title: A "primer"-based mechanism underlies branched actin filament network formation and motility.
abstract: Cells use actin assembly to generate forces for membrane protrusions during movement [1] or, in the case of pathogens, to propel themselves in the host cells, in crude extracts [2], or in mixtures of actin and other purified proteins [3]. Significant progress has been made in understanding the mechanism of actin-based motility at a macroscopic level by using biomimetic systems in vitro [4-6]. Here, we combined such a system with evanescent wave microscopy to visualize Arp2/3-mediated actin network formation at single-actin-filament resolution. We found that actin filaments that we call "primers" determine the origin of the autocatalytic and propagative formation of the actin network. In the presence of capping protein, multiple "primers" generate independent networks that merge around the object to form an outer "shell" made of entangled and capped filaments. Simultaneously, newly created filaments on the surface of the particle initiate mechanical stress, which develops until symmetry breaking. Our results and extensive modeling support that the stress, which releases into propulsive forces [7], is controlled not by any specific orientation of actin filaments toward the nucleation sites but only by new monomers added near the load surface.
authors.affiliation: Laboratoire de Physiologie Cellulaire Végétale, Institut de Recherches en Technologies et Sciences pour le Vivant, CNRS/CEA/INRA/UJF, 38054 Grenoble, France.
authors.forename: Vérane
authors.initials: V
authors.lastname: Achard
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Martiel
authors.forename: Alphée
authors.initials: A
authors.lastname: Michelot
authors.forename: Christophe
authors.initials: C
authors.lastname: Guérin
authors.forename: Anne-Cécile
authors.initials: AC
authors.lastname: Reymann
authors.forename: Laurent
authors.initials: L
authors.lastname: Blanchoin
authors.forename: Rajaa
authors.initials: R
authors.lastname: Boujemaa-Paterski
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000737:chemistry* / Q000502:physiology; D001696:Biomechanical Phenomena; D002465:Cell Movement / Q000502:physiology*; D008856:Microscopy, Fluorescence / Q000379:methods
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins