title: A novel mechanism for the formation of actin-filament bundles by a nonprocessive formin.
abstract: Actin-filament bundles (or cables) have a structural role during cell division and morphogenesis, but also serve as important "tracks" for the transport of materials during cytokinesis and polarized cell growth. However, the dynamic formation of these longitudinal actin-filament higher-order structures is not understood. Recently, several lines of evidence suggest that formins provide one avenue for the initiation of actin cables in vivo. A popular model for the mechanism of polymerization of actin filaments by formin involves the processive movement of formin attached at the barbed end of an elongating filament. In the present study, we use an in vitro system to reconstitute the dynamic formation of actin-filament bundles generated by Arabidopsis FORMIN1 (AFH1). To be able to visualize individual events in such a complex system, we used real-time evanescent-wave microscopy. Surprisingly, we find that AFH1 is a nonprocessive formin that moves from the barbed end to the side of an actin filament after the nucleation event. We show why this new mechanism of nucleation by a member of the formin family is important for bundle formation. Finally, we analyze the different parameters controlling the dynamic formation of such longitudinal actin-filament bundles.
authors.affiliation: Departement Réponse et Dynamique Cellulaire, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, F38054 Grenoble, France.
authors.forename: Alphée
authors.initials: A
authors.lastname: Michelot
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Derivery
authors.forename: Rajaa
authors.initials: R
authors.lastname: Paterski-Boujemaa
authors.forename: Christophe
authors.initials: C
authors.lastname: Guérin
authors.forename: Shanjin
authors.initials: S
authors.lastname: Huang
authors.forename: François
authors.initials: F
authors.lastname: Parcy
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Staiger
authors.forename: Laurent
authors.initials: L
authors.lastname: Blanchoin
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure*; D017360:Arabidopsis / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000145:classification / Q000378:metabolism / Q000502:physiology*; D005456:Fluorescent Dyes / Q000032:analysis; D000080865:Formins; D008565:Membrane Proteins / Q000145:classification / Q000378:metabolism / Q000502:physiology*; D008840:Microfilament Proteins / Q000145:classification / Q000378:metabolism / Q000502:physiology*; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D012235:Rhodamines / Q000032:analysis
chemical_list: C417969:AFH1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D005456:Fluorescent Dyes; D000080865:Formins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D012235:Rhodamines