scholarly journals Unregulated actin polymerization by WASp causes defects of mitosis and cytokinesis in X-linked neutropenia

2007 ◽  
Vol 204 (9) ◽  
pp. 2213-2224 ◽  
Author(s):  
Dale A. Moulding ◽  
Michael P. Blundell ◽  
David G. Spiller ◽  
Michael R.H. White ◽  
Giles O. Cory ◽  
...  
Keyword(s):  
Live Cell Imaging ◽  
Actin Polymerization ◽  
Cell Imaging ◽  
Human Gene ◽  
Filamentous Actin ◽  
Gene Encoding ◽  
Activating Mutations ◽  
Spindle Midzone ◽  
Underlying Mechanisms ◽  
Syndrome Protein

Specific mutations in the human gene encoding the Wiskott-Aldrich syndrome protein (WASp) that compromise normal auto-inhibition of WASp result in unregulated activation of the actin-related protein 2/3 complex and increased actin polymerizing activity. These activating mutations are associated with an X-linked form of neutropenia with an intrinsic failure of myelopoiesis and an increase in the incidence of cytogenetic abnormalities. To study the underlying mechanisms, active mutant WASpI294T was expressed by gene transfer. This caused enhanced and delocalized actin polymerization throughout the cell, decreased proliferation, and increased apoptosis. Cells became binucleated, suggesting a failure of cytokinesis, and micronuclei were formed, indicative of genomic instability. Live cell imaging demonstrated a delay in mitosis from prometaphase to anaphase and confirmed that multinucleation was a result of aborted cytokinesis. During mitosis, filamentous actin was abnormally localized around the spindle and chromosomes throughout their alignment and separation, and it accumulated within the cleavage furrow around the spindle midzone. These findings reveal a novel mechanism for inhibition of myelopoiesis through defective mitosis and cytokinesis due to hyperactivation and mislocalization of actin polymerization.

scholarly journals A live-cell imaging system for visualizing the transport of Marburg virus nucleocapsid-like structures

2019 ◽  
Vol 16 (1) ◽  
Author(s):  
Yuki Takamatsu ◽  
Olga Dolnik ◽  
Takeshi Noda ◽  
Stephan Becker
Keyword(s):  
Live Cell Imaging ◽  
Intracellular Transport ◽  
Actin Polymerization ◽  
Ebola Virus ◽  
Cell Imaging ◽  
Temporal Dynamics ◽  
Imaging System ◽  
Marburg Virus ◽  
Live Cell ◽  
Infected Cells

Abstract Background Live-cell imaging is a powerful tool for visualization of the spatio-temporal dynamics of moving signals in living cells. Although this technique can be utilized to visualize nucleocapsid transport in Marburg virus (MARV)- or Ebola virus-infected cells, the experiments require biosafety level-4 (BSL-4) laboratories, which are restricted to trained and authorized individuals. Methods To overcome this limitation, we developed a live-cell imaging system to visualize MARV nucleocapsid-like structures using fluorescence-conjugated viral proteins, which can be conducted outside BSL-4 laboratories. Results Our experiments revealed that nucleocapsid-like structures have similar transport characteristics to those of nucleocapsids observed in MARV-infected cells, both of which are mediated by actin polymerization. Conclusions We developed a non-infectious live cell imaging system to visualize intracellular transport of MARV nucleocapsid-like structures. This system provides a safe platform to evaluate antiviral drugs that inhibit MARV nucleocapsid transport.

Thromboxane-induced actin polymerization in hypoxic neonatal pulmonary arterial myocytes involves Cdc42 signaling

2014 ◽  
Vol 307 (11) ◽  
pp. L877-L887 ◽  
Author(s):  
Jena Fediuk ◽  
Anurag S. Sikarwar ◽  
Nora Nolette ◽  
Shyamala Dakshinamurti
Keyword(s):  
Rho Gtpases ◽  
Laser Scanning ◽  
Actin Polymerization ◽  
Filamentous Actin ◽  
Actin Isoforms ◽  
Pi3k Activity ◽  
Laser Scanning Cytometry ◽  
Pulmonary Arterial ◽  
P21 Activated Kinase ◽  
Syndrome Protein

