title: Local Arp2/3-dependent actin assembly modulates applied traction force during apCAM adhesion site maturation.
abstract: Homophilic binding of immunoglobulin superfamily molecules such as the Aplysia cell adhesion molecule (apCAM) leads to actin filament assembly near nascent adhesion sites. Such actin assembly can generate significant localized forces that have not been characterized in the larger context of axon growth and guidance. We used apCAM-coated bead substrates applied to the surface of neuronal growth cones to characterize the development of forces evoked by varying stiffness of mechanical restraint. Unrestrained bead propulsion matched or exceeded rates of retrograde network flow and was dependent on Arp2/3 complex activity. Analysis of growth cone forces applied to beads at low stiffness of restraint revealed switching between two states: frictional coupling to retrograde flow and Arp2/3-dependent propulsion. Stiff mechanical restraint led to formation of an extensive actin cup matching the geometric profile of the bead target and forward growth cone translocation; pharmacological inhibition of the Arp2/3 complex or Rac attenuated F-actin assembly near bead binding sites, decreased the efficacy of growth responses, and blocked accumulation of signaling molecules associated with nascent adhesions. These studies introduce a new model for regulation of traction force in which local actin assembly forces buffer nascent adhesion sites from the mechanical effects of retrograde flow.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520.
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Buck
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Schaefer
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520.
authors.forename: Vincent T
authors.initials: VT
authors.lastname: Schoonderwoert
authors.affiliation: Interdepartmental Neuroscience Program, Yale University, New Haven, CT 06520.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Creamer
authors.affiliation: Department of Mechanical Engineering and Materials Science, Yale University, New Haven, CT 06520.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Dufresne
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520 paul.forscher@yale.edu.
authors.forename: Paul
authors.initials: P
authors.lastname: Forscher
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D001048:Aplysia / Q000378:metabolism; D002448:Cell Adhesion / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D020439:Growth Cones / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D014143:Traction; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D015815:Cell Adhesion Molecules; D020744:rac GTP-Binding Proteins