101
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Evolutionary conservation of actin-binding proteins in Trypanosoma cruzi and unusual subcellular localization of the actin homologue. Parasitology 2008; 135:955-65. [PMID: 18477418 DOI: 10.1017/s0031182008004496] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The actin cytoskeleton controls pivotal cellular processes such as motility and cytokinesis, as well as cell-cell and cell-substrate interactions. Assembly and spatial organization of actin filaments are dynamic events regulated by a large repertoire of actin-binding proteins. This report presents the first detailed characterization of the Trypanosoma cruzi actin (TcActin). Protein sequence analysis and homology modelling revealed that the overall structure of T. cruzi actin is conserved and that the majority of amino-acid changes are concentrated on the monomer surface. Immunofluorescence assays using specific polyclonal antibody against TcActin revealed numerous rounded and punctated structures spread all over the parasitic body. No pattern differences could be found between epimastigotes and trypomastigotes or amastigotes. Moreover, in detergent extracts, TcActin was localized only in the soluble fraction, indicating its presence in the G-actin form or in short filaments dissociated from the microtubule cytoskeleton. The trypanosomatid genome was prospected to identify actin-binding and actin-related conserved proteins. The main proteins responsible for actin nucleation and treadmilling in higher eukaryotes are conserved in T. cruzi.
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102
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Egelhofer TA, Villén J, McCusker D, Gygi SP, Kellogg DR. The septins function in G1 pathways that influence the pattern of cell growth in budding yeast. PLoS One 2008; 3:e2022. [PMID: 18431499 PMCID: PMC2291192 DOI: 10.1371/journal.pone.0002022] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2008] [Accepted: 03/24/2008] [Indexed: 11/21/2022] Open
Abstract
The septins are a conserved family of proteins that have been proposed to carry out diverse functions. In budding yeast, the septins become localized to the site of bud emergence in G1 but have not been thought to carry out important functions at this stage of the cell cycle. We show here that the septins function in redundant mechanisms that are required for formation of the bud neck and for the normal pattern of cell growth early in the cell cycle. The Shs1 septin shows strong genetic interactions with G1 cyclins and is directly phosphorylated by G1 cyclin-dependent kinases, consistent with a role in early cell cycle events. However, Shs1 phosphorylation site mutants do not show genetic interactions with the G1 cyclins or obvious defects early in the cell cycle. Rather, they cause an increased cell size and aberrant cell morphology that are dependent upon inhibitory phosphorylation of Cdk1 at the G2/M transition. Shs1 phosphorylation mutants also show defects in interaction with the Gin4 kinase, which associates with the septins during G2/M and plays a role in regulating inhibitory phosphorylation of Cdk1. Phosphorylation of Shs1 by G1 cyclin-dependent kinases plays a role in events that influence Cdk1 inhibitory phosphorylation.
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Affiliation(s)
- Thea A. Egelhofer
- Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Judit Villén
- Department of Cell Biology, Taplin Biological Mass Spectrometry Facility, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Derek McCusker
- Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Steven P. Gygi
- Department of Cell Biology, Taplin Biological Mass Spectrometry Facility, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Douglas R. Kellogg
- Department of Molecular, Cell and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
- * To whom correspondence should be addressed. E-mail:
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103
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Yu L, Qi M, Sheff MA, Elion EA. Counteractive control of polarized morphogenesis during mating by mitogen-activated protein kinase Fus3 and G1 cyclin-dependent kinase. Mol Biol Cell 2008; 19:1739-52. [PMID: 18256288 PMCID: PMC2291402 DOI: 10.1091/mbc.e07-08-0757] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2007] [Revised: 01/18/2008] [Accepted: 01/29/2008] [Indexed: 01/10/2023] Open
Abstract
Cell polarization in response to external cues is critical to many eukaryotic cells. During pheromone-induced mating in Saccharomyces cerevisiae, the mitogen-activated protein kinase (MAPK) Fus3 induces polarization of the actin cytoskeleton toward a landmark generated by the pheromone receptor. Here, we analyze the role of Fus3 activation and cell cycle arrest in mating morphogenesis. The MAPK scaffold Ste5 is initially recruited to the plasma membrane in random patches that polarize before shmoo emergence. Polarized localization of Ste5 is important for shmooing. In fus3 mutants, Ste5 is recruited to significantly more of the plasma membrane, whereas recruitment of Bni1 formin, Cdc24 guanine exchange factor, and Ste20 p21-activated protein kinase are inhibited. In contrast, polarized recruitment still occurs in a far1 mutant that is also defective in G1 arrest. Remarkably, loss of Cln2 or Cdc28 cyclin-dependent kinase restores polarized localization of Bni1, Ste5, and Ste20 to a fus3 mutant. These and other findings suggest Fus3 induces polarized growth in G1 phase cells by down-regulating Ste5 recruitment and by inhibiting Cln/Cdc28 kinase, which prevents basal recruitment of Ste5, Cdc42-mediated asymmetry, and mating morphogenesis.
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Affiliation(s)
- Lu Yu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115-5730
| | - Maosong Qi
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115-5730
| | - Mark A. Sheff
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115-5730
| | - Elaine A. Elion
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115-5730
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104
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Noguchi T, Lenartowska M, Rogat AD, Frank DJ, Miller KG. Proper cellular reorganization during Drosophila spermatid individualization depends on actin structures composed of two domains, bundles and meshwork, that are differentially regulated and have different functions. Mol Biol Cell 2008; 19:2363-72. [PMID: 18353976 DOI: 10.1091/mbc.e07-08-0840] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
During spermatid individualization in Drosophila, actin structures (cones) mediate cellular remodeling that separates the syncytial spermatids into individual cells. These actin cones are composed of two structural domains, a front meshwork and a rear region of parallel bundles. We show here that the two domains form separately in time, are regulated by different sets of actin-associated proteins, can be formed independently, and have different roles. Newly forming cones were composed only of bundles, whereas the meshwork formed later, coincident with the onset of cone movement. Polarized distributions of myosin VI, Arp2/3 complex, and the actin-bundling proteins, singed (fascin) and quail (villin), occurred when movement initiated. When the Arp2/3 complex was absent, meshwork formation was compromised, but surprisingly, the cones still moved. Despite the fact that the cones moved, membrane reorganization and cytoplasmic exclusion were abnormal and individualization failed. In contrast, when profilin, a regulator of actin assembly, was absent, bundle formation was greatly reduced. The meshwork still formed, but no movement occurred. Analysis of this actin structure's formation and participation in cellular reorganization provides insight into how the mechanisms used in cell motility are modified to mediate motile processes within specialized cells.
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Affiliation(s)
- Tatsuhiko Noguchi
- Laboratory for Morphogenetic Signaling, Center for Developmental Biology, RIKEN Kobe, Kobe 650-0047, Japan
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105
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Plattner F, Yarovinsky F, Romero S, Didry D, Carlier MF, Sher A, Soldati-Favre D. Toxoplasma profilin is essential for host cell invasion and TLR11-dependent induction of an interleukin-12 response. Cell Host Microbe 2008; 3:77-87. [PMID: 18312842 DOI: 10.1016/j.chom.2008.01.001] [Citation(s) in RCA: 263] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2007] [Revised: 11/14/2007] [Accepted: 01/08/2008] [Indexed: 11/24/2022]
Abstract
Apicomplexan parasites exhibit actin-dependent gliding motility that is essential for migration across biological barriers and host cell invasion. Profilins are key contributors to actin polymerization, and the parasite Toxoplasma gondii possesses a profilin-like protein that is recognized by Toll-like receptor TLR11 in the host innate immune system. Here, we show by conditional disruption of the corresponding gene that T.gondii profilin, while not required for intracellular growth, is indispensable for gliding motility, host cell invasion, active egress from host cells, and virulence in mice. Furthermore, parasites lacking profilin are unable to induce TLR11-dependent production in vitro and in vivo of the defensive host cytokine interleukin-12. Thus, profilin is an essential element of two aspects of T. gondii infection. Like bacterial flagellin, profilin plays a role in motility while serving as a microbial ligand recognized by the host innate immune system.
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Affiliation(s)
- Fabienne Plattner
- Department of Microbiology and Molecular Medicine, CMU, University of Geneva, 1 rue Michel-Servet, 1211 Geneva 4, Switzerland
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106
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Kim J, Lee CD, Rath A, Davidson AR. Recognition of non-canonical peptides by the yeast Fus1p SH3 domain: elucidation of a common mechanism for diverse SH3 domain specificities. J Mol Biol 2008; 377:889-901. [PMID: 18280496 DOI: 10.1016/j.jmb.2008.01.063] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2007] [Revised: 12/18/2007] [Accepted: 01/14/2008] [Indexed: 01/14/2023]
Abstract
The yeast Fus1p SH3 domain binds to peptides containing the consensus motif, R(S/T)(S/T)SL, which is a sharp contrast to most SH3 domains, which bind to PXXP-containing peptides. Here, we have demonstrated that this domain binds to R(S/T)(S/T)SL-containing peptides derived from two putative in vivo binding partners from yeast proteins, Bnr1p and Ste5p, with K(d) values in the low micromolar range. The R(S/T)(S/T)SL consensus motif is necessary, but not sufficient for binding to the Fus1p SH3 domain, as residues lying N-terminal to the consensus motif also play a critical role in the binding reaction. Through mutagenesis studies and comparisons to other SH3 domains, we have discovered that the Fus1p SH3 domain utilizes a portion of the same binding surface as typical SH3 domains. However, the PXXP-binding surface, which plays the predominant role in binding for most SH3 domains, is debilitated in the WT domain by the substitution of unusual residues at three key conserved positions. By replacing these residues, we created a version of the Fus1p SH3 domain that binds to a PXXP-containing peptide with extremely high affinity (K(d)= 40 nM). Based on our data and analysis, we have clearly delineated two distinct surfaces comprising the typical SH3-domain-binding interface and show that one of these surfaces is the primary mediator of almost every "non-canonical" SH3-domain-mediated interaction described in the literature. Within this framework, dramatic alterations in SH3 domain specificity can be simply explained as a modulation of the binding strengths of these two surfaces.