In hypoxic pulmonary arterial (PA) myocytes, challenge with thromboxane mimetic U46619 induces marked actin polymerization and contraction, phenotypic features of persistent pulmonary hypertension of the newborn (PPHN). Rho GTPases regulate the actin cytoskeleton. We previously reported that U46619-induced actin polymerization in hypoxic PA myocytes occurs independently of the RhoA pathway and hypothesized involvement of the Cdc42 pathway. PA myocytes grown in normoxia or hypoxia for 72 h were stimulated with U46619, then analyzed for Rac/Cdc42 activation by affinity precipitation, phosphatidylinositide-3-kinase (PI3K) activity by phospho-Akt, phospho-p21-activated kinase (PAK) by immunoblot, and association of Cdc42 with neuronal Wiskott Aldrich Syndrome protein (N-WASp) by immunoprecipitation. The effect of Rac or PAK inhibition on filamentous actin was quantified by laser-scanning cytometry and by cytoskeletal fractionation; effects of actin-modifying agents were measured by isometric myography. Basal Cdc42 activity increased in hypoxia, whereas Rac activity decreased. U46619 challenge increased Cdc42 and Rac activity in hypoxic cells, independently of PI3K. Hypoxia increased phospho-PAK, unaltered by U46619. Association of Cdc42 with N-WASp decreased in hypoxia but increased after U46619 exposure. Hypoxia doubled filamentous-to-globular ratios of α- and γ-actin isoforms. Jasplakinolide stabilized γ-filaments, increasing force; cytochalasin D depolymerized all actin isoforms, decreasing force. Rac and PAK inhibition decreased filamentous actin in tissues although without decrease in force. Rho inhibition decreased myosin phosphorylation and force. Hypoxia induces actin polymerization in PA myocytes, particularly increasing filamentous α- and γ-actin, contributing to U46619-induced contraction. Hypoxic PA myocytes challenged with a thromboxane mimetic polymerize actin via the Cdc42 pathway, reflecting increased Cdc42 association with N-WASp. Mechanisms regulating thromboxane-mediated actin polymerization are potential targets for future PPHN pharmacotherapy.

scholarly journals A Mutant Defective in Sexual Development Produces Aseptate Ascogonia

2010 ◽  
Vol 9 (12) ◽  
pp. 1856-1866 ◽  
Author(s):  
Sandra Bloemendal ◽  
Kathryn M. Lord ◽  
Christine Rech ◽  
Birgit Hoff ◽  
Ines Engh ◽  
...  
Keyword(s):  
Sexual Development ◽  
Live Cell Imaging ◽  
Cell Imaging ◽  
Sexual Cycle ◽  
Sequence Analyses ◽  
Gene Encoding ◽  
Content Type ◽  
Domain Of Unknown Function ◽  
Sterile Mutant

ABSTRACT The transition from the vegetative to the sexual cycle in filamentous ascomycetes is initiated with the formation of ascogonia. Here, we describe a novel type of sterile mutant from Sordaria macrospora with a defect in ascogonial septum formation. This mutant, named pro22, produces only small, defective protoperithecia and carries a point mutation in a gene encoding a protein that is highly conserved throughout eukaryotes. Sequence analyses revealed three putative transmembrane domains and a C-terminal domain of unknown function. Live-cell imaging showed that PRO22 is predominantly localized in the dynamic tubular and vesicular vacuolar network of the peripheral colony region close to growing hyphal tips and in ascogonia; it is absent from the large spherical vacuoles in the vegetative hyphae of the subperipheral region of the colony. This points to a specific role of PRO22 in the tubular and vesicular vacuolar network, and the loss of intercalary septation in ascogonia suggests that PRO22 functions during the initiation of sexual development.

scholarly journals Type-I myosins promote actin polymerization to drive membrane bending in endocytosis

2018 ◽  
Author(s):  
Hetty E Manenschijn ◽  
Andrea Picco ◽  
Markus Mund ◽  
Jonas Ries ◽  
Marko Kaksonen
Keyword(s):  
Live Cell Imaging ◽  
Actin Polymerization ◽  
Cell Imaging ◽  
Turgor Pressure ◽  
Type I ◽  
Actin Network ◽  
Actin Nucleation ◽  
Genetic Perturbations ◽  
Membrane Bending ◽  
Dose Dependent

