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Stephan OOH. Effects of environmental stress factors on the actin cytoskeleton of fungi and plants: Ionizing radiation and ROS. Cytoskeleton (Hoboken) 2023; 80:330-355. [PMID: 37066976 DOI: 10.1002/cm.21758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 03/20/2023] [Accepted: 03/29/2023] [Indexed: 04/18/2023]
Abstract
Actin is an abundant and multifaceted protein in eukaryotic cells that has been detected in the cytoplasm as well as in the nucleus. In cooperation with numerous interacting accessory-proteins, monomeric actin (G-actin) polymerizes into microfilaments (F-actin) which constitute ubiquitous subcellular higher order structures. Considering the extensive spatial dimensions and multifunctionality of actin superarrays, the present study analyses the issue if and to what extent environmental stress factors, specifically ionizing radiation (IR) and reactive oxygen species (ROS), affect the cellular actin-entity. In that context, this review particularly surveys IR-response of fungi and plants. It examines in detail which actin-related cellular constituents and molecular pathways are influenced by IR and related ROS. This comprehensive survey concludes that the general integrity of the total cellular actin cytoskeleton is a requirement for IR-tolerance. Actin's functions in genome organization and nuclear events like chromatin remodeling, DNA-repair, and transcription play a key role. Beyond that, it is highly significant that the macromolecular cytoplasmic and cortical actin-frameworks are affected by IR as well. In response to IR, actin-filament bundling proteins (fimbrins) are required to stabilize cables or patches. In addition, the actin-associated factors mediating cellular polarity are essential for IR-survivability. Moreover, it is concluded that a cellular homeostasis system comprising ROS, ROS-scavengers, NADPH-oxidases, and the actin cytoskeleton plays an essential role here. Consequently, besides the actin-fraction which controls crucial genome-integrity, also the portion which facilitates orderly cellular transport and polarized growth has to be maintained in order to survive IR.
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Affiliation(s)
- Octavian O H Stephan
- Department of Biology, Friedrich-Alexander University of Erlangen-Nuremberg, Erlangen, Bavaria, 91058, Germany
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2
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Lawson MJ, Drawert B, Petzold L, Yi TM. A positive feedback loop involving the Spa2 SHD domain contributes to focal polarization. PLoS One 2022; 17:e0263347. [PMID: 35134079 PMCID: PMC8824340 DOI: 10.1371/journal.pone.0263347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2021] [Accepted: 01/16/2022] [Indexed: 11/18/2022] Open
Abstract
Focal polarization is necessary for finely arranged cell-cell interactions. The yeast mating projection, with its punctate polarisome, is a good model system for this process. We explored the critical role of the polarisome scaffold protein Spa2 during yeast mating with a hypothesis motivated by mathematical modeling and tested by in vivo experiments. Our simulations predicted that two positive feedback loops generate focal polarization, including a novel feedback pathway involving the N-terminal domain of Spa2. We characterized the latter using loss-of-function and gain-of-function mutants. The N-terminal region contains a Spa2 Homology Domain (SHD) which is conserved from yeast to humans, and when mutated largely reproduced the spa2Δ phenotype. Our work together with published data show that the SHD domain recruits Msb3/4 that stimulates Sec4-mediated transport of Bud6 to the polarisome. There, Bud6 activates Bni1-catalyzed actin cable formation, recruiting more Spa2 and completing the positive feedback loop. We demonstrate that disrupting this loop at any point results in morphological defects. Gain-of-function perturbations partially restored focal polarization in a spa2 loss-of-function mutant without restoring localization of upstream components, thus supporting the pathway order. Thus, we have collected data consistent with a novel positive feedback loop that contributes to focal polarization during pheromone-induced polarization in yeast.
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Affiliation(s)
- Michael J. Lawson
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States of America
| | - Brian Drawert
- Department of Computer Science, University of North Carolina Asheville, Asheville, NC, United States of America
| | - Linda Petzold
- Department of Computer Science, University of California, Santa Barbara, Santa Barbara, CA, United States of America
| | - Tau-Mu Yi
- Molecular, Cellular, and Developmental Biology, 3131 Biological Sciences II, University of California, Santa Barbara, Santa Barbara, CA, United States of America
- * E-mail:
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3
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Ghose D, Jacobs K, Ramirez S, Elston T, Lew D. Chemotactic movement of a polarity site enables yeast cells to find their mates. Proc Natl Acad Sci U S A 2021; 118:e2025445118. [PMID: 34050026 PMCID: PMC8179161 DOI: 10.1073/pnas.2025445118] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
How small eukaryotic cells can interpret dynamic, noisy, and spatially complex chemical gradients to orient growth or movement is poorly understood. We address this question using Saccharomyces cerevisiae, where cells orient polarity up pheromone gradients during mating. Initial orientation is often incorrect, but polarity sites then move around the cortex in a search for partners. We find that this movement is biased by local pheromone gradients across the polarity site: that is, movement of the polarity site is chemotactic. A bottom-up computational model recapitulates this biased movement. The model reveals how even though pheromone-bound receptors do not mimic the shape of external pheromone gradients, nonlinear and stochastic effects combine to generate effective gradient tracking. This mechanism for gradient tracking may be applicable to any cell that searches for a target in a complex chemical landscape.
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Affiliation(s)
- Debraj Ghose
- Computational Biology and Bioinformatics, Duke University, Durham, NC 27710
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710
| | - Katherine Jacobs
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710
| | - Samuel Ramirez
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Timothy Elston
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Daniel Lew
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710;
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4
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Dünkler A, Leda M, Kromer JM, Neller J, Gronemeyer T, Goryachev AB, Johnsson N. Type V myosin focuses the polarisome and shapes the tip of yeast cells. J Cell Biol 2021; 220:211845. [PMID: 33656555 PMCID: PMC7933982 DOI: 10.1083/jcb.202006193] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 01/25/2021] [Accepted: 02/04/2021] [Indexed: 11/22/2022] Open
Abstract
The polarisome is a cortical proteinaceous microcompartment that organizes the growth of actin filaments and the fusion of secretory vesicles in yeasts and filamentous fungi. Polarisomes are compact, spotlike structures at the growing tips of their respective cells. The molecular forces that control the form and size of this microcompartment are not known. Here we identify a complex between the polarisome subunit Pea2 and the type V Myosin Myo2 that anchors Myo2 at the cortex of yeast cells. We discovered a point mutation in the cargo-binding domain of Myo2 that impairs the interaction with Pea2 and consequently the formation and focused localization of the polarisome. Cells carrying this mutation grow round instead of elongated buds. Further experiments and biophysical modeling suggest that the interactions between polarisome-bound Myo2 motors and dynamic actin filaments spatially focus the polarisome and sustain its compact shape.
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Affiliation(s)
- Alexander Dünkler
- Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, Ulm, Germany
| | - Marcin Leda
- Centre for Synthetic and Systems Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh, UK
| | - Jan-Michael Kromer
- Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, Ulm, Germany
| | - Joachim Neller
- Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, Ulm, Germany
| | - Thomas Gronemeyer
- Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, Ulm, Germany
| | - Andrew B Goryachev
- Centre for Synthetic and Systems Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh, UK
| | - Nils Johnsson
- Institute of Molecular Genetics and Cell Biology, Department of Biology, Ulm University, Ulm, Germany
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5
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Xie Y, Miao Y. Polarisome assembly mediates actin remodeling during polarized yeast and fungal growth. J Cell Sci 2021; 134:134/1/jcs247916. [PMID: 33419950 DOI: 10.1242/jcs.247916] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Dynamic assembly and remodeling of actin is critical for many cellular processes during development and stress adaptation. In filamentous fungi and budding yeast, actin cables align in a polarized manner along the mother-to-daughter cell axis, and are essential for the establishment and maintenance of polarity; moreover, they rapidly remodel in response to environmental cues to achieve an optimal system response. A formin at the tip region within a macromolecular complex, called the polarisome, is responsible for driving actin cable polymerization during polarity establishment. This polarisome undergoes dynamic assembly through spatial and temporally regulated interactions between its components. Understanding this process is important to comprehend the tuneable activities of the formin-centered nucleation core, which are regulated through divergent molecular interactions and assembly modes within the polarisome. In this Review, we focus on how intrinsically disordered regions (IDRs) orchestrate the condensation of the polarisome components and the dynamic assembly of the complex. In addition, we address how these components are dynamically distributed in and out of the assembly zone, thereby regulating polarized growth. We also discuss the potential mechanical feedback mechanisms by which the force-induced actin polymerization at the tip of the budding yeast regulates the assembly and function of the polarisome.
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Affiliation(s)
- Ying Xie
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - Yansong Miao
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
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6
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Waszczak N, DeFlorio R, Ismael A, Cheng N, Stone DE, Metodiev MV. Quantitative proteomics reveals a Gα/MAPK signaling hub that controls pheromone-induced cellular polarization in yeast. J Proteomics 2019; 207:103467. [PMID: 31351147 DOI: 10.1016/j.jprot.2019.103467] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 07/20/2019] [Accepted: 07/23/2019] [Indexed: 12/26/2022]
Abstract
The mating-specific yeast Gα controls pheromone signaling by sequestering Gβγ and by regulating the Fus3 MAP kinase. Disrupting Gα-Fus3 interaction leads to severe defects in chemotropism. Because Gα concentrates at the chemotropic growth site where Fus3 is required for the phosphorylation of two known targets, we screened for additional proteins whose phosphorylation depends on pheromone stimulation and Gα-Fus3 interaction. Using a mutant form of Gα severely defective in Fus3-binding, GαDSD, and quantitative mass spectrometry, fourteen proteins were identified as potential targets of Gα-recruited Fus3, ten of which were previously implicated in cell polarity and morphogenesis. To explore the biological relevance of these findings, we focused on the Spa2 polarisome protein, which was hypophosphorylated on multiple serine residues in pheromone-treated GαDSD cells. Six sites were mutagenized to create the Spa26XSA mutant protein. Spa26XSA exhibited increased affinity for Fus3, consistent with a kinase-substrate interaction, and Spa26XSA cells exhibited dramatic defects in gradient sensing and zygote formation. These results suggest that Gα promotes the phosphorylation of Spa2 by Fus3 at the cortex of pheromone-stimulated cells, and that this mechanism plays a role in chemotropism. How the Gα-Fus3 signaling hub affects the other putative targets identified here has yet to be determined. SIGNIFICANCE: Previously, interaction between the G alpha protein, Gpa1, and the MAPK of the pheromone response pathway, Fus3, was shown to be important for efficient sensing of the pheromone gradient and for the maintenance of cell polarity during mating. Here we show that the underlying molecular mechanisms involve the phosphorylation of specific cortical targets of Gpa1/Fus3. These have been identified by quantitative phosphoproteomics using a mutant of Gpa1, which is defective in interacting with Fus3. One of these targets is the polarisome protein Spa2. Alanine substitution of the Spa2 phosphorylation sites targeted by Gpa1/Fus3 lead to a dramatic defect in pheromone gradient sensing and zygote formation. These results reveal how the G alpha protein and the MAPK control cell polarity in a prototypical model system. Our results have wider significance as similar mechanisms exist in higher eukaryotes and are involved in important biological such as neuron development, immunity, and cancer cell metastasis.