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Affiliation(s)
- JungMin Kim
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
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107
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Endlich N, Otey CA, Kriz W, Endlich K. Movement of stress fibers away from focal adhesions identifies focal adhesions as sites of stress fiber assembly in stationary cells. ACTA ACUST UNITED AC 2008; 64:966-76. [PMID: 17868136 DOI: 10.1002/cm.20237] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Force generated in contractile actin filament bundles (stress fibers-SFs) is transmitted to the extracellular matrix (ECM) via linker proteins and transmembrane integrins at focal adhesions (FAs). Though it has long been known that actin is rapidly exchanged in FAs, the connection between SFs and FAs has not been studied in detail. We introduced fiduciary marks on SFs by expressing GFP-palladin or GFP-alpha-actinin-1, which are both FA and dense body proteins, and by pattern bleaching of GFP-actin. Following fiduciary marks on SFs over time by time-lapse fluorescence microscopy, we detected assembly of SFs at FAs in stationary cells resulting in movement of SFs away from FAs with a velocity of 0.2-0.4 microm/min. Visualization of FAs in GFP-palladin/DsRed-paxillin double transfected cells showed that SF elongation was not accompanied by a change in FA length. SF elongation at FAs depended on actin polymerization and force as demonstrated by inhibitors of actin polymerization (cytochalasin D, jasplakinolide) and inhibitors of myosin-dependent contraction (blebbistatin, Y-27632), respectively. Our finding of SF assembly at FAs has important implications for SF formation, force transmission, and tension distribution within the actin cytoskeletal network of stationary cells.
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Affiliation(s)
- Nicole Endlich
- Department of Anatomy and Cell Biology, Ernst Moritz Arndt University, D-17487 Greifswald, Germany
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108
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Lindberg U, Schutt CE, Goldman RD, Nyåkern-Meazza M, Hillberg L, Rathje LSZ, Grenklo S. Tropomyosins Regulate the Impact of Actin Binding Proteins on Actin Filaments. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 644:223-31. [DOI: 10.1007/978-0-387-85766-4_17] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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109
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Yang C, Czech L, Gerboth S, Kojima SI, Scita G, Svitkina T. Novel roles of formin mDia2 in lamellipodia and filopodia formation in motile cells. PLoS Biol 2007; 5:e317. [PMID: 18044991 PMCID: PMC2229861 DOI: 10.1371/journal.pbio.0050317] [Citation(s) in RCA: 254] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 09/27/2007] [Indexed: 12/26/2022] Open
Abstract
Actin polymerization-driven protrusion of the leading edge is a key element of cell motility. The important actin nucleators formins and the Arp2/3 complex are believed to have nonoverlapping functions in inducing actin filament bundles in filopodia and dendritic networks in lamellipodia, respectively. We tested this idea by investigating the role of mDia2 formin in leading-edge protrusion by loss-of-function and gain-of-function approaches. Unexpectedly, mDia2 depletion by short interfering RNA (siRNA) severely inhibited lamellipodia. Structural analysis of the actin network in the few remaining lamellipodia suggested an mDia2 role in generation of long filaments. Consistently, constitutively active mDia2 (DeltaGBD-mDia2) induced accumulation of long actin filaments in lamellipodia and increased persistence of lamellipodial protrusion. Depletion of mDia2 also inhibited filopodia, whereas expression of DeltaGBD-mDia2 promoted their formation. Correlative light and electron microscopy showed that DeltaGBD-mDia2-induced filopodia were formed from lamellipodial network through gradual convergence of long lamellipodial filaments into bundles. Efficient filopodia induction required mDia2 targeting to the membrane, likely through a scaffolding protein Abi1. Furthermore, mDia2 and Abi1 interacted through the N-terminal regulatory sequences of mDia2 and the SH3-containing Abi1 sequences. We propose that mDia2 plays an important role in formation of lamellipodia by nucleating and/or protecting from capping lamellipodial actin filaments, which subsequently exhibit high tendency to converge into filopodia.
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Affiliation(s)
- Changsong Yang
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Lubov Czech
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
| | - Silke Gerboth
- The Italian Foundation for Cancer Research (FIRC) Institute for Molecular Oncology, Milan, Italy
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
| | - Shin-ichiro Kojima
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
| | - Giorgio Scita
- The Italian Foundation for Cancer Research (FIRC) Institute for Molecular Oncology, Milan, Italy
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
| | - Tatyana Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * To whom correspondence should be addressed. E-mail:
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110
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Loewen CJR, Young BP, Tavassoli S, Levine TP. Inheritance of cortical ER in yeast is required for normal septin organization. ACTA ACUST UNITED AC 2007; 179:467-83. [PMID: 17984322 PMCID: PMC2064793 DOI: 10.1083/jcb.200708205] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
How cells monitor the distribution of organelles is largely unknown. In budding yeast, the largest subdomain of the endoplasmic reticulum (ER) is a network of cortical ER (cER) that adheres to the plasma membrane. Delivery of cER from mother cells to buds, which is termed cER inheritance, occurs as an orderly process early in budding. We find that cER inheritance is defective in cells lacking Scs2, a yeast homologue of the integral ER membrane protein VAP (vesicle-associated membrane protein–associated protein) conserved in all eukaryotes. Scs2 and human VAP both target yeast bud tips, suggesting a conserved action of VAP in attaching ER to sites of polarized growth. In addition, the loss of either Scs2 or Ice2 (another protein involved in cER inheritance) perturbs septin assembly at the bud neck. This perturbation leads to a delay in the transition through G2, activating the Saccharomyces wee1 kinase (Swe1) and the morphogenesis checkpoint. Thus, we identify a mechanism involved in sensing the distribution of ER.
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Affiliation(s)
- Christopher J R Loewen
- Division of Cell Biology, University College London Institute of Ophthalmology, London EC1V 9EL, England, UK
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111
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Abstract
Cytokinesis is the process by which cells physically separate after the duplication and spatial segregation of the genetic material. A number of general principles apply to this process. First the microtubule cytoskeleton plays an important role in the choice and positioning of the division site. Once the site is chosen, the local assembly of the actomyosin contractile ring remodels the plasma membrane. Finally, membrane trafficking to and membrane fusion at the division site cause the physical separation of the daughter cells, a process termed abscission. Here we will discuss recent advances in our understanding of the mechanisms of cytokinesis in animals, yeast, and plants.
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Affiliation(s)
- Francis A Barr
- University of Liverpool, Cancer Research Centre, 200 London Road, Liverpool L3 9TA, UK.
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112
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Lindberg U, Karlsson R, Lassing I, Schutt CE, Höglund AS. The microfilament system and malignancy. Semin Cancer Biol 2007; 18:2-11. [PMID: 18024149 DOI: 10.1016/j.semcancer.2007.10.002] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Increased motile activity, increased rate of cell proliferation and removal of growth inhibiting cell-cell contacts are hallmarks of tumorigenesis. Activation of cell motility and migration is caused by activation of receptors, turning on the growth cycle. Increased expression of metalloproteinases, breaking cell:cell contacts and organ confines, allows the spread of malignant cancer cells to other sites in the organism. It has become increasingly clear that most transmembrane proteins (growth factor receptors, adhesion proteins and ion channels) are either permanently or transiently associated with the sub-membraneous system of actin microfilaments (MF), whose force generating capacity they control. Although there has been great progress in our understanding of the physiological importance of the MF-system, as will be exemplified in this issue of SCB, many aspects of actin microfilament formation and its regulation are still unclear. Redox control of the actin (MF)-system in cell motility and migration and its perturbations in pathophysiology, including cancer, is an emerging field of research.
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Affiliation(s)
- Uno Lindberg
- Department of Microbiology, Tumor Biology, and Cell Biology, The Karolinska Institute, Stockholm, Sweden.
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113
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Mustapha M, Beyer LA, Izumikawa M, Swiderski DL, Dolan DF, Raphael Y, Camper SA. Whirler mutant hair cells have less severe pathology than shaker 2 or double mutants. J Assoc Res Otolaryngol 2007; 8:329-37. [PMID: 17619105 PMCID: PMC2538434 DOI: 10.1007/s10162-007-0083-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2007] [Accepted: 04/23/2007] [Indexed: 01/16/2023] Open
Abstract
MYOSIN XV is a motor protein that interacts with the PDZ domain-containing protein WHIRLIN and transports WHIRLIN to the tips of the stereocilia. Shaker 2 (sh2) mice have a mutation in the motor domain of MYOSIN XV and exhibit congenital deafness and circling behavior, probably because of abnormally short stereocilia. Whirler (wi) mice have a similar phenotype caused by a deletion in the third PDZ domain of WHIRLIN. We compared the morphology of Whrn (wi/wi) and Myo15 (sh2/sh2) sensory hair cells and found that Myo15 (sh2/sh2) have more frequent pathology at the base of inner hair cells than Whrn (wi/wi), and shorter outer hair cell stereocilia. Considering the functional and morphologic similarities in the phenotypes caused by mutations in Myo15 and Whrn, and the physical interaction between their encoded proteins, we used a genetic approach to test for functional overlap. Double heterozygotes (Myo15 (sh2/+), Whrn (wi/+)) have normal hearing and no increase in hearing loss compared to normal littermates. Single and double mutants (Myo15 (sh2/sh2), Whrn (wi/wi)) exhibit abnormal persistence of kinocilia and microvilli, and develop abnormal cytoskeletal architecture. Double mutants are also similar to the single mutants in viability, circling behavior, and lack of a Preyer reflex. The morphology of cochlear hair cell stereocilia in double mutants reflects a dominance of the more severe Myo15 (sh2/sh2) phenotype over the Whrn (wi/wi) phenotype. This suggests that MYOSIN XV may interact with other proteins besides WHIRLIN that are important for hair cell maturation.
