title: Adhesion-Dependent Wave Generation in Crawling Cells.
abstract: Dynamic actin networks are excitable. In migrating cells, feedback loops can amplify stochastic fluctuations in actin dynamics, often resulting in traveling waves of protrusion. The precise contributions of various molecular and mechanical interactions to wave generation have been difficult to disentangle, in part due to complex cellular morphodynamics. Here we used a relatively simple cell type-the fish epithelial keratocyte-to define a set of mechanochemical feedback loops underlying actin network excitability and wave generation. Although keratocytes are normally characterized by the persistent protrusion of a broad leading edge, increasing cell-substrate adhesion strength results in waving protrusion of a short leading edge. We show that protrusion waves are due to fluctuations in actin polymerization rates and that overexpression of VASP, an actin anti-capping protein that promotes actin polymerization, switches highly adherent keratocytes from waving to persistent protrusion. Moreover, VASP localizes both to adhesion complexes and to the leading edge. Based on these results, we developed a mathematical model for protrusion waves in which local depletion of VASP from the leading edge by adhesions-along with lateral propagation of protrusion due to the branched architecture of the actin network and negative mechanical feedback from the cell membrane-results in regular protrusion waves. Consistent with our model simulations, we show that VASP localization at the leading edge oscillates, with VASP leading-edge enrichment greatest just prior to protrusion initiation. We propose that the mechanochemical feedbacks underlying wave generation in keratocytes may constitute a general module for establishing excitable actin dynamics in other cellular contexts.
authors.affiliation: Department of Biochemistry and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Erin L
authors.initials: EL
authors.lastname: Barnhart
authors.affiliation: Department of Mathematics and Department of Physics, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Allard
authors.affiliation: Department of Biochemistry and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Chemical and Systems Biology, Stanford University, Stanford, CA 94305, USA.
authors.forename: Sunny S
authors.initials: SS
authors.lastname: Lou
authors.affiliation: Department of Biochemistry and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Microbiology and Immunology, Stanford University, Stanford, CA 94305, USA. Electronic address: theriot@stanford.edu.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Theriot
authors.affiliation: Courant Institute and Department of Biology, New York University, New York, NY 10012, USA. Electronic address: mogilner@cims.nyu.edu.
authors.forename: Alex
authors.initials: A
authors.lastname: Mogilner
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002465:Cell Movement; D002478:Cells, Cultured; D029941:Fish Proteins / Q000378:metabolism; D005399:Fishes / Q000378:metabolism*; D005786:Gene Expression Regulation; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism; D008954:Models, Biological; D013269:Stochastic Processes
chemical_list: D015815:Cell Adhesion Molecules; D029941:Fish Proteins
keywords: VASP; actin dynamics; actin waves; adhesion dynamics; cell motility; excitable system; keratocyte; leading edge