Clathrin-mediated endocytosis in budding yeast requires the formation of a dynamic actin network that produces the force to invaginate the plasma membrane against the intracellular turgor pressure. The type-I myosins Myo3 and Myo5 are important for endocytic membrane reshaping, but mechanistic details of their function remain scarce. Here, we studied the function of Myo3 and Myo5 during endocytosis using quantitative live-cell imaging and genetic perturbations. We show that the type-I myosins promote, in a dose-dependent way, the growth and expansion of the actin network, which controls the speed of membrane and coat internalization. We found that this myosin-activity is independent of the actin nucleation promoting activity of myosins, and cannot be compensated for by increasing actin nucleation. Our results suggest a new mechanism for type-I myosins to produce force by promoting actin filament polymerization.

scholarly journals Distinct acto/myosin-I structures associate with endocytic profiles at the plasma membrane

2008 ◽  
Vol 180 (6) ◽  
pp. 1219-1232 ◽  
Author(s):  
Fatima-Zahra Idrissi ◽  
Helga Grötsch ◽  
Isabel M. Fernández-Golbano ◽  
Cristina Presciatto-Baschong ◽  
Howard Riezman ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Immunoelectron Microscopy ◽  
Live Cell Imaging ◽  
Actin Polymerization ◽  
Cell Imaging ◽  
Live Cell ◽  
Endocytic Vesicle ◽  
Myosin I ◽  
Initial Membrane ◽  
Membrane Bending

Endocytosis in yeast requires actin and clathrin. Live cell imaging has previously shown that massive actin polymerization occurs concomitant with a slow 200-nm inward movement of the endocytic coat (Kaksonen, M., Y. Sun, and D.G. Drubin. 2003. Cell. 115:475–487). However, the nature of the primary endocytic profile in yeast and how clathrin and actin cooperate to generate an endocytic vesicle is unknown. In this study, we analyze the distribution of nine different proteins involved in endocytic uptake along plasma membrane invaginations using immunoelectron microscopy. We find that the primary endocytic profiles are tubular invaginations of up to 50 nm in diameter and 180 nm in length, which accumulate the endocytic coat components at the tip. Interestingly, significant actin labeling is only observed on invaginations longer than 50 nm, suggesting that initial membrane bending occurs before initiation of the slow inward movement. We also find that in the longest profiles, actin and the myosin-I Myo5p form two distinct structures that might be implicated in vesicle fission.

scholarly journals Transport of Ebolavirus Nucleocapsids Is Dependent on Actin Polymerization: Live-Cell Imaging Analysis of Ebolavirus-Infected Cells

2015 ◽  
Vol 212 (suppl 2) ◽  
pp. S160-S166 ◽  
Author(s):  
Gordian Schudt ◽  
Olga Dolnik ◽  
Larissa Kolesnikova ◽  
Nadine Biedenkopf ◽  
Astrid Herwig ◽  
...  
Keyword(s):  
Live Cell Imaging ◽  
Actin Polymerization ◽  
Cell Imaging ◽  
Live Cell ◽  
Imaging Analysis ◽  
Infected Cells

scholarly journals SLAC, a complex between Sla1 and Las17, regulates actin polymerization during clathrin-mediated endocytosis

2012 ◽  
Vol 23 (21) ◽  
pp. 4256-4272 ◽  
Author(s):  
Daniel Feliciano ◽  
Santiago M. Di Pietro
Keyword(s):  
Live Cell Imaging ◽  
Actin Polymerization ◽  
Cell Imaging ◽  
Class Ii ◽  
Yeast Cells ◽  
Class I ◽  
Stable Complex ◽  
Clathrin Adaptor ◽  
Late Stages