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Affiliation(s)
- Mirna Mustapha
- Department of Human Genetics, University of Michigan, 4909 Buhl Building, 1241 East Catherine Street, Ann Arbor, MI 48109-0618 USA
| | - Lisa A. Beyer
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI 48109 USA
| | - Masahiko Izumikawa
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI 48109 USA
| | - Donald L. Swiderski
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI 48109 USA
| | - David F. Dolan
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI 48109 USA
| | - Yehoash Raphael
- Department of Otolaryngology, University of Michigan, Ann Arbor, MI 48109 USA
| | - Sally A. Camper
- Department of Human Genetics, University of Michigan, 4909 Buhl Building, 1241 East Catherine Street, Ann Arbor, MI 48109-0618 USA
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114
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Bertling E, Quintero-Monzon O, Mattila PK, Goode BL, Lappalainen P. Mechanism and biological role of profilin-Srv2/CAP interaction. J Cell Sci 2007; 120:1225-34. [PMID: 17376963 DOI: 10.1242/jcs.000158] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Profilin and cyclase-associated protein (CAP, known in yeast as Srv2) are ubiquitous and abundant actin monomer-binding proteins. Profilin catalyses the nucleotide exchange on actin monomers and promotes their addition to filament barbed ends. Srv2/CAP recycles newly depolymerized actin monomers from ADF/cofilin for subsequent rounds of polymerization. Srv2/CAP also harbors two proline-rich motifs and has been suggested to interact with profilin. However, the mechanism and biological role of the possible profilin-Srv2/CAP interaction has not been investigated. Here, we show that Saccharomyces cerevisiae Srv2 and profilin interact directly (K(D) approximately 1.3 microM) and demonstrate that a specific proline-rich motif in Srv2 mediates this interaction in vitro and in vivo. ADP-actin monomers and profilin do not interfere with each other's binding to Srv2, suggesting that these three proteins can form a ternary complex. Genetic and cell biological analyses on an Srv2 allele (srv2-201) defective in binding profilin reveals that a direct interaction with profilin is not essential for Srv2 cellular function. However, srv2-201 causes a moderate increase in cell size and partially suppresses the cell growth and actin organization defects of an actin binding mutant profilin (pfy1-4). Together these data suggest that Srv2 is an important physiological interaction partner of profilin.
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Affiliation(s)
- Enni Bertling
- Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
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115
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Abstract
It is an established assumption that the inheritance of intracellular organelles into daughter cells is not left to chance. A recent study by Rob Jensen and coworkers provides a new link between a protein required for the inheritance of nuclei in yeast with the positioning and morphology of the mitochondria.
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Affiliation(s)
- Astrid C Schauss
- University of Ottawa Heart Institute, Rm H445A, 40 Ruskin St, Ottawa, Ontario, K1Y 4W7 Canada
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116
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Applewhite DA, Barzik M, Kojima SI, Svitkina TM, Gertler FB, Borisy GG. Ena/VASP proteins have an anti-capping independent function in filopodia formation. Mol Biol Cell 2007; 18:2579-91. [PMID: 17475772 PMCID: PMC1924831 DOI: 10.1091/mbc.e06-11-0990] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Filopodia have been implicated in a number of diverse cellular processes including growth-cone path finding, wound healing, and metastasis. The Ena/VASP family of proteins has emerged as key to filopodia formation but the exact mechanism for how they function has yet to be fully elucidated. Using cell spreading as a model system in combination with small interfering RNA depletion of Capping Protein, we determined that Ena/VASP proteins have a role beyond anticapping activity in filopodia formation. Analysis of mutant Ena/VASP proteins demonstrated that the entire EVH2 domain was the minimal domain required for filopodia formation. Fluorescent recovery after photobleaching data indicate that Ena/VASP proteins rapidly exchange at the leading edge of lamellipodia, whereas virtually no exchange occurred at filopodial tips. Mutation of the G-actin-binding motif (GAB) partially compromised stabilization of Ena/VASP at filopodia tips. These observations led us to propose a model where the EVH2 domain of Ena/VASP induces and maintains clustering of the barbed ends of actin filaments, which putatively corresponds to a transition from lamellipodial to filopodial localization. Furthermore, the EVH1 domain, together with the GAB motif in the EVH2 domain, helps to maintain Ena/VASP at the growing barbed ends.
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Affiliation(s)
- Derek A. Applewhite
- *Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611
| | - Melanie Barzik
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Shin-ichiro Kojima
- *Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611
| | - Tatyana M. Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104; and
| | - Frank B. Gertler
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Gary G. Borisy
- *Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611
- Marine Biological Laboratory, Woods Hole, MA 02453
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117
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van der Honing HS, Emons AMC, Ketelaar T. Actin based processes that could determine the cytoplasmic architecture of plant cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:604-14. [PMID: 16962185 DOI: 10.1016/j.bbamcr.2006.07.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Revised: 06/09/2006] [Accepted: 07/21/2006] [Indexed: 10/24/2022]
Abstract
Actin polymerisation can generate forces that are necessary for cell movement, such as the propulsion of a class of bacteria, including Listeria, and the protrusion of migrating animal cells. Force generation by the actin cytoskeleton in plant cells has not been studied. One process in plant cells that is likely to depend on actin-based force generation is the organisation of the cytoplasm. We compare the function of actin binding proteins of three well-studied mammalian models that depend on actin-based force generation with the function of their homologues in plants. We predict the possible role of these proteins, and thus the role of actin-based force generation, in the production of cytoplasmic organisation in plant cells.
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Affiliation(s)
- Hannie S van der Honing
- Laboratory of Plant Cell Biology, Wageningen University, Arboretumlaan 4, 6703BD Wageningen, The Netherlands
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118
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Aronov S, Gelin-Licht R, Zipor G, Haim L, Safran E, Gerst JE. mRNAs encoding polarity and exocytosis factors are cotransported with the cortical endoplasmic reticulum to the incipient bud in Saccharomyces cerevisiae. Mol Cell Biol 2007; 27:3441-55. [PMID: 17339339 PMCID: PMC1899969 DOI: 10.1128/mcb.01643-06] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2006] [Revised: 11/13/2006] [Accepted: 02/09/2007] [Indexed: 11/20/2022] Open
Abstract
Polarized growth in the budding yeast Saccharomyces cerevisiae depends upon the asymmetric localization and enrichment of polarity and secretion factors at the membrane prior to budding. We examined how these factors (i.e., Cdc42, Sec4, and Sro7) reach the bud site and found that their respective mRNAs localize to the tip of the incipient bud prior to nuclear division. Asymmetric mRNA localization depends upon factors that facilitate ASH1 mRNA localization (e.g., the 3' untranslated region, She proteins 1 to 5, Puf6, actin cytoskeleton, and a physical association with She2). mRNA placement precedes protein enrichment and subsequent bud emergence, implying that mRNA localization contributes to polarization. Correspondingly, mRNAs encoding proteins which are not asymmetrically distributed (i.e., Snc1, Mso1, Tub1, Pex3, and Oxa1) are not polarized. Finally, mutations which affect cortical endoplasmic reticulum (ER) entry and anchoring in the bud (myo4Delta, sec3Delta, and srp101) also affect asymmetric mRNA localization. Bud-localized mRNAs, including ASH1, were found to cofractionate with ER microsomes in a She2- and Sec3-dependent manner; thus, asymmetric mRNA transport and cortical ER inheritance are connected processes in yeast.
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Affiliation(s)
- Stella Aronov
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
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119
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Sheng Zhu S, Li Liu X, Fei Liu P, Li Y, Qiang Li J, Min Wang H, Kui Yuan S, Guo Si N. Flumorph Is a Novel Fungicide That Disrupts Microfilament Organization in Phytophthora melonis. PHYTOPATHOLOGY 2007; 97:643-9. [PMID: 18943584 DOI: 10.1094/phyto-97-5-0643] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
ABSTRACT The mechanism of the effects of flumorph (a novel fungicide) was investigated by analyzing alterations of hyphal morphology, cell wall deposition patterns, F-actin organization, and other organelles in Phytophthora melonis. Calcofluor white staining suggested that flumorph did not inhibit the synthesis of cell wall materials, but disturbed the polar deposition of newly synthesized cell wall materials during cystospore germination and hyphal growth. After exposure to flumorph, zoospores were able to switch into cystospores accompanied with the formation of a cell wall, whereas cystospores failed to induce the isotropic-polar switch and did not produce germ tubes but continued the isotropic growth phase. In flumorph-treated hyphae, the most characteristic change was the development of periodic swelling ("beaded" morphology) and the disruption of tip growth. Newly synthesized cell wall materials were deposited uniformly throughout the diffuse expanded region of hyphae, in contrast to their normal polarized patterns of deposition. These alterations were the result of F-actin disruption, identified with the fluorescein isothiocynate (FITC)-phalloidin staining. The disruption of F-actin also was accompanied by disorganized organelles: each swelling of subapical hyphae was associated with a nucleus. Vesicles did not undergo polarized secretion to the apical hyphae, but diffused around nuclei for the subapical growth; thus, the cell wall was thickened with periodic expansion along the hyphae. Upon removing flumorph, normal tip growth and organized F-actin were observed again. These data, as well as data published earlier, suggest that flumorph may be involved in the impairment of cell polar growth through directly or indirectly disrupting the organization of F-actin. The primary site of action by flumorph in the disruption of the F-actin organization is under investigation.