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Affiliation(s)
- Nicholaz Waszczak
- Department of Biological Sciences, University of Illinois at Chicago, 900 South Ashland Ave, Chicago, USA
| | - Reagan DeFlorio
- Department of Biological Sciences, University of Illinois at Chicago, 900 South Ashland Ave, Chicago, USA
| | - Amber Ismael
- Department of Biological Sciences, University of Illinois at Chicago, 900 South Ashland Ave, Chicago, USA
| | - Naiyuan Cheng
- Department of Biological Sciences, University of Illinois at Chicago, 900 South Ashland Ave, Chicago, USA
| | - David E Stone
- Department of Biological Sciences, University of Illinois at Chicago, 900 South Ashland Ave, Chicago, USA.
| | - Metodi V Metodiev
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, UK.
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7
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Kang PJ, Miller KE, Guegueniat J, Beven L, Park HO. The shared role of the Rsr1 GTPase and Gic1/Gic2 in Cdc42 polarization. Mol Biol Cell 2018; 29:2359-2369. [PMID: 30091649 PMCID: PMC6233053 DOI: 10.1091/mbc.e18-02-0145] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The Cdc42 GTPase plays a central role in polarity development in many species. In budding yeast, Cdc42 is essential for polarized growth at the proper site and also for spontaneous cell polarization in the absence of spatial cues. Cdc42 polarization is critical for multiple events in the G1 phase prior to bud emergence, including bud-site assembly, polarization of the actin cytoskeleton, and septin filament assembly to form a ring at the new bud site. Yet the mechanism by which Cdc42 polarizes is not fully understood. Here we report that biphasic Cdc42 polarization in the G1 phase is coupled to stepwise assembly of the septin ring for bud emergence. We show that the Rsr1 GTPase shares a partially redundant role with Gic1 and Gic2, two related Cdc42 effectors, in the first phase of Cdc42 polarization in haploid cells. We propose that the first phase of Cdc42 polarization is mediated by positive feedback loops that function in parallel-one involving Rsr1 via local activation of Cdc42 in response to spatial cues and another involving Gic1 or Gic2 via reduction of diffusion of active Cdc42.
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Affiliation(s)
- Pil Jung Kang
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Kristi E Miller
- Molecular Cellular Developmental Biology Program, The Ohio State University, Columbus, OH 43210
| | - Julia Guegueniat
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Laure Beven
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Hay-Oak Park
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210.,Molecular Cellular Developmental Biology Program, The Ohio State University, Columbus, OH 43210
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8
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Miao Y, Tipakornsaowapak T, Zheng L, Mu Y, Lewellyn E. Phospho-regulation of intrinsically disordered proteins for actin assembly and endocytosis. FEBS J 2018; 285:2762-2784. [PMID: 29722136 DOI: 10.1111/febs.14493] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Revised: 04/04/2018] [Accepted: 04/26/2018] [Indexed: 12/13/2022]
Abstract
Actin filament assembly contributes to the endocytic pathway pleiotropically, with active roles in clathrin-dependent and clathrin-independent endocytosis as well as subsequent endosomal trafficking. Endocytosis comprises a series of dynamic events, including the initiation of membrane curvature, bud invagination, vesicle abscission and subsequent vesicular transport. The ultimate success of endocytosis requires the coordinated activities of proteins that trigger actin polymerization, recruit actin-binding proteins (ABPs) and organize endocytic proteins (EPs) that promote membrane curvature through molecular crowding or scaffolding mechanisms. A particularly interesting phenomenon is that multiple EPs and ABPs contain a substantial percentage of intrinsically disordered regions (IDRs), which can contribute to protein coacervation and phase separation. In addition, intrinsically disordered proteins (IDPs) frequently contain sites for post-translational modifications (PTMs) such as phosphorylation, and these modifications exhibit a high preference for IDR residues [Groban ES et al. (2006) PLoS Comput Biol 2, e32]. PTMs are implicated in regulating protein function by modulating the protein conformation, protein-protein interactions and the transition between order and disorder states of IDPs. The molecular mechanisms by which IDRs of ABPs and EPs fine-tune actin assembly and endocytosis remain mostly unexplored and elusive. In this review, we analyze protein sequences of budding yeast EPs and ABPs, and discuss the potential underlying mechanisms for regulating endocytosis and actin assembly through the emerging concept of IDR-mediated protein multivalency, coacervation, and phase transition, with an emphasis on the phospho-regulation of IDRs. Finally, we summarize the current understanding of how these mechanisms coordinate actin cytoskeleton assembly and membrane curvature formation during endocytosis in budding yeast.
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Affiliation(s)
- Yansong Miao
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.,School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, Singapore
| | | | - Liangzhen Zheng
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Yuguang Mu
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Eric Lewellyn
- Department of Biology, Division of Natural Sciences, St Norbert College, De Pere, WI, USA
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9
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Foltman M, Filali-Mouncef Y, Crespo D, Sanchez-Diaz A. Cell polarity protein Spa2 coordinates Chs2 incorporation at the division site in budding yeast. PLoS Genet 2018; 14:e1007299. [PMID: 29601579 PMCID: PMC5895073 DOI: 10.1371/journal.pgen.1007299] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Revised: 04/11/2018] [Accepted: 03/07/2018] [Indexed: 01/06/2023] Open
Abstract
Deposition of additional plasma membrane and cargoes during cytokinesis in eukaryotic cells must be coordinated with actomyosin ring contraction, plasma membrane ingression and extracellular matrix remodelling. The process by which the secretory pathway promotes specific incorporation of key factors into the cytokinetic machinery is poorly understood. Here, we show that cell polarity protein Spa2 interacts with actomyosin ring components during cytokinesis. Spa2 directly binds to cytokinetic factors Cyk3 and Hof1. The lethal effects of deleting the SPA2 gene in the absence of either Cyk3 or Hof1 can be suppressed by expression of the hypermorphic allele of the essential chitin synthase II (Chs2), a transmembrane protein transported on secretory vesicles that makes the primary septum during cytokinesis. Spa2 also interacts directly with the chitin synthase Chs2. Interestingly, artificial incorporation of Chs2 into the cytokinetic machinery allows the localisation of Spa2 at the site of division. In addition, increased Spa2 protein levels promote Chs2 incorporation at the site of division and primary septum formation. Our data indicate that Spa2 is recruited to the cleavage site to co-operate with the secretory vesicle system and particular actomyosin ring components to promote the incorporation of Chs2 into the so-called 'ingression progression complexes' during cytokinesis in budding yeast.
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Affiliation(s)
- Magdalena Foltman
- Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, CSIC, Santander, Spain
- Departamento de Biología Molecular, Facultad de Medicina, Universidad de Cantabria, Santander, Spain
| | - Yasmina Filali-Mouncef
- Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, CSIC, Santander, Spain
- Departamento de Biología Molecular, Facultad de Medicina, Universidad de Cantabria, Santander, Spain
| | - Damaso Crespo
- Departamento de Anatomía y Biología Celular, Facultad de Medicina, Universidad de Cantabria, Santander, Spain
| | - Alberto Sanchez-Diaz
- Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, CSIC, Santander, Spain
- Departamento de Biología Molecular, Facultad de Medicina, Universidad de Cantabria, Santander, Spain
- * E-mail:
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10
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Evolutionary dynamics in the fungal polarization network, a mechanistic perspective. Biophys Rev 2017; 9:375-387. [PMID: 28812259 PMCID: PMC5578929 DOI: 10.1007/s12551-017-0286-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 07/24/2017] [Indexed: 12/21/2022] Open
Abstract
Polarity establishment underlies proper cell cycle completion across virtually all organisms. Much progress has been made in generating an understanding of the structural and functional components of this process, especially in model species. Here we focus on the evolutionary dynamics of the fungal polarization protein network in order to determine general components and mechanistic principles, species- or lineage-specific adaptations and the evolvability of the network. The currently available genomic and proteomic screens in a variety of fungal species have shown three main characteristics: (1) certain proteins, processes and functions are conserved throughout the fungal clade; (2) orthologous functions can never be assumed, as various cases have been observed of homologous loci with dissimilar functions; (3) species have, typically, various species- or lineage-specific proteins incorporated in their polarization network. Further large-scale comparative and experimental studies, including those on non-model species representing the great fungal diversity, are needed to gain a better understanding of the evolutionary dynamics and generalities of the polarization network in fungi.
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11
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Duan B, Cui J, Sun S, Zheng J, Zhang Y, Ye B, Chen Y, Deng W, Du J, Zhu Y, Chen Y, Gu L. EGF-stimulated activation of Rab35 regulates RUSC2-GIT2 complex formation to stabilize GIT2 during directional lung cancer cell migration. Cancer Lett 2016; 379:70-83. [PMID: 27238570 DOI: 10.1016/j.canlet.2016.05.027] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Revised: 04/20/2016] [Accepted: 05/25/2016] [Indexed: 10/21/2022]
Abstract
Non-small cell lung cancer (NSCLC) remains one of the most metastasizing tumors, and directional cell migration is critical for targeting tumor metastasis. GIT2 has been known to bind to Paxillin to control cell polarization and directional migration. However, the molecular mechanisms underlying roles of GIT2 in controlling cell polarization and directional migration remain elusive. Here we demonstrated GIT2 control cell polarization and direction dependent on the regulation of Golgi through RUSC2. RUSC2 interacts with SHD of GIT2 in various lung cancer cells, and stabilizes GIT2 (Mazaki et al., 2006; Yu et al., 2009) by decreasing degradation and increasing its phosphorylation. Silencing of RUSC2 showed reduced stability of GIT2, defective Golgi reorientation toward the wound edge and decreased directional migration. Moreover, short-term EGF stimulation can increase the interaction between RUSC2 and GIT2, prolonged stimulation leads to a decrease of their interaction through activating Rab35. Silencing of Rab35 also reduced stability and phosphorylation of GIT2 and decreased cell migration. Taken together, our study indicated that RUSC2 participates in EGFR signaling and regulates lung cancer progression, and may be a new therapeutic target against lung cancer metastasis.
