nitta M, Ivanova EV, Bronson RT, Pellman D. 2005. Cytokinesis failure generating tetraploids promotes tumorigenesis in p53-null cells. Nature 437:1043–1047); reviewed by Ganem et al., 2007 (Ganem NJ, Storchova Z, Pellman D. 2007. Tetraploidy, aneuploidy and cancer. Curr Opin Genet Dev 17:157–162.)]. Asymmetric cytokinesis, which permits the generation of two daughter cells that differ in their shape, size and properties, is important both during development, and for cellular homeostasis in multicellular organisms [reviewed by Li, 2007 (Li R. 2007. Cytokinesis in development and disease: variations on a common theme. Cell Mol Life Sci 64:3044–3058)]. The principal focus of this review will be the mechanisms of cytokinesis in the mitotic cycle of the yeast Schizosaccharomyces pombe. This simple model has contributed significantly to our understanding of how the cell cycle is regulated, and serves as an excellent model for studying aspects of cytokinesis. Here we will discuss the state of our knowledge of how the contractile ring is assembled and disassembled, how it contracts, and what we know of the regulatory mechanisms that control these events and assure their coordination with chromosome segregation.
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Affiliation(s)
- Anupama Goyal
- EPFL SV ISREC UPSIMSV2.1830, Station 19, CH 1015 Lausanne, Switzerland
| | - Masak Takaine
- Structural Biosciences, Graduate School of Environmental and Life Sciences, University of Tsukuba1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Viesturs Simanis
- EPFL SV ISREC UPSIMSV2.1830, Station 19, CH 1015 Lausanne, Switzerland
| | - Kentaro Nakano
- Structural Biosciences, Graduate School of Environmental and Life Sciences, University of Tsukuba1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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42
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Fang X, Luo J, Nishihama R, Wloka C, Dravis C, Travaglia M, Iwase M, Vallen EA, Bi E. Biphasic targeting and cleavage furrow ingression directed by the tail of a myosin II. J Cell Biol 2010; 191:1333-50. [PMID: 21173112 PMCID: PMC3010076 DOI: 10.1083/jcb.201005134] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Accepted: 11/29/2010] [Indexed: 02/07/2023] Open
Abstract
Cytokinesis in animal and fungal cells utilizes a contractile actomyosin ring (AMR). However, how myosin II is targeted to the division site and promotes AMR assembly, and how the AMR coordinates with membrane trafficking during cytokinesis, remains poorly understood. Here we show that Myo1 is a two-headed myosin II in Saccharomyces cerevisiae, and that Myo1 localizes to the division site via two distinct targeting signals in its tail that act sequentially during the cell cycle. Before cytokinesis, Myo1 localization depends on the septin-binding protein Bni5. During cytokinesis, Myo1 localization depends on the IQGAP Iqg1. We also show that the Myo1 tail is sufficient for promoting the assembly of a "headless" AMR, which guides membrane deposition and extracellular matrix remodeling at the division site. Our study establishes a biphasic targeting mechanism for myosin II and highlights an underappreciated role of the AMR in cytokinesis beyond force generation.
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Affiliation(s)
- Xiaodong Fang
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Jianying Luo
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Ryuichi Nishihama
- Department of Genetics, Stanford University of School of Medicine, Stanford, CA 94305
| | - Carsten Wloka
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
- Department of Biology, Chemistry and Pharmacy, Free University of Berlin, D-14195 Berlin, Germany
| | - Christopher Dravis
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Mirko Travaglia
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Masayuki Iwase
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | | | - Erfei Bi
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
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43
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Three's company: the fission yeast actin cytoskeleton. Trends Cell Biol 2010; 21:177-87. [PMID: 21145239 DOI: 10.1016/j.tcb.2010.11.001] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2010] [Revised: 10/22/2010] [Accepted: 11/04/2010] [Indexed: 11/20/2022]
Abstract
How the actin cytoskeleton assembles into different structures to drive diverse cellular processes is a fundamental cell biological question. In addition to orchestrating the appropriate combination of regulators and actin-binding proteins, different actin-based structures must insulate themselves from one another to maintain specificity within a crowded cytoplasm. Actin specification is particularly challenging in complex eukaryotes where a multitude of protein isoforms and actin structures operate within the same cell. Fission yeast Schizosaccharomyces pombe possesses a single actin isoform that functions in three distinct structures throughout the cell cycle. In this review we explore recent studies in fission yeast that help unravel how different actin structures operate in cells.