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120
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Stirling PC, Srayko M, Takhar KS, Pozniakovsky A, Hyman AA, Leroux MR. Functional interaction between phosducin-like protein 2 and cytosolic chaperonin is essential for cytoskeletal protein function and cell cycle progression. Mol Biol Cell 2007; 18:2336-45. [PMID: 17429077 PMCID: PMC1877119 DOI: 10.1091/mbc.e07-01-0069] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Chaperonin Containing Tcp1 (CCT) maintains cellular protein folding homeostasis in the eukaryotic cytosol by assisting the biogenesis of many proteins, including actins, tubulins, and regulators of the cell cycle. Here, we demonstrate that the essential and conserved eukaryotic phosducin-like protein 2 (PhLP2/PLP2) physically interacts with CCT and modulates its folding activity. Consistent with this functional interaction, temperature-sensitive alleles of Saccharomyces cerevisiae PLP2 exhibit cytoskeletal and cell cycle defects. We uncovered several high-copy suppressors of the plp2 alleles, all of which are associated with G1/S cell cycle progression but which do not appreciably affect cytoskeletal protein function or fully rescue the growth defects. Our data support a model in which Plp2p modulates the biogenesis of several CCT substrates relating to cell cycle and cytoskeletal function, which together contribute to the essential function of PLP2.
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Affiliation(s)
- Peter C. Stirling
- *Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; and
| | - Martin Srayko
- Max-Planck Institute of Molecular Cell Biology and Genetics, 03107 Dresden, Germany
| | - Karam S. Takhar
- *Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; and
| | - Andrei Pozniakovsky
- Max-Planck Institute of Molecular Cell Biology and Genetics, 03107 Dresden, Germany
| | - Anthony A. Hyman
- Max-Planck Institute of Molecular Cell Biology and Genetics, 03107 Dresden, Germany
| | - Michel R. Leroux
- *Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; and
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121
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Lambert AA, Perron MP, Lavoie E, Pallotta D. The Saccharomyces cerevisiae Arf3 protein is involved in actin cable and cortical patch formation. FEMS Yeast Res 2007; 7:782-95. [PMID: 17425670 DOI: 10.1111/j.1567-1364.2007.00239.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
We show that Arf3p, a member of the ADP ribosylation family, is involved in the organization of actin cables and cortical patches in Saccharomyces cerevisiae. Profilin-deficient cells (pfy1Delta) have severe growth defects and lack actin cables. Overexpression of ARF3 restores actin cables and corrects growth defects in these cells. Cells deficient for the cortical patch proteins Las17p and Vrp1p have growth defects and a random cortical patch distribution. Overexpression of ARF3 in las17Delta and in vrp1Delta cells partially corrects growth defects and restores the polarized distribution of cortical patches. The N-terminal glycine, a myristoylation site in Arf3p, is necessary for its suppressor activity. arf3Delta cells show a random budding pattern. Overexpression of BNI1, GEA2 or SYP1, three genes involved in actin cytoskeleton formation, restores the normal axial budding pattern of arf3Delta cells. BUD6 is a polarity gene and GEA2 is involved in retrograde transport and the organization of the actin cytoskeleton. We have identified genetic interactions between ARF3 and BUD6, and between ARF3 and GEA2. Both double mutant strains have actin cytoskeleton defects. Our results support a role for ARF3 in cell polarity and the organization of the actin cytoskeleton.
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Affiliation(s)
- Alexandra A Lambert
- Centre de Recherche sur la Structure, la Fonction et l'Ingénierie des Protéines (CREFSIP), Pavillon Charles-Eugène Marchand, Université Laval Québec, Canada
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122
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Mongiu AK, Weitzke EL, Chaga OY, Borisy GG. Kinetic-structural analysis of neuronal growth cone veil motility. J Cell Sci 2007; 120:1113-25. [PMID: 17327278 DOI: 10.1242/jcs.03384] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Neuronal growth cone advance was investigated by correlative light and electron microscopy carried out on chick dorsal root ganglion cells. Advance was analyzed in terms of the two principal organelles responsible for protrusive motility in the growth cone – namely, veils and filopodia. Veils alternated between rapid phases of protrusion and retraction. Electron microscopy revealed characteristic structural differences between the phases. Our results provide a significant advance in three respects: first, protruding veils are comprised of a densely branched network of actin filaments that is lamellipodial in appearance and includes the Arp2/3 complex. On the basis of this structural and biomarker evidence, we infer that the dendritic nucleation and/or array-treadmilling mechanism of protrusive motility is conserved in veil protrusion of growth cones as in the motility of fibroblasts; second, retracting veils lack dendritic organization but contain a sparse network of long filaments; and third, growth cone filopodia have the capacity to nucleate dendritic networks along their length, a property consistent with veil formation seen at the light microscopic level but not previously understood in supramolecular terms. These elements of veil and filopodial organization, when taken together, provide a conceptual framework for understanding the structural basis of growth cone advance.
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Affiliation(s)
- Anne K Mongiu
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Marine Biological Laboratory, 303 E. Chicago Avenue, Chicago, IL 60611, USA.
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123
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Buttery SM, Yoshida S, Pellman D. Yeast formins Bni1 and Bnr1 utilize different modes of cortical interaction during the assembly of actin cables. Mol Biol Cell 2007; 18:1826-38. [PMID: 17344480 PMCID: PMC1855024 DOI: 10.1091/mbc.e06-09-0820] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The budding yeast formins Bni1 and Bnr1 control the assembly of actin cables. These formins exhibit distinct patterns of localization and polymerize two different populations of cables: Bni1 in the bud and Bnr1 in the mother cell. We generated a functional Bni1-3GFP that improved the visualization of Bni1 in vivo at endogenous levels. Bni1 exists as speckles in the cytoplasm, some of which colocalize on actin cables. These Bni1 speckles display linear, retrograde-directed movements. Loss of polymerized actin or specifically actin cables abolished retrograde movement, and resulted in depletion of Bni1 speckles from the cytoplasm, with enhanced targeting of Bni1 to the bud tip. Mutations that impair the actin assembly activity of Bni1 abolished the movement of Bni1 speckles, even when actin cables were present. In contrast, Bnr1-GFP or 3GFP-Bnr1 did not detectably associate with actin cables and was not observed as cytoplasmic speckles. Finally, fluorescence recovery after photobleaching demonstrated that Bni1 was very dynamic, exchanging between polarized sites and the cytoplasm, whereas Bnr1 was confined to the bud neck and did not exchange with a cytoplasmic pool. In summary, our results indicate that formins can have distinct modes of cortical interaction during actin cable assembly.
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Affiliation(s)
- Shawnna M. Buttery
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02115
| | - Satoshi Yoshida
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02115
| | - David Pellman
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02115
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124
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Park HO, Bi E. Central roles of small GTPases in the development of cell polarity in yeast and beyond. Microbiol Mol Biol Rev 2007; 71:48-96. [PMID: 17347519 PMCID: PMC1847380 DOI: 10.1128/mmbr.00028-06] [Citation(s) in RCA: 323] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
SUMMARY The establishment of cell polarity is critical for the development of many organisms and for the function of many cell types. A large number of studies of diverse organisms from yeast to humans indicate that the conserved, small-molecular-weight GTPases function as key signaling proteins involved in cell polarization. The budding yeast Saccharomyces cerevisiae is a particularly attractive model because it displays pronounced cell polarity in response to intracellular and extracellular cues. Cells of S. cerevisiae undergo polarized growth during various phases of their life cycle, such as during vegetative growth, mating between haploid cells of opposite mating types, and filamentous growth upon deprivation of nutrition such as nitrogen. Substantial progress has been made in deciphering the molecular basis of cell polarity in budding yeast. In particular, it becomes increasingly clear how small GTPases regulate polarized cytoskeletal organization, cell wall assembly, and exocytosis at the molecular level and how these GTPases are regulated. In this review, we discuss the key signaling pathways that regulate cell polarization during the mitotic cell cycle and during mating.
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Affiliation(s)
- Hay-Oak Park
- Department of Molecular Genetics, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210-1292, USA.
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125
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Abstract
Fungi invade substrates, such as host tissues, through hyphal tip growth. This article focuses on the corn smut fungus Ustilago maydis, in which tip growth and pathogenicity involve apical endocytic recycling by early endosomes. These organelles rapidly move bi-directionally along microtubules and this movement is mediated by opposing molecular motors. This motility seems to be essential for extended hyphal growth, possibly because it focuses the endocytic machinery at the hyphal tip and mediates communication between the tip and the sub-apical nucleus.
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Affiliation(s)
- Gero Steinberg
- Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch Strabe D-35043 Marburg, Germany.