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Affiliation(s)
- Biao Duan
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Jie Cui
- Department of Biochemistry and Molecular Biology, Nanjing Medical University, Nanjing, Jiangsu 210029, China; Department of Physiology, Xuzhou Medical University, Xuzhou, Jiangsu 221004, China
| | - Shixiu Sun
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Jianchao Zheng
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Yujie Zhang
- Department of Biochemistry and Molecular Biology, Nanjing Medical University, Nanjing, Jiangsu 210029, China; Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Collaborative Innovation Center For Cancer Personalized Medicine, Nanjing Medical University, Nanjing, Jiangsu 211166, China
| | - Bixing Ye
- Department of Gastroenterology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Yan Chen
- Department of Biochemistry and Molecular Biology, Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Wenjie Deng
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Jun Du
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China; Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Collaborative Innovation Center For Cancer Personalized Medicine, Nanjing Medical University, Nanjing, Jiangsu 211166, China
| | - Yichao Zhu
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Yongchang Chen
- Department of Physiology, School of Medicine, Jiangsu University, Zhenjiang, Jiangsu 212013, China
| | - Luo Gu
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu 210029, China; Department of Biochemistry and Molecular Biology, Nanjing Medical University, Nanjing, Jiangsu 210029, China; Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Collaborative Innovation Center For Cancer Personalized Medicine, Nanjing Medical University, Nanjing, Jiangsu 211166, China.
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12
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Chou CS, Moore TI, Nie Q, Yi TM. Alternative cell polarity behaviours arise from changes in G-protein spatial dynamics. IET Syst Biol 2015; 9:52-63. [PMID: 26029251 DOI: 10.1049/iet-syb.2013.0018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Yeast cells form a single mating projection when exposed to mating pheromone, a classic example of cell polarity. Prolonged treatment with pheromone or specific mutations results in alternative cell polarity behaviours. The authors performed mathematical modelling to investigate these unusual cell morphologies from the perspective of balancing spatial amplification (i.e. positive feedback that localises components) with spatial tracking (i.e. negative feedback that allows sensing of gradient). First, they used generic models of cell polarity to explore different cell polarity behaviours that arose from changes in the model spatial dynamics. By exploring the positive and negative feedback loops in each stage of a two-stage model, they simulated a variety of cell morphologies including single bending projections, single straight projections, periodic multiple projections and simultaneous double projections. In the second half of the study, they used a two-stage mechanistic model of yeast cell polarity focusing on G-protein signalling to integrate the modelling results more closely with the authors' previously published experimental observations. In summary, the combination of modelling and experiments describes how yeast cells exhibit a diversity of cell morphologies arising from two-stage G-protein signalling dynamics modulated by positive and negative feedbacks.
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13
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Li T, Belda-Palazón B, Ferrando A, Alepuz P. Fertility and polarized cell growth depends on eIF5A for translation of polyproline-rich formins in Saccharomyces cerevisiae. Genetics 2014; 197:1191-200. [PMID: 24923804 PMCID: PMC4125393 DOI: 10.1534/genetics.114.166926] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 06/05/2014] [Indexed: 01/15/2023] Open
Abstract
eIF5A is an essential and evolutionary conserved translation elongation factor, which has recently been proposed to be required for the translation of proteins with consecutive prolines. The binding of eIF5A to ribosomes occurs upon its activation by hypusination, a modification that requires spermidine, an essential factor for mammalian fertility that also promotes yeast mating. We show that in response to pheromone, hypusinated eIF5A is required for shmoo formation, localization of polarisome components, induction of cell fusion proteins, and actin assembly in yeast. We also show that eIF5A is required for the translation of Bni1, a proline-rich formin involved in polarized growth during shmoo formation. Our data indicate that translation of the polyproline motifs in Bni1 is eIF5A dependent and this translation dependency is lost upon deletion of the polyprolines. Moreover, an exogenous increase in Bni1 protein levels partially restores the defect in shmoo formation seen in eIF5A mutants. Overall, our results identify eIF5A as a novel and essential regulator of yeast mating through formin translation. Since eIF5A and polyproline formins are conserved across species, our results also suggest that eIF5A-dependent translation of formins could regulate polarized growth in such processes as fertility and cancer in higher eukaryotes.
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Affiliation(s)
- Tianlu Li
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universitat de València, E-46100 Burjassot, Valencia, Spain
| | - Borja Belda-Palazón
- Instituto de Biología Molecular y Celular de Plantas, Centro Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain
| | - Alejandro Ferrando
- Instituto de Biología Molecular y Celular de Plantas, Centro Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain
| | - Paula Alepuz
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universitat de València, E-46100 Burjassot, Valencia, Spain
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14
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Lawson MJ, Drawert B, Khammash M, Petzold L, Yi TM. Spatial stochastic dynamics enable robust cell polarization. PLoS Comput Biol 2013; 9:e1003139. [PMID: 23935469 PMCID: PMC3723497 DOI: 10.1371/journal.pcbi.1003139] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 05/31/2013] [Indexed: 11/18/2022] Open
Abstract
Although cell polarity is an essential feature of living cells, it is far from being well-understood. Using a combination of computational modeling and biological experiments we closely examine an important prototype of cell polarity: the pheromone-induced formation of the yeast polarisome. Focusing on the role of noise and spatial heterogeneity, we develop and investigate two mechanistic spatial models of polarisome formation, one deterministic and the other stochastic, and compare the contrasting predictions of these two models against experimental phenotypes of wild-type and mutant cells. We find that the stochastic model can more robustly reproduce two fundamental characteristics observed in wild-type cells: a highly polarized phenotype via a mechanism that we refer to as spatial stochastic amplification, and the ability of the polarisome to track a moving pheromone input. Moreover, we find that only the stochastic model can simultaneously reproduce these characteristics of the wild-type phenotype and the multi-polarisome phenotype of a deletion mutant of the scaffolding protein Spa2. Significantly, our analysis also demonstrates that higher levels of stochastic noise results in increased robustness of polarization to parameter variation. Furthermore, our work suggests a novel role for a polarisome protein in the stabilization of actin cables. These findings elucidate the intricate role of spatial stochastic effects in cell polarity, giving support to a cellular model where noise and spatial heterogeneity combine to achieve robust biological function. Cell polarity is the fundamental process of breaking symmetry to create asymmetric cellular structures. It is an open question how randomness (stochasticity) in the cell hinders or helps cell polarity. In this work, we focus on the ability of yeast cells to sense a spatial gradient of mating pheromone and respond by forming a projection in the direction of the mating partner. A key element is the polarisome, which is at the tip of the mating projection. We introduce the first model of polarisome formation in yeast. The model is well-supported by experimental data. We perform modeling to explore the role of noise in the formation of the polarisome. By running simulations with and without noise, we arrive at the surprising conclusion, that gradient-dependent polarization is enhanced by stochasticity. Both the tight localization (amplification) and the ability to respond to directional change of the input (tracking) are enhanced by stochastic dynamics, resulting in a more robust behavior. Mutants in which key polarisome proteins have been deleted exhibit broader, noisier polarisome than the wild type. The mutant phenotype is accurately captured by our stochastic simulations. These results demonstrate the importance of stochasticity in the study of cell polarity.
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Affiliation(s)
- Michael J. Lawson
- Department of BioMolecular Science and Engineering, University of California, Santa Barbara, California, United States of America
| | - Brian Drawert
- Department of Computer Science, University of California, Santa Barbara, California, United States of America
| | - Mustafa Khammash
- Department of Mechanical Engineering, University of California, Santa Barbara, California, United States of America
- Department of Biosystems Science and Engineering, ETH-Zürich, Basel, Switzerland
| | - Linda Petzold
- Department of Computer Science, University of California, Santa Barbara, California, United States of America
- Department of Mechanical Engineering, University of California, Santa Barbara, California, United States of America
| | - Tau-Mu Yi
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California, United States of America
- * E-mail:
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15
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Guillas I, Vernay A, Vitagliano JJ, Arkowitz RA. Phosphatidylinositol 4,5-bisphosphate is required for invasive growth in Saccharomyces cerevisiae. J Cell Sci 2013; 126:3602-14. [PMID: 23781030 DOI: 10.1242/jcs.122606] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Phosphatidylinositol phosphates are important regulators of processes such as the cytoskeleton organization, membrane trafficking and gene transcription, which are all crucial for polarized cell growth. In particular, phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] has essential roles in polarized growth as well as in cellular responses to stress. In the yeast Saccharomyces cerevisiae, the sole phosphatidylinositol-4-phosphate 5-kinase (PI4P5K) Mss4p is essential for generating plasma membrane PtdIns(4,5)P2. Here, we show that Mss4p is required for yeast invasive growth in low-nutrient conditions. We isolated specific mss4 mutants that were defective in cell elongation, induction of the Flo11p flocculin, adhesion and cell wall integrity. We show that mss4-f12 cells have reduced plasma membrane PtdIns(4,5)P2 levels as well as a defect in its polarized distribution, yet Mss4-f12p is catalytically active in vitro. In addition, the Mss4-f12 protein was defective in localizing to the plasma membrane. Furthermore, addition of cAMP, but not an activated MAPKKK allele, partially restored the invasive growth defect of mss4-f12 cells. Taken together, our results indicate that plasma membrane PtdIns(4,5)P2 is crucial for yeast invasive growth and suggest that this phospholipid functions upstream of the cAMP-dependent protein kinase A signaling pathway.