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44
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Cooperation between the septins and the actomyosin ring and role of a cell-integrity pathway during cell division in fission yeast. Genetics 2010; 186:897-915. [PMID: 20739711 DOI: 10.1534/genetics.110.119842] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
A major question about cytokinesis concerns the role of the septin proteins, which localize to the division site in all animal and fungal cells but are essential for cytokinesis only in some cell types. For example, in Schizosaccharomyces pombe, four septins localize to the division site, but deletion of the four genes produces only a modest delay in cell separation. To ask if the S. pombe septins function redundantly in cytokinesis, we conducted a synthetic-lethal screen in a septin-deficient strain and identified seven mutations. One mutation affects Cdc4, a myosin light chain that is an essential component of the cytokinetic actomyosin ring. Five others cause frequent cell lysis during cell separation and map to two loci. These mutations and their dosage suppressors define a signaling pathway (including Rho1 and a novel arrestin) for repairing cell-wall damage. The seventh mutation affects the poorly understood RNA-binding protein Scw1 and severely delays cell separation when combined either with a septin mutation or with a mutation affecting the septin-interacting, anillin-like protein Mid2, suggesting that Scw1 functions in a pathway parallel to that of the septins. Taken together, our results suggest that the S. pombe septins participate redundantly in one or more pathways that cooperate with the actomyosin ring during cytokinesis and that a septin defect causes septum defects that can be repaired effectively only when the cell-integrity pathway is intact.
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45
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Lee S, Shen Z, Robinson DN, Briggs S, Firtel RA. Involvement of the cytoskeleton in controlling leading-edge function during chemotaxis. Mol Biol Cell 2010; 21:1810-24. [PMID: 20375144 PMCID: PMC2877640 DOI: 10.1091/mbc.e10-01-0009] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Cells activate signaling pathways at the site closest to the chemoattractant source that lead to pseudopod formation and directional movement up the gradient. We demonstrate that cytoskeletal components required for cortical tension, including MyoII and IQGAP/cortexillins help regulate the level and timing of leading-edge pathways. In response to directional stimulation by a chemoattractant, cells rapidly activate a series of signaling pathways at the site closest to the chemoattractant source that leads to F-actin polymerization, pseudopod formation, and directional movement up the gradient. Ras proteins are major regulators of chemotaxis in Dictyostelium; they are activated at the leading edge, are required for chemoattractant-mediated activation of PI3K and TORC2, and are one of the most rapid responders, with activity peaking at ∼3 s after stimulation. We demonstrate that in myosin II (MyoII) null cells, Ras activation is highly extended and is not restricted to the site closest to the chemoattractant source. This causes elevated, extended, and spatially misregulated activation of PI3K and TORC2 and their effectors Akt/PKB and PKBR1, as well as elevated F-actin polymerization. We further demonstrate that disruption of specific IQGAP/cortexillin complexes, which also regulate cortical mechanics, causes extended activation of PI3K and Akt/PKB but not Ras activation. Our findings suggest that MyoII and IQGAP/cortexillin play key roles in spatially and temporally regulating leading-edge activity and, through this, the ability of cells to restrict the site of pseudopod formation.