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126
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Lartey J, Smith M, Pawade J, Strachan B, Mellor H, López Bernal A. Up-regulation of myometrial RHO effector proteins (PKN1 and DIAPH1) and CPI-17 (PPP1R14A) phosphorylation in human pregnancy is associated with increased GTP-RHOA in spontaneous preterm labor. Biol Reprod 2007; 76:971-82. [PMID: 17301291 DOI: 10.1095/biolreprod.106.058982] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
RHO GTP-binding proteins are important regulators of actin-myosin interactions in uterine smooth muscle cells. Active (GTP-bound) RHOA binds to RHO-associated protein kinase (ROCK1), which inhibits the myosin-binding subunit (PPP1R12A) of myosin light chain phosphatase, leading to calcium-independent increases in myosin light chain phosphorylation and tension, which are termed "calcium sensitization." The RHO effector protein kinase N (PKN1) also increases calcium sensitization by phosphorylating the protein kinase C (PRKCB)-dependent protein CPI-17 (PPP1R14A) to inhibit the PPP1c subunit of myosin phosphatase. Moreover, other RHO proteins, such as RHOB, RHOD, and their effectors (DIAPH1 and DIAPH2), may modulate PKN1/ ROCK1 signaling to effect changes in myosin phosphatase activity and myosin light chain phosphorylation. The increases in contractile activity observed in term and preterm labor may be due to an increase in RHO activity and/or changes in RHO-related proteins. We found that the RHOA and RHOB mRNA levels in the myometrium were increased in pregnancy, although the expression levels of the RHOA and RHOB proteins did not change with pregnancy or labor. GTP-bound RHOA was increased in pregnancy, and this increase was significant in spontaneous preterm labor myometrium. PKN1 expression and PPP1R14A phosphorylation were dramatically increased in the pregnant myometrium. We also observed increases in DIAPH1 expression in spontaneous term and preterm labor myometrial tissues. The present study shows that human pregnancy is characterized by increases in PKN1 expression and PPP1R14A phosphorylation in the myometrium. Moreover, increases in GTP-bound RHOA and DIAPH1 expression may contribute to the increase in uterine activity in idiopathic preterm labor.
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Affiliation(s)
- J Lartey
- Clinical Sciences at South Bristol, Division of Obstetrics and Gynaecology, Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, Dorothy Hodgkin Building, University of Bristol, Bristol BS1 3NY, United Kingdom
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127
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Sigal YJ, Quintero OA, Cheney RE, Morris AJ. Cdc42 and ARP2/3-independent regulation of filopodia by an integral membrane lipid-phosphatase-related protein. J Cell Sci 2007; 120:340-52. [PMID: 17200142 DOI: 10.1242/jcs.03335] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Filopodia are dynamic cell surface protrusions that are required for proper cellular development and function. We report that the integral membrane protein lipid-phosphatase-related protein 1 (LPR1) localizes to and promotes the formation of actin-rich, dynamic filopodia, both along the cell periphery and the dorsal cell surface. Regulation of filopodia by LPR1 was not mediated by cdc42 or Rif, and is independent of the Arp2/3 complex. We found that LPR1 can induce filopodia formation in the absence of the Ena/Vasp family of proteins, suggesting that these molecules are not essential for the development of the protrusions. Mutagenesis experiments identified residues and regions of LPR1 that are important for the induction of filopodia. RNA interference experiments in an ovarian epithelial cancer cell line demonstrated a role for LPR1 in the maintenance of filopodia-like membrane protrusions. These observations, and our finding that LPR1 is a not an active lipid phosphatase, suggest that LPR1 may be a novel integral membrane protein link between the actin core and the surrounding lipid layer of a nascent filopodium.
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Affiliation(s)
- Yury J Sigal
- Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA
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128
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Ren H, Xiang Y. The function of actin-binding proteins in pollen tube growth. PROTOPLASMA 2007; 230:171-82. [PMID: 17458632 DOI: 10.1007/s00709-006-0231-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Accepted: 03/29/2006] [Indexed: 05/03/2023]
Abstract
Pollen tube growth is a key step in sexual reproduction of higher plants. The pollen tube is a typical example of tip-growing cells and shows a polarized cytoplasm. To develop and maintain polarized growth, pollen tubes need a carefully regulated actin cytoskeleton. It is well known that actin-binding proteins are responsible for the direct control of dynamic actin filaments and serve as a link between signal transduction pathways and dynamic actin changes in determining cellular architecture. Several of these classes have been identified in pollen tubes and their detailed characterisation is progressing rapidly. Here, we aim to survey what is known about the major actin-binding proteins that affect actin assembly and dynamics, and their higher-order organisation in pollen tube growth.
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Affiliation(s)
- Haiyun Ren
- Key Laboratory of Cell Proliferation and Regulation Biology of the Ministry of Education, College of Life Science, Beijing Normal University, Beijing, People's Republic of China.
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129
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Dumont J, Million K, Sunderland K, Rassinier P, Lim H, Leader B, Verlhac MH. Formin-2 is required for spindle migration and for the late steps of cytokinesis in mouse oocytes. Dev Biol 2007; 301:254-65. [PMID: 16989804 DOI: 10.1016/j.ydbio.2006.08.044] [Citation(s) in RCA: 141] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2006] [Revised: 08/17/2006] [Accepted: 08/18/2006] [Indexed: 12/29/2022]
Abstract
Female meiotic divisions in higher organisms are asymmetric and lead to the formation of a large oocyte and small polar bodies. These asymmetric divisions are due to eccentric spindle positioning which, in the mouse, requires actin filaments. Recently Formin-2, a straight actin filaments nucleator, has been proposed to control spindle positioning, chromosome segregation as well as first polar body extrusion in mouse oocytes. We reexamine here the possible role of Formin-2 during mouse meiotic maturation by live videomicroscopy. We show that Formin-2 controls first meiotic spindle migration to the cortex but not chromosome congression or segregation. We also show that the lack of first polar body extrusion in fmn2(-/-) oocytes is not due to a lack of cortical differentiation or central spindle formation but to a defect in the late steps of cytokinesis. Indeed, Survivin, a component of the passenger protein complex, is correctly localized on the central spindle at anaphase in fmn2(-/-) oocytes. We show here that attempts of cytokinesis in these oocytes abort due to phospho-myosin II mislocalization.
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Affiliation(s)
- Julien Dumont
- Equipe Divisions Méiotiques Chez la Souris, UMR7622, CNRS, Université Pierre et Marie Curie-Paris 6, Bat C, 5e, 9 Quai Saint Bernard 75005, Paris, France
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130
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Formins: Bringing new insights to the organization of actin cytoskeleton. CHINESE SCIENCE BULLETIN-CHINESE 2006. [DOI: 10.1007/s11434-006-2214-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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131
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Gallo G. RhoA-kinase coordinates F-actin organization and myosin II activity during semaphorin-3A-induced axon retraction. J Cell Sci 2006; 119:3413-23. [PMID: 16899819 PMCID: PMC2821207 DOI: 10.1242/jcs.03084] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Axon guidance is mediated by the effects of attractant and repellent guidance cues on the cytoskeleton of growth cones and axons. During development, axon retraction is an important aspect of the pruning of inappropriately targeted axons in response to repellent guidance cues. I investigated the roles of RhoA-kinase and myosin II in semaphorin-3A-induced growth cone collapse and axon retraction. I report that semaphorin 3A activates myosin II in growth cones and axons. Myosin II activity is required for axon retraction but not growth cone collapse. Furthermore, semaphorin 3A promotes the formation of intra-axonal F-actin bundles in concert with the loss of F-actin in growth cone lamellipodia and filopodia. Formation of axonal F-actin bundles was independent of myosin II, but partially required RhoA-kinase activity. Conversely, RhoA-kinase activity was required to shut down F-actin polymerization underlying protrusive activity. Collectively, these observations suggest that guidance cues cause axon retraction through the coordinated activation of myosin II and the formation of intra-axonal F-actin bundles for myosin-II-based force generation. I suggest that in the context of semaphorin 3A signaling, RhoA-kinase serves as a switch to change the function of the F-actin cytoskeleton from promoting protrusive activity to generating contractile forces.
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Affiliation(s)
- Gianluca Gallo
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA 19129, USA.
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132
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Moseley JB, Goode BL. The yeast actin cytoskeleton: from cellular function to biochemical mechanism. Microbiol Mol Biol Rev 2006; 70:605-45. [PMID: 16959963 PMCID: PMC1594590 DOI: 10.1128/mmbr.00013-06] [Citation(s) in RCA: 287] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
All cells undergo rapid remodeling of their actin networks to regulate such critical processes as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. These events are driven by the coordinated activities of a set of 20 to 30 highly conserved actin-associated proteins, in addition to many cell-specific actin-associated proteins and numerous upstream signaling molecules. The combined activities of these factors control with exquisite precision the spatial and temporal assembly of actin structures and ensure dynamic turnover of actin structures such that cells can rapidly alter their cytoskeletons in response to internal and external cues. One of the most exciting principles to emerge from the last decade of research on actin is that the assembly of architecturally diverse actin structures is governed by highly conserved machinery and mechanisms. With this realization, it has become apparent that pioneering efforts in budding yeast have contributed substantially to defining the universal mechanisms regulating actin dynamics in eukaryotes. In this review, we first describe the filamentous actin structures found in Saccharomyces cerevisiae (patches, cables, and rings) and their physiological functions, and then we discuss in detail the specific roles of actin-associated proteins and their biochemical mechanisms of action.