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Affiliation(s)
- Isabelle Guillas
- Université Nice - Sophia Antipolis, Institute of Biology Valrose, 06108 Nice Cedex 2, France
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16
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DeFlorio R, Brett ME, Waszczak N, Apollinari E, Metodiev MV, Dubrovskyi O, Eddington D, Arkowitz RA, Stone DE. Gβ phosphorylation is critical for efficient chemotropism in yeast. J Cell Sci 2013; 126:2997-3009. [DOI: 10.1242/jcs.112797] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mating yeast cells interpret complex pheromone gradients and polarize their growth in the direction of the closest partner. Chemotropic growth depends on both the pheromone receptor and its associated G-protein. Upon activation by the receptor, Gα dissociates from Gβγ and Gβ is subsequently phosphorylated. Free Gβγ signals to the nucleus via a MAPK cascade and recruits Far1-Cdc24 to the incipient growth site. It is not clear how the cell establishes and stabilizes the axis of polarity, but this process is thought to require local signal amplification via the Gβγ-Far1-Cdc24 chemotropic complex, as well as communication between this complex and the activated receptor. Here we show that a mutant form of Gβ that cannot be phosphorylated confers defects in directional sensing and chemotropic growth. Our data suggest that phosphorylation of Gβ plays a role in localized signal amplification and in the dynamic communication between the receptor and the chemotropic complex, which underlie growth site selection and maintenance.
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17
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Moore TI, Tanaka H, Kim HJ, Jeon NL, Yi TM. Yeast G-proteins mediate directional sensing and polarization behaviors in response to changes in pheromone gradient direction. Mol Biol Cell 2012; 24:521-34. [PMID: 23242998 PMCID: PMC3571874 DOI: 10.1091/mbc.e12-10-0739] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
G-proteins, heterotrimeric and Cdc42, modulate in a ligand-dependent fashion two fundamental cell polarity behaviors (projection bending growth and second projection formation) in response to gradient directional change. Yeast cells polarize by projecting up mating pheromone gradients, a classic cell polarity behavior. However, these chemical gradients may shift direction. We examine how yeast cells sense and respond to a 180o switch in the direction of microfluidically generated pheromone gradients. We identify two behaviors: at low concentrations of α-factor, the initial projection grows by bending, whereas at high concentrations, cells form a second projection toward the new source. Mutations that increase heterotrimeric G-protein activity expand the bending-growth morphology to high concentrations; mutations that increase Cdc42 activity result in second projections at low concentrations. Gradient-sensing projection bending requires interaction between Gβγ and Cdc24, whereas gradient-nonsensing projection extension is stimulated by Bem1 and hyperactivated Cdc42. Of interest, a mutation in Gα affects both bending and extension. Finally, we find a genetic perturbation that exhibits both behaviors. Overexpression of the formin Bni1, a component of the polarisome, makes both bending-growth projections and second projections at low and high α-factor concentrations, suggesting a role for Bni1 downstream of the heterotrimeric G-protein and Cdc42 during gradient sensing and response. Thus we demonstrate that G-proteins modulate in a ligand-dependent manner two fundamental cell-polarity behaviors in response to gradient directional change.
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Affiliation(s)
- Travis I Moore
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697, USA
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18
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Chen H, Kuo CC, Kang H, Howell AS, Zyla TR, Jin M, Lew DJ. Cdc42p regulation of the yeast formin Bni1p mediated by the effector Gic2p. Mol Biol Cell 2012; 23:3814-26. [PMID: 22918946 PMCID: PMC3459858 DOI: 10.1091/mbc.e12-05-0400] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Regulation of the formin Bni1p by Cdc42p in yeast does not require direct interaction between Bni1p and Cdc42p. The Cdc42p effector Gic2p can bind both Bni1p and GTP-Cdc42p, providing a novel regulatory input. Actin filaments are dynamically reorganized to accommodate ever-changing cellular needs for intracellular transport, morphogenesis, and migration. Formins, a major family of actin nucleators, are believed to function as direct effectors of Rho GTPases, such as the polarity regulator Cdc42p. However, the presence of extensive redundancy has made it difficult to assess the in vivo significance of the low-affinity Rho GTPase–formin interaction and specifically whether Cdc42p polarizes the actin cytoskeleton via direct formin binding. Here we exploit a synthetically rewired budding yeast strain to eliminate the redundancy, making regulation of the formin Bni1p by Cdc42p essential for viability. Surprisingly, we find that direct Cdc42p–Bni1p interaction is dispensable for Bni1p regulation. Alternative paths linking Cdc42p and Bni1p via “polarisome” components Spa2p and Bud6p are also collectively dispensable. We identify a novel regulatory input to Bni1p acting through the Cdc42p effector, Gic2p. This pathway is sufficient to localize Bni1p to the sites of Cdc42p action and promotes a polarized actin organization in both rewired and wild-type contexts. We suggest that an indirect mechanism linking Rho GTPases and formins via Rho effectors may provide finer spatiotemporal control for the formin-nucleated actin cytoskeleton.
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Affiliation(s)
- Hsin Chen
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA
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19
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Phosphorylation of GIT1 tyrosine 321 is required for association with FAK at focal adhesions and for PDGF-activated migration of osteoblasts. Mol Cell Biochem 2012; 365:109-18. [DOI: 10.1007/s11010-012-1249-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Accepted: 01/14/2012] [Indexed: 01/26/2023]
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20
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The mating projections of Saccharomyces cerevisiae and Candida albicans show key characteristics of hyphal growth. Fungal Biol 2011; 115:547-56. [DOI: 10.1016/j.funbio.2011.02.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2010] [Revised: 02/01/2011] [Accepted: 02/02/2011] [Indexed: 02/06/2023]
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21
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Abstract
Chemical gradients of peptide mating pheromones are necessary for directional growth, which is critical for yeast mating. These gradients are generated by cell-type specific secretion or export and specific degradation in receiving cells. Spatial information is sensed by dedicated seven-transmembrane G-protein coupled receptors and yeast cells are able to detect extremely small differences in ligand concentration across their approximately 5-microm cell surface. Here, I will discuss our current knowledge of how cells detect and respond to such shallow chemical gradients and in particular what is known about the proteins that are involved in directional growth and the establishment of the polarity axis during yeast mating.
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Affiliation(s)
- Robert A Arkowitz
- Institute of Developmental Biology and Cancer, Université de Nice-Sophia Antipolis-CNRS UMR6543, Centre de Biochimie, Faculté des Sciences, Parc Valrose, 06108 Nice Cedex 2, France.
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22
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Yamamoto T, Mochida J, Kadota J, Takeda M, Bi E, Tanaka K. Initial polarized bud growth by endocytic recycling in the absence of actin cable-dependent vesicle transport in yeast. Mol Biol Cell 2010; 21:1237-52. [PMID: 20147449 PMCID: PMC2847527 DOI: 10.1091/mbc.e09-05-0412] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Budding yeast mutants in assembly of actin cables, which are thought to be the only actin structures essential for budding, still could form a small bud. Mutations in actin patch endocytic machineries/endocytic recycling factors inhibited this budding, suggesting a mechanism that promotes polarized growth by local recycling of endocytic vesicles. The assembly of filamentous actin is essential for polarized bud growth in budding yeast. Actin cables, which are assembled by the formins Bni1p and Bnr1p, are thought to be the only actin structures that are essential for budding. However, we found that formin or tropomyosin mutants, which lack actin cables, are still able to form a small bud. Additional mutations in components for cortical actin patches, which are assembled by the Arp2/3 complex to play a pivotal role in endocytic vesicle formation, inhibited this budding. Genes involved in endocytic recycling were also required for small-bud formation in actin cable-less mutants. These results suggest that budding yeast possesses a mechanism that promotes polarized growth by local recycling of endocytic vesicles. Interestingly, the type V myosin Myo2p, which was thought to use only actin cables to track, also contributed to budding in the absence of actin cables. These results suggest that some actin network may serve as the track for Myo2p-driven vesicle transport in the absence of actin cables or that Myo2p can function independent of actin filaments. Our results also show that polarity regulators including Cdc42p were still polarized in mutants defective in both actin cables and cortical actin patches, suggesting that the actin cytoskeleton does not play a major role in cortical assembly of polarity regulators in budding yeast.
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Affiliation(s)
- Takaharu Yamamoto
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University, Sapporo, Japan
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23
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Schlenker O, Rittinger K. Structures of dimeric GIT1 and trimeric beta-PIX and implications for GIT-PIX complex assembly. J Mol Biol 2008; 386:280-9. [PMID: 19136011 DOI: 10.1016/j.jmb.2008.12.050] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2008] [Revised: 12/17/2008] [Accepted: 12/17/2008] [Indexed: 01/05/2023]
Abstract
GIT (G protein-coupled receptor kinase-interacting protein) and PIX (p21-activated kinase-interacting exchange factor) family proteins integrate signaling pathways involving Arf and Rho family GTPases. GIT1 and beta-PIX form a constitutively associated complex that acts as a scaffold to allow the formation of large multiprotein assemblies that regulate synaptogenesis, cell polarity and cell migration among other physiological processes. Complex formation is mediated by the GIT binding domain (GBD) in beta-PIX, which recognizes the Spa homology domain of GIT1. Both binding domains are adjacent to predicted coiled-coil segments that allow homo-oligomerization of GIT1 and beta-PIX, respectively. Oligomerization of GIT and PIX proteins is important for their physiological functions, and deletion of the coiled-coil domains interferes with correct subcellular localization and the GEF (guanine nucleotide exchange factor) activity of PIX. We have solved the crystal structures of the CC domains of GIT1 and beta-PIX and determined the stoichiometry of complex formation between the two proteins in order to understand the molecular architecture of the GIT1-beta-PIX complex. The crystal structure of the CC domain of GIT1 solved at 1.4 A resolution shows a dimeric, parallel CC that spans 67 A in length. Unexpectedly, and in contrast to prevalent dimeric models, the structure of the CC region of beta-PIX determined at 2.8 A resolution, combined with hydrodynamic studies, reveals that this protein forms a parallel trimer. Furthermore, we demonstrate that dimeric GIT and trimeric PIX form an unusual high-affinity heteropentameric complex in which each Spa homology domain of the GIT1 dimer recognizes one GBD of the beta-PIX trimer, leaving one GBD unoccupied. These results can serve as a basis to better understand oligomerization-dependent GIT1-beta-PIX-regulated signaling events and provide an insight into the architecture of large signaling complexes involving GIT1 and beta-PIX.