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Affiliation(s)
- Susan Lee
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093-0380, USA
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Coffman VC, Nile AH, Lee IJ, Liu H, Wu JQ. Roles of formin nodes and myosin motor activity in Mid1p-dependent contractile-ring assembly during fission yeast cytokinesis. Mol Biol Cell 2010; 20:5195-210. [PMID: 19864459 DOI: 10.1091/mbc.e09-05-0428] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Two prevailing models have emerged to explain the mechanism of contractile-ring assembly during cytokinesis in the fission yeast Schizosaccharomyces pombe: the spot/leading cable model and the search, capture, pull, and release (SCPR) model. We tested some of the basic assumptions of the two models. Monte Carlo simulations of the SCPR model require that the formin Cdc12p is present in >30 nodes from which actin filaments are nucleated and captured by myosin-II in neighboring nodes. The force produced by myosin motors pulls the nodes together to form a compact contractile ring. Live microscopy of cells expressing Cdc12p fluorescent fusion proteins shows for the first time that Cdc12p localizes to a broad band of 30-50 dynamic nodes, where actin filaments are nucleated in random directions. The proposed progenitor spot, essential for the spot/leading cable model, usually disappears without nucleating actin filaments. alpha-Actinin ain1 deletion cells form a normal contractile ring through nodes in the absence of the spot. Myosin motor activity is required to condense the nodes into a contractile ring, based on slower or absent node condensation in myo2-E1 and UCS rng3-65 mutants. Taken together, these data provide strong support for the SCPR model of contractile-ring formation in cytokinesis.
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Affiliation(s)
- Valerie C Coffman
- Department of Molecular Genetics, Graduate Program of Molecular, Cellular, and Developmental Biology, The Ohio State University, Columbus, OH 43210, USA
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Stark BC, Sladewski TE, Pollard LW, Lord M. Tropomyosin and myosin-II cellular levels promote actomyosin ring assembly in fission yeast. Mol Biol Cell 2010; 21:989-1000. [PMID: 20110347 PMCID: PMC2836979 DOI: 10.1091/mbc.e09-10-0852] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
A combination of in vivo and in vitro approaches were used to show how tropomyosin and myosin-II contribute to contractile ring assembly in fission yeast. Ring assembly is sensitive to changes in the cellular levels of myosin-II, and tropomyosin works to maximize myosin-II motor function during this process by stabilizing actomyosin interactions. Myosin-II (Myo2p) and tropomyosin are essential for contractile ring formation and cytokinesis in fission yeast. Here we used a combination of in vivo and in vitro approaches to understand how these proteins function at contractile rings. We find that ring assembly is delayed in Myo2p motor and tropomyosin mutants, but occurs prematurely in cells engineered to express two copies of myo2. Thus, the timing of ring assembly responds to changes in Myo2p cellular levels and motor activity, and the emergence of tropomyosin-bound actin filaments. Doubling Myo2p levels suppresses defects in ring assembly associated with a tropomyosin mutant, suggesting a role for tropomyosin in maximizing Myo2p function. Correspondingly, tropomyosin increases Myo2p actin affinity and ATPase activity and promotes Myo2p-driven actin filament gliding in motility assays. Tropomyosin achieves this by favoring the strong actin-bound state of Myo2p. This mode of regulation reflects a role for tropomyosin in specifying and stabilizing actomyosin interactions, which facilitates contractile ring assembly in the fission yeast system.