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Affiliation(s)
- James B Moseley
- Department of Biology and The Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA
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133
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Seth A, Otomo C, Rosen MK. Autoinhibition regulates cellular localization and actin assembly activity of the diaphanous-related formins FRLalpha and mDia1. ACTA ACUST UNITED AC 2006; 174:701-13. [PMID: 16943183 PMCID: PMC2064313 DOI: 10.1083/jcb.200605006] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Diaphanous-related formins (DRFs) are key regulators of actin cytoskeletal dynamics whose in vitro actin assembly activities are thought to be regulated by autoinhibition. However, the in vivo consequences of autoinhibition and the involvement of DRFs in specific biological processes are not well understood. In this study, we show that in the DRFs FRLα (formin-related gene in leukocytes α) and mouse diaphanous 1, autoinhibition regulates a novel membrane localization activity in vivo as well as actin assembly activity in vitro. In FRLα, the Rho family guanosine triphosphatase Cdc42 relieves the autoinhibition of both membrane localization and biochemical actin assembly activities. FRLα is required for efficient Fc-γ receptor–mediated phagocytosis and is recruited to the phagocytic cup by Cdc42. These results suggest that mutual autoinhibition of biochemical activity and cellular localization may be a general regulatory principle for DRFs and demonstrate a novel role for formins in immune function.
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Affiliation(s)
- Abhinav Seth
- Department of Biochemistry, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA
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134
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Michelot A, Derivery E, Paterski-Boujemaa R, Guérin C, Huang S, Parcy F, Staiger CJ, Blanchoin L. A Novel Mechanism for the Formation of Actin-Filament Bundles by a Nonprocessive Formin. Curr Biol 2006; 16:1924-30. [PMID: 17027489 DOI: 10.1016/j.cub.2006.07.054] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Revised: 06/28/2006] [Accepted: 07/21/2006] [Indexed: 11/16/2022]
Abstract
Actin-filament bundles (or cables) have a structural role during cell division and morphogenesis, but also serve as important "tracks" for the transport of materials during cytokinesis and polarized cell growth. However, the dynamic formation of these longitudinal actin-filament higher-order structures is not understood. Recently, several lines of evidence suggest that formins provide one avenue for the initiation of actin cables in vivo. A popular model for the mechanism of polymerization of actin filaments by formin involves the processive movement of formin attached at the barbed end of an elongating filament. In the present study, we use an in vitro system to reconstitute the dynamic formation of actin-filament bundles generated by Arabidopsis FORMIN1 (AFH1). To be able to visualize individual events in such a complex system, we used real-time evanescent-wave microscopy. Surprisingly, we find that AFH1 is a nonprocessive formin that moves from the barbed end to the side of an actin filament after the nucleation event. We show why this new mechanism of nucleation by a member of the formin family is important for bundle formation. Finally, we analyze the different parameters controlling the dynamic formation of such longitudinal actin-filament bundles.
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Affiliation(s)
- Alphée Michelot
- Departement Réponse et Dynamique Cellulaire, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, F38054 Grenoble, France
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135
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Ménard I, Gervais FG, Nicholson DW, Roy S. Caspase-3 cleaves the formin-homology-domain-containing protein FHOD1 during apoptosis to generate a C-terminal fragment that is targeted to the nucleolus. Apoptosis 2006; 11:1863-76. [PMID: 17013756 DOI: 10.1007/s10495-006-0087-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The formin homology (FH) proteins play a crucial role in cytoskeleton remodelling during many essential processes. In this study, we demonstrate for the first time that the formin-homology-domain-containing protein FHOD1 is cleaved by caspase-3 at the SVPD(616) site during apoptosis. Using confocal microscopy, we further demonstrate that while full length FHOD1 is mostly cytoplasmic, the FHOD1 N-terminal cleavage product is diffusely localized throughout the cytoplasm and the nucleoplasm, whereas the C-terminal cleavage product is almost exclusively nuclear with some nucleolar localization. Finally, using a run-on transcription assay we show that the C-terminal FHOD1 cleavage product has the ability to inhibit RNA polymerase I transcription when overexpressed in HeLa cells as shown by blockage of BrUTP incorporation.
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Affiliation(s)
- Isabelle Ménard
- Department of Biochemistry, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada, H3G 1Y6
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136
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Yae K, Keng VW, Koike M, Yusa K, Kouno M, Uno Y, Kondoh G, Gotow T, Uchiyama Y, Horie K, Takeda J. Sleeping beauty transposon-based phenotypic analysis of mice: lack of Arpc3 results in defective trophoblast outgrowth. Mol Cell Biol 2006; 26:6185-96. [PMID: 16880528 PMCID: PMC1592801 DOI: 10.1128/mcb.00018-06] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Sleeping Beauty (SB) transposon system has generated many transposon-insertional mutant mouse lines, some of which have resulted in embryonic lethality when bred to homozygosity. Here we report one such insertion mapped to the mouse actin-related protein complex subunit 3 gene (Arpc3). Arpc3 is a component of the Arp2/3 complex, which plays a major role in actin nucleation with Y-shaped branching from the mother actin filament in response to migration signaling. Arpc3 transposon-inserted mutants developed only to the blastocyst stage. In vitro blastocyst culture of Arpc3 mutants exhibited severe spreading impairment of trophoblasts. This phenotype was also observed in compound heterozygotes generated using conventional gene-targeted and transposon-inserted alleles. Arpc3-deficient mutants were shown to lack actin-rich structures in the spreading trophoblast. Electron microscopic analysis demonstrated the lack of mesh-like structures at the cell periphery, suggesting a role of Arpc3 in Y-shaped branching formation. These data indicate the importance of Arpc3 in the Arp2/3 complex for trophoblast outgrowth and suggest that Arpc3 may be indispensable for implantation.
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Affiliation(s)
- Kojiro Yae
- Department of Social and Environmental Medicine H3, Osaka University, Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
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137
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Sun QY, Schatten H. Regulation of dynamic events by microfilaments during oocyte maturation and fertilization. Reproduction 2006; 131:193-205. [PMID: 16452714 DOI: 10.1530/rep.1.00847] [Citation(s) in RCA: 200] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Actin filaments (microfilaments) regulate various dynamic events during oocyte meiotic maturation and fertilization. In most species, microfilaments are not required for germinal vesicle breakdown and meiotic spindle formation, but they mediate peripheral nucleus (chromosome) migration, cortical spindle anchorage, homologous chromosome separation, cortex development/maintenance, polarity establishment, and first polar body emission during oocyte maturation. Peripheral cortical granule migration is controlled by microfilaments, while mitochondria movement is mediated by microtubules. During fertilization, microfilaments are involved in sperm incorporation, spindle rotation (mouse), cortical granule exocytosis, second polar body emission and cleavage ring formation, but are not required for pronuclear apposition (except for the mouse). Many of the events are driven by the dynamic interactions between myosin and actin filaments whose polymerization is regulated by RhoA, Cdc42, Arp2/3 and other signaling molecules. Studies have also shown that oocyte cortex organization and polarity formation mediated by actin filaments are regulated by mitogen-activated protein kinase, myosin light-chain kinase, protein kinase C and its substrate p-MARKS as well as PAR proteins. The completion of several dynamic events, including homologous chromosome separation, spindle anchorage, spindle rotation, vesicle organelle transport and pronuclear apposition (mouse), requires interactions between microfilaments and microtubules, but determination of how the two systems of the cytoskeleton precisely cross-link, and which proteins link microfilaments to microtubules to perform functions in eggs, requires further studies. Finally, the meaning of microfilament-mediated oocyte polarity versus embryo polarity and embryo development in different species (Drosophila, Xenopus and mouse) is discussed.
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Affiliation(s)
- Qing-Yuan Sun
- State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China
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138
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Rida PC, Nishikawa A, Won GY, Dean N. Yeast-to-hyphal transition triggers formin-dependent Golgi localization to the growing tip in Candida albicans. Mol Biol Cell 2006; 17:4364-78. [PMID: 16855023 PMCID: PMC1635370 DOI: 10.1091/mbc.e06-02-0143] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Rapid and long-distance secretion of membrane components is critical for hyphal formation in filamentous fungi, but the mechanisms responsible for polarized trafficking are not well understood. Here, we demonstrate that in Candida albicans, the majority of the Golgi complex is redistributed to the distal region during hyphal formation. Randomly distributed Golgi puncta in yeast cells cluster toward the growing tip during hyphal formation, remain associated with the distal portion of the filament during its extension, and are almost absent from the cell body. This restricted Golgi localization pattern is distinct from other organelles, including the endoplasmic reticulum, vacuole and mitochondria, which remain distributed throughout the cell body and hypha. Hyphal-induced positioning of the Golgi and the maintenance of its structural integrity requires actin cytoskeleton, but not microtubules. Absence of the formin Bni1 causes a hyphal-specific dispersal of the Golgi into a haze of finely dispersed vesicles with a sedimentation density no different from that of normal Golgi. These results demonstrate the existence of a hyphal-specific, Bni1-dependent cue for Golgi integrity and positioning at the distal portion of the hyphal tip, and suggest that filamentous fungi have evolved a novel strategy for polarized secretion, involving a redistribution of the Golgi to the growing tip.
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Affiliation(s)
- Padmashree C.G. Rida
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Akiko Nishikawa
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Gena Y. Won
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Neta Dean
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
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139
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Abstract
Formins constitute a diverse protein family present in all eukaryotes examined. They are defined by the presence of a formin homology 2 (FH2) domain, which possesses intrinsic and conserved functions regulating cytoskeletal dynamics. Over the past few years, formins have become recognized as potent nucleators of linear actin filaments that control a large variety of cellular and morphogenetic functions. Here, we review the molecular principles of formin-induced cytoskeletal rearrangements and their consequences for a growing number of biological processes.
