title: Cellular control of cortical actin nucleation.
abstract: The contractile actin cortex is a thin layer of actin, myosin, and actin-binding proteins that subtends the membrane of animal cells. The cortex is the main determinant of cell shape and plays a fundamental role in cell division [1-3], migration [4], and tissue morphogenesis [5]. For example, cortex contractility plays a crucial role in amoeboid migration of metastatic cells [6] and during division, where its misregulation can lead to aneuploidy [7]. Despite its importance, our knowledge of the cortex is poor, and even the proteins nucleating it remain unknown, though a number of candidates have been proposed based on indirect evidence [8-15]. Here, we used two independent approaches to identify cortical actin nucleators: a proteomic analysis using cortex-rich isolated blebs, and a localization/small hairpin RNA (shRNA) screen searching for phenotypes with a weakened cortex or altered contractility. This unbiased study revealed that two proteins generated the majority of cortical actin: the formin mDia1 and the Arp2/3 complex. Each nucleator contributed a similar amount of F-actin to the cortex but had very different accumulation kinetics. Electron microscopy examination revealed that each nucleator affected cortical network architecture differently. mDia1 depletion led to failure in division, but Arp2/3 depletion did not. Interestingly, despite not affecting division on its own, Arp2/3 inhibition potentiated the effect of mDia1 depletion. Our findings indicate that the bulk of the actin cortex is nucleated by mDia1 and Arp2/3 and suggest a mechanism for rapid fine-tuning of cortex structure and mechanics by adjusting the relative contribution of each nucleator.
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK; Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK.
authors.forename: Miia
authors.initials: M
authors.lastname: Bovellan
authors.affiliation: Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, QC H3N 3J7, Canada.
authors.forename: Yves
authors.initials: Y
authors.lastname: Romeo
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany; International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland.
authors.forename: Maté
authors.initials: M
authors.lastname: Biro
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany; International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland.
authors.forename: Annett
authors.initials: A
authors.lastname: Boden
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany; International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland; Medical Research Council Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK.
authors.forename: Priyamvada
authors.initials: P
authors.lastname: Chugh
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK; Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK.
authors.forename: Amina
authors.initials: A
authors.lastname: Yonis
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK; Department of Physics and Astronomy, University College London, London WC1E 6BT, UK.
authors.forename: Malti
authors.initials: M
authors.lastname: Vaghela
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK; Department of Physics and Astronomy, University College London, London WC1E 6BT, UK.
authors.forename: Marco
authors.initials: M
authors.lastname: Fritzsche
authors.affiliation: Institute of Child Health, University College London, London WC1N 1EH, UK.
authors.forename: Dale
authors.initials: D
authors.lastname: Moulding
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Thorogate
authors.affiliation: Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Jégou
authors.affiliation: Institute of Child Health, University College London, London WC1N 1EH, UK.
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Thrasher
authors.affiliation: Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Romet-Lemonne
authors.affiliation: Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, QC H3N 3J7, Canada. Electronic address: philippe.roux@umontreal.ca.
authors.forename: Philippe P
authors.initials: PP
authors.lastname: Roux
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany; International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland; Medical Research Council Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK. Electronic address: e.paluch@ucl.ac.uk.
authors.forename: Ewa K
authors.initials: EK
authors.lastname: Paluch
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, UK; Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK. Electronic address: g.charras@ucl.ac.uk.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Charras
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D051376:Actin-Related Protein 2-3 Complex / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D048430:Cell Shape / Q000502:physiology; D022081:Cell Surface Extensions / Q000378:metabolism; D000080865:Formins; D006367:HeLa Cells; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D034622:RNA Interference; D034741:RNA, Small Interfering
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C108962:DIAPH1 protein, human; D000080865:Formins; D008840:Microfilament Proteins; D034741:RNA, Small Interfering