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Affiliation(s)
- Oliver Schlenker
- Medical Research Council National Institute for Medical Research, The Ridgeway, London, UK
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24
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Moore TI, Chou CS, Nie Q, Jeon NL, Yi TM. Robust spatial sensing of mating pheromone gradients by yeast cells. PLoS One 2008; 3:e3865. [PMID: 19052645 PMCID: PMC2586657 DOI: 10.1371/journal.pone.0003865] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 10/29/2008] [Indexed: 01/27/2023] Open
Abstract
Projecting or moving up a chemical gradient is a universal behavior of living organisms. We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone α-factor produced in a microfluidics chamber; the focus was on bar1Δ strains, which do not degrade the pheromone input. The yeast cells exhibited good accuracy with the mating projection typically pointing in the correct direction up the gradient (∼80% under certain conditions), excellent sensitivity to shallow gradients, and broad dynamic range so that gradient-sensing was relatively robust over a 1000-fold range of average α-factor concentrations. Optimal directional sensing occurred at lower concentrations (5 nM) close to the Kd of the receptor and with steeper gradient slopes. Pheromone supersensitive mutations (sst2Δ and ste2300Δ) that disrupt the down-regulation of heterotrimeric G-protein signaling caused defects in both sensing and response. Interestingly, yeast cells employed adaptive mechanisms to increase the robustness of the process including filamentous growth (i.e. directional distal budding) up the gradient at low pheromone concentrations, bending of the projection to be more aligned with the gradient, and forming a more accurate second projection when the first projection was in the wrong direction. Finally, the cells were able to amplify a shallow external gradient signal of α-factor to produce a dramatic polarization of signaling proteins at the front of the cell. Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization. Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.
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Affiliation(s)
- Travis I. Moore
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
| | - Ching-Shan Chou
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Mathematics, University of California Irvine, Irvine, California, United States of America
| | - Qing Nie
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Mathematics, University of California Irvine, Irvine, California, United States of America
| | - Noo Li Jeon
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Biomedical Engineering, University of California Irvine, Irvine, California, United States of America
| | - Tau-Mu Yi
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- * E-mail:
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25
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Chesneau L, Prigent M, Boy-Marcotte E, Daraspe J, Fortier G, Jacquet M, Verbavatz JM, Cuif MH. Interdependence of the Ypt/RabGAP Gyp5p and Gyl1p for Recruitment to the Sites of Polarized Growth. Traffic 2008; 9:608-22. [DOI: 10.1111/j.1600-0854.2007.00699.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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26
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Mionnet C, Bogliolo S, Arkowitz RA. Oligomerization regulates the localization of Cdc24, the Cdc42 activator in Saccharomyces cerevisiae. J Biol Chem 2008; 283:17515-30. [PMID: 18378681 DOI: 10.1074/jbc.m800305200] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Guanine nucleotide exchange factor activation of Rho G-proteins is critical for cytoskeletal reorganization. In the yeast Saccharomyces cerevisiae, the sole guanine nucleotide exchange factor for the Rho G-protein Cdc42p, Cdc24p, is essential for its site-specific activation. Several mammalian exchange factors have been shown to oligomerize; however, the function of this homotypic interaction is unclear. Here we show that Cdc24p forms oligomers in yeast via its catalytic Dbl homology domain. Mutation of residues critical for Cdc24p oligomerization also perturbs the localization of this exchange factor yet does not alter its catalytic activity in vitro. Chemically induced oligomerization of one of these oligomerization-defective mutants partially restored its localization to the bud tip and nucleus. Furthermore, chemically induced oligomerization of wild-type Cdc24p does not affect in vitro exchange factor activity, yet it results in a decrease of activated Cdc42p in vivo and the presence of Cdc24p in the nucleus at all cell cycle stages. Together, our results suggest that Cdc24p oligomerization regulates Cdc42p activation via its localization.
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Affiliation(s)
- Cyril Mionnet
- Institute of Developmental Biology and Cancer, CNRS UMR 6543, Université de Nice, Faculté des Sciences-Parc Valrose, 06108 Nice Cedex 2, France
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27
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Meyer V, Arentshorst M, van den Hondel CAMJJ, Ram AFJ. The polarisome component SpaA localises to hyphal tips of Aspergillus niger and is important for polar growth. Fungal Genet Biol 2008; 45:152-64. [PMID: 17826199 DOI: 10.1016/j.fgb.2007.07.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 07/09/2007] [Accepted: 07/11/2007] [Indexed: 11/23/2022]
Abstract
Hyphal tip growth is a key feature of filamentous fungi, however, the molecular mechanism(s) that regulate cell polarity are poorly understood. On the other hand, much more is known about polarised growth in the yeast Saccharomyces cerevisiae. Here, the proteins Spa2p, Bni1p, Bud6p and Pea2p form a protein complex named the polarisome known to be important for the assurance of polar growth. We searched the genome of Aspergillus niger and identified homologues for Spa2p, Bni1p, Bud6p but not for Pea2p. We characterised the function of the Spa2p homologue SpaA by determining its cellular localisation and by constructing deletion and overexpressing mutant strains. SpaA was found to be localised exclusively at the hyphal tip, suggesting that SpaA can be used as marker for polarisation. Deletion and overexpression of spaA resulted in reduced growth rate, increased hyphal diameter and polarity defects, indicating that one of the functions of SpaA is to ensure polarity maintenance. In addition, we could show that SpaA is able to complement the defective haploid invasive growth phenotype of a S. cerevisiae SPA2 null mutant. We suggest that the function of SpaA is to ensure maximal polar growth rate in A. niger.
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Affiliation(s)
- Vera Meyer
- Department of Microbiology and Genetics, Institute of Biotechnology, Berlin University of Technology, Gustav-Meyer-Allee 25, D-13355 Berlin, Germany.
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28
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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: 100] [Impact Index Per Article: 5.9] [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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29
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Juanes MA, Queralt E, Bañó MC, Igual JC. Rot1 plays an antagonistic role to Clb2 in actin cytoskeleton dynamics throughout the cell cycle. J Cell Sci 2007; 120:2390-401. [PMID: 17606994 DOI: 10.1242/jcs.002758] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
ROT1 is an essential gene whose inactivation causes defects in cell cycle progression and morphogenesis in budding yeast. Rot1 affects the actin cytoskeleton during the cell cycle at two levels. First, it is required for the maintenance of apical growth during bud growth. Second, Rot1 is necessary to polarize actin cytoskeleton to the neck region at the end of mitosis; because of this defect, rot1 cells do not properly form a septum to complete cell division. The inability to polarize the actin cytoskeleton at the end of mitosis is not due to a defect in the recruitment of the polarisome scaffold protein Spa2 or the actin cytoskeleton regulators Cdc42 and Cdc24 in the neck region. Previous results indicate a connection between Rot1 and the cyclin Clb2. In fact, overexpression of CLB2 is toxic when ROT1 is partially inactivated, and reciprocally, deletion of CLB2 suppresses the lethality of the rot1 mutant, which indicates a functional antagonism between Clb2 and Rot1. Several genetic interactions suggest a link between Rot1 and the ubiquitin-proteasome system and we show that the Clb2 cyclin is not properly degraded in rot1 cells.
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Affiliation(s)
- M Angeles Juanes
- Departament de Bioquímica i Biologia Molecular, Facultat de Ciències Biològiques, Universitat de València, 46100 Burjassot (Valencia), Spain
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30
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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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31
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Abstract
The G-protein-coupled receptor (GPCR)-kinase-interacting proteins 1 and 2 (GIT1 and GIT2) are ubiquitous multidomain proteins involved in diverse cellular processes. They traffic between three distinct cellular compartments (cytoplasmic complexes, focal adhesions and the cell periphery) through interactions with proteins including ARF, Rac1 and Cdc42 GTPases, p21-activated kinase (PAK), PAK-interacting exchange factor (PIX), the kinase MEK1, phospholipase Cgamma (PLCgamma) and paxillin. GITs and PIX cooperate to form large oligomeric complexes to which other proteins are transiently recruited. Activation of Rac1 and Cdc42 drives association of PAK with these oligomers, which unmasks the paxillin-binding site in GITs that recruits them to focal complexes. There, they regulate cytoskeletal dynamics by feedback inhibition of Rac1. GITs also participate in receptor internalization by regulating membrane trafficking between the plasma membrane and endosomes, targeting ARF GTPases through their ARF GTPase-activating protein (ARF-GAP) activity. Furthermore, GITs act as scaffolds to control spatial activation of several signaling molecules. Finally, recent results suggest pathogenic roles for GIT proteins in Huntington's disease and HIV infection.
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Affiliation(s)
- Ryan J Hoefen
- Cardiovascular Research Institute and Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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32
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Kozminski KG, Alfaro G, Dighe S, Beh CT. Homologues of Oxysterol-Binding Proteins Affect Cdc42p- and Rho1p-Mediated Cell Polarization in Saccharomyces cerevisiae. Traffic 2006; 7:1224-42. [PMID: 17004323 DOI: 10.1111/j.1600-0854.2006.00467.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Polarized cell growth requires the establishment of an axis of growth along which secretion can be targeted to a specific site on the cell cortex. How polarity establishment and secretion are choreographed is not fully understood, though Rho GTPase- and Rab GTPase-mediated signaling is required. Superimposed on this regulation are the functions of specific lipids and their cognate binding proteins. In a screen for Saccharomyces cerevisiae genes that interact with Rho family CDC42 to promote polarity establishment, we identified KES1/OSH4, which encodes a homologue of mammalian oxysterol-binding protein (OSBP). Other yeast OSH genes (OSBP homologues) had comparable genetic interactions with CDC42, implicating OSH genes in the regulation of CDC42-dependent polarity establishment. We found that the OSH gene family (OSH1-OSH7) promotes cell polarization by maintaining the proper localization of septins, the Rho GTPases Cdc42p and Rho1p, and the Rab GTPase Sec4p. Disruption of all OSH gene function caused specific defects in polarized exocytosis, indicating that the Osh proteins are collectively required for a secretory pathway implicated in the maintenance of polarized growth.