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Affiliation(s)
- Jan Faix
- Institute for Biophysical Chemistry, Hannover Medical School, 30623 Hannover, Germany.
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140
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Virag A, Harris SD. Functional characterization of Aspergillus nidulans homologues of Saccharomyces cerevisiae Spa2 and Bud6. EUKARYOTIC CELL 2006; 5:881-95. [PMID: 16757736 PMCID: PMC1489272 DOI: 10.1128/ec.00036-06] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2006] [Accepted: 04/12/2006] [Indexed: 11/20/2022]
Abstract
The importance of polarized growth for fungi has elicited significant effort directed at better understanding underlying mechanisms of polarization, with a focus on yeast systems. At sites of tip growth, multiple protein complexes assemble and coordinate to ensure that incoming building material reaches the appropriate destination sites, and polarized growth is maintained. One of these complexes is the polarisome that consists of Spa2, Bud6, Pea2, and Bni1 in Saccharomyces cerevisiae. Filamentous hyphae differ in their development and life style from yeasts and likely regulate polarized growth in a different way. This is expected to reflect on the composition and presence of protein complexes that assemble at the hyphal tip. In this study we searched for polarisome homologues in the model filamentous fungus Aspergillus nidulans and characterized the S. cerevisiae Spa2 and Bud6 homologues, SpaA and BudA. Compared to the S. cerevisiae Spa2, SpaA lacks domain II but has three additional domains that are conserved within filamentous fungi. Gene replacement strains and localization studies show that SpaA functions exclusively at the hyphal tip, while BudA functions at sites of septum formation and possibly at hyphal tips. We show that SpaA is not required for the assembly or maintenance of the Spitzenkörper. We propose that the core function of the polarisome in polarized growth is maintained but with different contributions of polarisome components to the process.
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Affiliation(s)
- Aleksandra Virag
- Plant Science Initiative, and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68588-0660, USA
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141
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Matusek T, Djiane A, Jankovics F, Brunner D, Mlodzik M, Mihály J. The Drosophila formin DAAM regulates the tracheal cuticle pattern through organizing the actin cytoskeleton. Development 2006; 133:957-66. [PMID: 16469972 DOI: 10.1242/dev.02266] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Formins are involved in a wide range of cellular processes that require the remodeling of the actin cytoskeleton. Here, we have analyzed a novel Drosophila formin, belonging to the recently described DAAM subfamily. In contrast to previous assumptions, we show that DAAM plays no essential role in planar cell polarity signaling, but it has striking requirements in organizing apical actin cables that define the taenidial fold pattern of the tracheal cuticle. These observations provide evidence the first time that the function of the taenidial organization is to prevent the collapse of the tracheal tubes. Our results indicate that although DAAM is regulated by RhoA, it functions upstream or parallel to the non-receptor tyrosine kinases Src42A and Tec29 to organize the actin cytoskeleton and to determine the cuticle pattern of the Drosophila respiratory system.
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Affiliation(s)
- Tamás Matusek
- Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, H-6726 Szeged, Temesvári krt. 62, Hungary
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142
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Bugyi B, Papp G, Hild G, Lõrinczy D, Nevalainen EM, Lappalainen P, Somogyi B, Nyitrai M. Formins regulate actin filament flexibility through long range allosteric interactions. J Biol Chem 2006; 281:10727-36. [PMID: 16490788 PMCID: PMC2865996 DOI: 10.1074/jbc.m510252200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The members of the formin family nucleate actin polymerization and play essential roles in the regulation of the actin cytoskeleton during a wide range of cellular and developmental processes. In the present work, we describe the effects of mDia1-FH2 on the conformation of actin filaments by using a temperature-dependent fluorescence resonance energy transfer method. Our results revealed that actin filaments were more flexible in the presence than in the absence of formin. The effect strongly depends on the mDia1-FH2 concentration in a way that indicates that more than one mechanism is responsible for the formin effect. In accordance with the more flexible filament structure, the thermal stability of actin decreased and the rate of phosphate dissociation from actin filaments increased in the presence of formin. The interpretation of the results supports a model in which formin binding to barbed ends makes filaments more flexible through long range allosteric interactions, whereas binding of formin to the sides of the filaments stabilizes the protomer-protomer interactions. These results suggest that formins can regulate the conformation of actin filaments and may thus also modulate the affinity of actin-binding proteins to filaments nucleated/capped by formins.
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Affiliation(s)
- Beáta Bugyi
- Department of Biophysics, Faculty of Medicine, University of Pécs, Pécs, Szigeti str. 12, H-7624, Hungary
| | - Gábor Papp
- Department of Biophysics, Faculty of Medicine, University of Pécs, Pécs, Szigeti str. 12, H-7624, Hungary
| | - Gábor Hild
- Research Group for Fluorescence Spectroscopy, Office for Academy Research Groups Attached to Universities and Other Institutions at the:
| | - Dénes Lõrinczy
- Department of Biophysics, Faculty of Medicine, University of Pécs, Pécs, Szigeti str. 12, H-7624, Hungary
| | - Elisa M. Nevalainen
- Program in Cellular Biotechnology, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Pekka Lappalainen
- Program in Cellular Biotechnology, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | - Béla Somogyi
- Research Group for Fluorescence Spectroscopy, Office for Academy Research Groups Attached to Universities and Other Institutions at the:
- Department of Biophysics, Faculty of Medicine, University of Pécs, Pécs, Szigeti str. 12, H-7624, Hungary
| | - Miklós Nyitrai
- Department of Biophysics, Faculty of Medicine, University of Pécs, Pécs, Szigeti str. 12, H-7624, Hungary
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143
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Abstract
Acanthamoeba CARMIL was previously shown to co-purify with capping protein (CP) and to bind pure CP. Here we show that this interaction inhibits the barbed end-capping activity of CP. Even more strikingly, this interaction drives the uncapping of actin filaments previously capped with CP. These activities are CP-specific; CARMIL does not inhibit the capping activities of either gelsolin or CapG and does not uncap gelsolin-capped filaments. Although full-length (FL) CARMIL (residues 1-1121) possesses both anti-CP activities, C-terminal fragments like glutathione S-transferase (GST)-P (940-1121) that contain the CARMIL CP binding site are at least 10 times more active. We localized the full activities of GST-P to its C-terminal 51 residues (1071-1121). This sequence contains a stretch of 25 residues that is highly conserved in CARMIL proteins from protozoa, flies, worms, and vertebrates (CARMIL Homology domain 3; CAH3). Point mutations showed that the majority of the most highly conserved residues within CAH3 are critical for the anti-CP activity of GST-AP (862-1121). Finally, we found that GST-AP binds CP approximately 20-fold more tightly than does FL-CARMIL. This observation together with the elevated activities of C-terminal fragments relative to FL-CARMIL suggests that FL-CARMIL might exist primarily in an autoinhibited state. Consistent with this idea, proteolytic cleavage of FL-CARMIL with thrombin generated an approximately 14-kDa C-terminal fragment that expresses full anti-CP activities. We propose that, after some type of physiological activation event, FL-CARMIL could function in vivo as a potent CP antagonist. Given the pivotal role that CP plays in determining the global actin phenotype of cells, our results suggest that CARMIL may play an important role in the physiological regulation of actin assembly.
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Affiliation(s)
- Takehito Uruno
- Laboratory of Cell Biology, Section on Molecular Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Rm. 2523, 9000 Rockville Pike, Bethesda, MD 20892-8017, USA
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144
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Yoshiuchi S, Yamamoto T, Sakane H, Kadota J, Mochida J, Asaka M, Tanaka K. Identification of novel mutations in ACT1 and SLA2 that suppress the actin-cable-overproducing phenotype caused by overexpression of a dominant active form of Bni1p in Saccharomyces cerevisiae. Genetics 2006; 173:527-39. [PMID: 16547104 PMCID: PMC1526543 DOI: 10.1534/genetics.105.055210] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A formin Bni1p nucleates actin to assemble actin cables, which guide the polarized transport of secretory vesicles in budding yeast. We identified mutations that suppressed both the lethality and the excessive actin cable formation caused by overexpression of a truncated Bni1p (BNI1DeltaN). Two recessive mutations, act1-301 in the actin gene and sla2-82 in a gene involved in cortical actin patch assembly, were identified. The isolation of sla2-82 was unexpected, because cortical actin patches are required for the internalization step of endocytosis. Both act1-301 and sla2-82 exhibited synthetic growth defects with bni1Delta. act1-301, which resulted in an E117K substitution, interacted genetically with mutations in profilin (PFY1) and BUD6, suggesting that Act1-301p was not fully functional in formin-mediated polymerization. sla2-82 also interacted genetically with genes involved in actin cable assembly. Some experiments, however, suggested that the effects of sla2-82 were caused by depletion of actin monomers, because the temperature-sensitive growth phenotype of the bni1Delta sla2-82 mutant was suppressed by increased expression of ACT1. The isolation of suppressors of the BNI1DeltaN phenotype may provide a useful system for identification of actin amino-acid residues that are important for formin-mediated actin polymerization and mutations that affect the availability of actin monomers.
