title: Dynamic actin patterns and Arp2/3 assembly at the substrate-attached surface of motile cells.
abstract: BACKGROUND
  In the cortical region of motile cells, the actin network rapidly reorganizes as required for movement in various directions and for cell-to-substrate adhesion. The analysis of actin network dynamics requires the combination of high-resolution imaging with a specific fluorescent probe that highlights the filamentous actin structures in live cells.
  
  
  RESULTS
  Combining total internal reflection fluorescence (TIRF) microscopy with a method for labeling actin filaments, we analyze the dynamics of actin patterns in the highly motile cells of Dictyostelium. A rapidly restructured network of single or bundled actin filaments provides a scaffold for the assembly of differentiated actin complexes. Recruitment of the Arp2/3 complex characterizes stationary foci with a lifetime of 7-10 s and traveling waves. These structures are also formed in the absence of myosin-II. Arp2/3-actin assemblies similar to those driving the protrusion of a leading edge form freely at the inner face of the plasma membrane.
  
  
  CONCLUSIONS
  The actin system of highly motile cells runs far from equilibrium and generates a multitude of patterns within a dynamic filamentous network. Traveling waves are the most complicated patterns based on recruitment of the Arp2/3 complex. They are governed by the propagated induction of actin polymerization. We hypothesize that the actin system autonomously generates primordia of specialized structures such as phagocytic cups or lamellipodia. These primordia would represent an activated state of the actin system and enable cells to respond within seconds to local stimuli by chemotaxis or phagocytic-cup formation.
authors.affiliation: Max-Planck-Institut für Biochemie, D-82152, Martinsried, Germany.
authors.forename: Till
authors.initials: T
authors.lastname: Bretschneider
authors.forename: Stefan
authors.initials: S
authors.lastname: Diez
authors.forename: Kurt
authors.initials: K
authors.lastname: Anderson
authors.forename: John
authors.initials: J
authors.lastname: Heuser
authors.forename: Margaret
authors.initials: M
authors.lastname: Clarke
authors.forename: Annette
authors.initials: A
authors.lastname: Müller-Taubenberger
authors.forename: Jana
authors.initials: J
authors.lastname: Köhler
authors.forename: Günther
authors.initials: G
authors.lastname: Gerisch
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002633:Chemotaxis / Q000502:physiology; D004023:Dictyostelium; D007150:Immunohistochemistry; D008840:Microfilament Proteins / Q000378:metabolism*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D024462:Myosin Type II / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D024462:Myosin Type II