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Affiliation(s)
- Keith G Kozminski
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA
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33
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Barale S, McCusker D, Arkowitz RA. Cdc42p GDP/GTP cycling is necessary for efficient cell fusion during yeast mating. Mol Biol Cell 2006; 17:2824-38. [PMID: 16571678 PMCID: PMC1475363 DOI: 10.1091/mbc.e05-11-1040] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The highly conserved small Rho G-protein, Cdc42p plays a critical role in cell polarity and cytoskeleton organization in all eukaryotes. In the yeast Saccharomyces cerevisiae, Cdc42p is important for cell polarity establishment, septin ring assembly, and pheromone-dependent MAP-kinase signaling during the yeast mating process. In this study, we further investigated the role of Cdc42p in the mating process by screening for specific mating defective cdc42 alleles. We have identified and characterized novel mating defective cdc42 alleles that are unaffected in vegetative cell polarity. Replacement of the Cdc42p Val36 residue with Met resulted in a specific cell fusion defect. This cdc42[V36M] mutant responded to mating pheromone but was defective in cell fusion and in localization of the cell fusion protein Fus1p, similar to a previously isolated cdc24 (cdc24-m6) mutant. Overexpression of a fast cycling Cdc42p mutant suppressed the cdc24-m6 fusion defect and conversely, overexpression of Cdc24p suppressed the cdc42[V36M] fusion defect. Taken together, our results indicate that Cdc42p GDP-GTP cycling is critical for efficient cell fusion.
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Affiliation(s)
- Sophie Barale
- *Institute of Signaling, Developmental Biology, and Cancer, Centre National de la Recherche Scientifique UMR 6543, Université de Nice, Faculté des Sciences-Parc Valrose, 06108 Nice Cedex 2, France; and
| | - Derek McCusker
- Department of Biology, Sinsheimer Laboratories, University of California at Santa Cruz, Santa Cruz, CA 95064
| | - Robert A. Arkowitz
- *Institute of Signaling, Developmental Biology, and Cancer, Centre National de la Recherche Scientifique UMR 6543, Université de Nice, Faculté des Sciences-Parc Valrose, 06108 Nice Cedex 2, France; and
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34
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Noma S, Iida K, Iida H. Polarized morphogenesis regulator Spa2 is required for the function of putative stretch-activated Ca2+-permeable channel component Mid1 in Saccharomyces cerevisiae. EUKARYOTIC CELL 2005; 4:1353-63. [PMID: 16087740 PMCID: PMC1214535 DOI: 10.1128/ec.4.8.1353-1363.2005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mid1 is a putative stretch-activated Ca2+ channel component and is required for the maintenance of viability in the mating process. In response to mating pheromone, the mid1 mutant normally forms a pointed mating projection but eventually dies. This phenotype is called the mid phenotype. To identify a protein regulating Mid1 or regulated by Mid1, we isolated a multicopy suppressor that rescues the mid1-1 mutant from mating pheromone-induced death and found that it encodes a truncated Spa2 protein lacking an amino-terminal region responsible for interaction with components of the mitogen-activated protein kinase cascades. One of these SPA2 alleles was SPA2DeltaN, whose product lacked the region from Ser5 to Leu230. SPA2DeltaN on a multicopy plasmid (YEpSPA2DeltaN) complemented the mid phenotype but not another phenotype, low Ca2+ accumulation, of the mid1-1 mutant. Neither SPA2DeltaN on a low-copy plasmid nor wild-type SPA2 on a multicopy plasmid had suppressive activity. The SPA2 gene is involved in the formation of a pointed mating projection, and cells of the spa2Delta mutant lacking Spa2 are viable and develop a peanut shell-like structure when exposed to mating pheromone. Like the spa2Delta mutant, the mid1-1 spa2Delta double mutant and the mid1-1/YEpSPA2DeltaN strain developed the peanut shell-like structure. The mid1-1 spa2Delta double mutant did not have the mid phenotype, indicating that SPA2 is epistatic to MID1. Overexpression of Spa2DeltaN abolished the localization of Spa2-green fluorescent protein to the tip of the mating projection. These results suggest that the Spa2DeltaN protein interferes with the localization of the normal Spa2 protein and thereby prevents cells from entering the mating process. Therefore, we suggest that Mid1 function is influenced by Spa2 function through polarized morphogenesis.
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Affiliation(s)
- Shigeko Noma
- Department of Biology, Tokyo Gakugei University, Tokyo 184-8501, Japan
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35
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Bassilana M, Hopkins J, Arkowitz RA. Regulation of the Cdc42/Cdc24 GTPase module during Candida albicans hyphal growth. EUKARYOTIC CELL 2005; 4:588-603. [PMID: 15755921 PMCID: PMC1087799 DOI: 10.1128/ec.4.3.588-603.2005] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Rho G protein Cdc42 and its exchange factor Cdc24 are required for hyphal growth of the human fungal pathogen Candida albicans. Previously, we reported that strains ectopically expressing Cdc24 or Cdc42 are unable to form hyphae in response to serum. Here we investigated the role of these two proteins in hyphal growth, using quantitative real-time PCR to measure induction of hypha-specific genes together with time lapse microscopy. Expression of the hypha-specific genes examined depends on the cyclic AMP-dependent protein kinase A pathway culminating in the Efg1 and Tec1 transcription factors. We show that strains with reduced levels of CDC24 or CDC42 transcripts induce hypha-specific genes yet cannot maintain their expression in response to serum. Furthermore, in serum these mutants form elongated buds compared to the wild type and mutant budding cells, as observed by time lapse microscopy. Using Cdc24 fused to green fluorescent protein, we also show that Cdc24 is recruited to and persists at the germ tube tip during hyphal growth. Altogether these data demonstrate that the Cdc24/Cdc42 GTPase module is required for maintenance of hyphal growth. In addition, overexpression studies indicate that specific levels of Cdc24 and Cdc42 are important for invasive hyphal growth. In response to serum, CDC24 transcript levels increase transiently in a Tec1-dependent fashion, as do the G-protein RHO3 and the Rho1 GTPase activating protein BEM2 transcript levels. These results suggest that a positive feedback loop between Cdc24 and Tec1 contributes to an increase in active Cdc42 at the tip of the germ tube which is important for hypha formation.
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Affiliation(s)
- Martine Bassilana
- Institute of Signaling, Developmental Biology, and Cancer, UMR 6543 Centre National de la Recherche Scientifique, Centre de Biochimie, University of Nice, 06108 Nice, France.
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36
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Tcheperegine SE, Gao XD, Bi E. Regulation of cell polarity by interactions of Msb3 and Msb4 with Cdc42 and polarisome components. Mol Cell Biol 2005; 25:8567-80. [PMID: 16166638 PMCID: PMC1265733 DOI: 10.1128/mcb.25.19.8567-8580.2005] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2005] [Revised: 03/04/2005] [Accepted: 07/14/2005] [Indexed: 11/20/2022] Open
Abstract
In Saccharomyces cerevisiae, polarized growth depends on interactions between the actin cytoskeleton and the secretory machinery. Here we show that the Rab GTPase-activating proteins (GAPs) Msb3 and Msb4 interact directly with Spa2, a scaffold protein of the "polarisome" that also interacts with the formin Bni1. Spa2 is required for the polarized localization of Msb3 and Msb4 at the bud tip. We also show that Msb3 and Msb4 bind specifically to Cdc42-GDP and Rho1-GDP in vitro and that Msb3 and Rho GDP dissociation inhibitor act independently but oppositely on Cdc42. Finally, we show that Msb3 and Msb4 are involved in Bni1-nucleated actin assembly in vivo. These results suggest that Msb3 and Msb4 regulate polarized growth by multiple mechanisms, directly regulating exocytosis through their GAP activity toward Sec4 and potentially coordinating the functions of Cdc42, Rho1, and Bni1 in the polarisome through their binding to these GTPases. A functional equivalent of the polarisome probably exists in other fungi and mammals.
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Affiliation(s)
- Serguei E Tcheperegine
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, 421 Curie Blvd., Room 1012, BRB II/III, Philadelphia, PA 19104-6058, USA
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37
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Barale S, McCusker D, Arkowitz RA. The exchange factor Cdc24 is required for cell fusion during yeast mating. EUKARYOTIC CELL 2005; 3:1049-61. [PMID: 15302837 PMCID: PMC500890 DOI: 10.1128/ec.3.4.1049-1061.2004] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
During Saccharomyces cerevisiae mating, chemotropic growth and cell fusion are critical for zygote formation. Cdc24p, the guanine nucleotide exchange factor for the Cdc42 G protein, is necessary for oriented growth along a pheromone gradient during mating. To understand the functions of this critical Cdc42p activator, we identified additional cdc24 mating mutants. Two mating-specific mutants, the cdc24-m5 and cdc24-m6 mutants, each were isolated with a mutated residue in the conserved catalytic domain. The cdc24-m6 mutant responds normally to pheromone and orients its growth towards a mating partner yet accumulates prezygotes during mating. cdc24-m6 prezygotes have two apposed intact cell walls and do not correctly localize proteins required for cell fusion, despite normal exocytosis. Our results indicate that the exchange factor Cdc24p is necessary for maintaining or restricting specific proteins required for cell fusion to the cell contact region during mating.