During clathrin-mediated endocytosis, branched actin polymerization nucleated by the Arp2/3 complex provides force needed to drive vesicle internalization. Las17 (yeast WASp) is the strongest activator of the Arp2/3 complex in yeast cells; it is not autoinhibited and arrives to endocytic sites 20 s before actin polymerization begins. It is unclear how Las17 is kept inactive for 20 s at endocytic sites, thus restricting actin polymerization to late stages of endocytosis. In this paper, we demonstrate that Las17 is part of a large and biochemically stable complex with Sla1, a clathrin adaptor that inhibits Las17 activity. The interaction is direct, multivalent, and strong, and was mapped to novel Las17 polyproline motifs that are simultaneously class I and class II. In vitro pyrene-actin polymerization assays established that Sla1 inhibition of Las17 activity depends on the class I/II Las17 polyproline motifs and is based on competition between Sla1 and monomeric actin for binding to Las17. Furthermore, live-cell imaging showed the interaction with Sla1 is important for normal Las17 recruitment to endocytic sites, inhibition during the initial 20 s, and efficient endocytosis. These results advance our understanding of the regulation of actin polymerization in endocytosis.

scholarly journals Discovery of functional interactions among actin regulators by analysis of image fluctuations in an unperturbed motile cell system

2018 ◽  
Vol 373 (1747) ◽  
pp. 20170110 ◽  
Author(s):  
Tadamoto Isogai ◽  
Gaudenz Danuser
Keyword(s):  
Cell Biology ◽  
Live Cell Imaging ◽  
Actin Polymerization ◽  
Cell Imaging ◽  
Cell System ◽  
Feedback Loops ◽  
Actin Dynamics ◽  
Actin Network ◽  
Theme Issue ◽  
Functional Interactions

Cell migration is driven by propulsive forces derived from polymerizing actin that pushes and extends the plasma membrane. The underlying actin network is constantly undergoing adaptation to new mechano-chemical environments and intracellular conditions. As such, mechanisms that regulate actin dynamics inherently contain multiple feedback loops and redundant pathways. Given the highly adaptable nature of such a system, studies that use only perturbation experiments (e.g. knockdowns, overexpression, pharmacological activation/inhibition, etc.) are challenged by the nonlinearity and redundancy of the pathway. In these pathway configurations, perturbation experiments at best describe the function(s) of a molecular component in an adapting (e.g. acutely drug-treated) or fully adapted (e.g. permanent gene silenced) cell system, where the targeted component now resides in a non-native equilibrium. Here, we propose how quantitative live-cell imaging and analysis of constitutive fluctuations of molecular activities can overcome these limitations. We highlight emerging actin filament barbed-end biology as a prime example of a complex, nonlinear molecular process that requires a fluctuation analytic approach, especially in an unperturbed cellular system, to decipher functional interactions of barbed-end regulators, actin polymerization and membrane protrusion. This article is part of the theme issue ‘Self-organization in cell biology’.

scholarly journals Ase1p Organizes Antiparallel Microtubule Arrays during Interphase and Mitosis in Fission Yeast

2005 ◽  
Vol 16 (4) ◽  
pp. 1756-1768 ◽  
Author(s):  
Isabelle Loïodice ◽  
Jayme Staub ◽  
Thanuja Gangi Setty ◽  
Nam-Phuong T. Nguyen ◽  
Anne Paoletti ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Schizosaccharomyces Pombe ◽  
Fission Yeast ◽  
Mitotic Spindle ◽  
Live Cell Imaging ◽  
Cell Imaging ◽  
Microtubule Organization ◽  
Cellular Processes ◽  
Spindle Midzone ◽  
Fluorescence Live Cell Imaging

Proper microtubule organization is essential for cellular processes such as organelle positioning during interphase and spindle formation during mitosis. The fission yeast Schizosaccharomyces pombe presents a good model for understanding microtubule organization. We identify fission yeast ase1p, a member of the conserved ASE1/PRC1/MAP65 family of microtubule bundling proteins, which functions in organizing the spindle midzone during mitosis. Using fluorescence live cell imaging, we show that ase1p localizes to sites of microtubule overlaps associated with microtubule organizing centers at both interphase and mitosis. ase1Δ mutants fail to form overlapping antiparallel microtubule bundles, leading to interphase nuclear positioning defects, and premature mitotic spindle collapse. FRAP analysis revealed that interphase ase1p at overlapping microtubule minus ends is highly dynamic. In contrast, mitotic ase1p at microtubule plus ends at the spindle midzone is more stable. We propose that ase1p functions to organize microtubules into overlapping antiparallel bundles both in interphase and mitosis and that ase1p may be differentially regulated through the cell cycle.

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