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Affiliation(s)
- Shiro Yoshiuchi
- Division of Molecular Interaction, Institute of Genetic Medicine, Hokkaido University Graduate School of Medicine, Sapporo 060-0815, Japan
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145
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Rosales-Nieves AE, Johndrow JE, Keller LC, Magie CR, Pinto-Santini DM, Parkhurst SM. Coordination of microtubule and microfilament dynamics by Drosophila Rho1, Spire and Cappuccino. Nat Cell Biol 2006; 8:367-76. [PMID: 16518391 PMCID: PMC1997291 DOI: 10.1038/ncb1385] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2005] [Accepted: 02/20/2006] [Indexed: 11/08/2022]
Abstract
The actin-nucleation factors Spire and Cappuccino (Capu) regulate the onset of ooplasmic streaming in Drosophila melanogaster. Although this streaming event is microtubule-based, actin assembly is required for its timing. It is not understood how the interaction of microtubules and microfilaments is mediated in this context. Here, we demonstrate that Capu and Spire have microtubule and microfilament crosslinking activity. The spire locus encodes several distinct protein isoforms (SpireA, SpireC and SpireD). SpireD was recently shown to nucleate actin, but the activity of the other isoforms has not been addressed. We find that SpireD does not have crosslinking activity, whereas SpireC is a potent crosslinker. We show that SpireD binds to Capu and inhibits F-actin/microtubule crosslinking, and activated Rho1 abolishes this inhibition, establishing a mechanistic basis for the regulation of Capu and Spire activity. We propose that Rho1, cappuccino and spire are elements of a conserved developmental cassette that is capable of directly mediating crosstalk between microtubules and microfilaments.
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Affiliation(s)
- Alicia E. Rosales-Nieves
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA
| | - James E. Johndrow
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA
| | - Lani C. Keller
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA
| | - Craig R. Magie
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA
| | - Delia M. Pinto-Santini
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA
| | - Susan M. Parkhurst
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, Washington 98109-1024, USA
- Correspondence should be addressed to S.M.P ()
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146
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Nezami AG, Poy F, Eck MJ. Structure of the Autoinhibitory Switch in Formin mDia1. Structure 2006; 14:257-63. [PMID: 16472745 DOI: 10.1016/j.str.2005.12.003] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2005] [Revised: 12/08/2005] [Accepted: 12/13/2005] [Indexed: 11/23/2022]
Abstract
Diaphanous-related formins (DRFs) regulate the nucleation and polymerization of unbranched actin filaments. The activity of DRFs is inhibited by an intramolecular interaction between their N-terminal regulatory region and a conserved C-terminal segment termed the Diaphanous autoinhibitory domain (DAD). Binding of GTP bound Rho to the mDia1 N terminus releases this autoinhibitory restraint. Here, we describe the crystal structure of the DAD segment of mDia1 in complex with the relevant N-terminal fragment, termed the DID domain. The structure reveals that the DAD segment forms an amphipathic helix that binds a conserved, concave surface on the DID domain. Comparison with the structure of the mDia1 N terminus bound to RhoC suggests that release of the autoinhibitory DAD interaction is accomplished largely by Rho-induced restructuring of the adjacent GTPase binding subdomain (GBD), but also by electrostatic repulsion and a small, direct steric occlusion of the DAD binding cleft by Rho itself.
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Affiliation(s)
- Azin G Nezami
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 44 Binney Street, Boston, Massachusetts 02115, USA
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147
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Abstract
The formation of highly polarized hyphae that grow by apical extension is a defining feature of the filamentous fungi. High-resolution microscopy and mathematical modeling have revealed the importance of the cytoskeleton and the Spitzenkorper (an apical vesicle cluster) in hyphal morphogenesis. However, the underlying molecular mechanisms remain poorly characterized. In this review, the pathways and functions known to be involved in polarized hyphal growth are summarized. A central theme is the notion that the polarized growth of hyphae is more complex than in yeast, though similar sets of core pathways are likely utilized. In addition, a model for the establishment and maintenance of hyphal polarity is presented. Key features of the model include the idea that polarity establishment is a stochastic process that occurs independent of internal landmarks. Moreover, the stabilization of nascent polarity axes may be the critical step that permits the emergence of a new hypha.
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Affiliation(s)
- Steven D Harris
- Plant Science Initiative and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68588, USA
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148
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Martin R, Walther A, Wendland J. Ras1-induced hyphal development in Candida albicans requires the formin Bni1. EUKARYOTIC CELL 2005; 4:1712-24. [PMID: 16215178 PMCID: PMC1265897 DOI: 10.1128/ec.4.10.1712-1724.2005] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Formins are downstream effector proteins of Rho-type GTPases and are involved in the organization of the actin cytoskeleton and actin cable assembly at sites of polarized cell growth. Here we show using in vivo time-lapse microscopy that deletion of the Candida albicans formin homolog BNI1 results in polarity defects during yeast growth and hyphal stages. Deletion of the second C. albicans formin, BNR1, resulted in elongated yeast cells with cell separation defects but did not interfere with the ability of bnr1 cells to initiate and maintain polarized hyphal growth. Yeast bni1 cells were swollen, showed an increased random budding pattern, and had a severe defect in cytokinesis, with enlarged bud necks. Induction of hyphal development in bni1 cells resulted in germ tube formation but was halted at the step of polarity maintenance. Bni1-green fluorescent protein is found persistently at the hyphal tip and colocalizes with a structure resembling the Spitzenkörper of true filamentous fungi. Introduction of constitutively active ras1G13V in the bni1 strain or addition of cyclic AMP to the growth medium did not bypass bni1 hyphal growth defects. Similarly, these agents were not able to suppress hyphal growth defects in the wal1 mutant which is lacking the Wiskott-Aldrich syndrome protein (WASP) homolog. These results suggest that the maintenance of polarized hyphal growth in C. albicans requires coordinated regulation of two actin cytoskeletal pathways, including formin-mediated secretion and WASP-dependent endocytosis.
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Affiliation(s)
- Ronny Martin
- Junior Research Group: Growth Control of Fungal Pathogens, Leibniz Institute for Natural Products Research and Infection Biology, Friedrich-Schiller-University, Beutenbergstr. 11a, D-07745 Jena, Germany
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149
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Kishimoto T, Yamamoto T, Tanaka K. Defects in structural integrity of ergosterol and the Cdc50p-Drs2p putative phospholipid translocase cause accumulation of endocytic membranes, onto which actin patches are assembled in yeast. Mol Biol Cell 2005; 16:5592-609. [PMID: 16195350 PMCID: PMC1289405 DOI: 10.1091/mbc.e05-05-0452] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Revised: 08/24/2005] [Accepted: 09/15/2005] [Indexed: 11/11/2022] Open
Abstract
Specific changes in membrane lipid composition are implicated in actin cytoskeletal organization, vesicle formation, and control of cell polarity. Cdc50p, a membrane protein in the endosomal/trans-Golgi network compartments, is a noncatalytic subunit of Drs2p, which is implicated in translocation of phospholipids across lipid bilayers. We found that the cdc50Delta mutation is synthetically lethal with mutations affecting the late steps of ergosterol synthesis (erg2 to erg6). Defects in cell polarity and actin organization were observed in the cdc50Delta erg3Delta mutant. In particular, actin patches, which are normally found at cortical sites, were assembled intracellularly along with their assembly factors, including Las17p, Abp1p, and Sla2p. The exocytic SNARE Snc1p, which is recycled by an endocytic route, was also intracellularly accumulated, and inhibition of endocytic internalization suppressed the cytoplasmic accumulation of both Las17p and Snc1p. Simultaneous loss of both phospholipid asymmetry and sterol structural integrity could lead to accumulation of endocytic intermediates capable of initiating assembly of actin patches in the cytoplasm.
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Affiliation(s)
- Takuma Kishimoto
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Medicine, N15 W7, Kita-ku, Sapporo 060-0815, Japan
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Lammers M, Rose R, Scrima A, Wittinghofer A. The regulation of mDia1 by autoinhibition and its release by Rho*GTP. EMBO J 2005; 24:4176-87. [PMID: 16292343 PMCID: PMC1356318 DOI: 10.1038/sj.emboj.7600879] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2005] [Accepted: 10/26/2005] [Indexed: 11/08/2022] Open
Abstract
Formins induce the nucleation and polymerisation of unbranched actin filaments via the formin-homology domains 1 and 2. Diaphanous-related formins (Drfs) are regulated by a RhoGTPase-binding domain situated in the amino-terminal (N-terminal) region and a carboxy-terminal Diaphanous-autoregulatory domain (DAD), whose interaction stabilises an autoinhibited inactive conformation. Binding of active Rho releases DAD and activates the catalytic activity of mDia. Here, we report on the interaction of DAD with the regulatory N-terminus of mDia1 (mDia(N)) and its release by Rho*GTP. We have defined the elements required for tight binding and solved the three-dimensional structure of a complex between an mDia(N) construct and DAD by X-ray crystallography. The core DAD region is an alpha-helical peptide, which binds in the most highly conserved region of mDia(N) using mainly hydrophobic interactions. The structure suggests a two-step mechanism for release of autoinhibition whereby Rho*GTP, although having a partially nonoverlapping binding site, displaces DAD by ionic repulsion and steric clashes. We show that Rho*GTP accelerates the dissociation of DAD from the mDia(N)*DAD complex.
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Affiliation(s)
- Michael Lammers
- Department of Structural Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
| | - Rolf Rose
- Department of Structural Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
| | - Andrea Scrima
- Department of Structural Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
| | - Alfred Wittinghofer
- Department of Structural Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
- Department of Structural Biology, Max-Planck-Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany. Tel.: +49 231 133 2100; Fax: +49 231 133 2199; E-mail:
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