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Affiliation(s)
- Sophie Barale
- Institute of Signaling, Developmental Biology, and Cancer, CNRS UMR 6543, Faculté des Sciences-Parc Valrose, Université de Nice, 06108 Nice Cedex 2, France
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38
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Shih JL, Reck-Peterson SL, Newitt R, Mooseker MS, Aebersold R, Herskowitz I. Cell polarity protein Spa2P associates with proteins involved in actin function in Saccharomyces cerevisiae. Mol Biol Cell 2005; 16:4595-608. [PMID: 16030260 PMCID: PMC1237067 DOI: 10.1091/mbc.e05-02-0108] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Spa2p is a nonessential protein that regulates yeast cell polarity. It localizes early to the presumptive bud site and remains at sites of growth throughout the cell cycle. To understand how Spa2p localization is regulated and to gain insight into its molecular function in cell polarity, we used a coimmunoprecipitation strategy followed by tandem mass spectrometry analysis to identify proteins that associate with Spa2p in vivo. We identified Myo1p, Myo2p, Pan1p, and the protein encoded by YFR016c as proteins that interact with Spa2p. Strikingly, all of these proteins are involved in cell polarity and/or actin function. Here we focus on the functional significance of the interactions of Spa2p with Myo2p and Myo1p. We find that localization of Spa2GFP to sites of polarized growth depends on functional Myo2p but not on Myo1p. We also find that Spa2p, like Myo2p, cosediments with F-actin in an ATP-sensitive manner. We hypothesize that Spa2p associates with actin via a direct or indirect interaction with Myo2p and that Spa2p may be involved in mediating polarized localization of polarity proteins via Myo2p. In addition, we observe an enhanced cell-separation defect in a myo1spa2 strain at 37 degrees C. This provides further evidence that Spa2p is involved in cytokinesis and cell wall morphogenesis.
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Affiliation(s)
- Judy L Shih
- Department of Biochemistry and Biophysics, University of California-San Francisco, San Francisco, CA 94143-2140, USA.
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39
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Pruyne D, Gao L, Bi E, Bretscher A. Stable and dynamic axes of polarity use distinct formin isoforms in budding yeast. Mol Biol Cell 2004; 15:4971-89. [PMID: 15371545 PMCID: PMC524755 DOI: 10.1091/mbc.e04-04-0296] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Bud growth in yeast is guided by myosin-driven delivery of secretory vesicles from the mother cell to the bud. We find transport occurs along two sets of actin cables assembled by two formin isoforms. The Bnr1p formin assembles cables that radiate from the bud neck into the mother, providing a stable mother-bud axis. These cables also depend on septins at the neck and are required for efficient transport from the mother to the bud. The Bni1p formin assembles cables that line the bud cortex and target vesicles to varying locations in the bud. Loss of these cables results in morphological defects as vesicles accumulate at the neck. Assembly of these cables depends on continued polarized secretion, suggesting vesicular transport provides a positive feedback signal for Bni1p activation, possibly by rho-proteins. By coupling different formin isoforms to unique cortical landmarks, yeast uses common cytoskeletal elements to maintain stable and dynamic axes in the same cell.
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Affiliation(s)
- David Pruyne
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA
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40
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Bailly E, Cabantous S, Sondaz D, Bernadac A, Simon MN. Differential cellular localization among mitotic cyclins from Saccharomyces cerevisiae: a new role for the axial budding protein Bud3 in targeting Clb2 to the mother-bud neck. J Cell Sci 2003; 116:4119-30. [PMID: 12972503 DOI: 10.1242/jcs.00706] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mitotic cyclin Clb2 plays a major role in promoting M-phase in budding yeast, despite its functional redundancy with three closely related cyclins Clb1, Clb3 and Clb4. Here, we further investigate the mechanisms controlling the cellular distribution of Clb2 in living cells. In agreement with observations recently made by Hood et al., we find that GFP-tagged Clb2 expressed from its natural promoter localizes to various cellular compartments, including the nucleus, the mitotic spindle, the spindle pole bodies as well as the mother-bud neck. The neck localization is specific to Clb2 as Clb1, Clb3 and Clb4 are never observed there, even when over-expressed. Mutational analysis identifies a central region of Clb2, comprising residues 213-255 and a phylogenetically conserved hydrophobic patch, as an essential cis-acting determinant. Clb2 co-localizes with the bud site selection protein Bud3. Consistent with a role of Bud3 in targeting Clb2 to the bud neck, we report a two-hybrid interaction between these proteins. Furthermore, Clb2 is shown to be specifically delocalized in Deltabud3 cells and in a bud3 mutant deleted for its C-terminal Clb2-interacting domain (bud3(Delta1221)), but not in a Deltabud10 mutant. Correlating with this phenotype, bud3(Delta1221) cells exhibit a pronounced (15-30 minutes) delay in cytokinesis and/or cell separation, suggesting an unanticipated function of Clb2 in these late mitotic events. Taken together, our data uncover a new role for Bud3 in cytokinesis that correlates with its capacity to target Clb2 at the neck, independently of its well established cell-type-specific function in bud site selection.
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Affiliation(s)
- Eric Bailly
- Laboratoire d'Ingenierie des Systemes Macromoleculaires CNRS UPR9027, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
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41
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Knechtle P, Dietrich F, Philippsen P. Maximal polar growth potential depends on the polarisome component AgSpa2 in the filamentous fungus Ashbya gossypii. Mol Biol Cell 2003; 14:4140-54. [PMID: 12937275 PMCID: PMC207006 DOI: 10.1091/mbc.e03-03-0167] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2003] [Revised: 06/17/2003] [Accepted: 06/17/2003] [Indexed: 11/11/2022] Open
Abstract
We used actin staining and videomicroscopy to analyze the development from a spore to a young mycelium in the filamentous ascomycete Ashbya gossypii. The development starts with an initial isotropic growth phase followed by the emergence of germ tubes. The initial tip growth speed of 6-10 microm/h increases during early stages of development. This increase is transiently interrupted in response to the establishment of lateral branches or septa. The hyphal tip growth speed finally reaches a maximum of up to 200 micro/h, and the tips of these mature hyphae have the ability to split into two equally fast-growing hyphae. A search for A. gossypii homologs of polarisome components of the yeast Saccharomyces cerevisiae revealed a remarkable size difference between Spa2p of both organisms, with AgSpa2p being double as long as ScSpa2p due to an extended internal domain. AgSpa2 colocalizes with sites of polarized actin. Using time-lapse videomicroscopy, we show that AgSpa2p-GFP polarization is established at sites of branch initiation and then permanently maintained at hyphal tips. Polarization at sites of septation is transient. During apical branching the existing AgSpa2p-GFP polarization is symmetrically divided. To investigate the function of AgSpa2p, we generated two AgSPA2 mutants, a partial deletion of the internal domain alone, and a complete deletion. The mutations had an impact on the maximal hyphal tip growth speed, on the hyphal diameter, and on the branching pattern. We suggest that AgSpa2p is required for the determination of the area of growth at the hyphal tip and that the extended internal domain plays an important role in this process.
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Affiliation(s)
- Philipp Knechtle
- Applied Microbiology, Biozentrum, Universitaet Basel, 4056 Basel, Switzerland
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42
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Zheng XD, Wang YM, Wang Y. CaSPA2 is important for polarity establishment and maintenance in Candida albicans. Mol Microbiol 2003; 49:1391-405. [PMID: 12940995 DOI: 10.1046/j.1365-2958.2003.03646.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Saccharomyces cerevisiae Spa2p is a component of polarisome that controls cell polarity. Here, we have characterized the role of its homologue, CaSpa2p, in the polarized growth in Candida albicans. During yeast growth, GFP-tagged CaSpa2p localized to distinct growth sites in a cell cycle-dependent manner, while during hyphal growth it persistently localized to hyphal tips throughout the cell cycle. Persistent tip localization of the protein was also observed in Catup1Delta and Canrg1Delta, mutants constitutive for filamentous growth. Caspa2Delta exhibited defects in polarity establishment and maintenance, such as random budding and failure to confine growth to a small surface area leading to round cells with wide, elongated bud necks and markedly thicker hyphae. It was also defective in nuclear positioning, presumably a result of defective interactions between cytoplasmic microtubules with certain polarity determinants. The highly conserved SHD-I and SHD-V domains were found to be important and responsible for different aspects of CaSpa2p function. Caspa2Delta exhibited no virulence in the mouse systemic candidiasis model. Because of the existence of distinct growth forms and the easy control of the switch between them in vitro, C. albicans may serve as a useful model in cell polarity research.
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Affiliation(s)
- Xin-De Zheng
- Microbial Collection and Screening Laboratory, Institute of Molecular and Cell Biology, Singapore 117609
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43
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Yuzyuk T, Amberg DC. Actin recovery and bud emergence in osmotically stressed cells requires the conserved actin interacting mitogen-activated protein kinase kinase kinase Ssk2p/MTK1 and the scaffold protein Spa2p. Mol Biol Cell 2003; 14:3013-26. [PMID: 12857882 PMCID: PMC165694 DOI: 10.1091/mbc.e02-11-0747] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Osmotic stress causes actin cytoskeleton disassembly, a cell cycle arrest, and activation of the high osmolarity growth mitogen-activated protein kinase pathway. A previous study showed that Ssk2p, a mitogen-activated protein kinase kinase kinase of the high osmolarity growth pathway, promotes actin cytoskeleton recovery to the neck of late cell cycle, osmotically stressed yeast cells. Data presented herein examined the role of Ssk2p in actin recovery early in the cell cycle. We found that actin recovery at all stages of the cell cycle is not controlled by Ssk1p, the known activator of Ssk2p, but required a polarized distribution of Ssk2p as well as its actin-interacting and kinase activity. Stress-induced localization of Ssk2p to the neck required the septin Shs1p, whereas localization to the bud cortex depended on the polarity scaffold protein Spa2p. spa2delta cells, like ssk2delta cells, were defective for actin recovery from osmotic stress. These spa2delta defects could be suppressed by overexpression of catalytically active Ssk2p. Furthermore, Spa2p could be precipitated by GST-Ssk2p from extracts of osmotically stressed cells. The Ssk2p mediated actin recovery pathway seems to be conserved; MTK1, a human mitogen-activated protein kinase kinase kinase of the p38 stress response pathway and Ssk2p homolog, was also able to localize at polarized growth sites, form a complex with actin and Spa2p, and complement actin recovery defects in osmotically stressed ssk2delta and spa2delta yeast cells. We hypothesize that osmotic stress-induced actin disassembly leads to the formation of an Ssk2p-actin complex and the polarized localization of Ssk2p. Polarized Ssk2p associates with the scaffold protein Spa2p in the bud and Shs1p in the neck, allowing Ssk2p to regulate substrates involved in polarized actin assembly.