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Affiliation(s)
- Benjamin C Stark
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA
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Martín-García R, Mulvihill DP. Myosin V spatially regulates microtubule dynamics and promotes the ubiquitin-dependent degradation of the fission yeast CLIP-170 homologue, Tip1. J Cell Sci 2009; 122:3862-72. [PMID: 19808886 DOI: 10.1242/jcs.054460] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Coordination between microtubule and actin cytoskeletons plays a crucial role during the establishment of cell polarity. In fission yeast, the microtubule cytoskeleton regulates the distribution of actin assembly at the new growing end during the monopolar-to-bipolar growth transition. Here, we describe a novel mechanism in which a myosin V modulates the spatial coordination of proteolysis and microtubule dynamics. In cells lacking a functional copy of the class V myosin, Myo52, the plus ends of microtubules fail to undergo catastrophe on contacting the cell end and continue to grow, curling around the end of the cell. We show that this actin-associated motor regulates the efficient ubiquitin-dependent proteolysis of the Schizosaccharomyces pombe CLIP-170 homologue, Tip1. Myo52 facilitates microtubule catastrophe by enhancing Tip1 removal from the plus end of growing microtubules at the cell tips. There, Myo52 and the ubiquitin receptor, Dph1, work in concert to target Tip1 for degradation.
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Takaine M, Numata O, Nakano K. Fission yeast IQGAP arranges actin filaments into the cytokinetic contractile ring. EMBO J 2009; 28:3117-31. [PMID: 19713940 DOI: 10.1038/emboj.2009.252] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2009] [Accepted: 07/27/2009] [Indexed: 11/09/2022] Open
Abstract
The contractile ring (CR) consists of bundled actin filaments and myosin II; however, the actin-bundling factor remains elusive. We show that the fission yeast Schizosaccharomyces pombe IQGAP Rng2 is involved in the generation of CR F-actin and required for its arrangement into a ring. An N-terminal fragment of Rng2 is necessary for the function of Rng2 and is localized to CR F-actin. In vitro the fragment promotes actin polymerization and forms linear arrays of F-actin, which are resistant to the depolymerization induced by the actin-depolymerizing factor Adf1. Our findings indicate that Rng2 is involved in the generation of CR F-actin and simultaneously bundles the filaments and regulates its dynamics by counteracting the effects of Adf1, thus enabling the reconstruction of CR F-actin bundles, which provides an insight into the physical properties of the building blocks that comprise the CR.
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Affiliation(s)
- Masak Takaine
- Department of Structural Biosciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
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Park JS, Steinbach SK, Desautels M, Hemmingsen SM. Essential role for Schizosaccharomyces pombe pik1 in septation. PLoS One 2009; 4:e6179. [PMID: 19587793 PMCID: PMC2704394 DOI: 10.1371/journal.pone.0006179] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Accepted: 05/24/2009] [Indexed: 11/29/2022] Open
Abstract
Background Schizosaccharomyces pombe pik1 encodes a phosphatidylinositol 4-kinase, reported to bind Cdc4, but not Cdc4G107S. Principal Findings Gene deletion revealed that pik1 is essential. In cells with pik1 deleted, ectopic expression of a loss-of-function allele, created by fusion to a temperature-sensitive dihydrofolate reductase, allowed normal cell proliferation at 25°C. At 36°C, cells arrested with abnormally thick, misplaced or supernumerary septa, indicating a defect late in septation. In addition to being Golgi associated, ectopically expressed GFP-tagged Pik1 was observed at the medial cell plane late in cytokinesis. New alleles, created by site-directed mutagenesis, were expressed ectopically. Lipid kinase and Cdc4-binding activity assays were performed. Pik1D709A was kinase-dead, but bound Cdc4. Pik1R838A did not bind Cdc4, but was an active kinase. Genomic integration of these substitutions in S. pombe and complementation studies in Saccharomyces cerevisiae pik1-101 cells revealed that D709 is essential in both cases while R838 is dispensable. In S. pombe, ectopic expression of pik1 was dominantly lethal; while, pik1D709A,R838A was innocuous, pik1R838A was almost innocuous, and pik1D709A produced partial lethality and septation defects. The pik1 ectopic expression lethal phenotype was suppressed in cdc4G107S. Thus, D709 is essential for kinase activity and septation. Conclusions Pik1 kinase activity is required for septation. The Pik1 R838 residue is required for important protein-protein interactions, possibly with Cdc4.
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Affiliation(s)
- Jae-Sook Park
- Department of Microbiology and Immunology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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