dictyNews Electronic Edition Volume 39, number 25 August 30 2013 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Inhibitory signalling to the Arp2/3 complex steers cell migration Irene Dang1, Roman Gorelik1, Carla Sousa-Blin1, Emmanuel Derivery1, Christophe GuŽrin2, Joern Linkner3, Maria Nemethova4, Tamara Tchipysheva5, Valeria Ermilova5, Sophie Vacher6, Julien G. Dumortier7, Florence A. Giger7, ValŽrie Campanacci8, Isaline Herrada9, Anne-Gaelle Planson8, Susan Fetics8, VŽronique Henriot1, Violaine David1, Ksenia Oguievetskaia1, Goran Lakisic1, Fabienne Pierre1, Adeline Boyreau11, Nadine PeyriŽras11, Anika Steffen10, Klemens Rottner10, Sophie Zinn-Justin9, Jacqueline Cherfils8, Nicolas B. David7, Ivan Biche6, Antonina Alexandrova5, J. Victor Small4, Jan Faix3, Laurent Blanchoin2, Alexis Gautreau1. 1 Group Cytoskeleton in Cell Morphogenesis Laboratoire dÕEnzymologie et Biochimie Structurales, CNRS, Gif-sur-Yvette, France 2 Physics of the Cytoskeleton and Morphogenesis, Grenoble, France 3 Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany 4 Institute of Molecular Biotechnology, Vienna, Austria 5 Institute of Carcinogenesis, N.N. Blokhin Cancer Research Center, Russian Academy of Medical Sciences, Moscow, Russian Federation 6 INSERM, CNRS, ENS, Institut de Biologie de l'ENS, Paris, France 7 Oncogenetic Laboratory, Institut Curie - H™pital RenŽ Huguenin, Saint-Cloud, France 8 Laboratoire dÕEnzymologie et Biochimie Structurales, CNRS, Gif-sur-Yvette, France 9 Laboratoire de Biologie Structurale et Radiobiologie, iBiTec-S and CNRS, CEA Saclay, Gif-sur-Yvette, France 10 Institute of Genetics, University of Bonn, Germany 11 Institut des Systmes complexes & NeD, Institut de Neurobiologie Alfred Fessard, CNRS, Gif-sur-Yvette, France. Nature, in press. Cell migration requires the generation of branched actin networks that power the protrusion of the plasma membrane in lamellipodia. The Arp2/3 complex is the molecular machine that nucleates these branched actin networks. This machine is activated at the leading edge of migrating cells by the WAVE complex. The WAVE complex is itself directly activated by the small GTPase Rac, which induces lamellipodia. However, how cells regulate the directionality of migration is poorly understood. Here we identify a novel protein that inhibits the Arp2/3 complex in vitro, Arpin, and show that Rac signalling recruits and activates Arpin at the lamellipodial tip, like WAVE. Consistently, upon depletion of the inhibitory Arpin, lamellipodia protrude faster and cells migrate faster. The major role of this inhibitory circuit, however, is to control directional persistence of migration. Indeed, Arpin depletion in both mammalian cells and Dictyostelium discoideum amoeba resulted in straighter trajectories, whereas Arpin microinjection in fish keratocytes, one of the most persistent systems of cell migration known, induced these cells to turn. The coexistence of the Rac-Arpin-Arp2/3 inhibitory circuit with the Rac-WAVE-Arp2/3 activatory circuit can account for this conserved role of Arpin in steering cell migration. Loss of this inhibitory circuit promotes exploratory behaviours and might commit carcinoma cells to the invasive state. Submitted by Hans Faix [faix.jan@mh-hannover.de] --------------------------------------------------------------------------- A novel human receptor involved in bitter tastant detection identified using the model organism Dictyostelium discoideum Steven Robery1, Richard Tyson2, Christopher Dinh3, Adam Kuspa3, Angelika A. Noegel4, Till Bretschneider2, Paul L. R. Andrews5, Robin S. B. Williams1* 1. Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK 2. Molecular Organization and Assembly in Cells, University of Warwick, Coventry, CV4 7AL, UK 3. Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA 4. Institute of Biochemistry I, Medical Faculty, University of Cologne, Cologne, Germany 5. Division of Biomedical Sciences, St George's University of London, London SW17 0RE, UK *Corresponding author; robin.williams@rhul.ac.uk Journal of Cell Science, in press Detection of substances tasting bitter to humans occurs in diverse organisms including the social amoeba, Dictyostelium discoideum. To establish a molecular mechanism for bitter tastant detection in Dictyostelium, we screened a mutant library for resistance to a commonly used bitter standard, phenylthiourea. This approach identified a G-protein coupled receptor mutant, grlJ-, showing a significantly increased tolerance to phenylthiourea in growth, survival and movement. This mutant was not resistant to a structurally dissimilar potent bitter tastant, denatonium benzoate, suggesting it is not a target for at least one other bitter tastant. Analysis of the cell signalling pathway involved in the detection of phenylthiourea showed dependence upon heterotrimeric G-protein and phosphatidylinositol 3-kinase activity, suggesting this signalling pathway is responsible for phenylthiourea cellular effects. This is further supported by a phenylthiourea-dependent block in the transient cAMP-induced production of PIP3 in wild type but not grlJ- cells. Finally, we have identified an uncharacterized human protein gamma-aminobutyric acid (GABA) type B receptor subunit 1 isoform with weak homology to GrlJ that restored grlJ- sensitivity to phenylthiourea in cell movement and PIP3 regulation. Our data thus identifies a novel pathway for the detection of the standard bitter tastant, phenylthiourea, in Dictyostelium and implicates a poorly characterized human protein in phenylthiourea dependent cell responses. Submitted by Robin Williams [robin.williams@rhul.ac.uk] ============================================================== [End dictyNews, volume 39, number 25]