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Affiliation(s)
- Tatiana Yuzyuk
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210, USA
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44
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Misu K, Fujimura-Kamada K, Ueda T, Nakano A, Katoh H, Tanaka K. Cdc50p, a conserved endosomal membrane protein, controls polarized growth in Saccharomyces cerevisiae. Mol Biol Cell 2003; 14:730-47. [PMID: 12589066 PMCID: PMC150004 DOI: 10.1091/mbc.e02-06-0314] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
During the cell cycle of the yeast Saccharomyces cerevisiae, the actin cytoskeleton and the growth of cell surface are polarized, mediating bud emergence, bud growth, and cytokinesis. We identified CDC50 as a multicopy suppressor of the myo3 myo5-360 temperature-sensitive mutant, which is defective in organization of cortical actin patches. The cdc50 null mutant showed cold-sensitive cell cycle arrest with a small bud as reported previously. Cortical actin patches and Myo5p, which are normally localized to polarization sites, were depolarized in the cdc50 mutant. Furthermore, actin cables disappeared, and Bni1p and Gic1p, effectors of the Cdc42p small GTPase, were mislocalized in the cdc50 mutant. As predicted by its amino acid sequence, Cdc50p appears to be a transmembrane protein because it was solubilized from the membranes by detergent treatment. Cdc50p colocalized with Vps21p in endosomal compartments and was also localized to the class E compartment in the vps27 mutant. The cdc50 mutant showed defects in a late stage of endocytosis but not in the internalization step. It showed, however, only modest defects in vacuolar protein sorting. Our results indicate that Cdc50p is a novel endosomal protein that regulates polarized cell growth.
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Affiliation(s)
- Kenjiro Misu
- 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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45
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Vallier LG, Segall JE, Snyder M. The alpha-factor receptor C-terminus is important for mating projection formation and orientation in Saccharomyces cerevisiae. CELL MOTILITY AND THE CYTOSKELETON 2002; 53:251-66. [PMID: 12378535 DOI: 10.1002/cm.10073] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Successful mating of MATa Saccharomyces cerevisiae cells is dependent on Ste2p, the alpha-factor receptor. Besides receiving the pheromone signal and transducing it through the G-protein coupled MAP kinase pathway, Ste2p is active in the establishment and orientation of the mating projection. We investigated the role of the carboxyl terminus of the receptor in mating projection formation and orientation using a spatial gradient assay. Cells carrying the ste2-T326 mutation, truncating 105 of the 135 amino acids in the receptor tail including a motif necessary for its ligand-mediated internalization, display slow onset of projection formation, abnormal shmoo morphology, and reduced ability to orient the mating projection toward a pheromone source. This reduction was due to the increased loss of mating projection orientation in a pheromone gradient. Cells with a mutated endocytosis motif were defective in reorientation in a pheromone gradient. ste2-Delta296 cells, which carry a complete truncation of the Ste2p tail, exhibit a severe defect in projection formation, and those projections that do form are unable to orient in a pheromone gradient. These results suggest a complex role for the Ste2p carboxy-terminal tail in the formation, orientation, and directional adjustment of the mating projection, and that endocytosis of the receptor is important for this process. In addition, mutations in RSR1/BUD1 and SPA2, genes necessary for budding polarity, exhibited little or no defect in formation or orientation of mating projections. We conclude that mating projection orientation depends upon the carboxyl terminus of the pheromone receptor and not the directional machinery used in budding.
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Affiliation(s)
- Laura G Vallier
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
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Michel S, Ushinsky S, Klebl B, Leberer E, Thomas D, Whiteway M, Morschhäuser J. Generation of conditional lethal Candida albicans mutants by inducible deletion of essential genes. Mol Microbiol 2002; 46:269-80. [PMID: 12366849 DOI: 10.1046/j.1365-2958.2002.03167.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The yeast Candida albicans is the most important fungal pathogen of humans and a model organism for studying fungal virulence. Sequencing of the C. albicans genome will soon be completed, allowing systematic approaches to analyse gene function. However, techniques to define and characterize essential genes in this permanently diploid yeast are limited. We have developed an efficient method to create conditional lethal C. albicans null mutants by inducible, FLP-mediated gene deletion. Both wild-type alleles of the CDC42 or the BEM1 gene were deleted in strains that carried an additional copy of the respective gene that could be excised from the genome by the site-specific recombinase FLP. Expression of a C. albicans-adapted FLP gene under the control of an inducible promoter generated cell populations consisting of > or = 99.9% null mutants. Upon plating, these cells were unable to form colonies, demonstrating that CDC42 and BEM1 are essential genes in C. albicans. The cdc42 null mutants failed to produce buds and hyphae and grew as large, round cells instead, suggesting that they lacked the ability to produce polarized cell growth. However, the cells still responded to hyphal inducing signals by aggregating and expressing hypha-specific genes, behaviours typical of the mycelial growth form of C. albicans. Budding cells and germ tubes of bem1 null mutants exhibited morphological abnormalities, demonstrating that BEM1 is essential for normal growth of both yeast and hyphae. Inducible, FLP-mediated gene deletion provides a powerful approach to generate conditional lethal C. albicans mutants and allows the functional analysis of essential genes.
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Affiliation(s)
- Sonja Michel
- Institüt für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, D-97070 Würzburg, Germany
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Dittmar GAG, Wilkinson CRM, Jedrzejewski PT, Finley D. Role of a ubiquitin-like modification in polarized morphogenesis. Science 2002; 295:2442-6. [PMID: 11923536 DOI: 10.1126/science.1069989] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Type I ubiquitin-like proteins constitute a family of protein modifiers. Here we report the identification of a posttranslational protein modifier from Saccharomyces cerevisiae, Hub1. Overexpression of Hub1 resulted in enhanced conjugate formation when its carboxyl-terminal residue was deleted, suggesting that mature Hub1 may be produced by proteolytic processing. In vivo targets of Hub1 conjugation included cell polarity factors Sph1 and Hbt1. In the hub1Delta mutant, the subcellular localization of both Hbt1 and Sph1 was disrupted, and cell polarization during the formation of mating projections was defective. Consistent with these polarization defects, the hub1Delta mutant was deficient in mating.
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Affiliation(s)
- Gunnar A G Dittmar
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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Duan XJ, Xenarios I, Eisenberg D. Describing biological protein interactions in terms of protein states and state transitions: the LiveDIP database. Mol Cell Proteomics 2002; 1:104-16. [PMID: 12096128 DOI: 10.1074/mcp.m100026-mcp200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Biological protein-protein interactions differ from the more general class of physical interactions; in a biological interaction, both proteins must be in their proper states (e.g. covalently modified state, conformational state, cellular location state, etc.). Also in every biological interaction, one or both interacting molecules undergo a transition to a new state. This regulation of protein states through protein-protein interactions underlies many dynamic biological processes inside cells. Therefore, understanding biological interactions requires information on protein states. Toward this goal, DIP (the Database of Interacting Proteins) has been expanded to LiveDIP, which describes protein interactions by protein states and state transitions. This additional level of characterization permits a more complete picture of the protein-protein interaction networks and is crucial to an integrated understanding of genome-scale biology. The search tools provided by LiveDIP, Pathfinder, and Batch Search allow users to assemble biological pathways from all the protein-protein interactions collated from the scientific literature in LiveDIP. Tools have also been developed to integrate the protein-protein interaction networks of LiveDIP with large scale genomic data such as microarray data. An example of these tools applied to analyzing the pheromone response pathway in yeast suggests that the pathway functions in the context of a complex protein-protein interaction network. Seven of the eleven proteins involved in signal transduction are under negative or positive regulation of up to five other proteins through biological protein-protein interactions. During pheromone response, the mRNA expression levels of these signaling proteins exhibit different time course profiles. There is no simple correlation between changes in transcription levels and the signal intensity. This points to the importance of proteomic studies to understand how cells modulate and integrate signals. Integrating large scale, yeast two-hybrid data with mRNA expression data suggests biological interactions that may participate in pheromone response. These examples illustrate how LiveDIP provides data and tools for biological pathway discovery and pathway analysis.
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Affiliation(s)
- Xiaoqun Joyce Duan
- Howard Hughes Medical Institute, UCLA-DOE Laboratory of Structural Biology and Molecular Medicine, University of California, Los Angeles, Los Angeles, California 90095-1570, USA
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Ozaki-Kuroda K, Yamamoto Y, Nohara H, Kinoshita M, Fujiwara T, Irie K, Takai Y. Dynamic localization and function of Bni1p at the sites of directed growth in Saccharomyces cerevisiae. Mol Cell Biol 2001; 21:827-39. [PMID: 11154270 PMCID: PMC86674 DOI: 10.1128/mcb.21.3.827-839.2001] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Formin homology (FH) proteins are implicated in cell polarization and cytokinesis through actin organization. There are two FH proteins in the yeast Saccharomyces cerevisiae, Bni1p and Bnr1p. Bni1p physically interacts with Rho family small G proteins (Rho1p and Cdc42p), actin, two actin-binding proteins (profilin and Bud6p), and a polarity protein (Spa2p). Here we analyzed the in vivo localization of Bni1p by using a time-lapse imaging system and investigated the regulatory mechanisms of Bni1p localization and function in relation to these interacting proteins. Bni1p fused with green fluorescent protein localized to the sites of cell growth throughout the cell cycle. In a small-budded cell, Bni1p moved along the bud cortex. This dynamic localization of Bni1p coincided with the apparent site of bud growth. A bni1-disrupted cell showed a defect in directed growth to the pre-bud site and to the bud tip (apical growth), causing its abnormally spherical cell shape and thick bud neck. Bni1p localization at the bud tips was absolutely dependent on Cdc42p, largely dependent on Spa2p and actin filaments, and partly dependent on Bud6p, but scarcely dependent on polarized cortical actin patches or Rho1p. These results indicate that Bni1p regulates polarized growth within the bud through its unique and dynamic pattern of localization, dependent on multiple factors, including Cdc42p, Spa2p, Bud6p, and the actin cytoskeleton.
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Affiliation(s)
- K Ozaki-Kuroda
- Department of Molecular Biology and Biochemistry, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita, Osaka 565-0871, Japan
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Abstract
The machinery that mediates membrane fusion during yeast mating has remained elusive. But now a post-genomics approach has provided a powerful wedge into this difficult problem: a pheromone-induced multimembrane spanning protein has been identified as a key part of the mating machine.
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Affiliation(s)
- J M White
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA.
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