title: Direct measurement of the lamellipodial protrusive force in a migrating cell.
abstract: There has been a great deal of interest in the mechanism of lamellipodial protrusion (Pollard, T., and G. Borisy. 2003. Cell. 112:453-465). However, one of this mechanism's endpoints, the force of protrusion, has never been directly measured. We place an atomic force microscopy cantilever in the path of a migrating keratocyte. The deflection of the cantilever, which occurs over a period of approximately 10 s, provides a direct measure of the force exerted by the lamellipodial leading edge. Stall forces are consistent with approximately 100 polymerizing actin filaments per micrometer of the leading edge, each working as an elastic Brownian ratchet and generating a force of several piconewtons. However, the force-velocity curves obtained from this measurement, in which velocity drops sharply under very small loads, is not sensitive to low loading forces, and finally stalls rapidly at large loads, are not consistent with current theoretical models for the actin polymerization force. Rather, the curves indicate that the protrusive force generation is a complex multiphase process involving actin and adhesion dynamics.
authors.affiliation: Institute of Biophysics, University of Bremen, D-28359 Bremen, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Prass
authors.forename: Ken
authors.initials: K
authors.lastname: Jacobson
authors.forename: Alex
authors.initials: A
authors.lastname: Mogilner
authors.forename: Manfred
authors.initials: M
authors.lastname: Radmacher
mesh_terms: D008841:Actin Cytoskeleton / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D002478:Cells, Cultured; D015603:Keratinocytes / Q000502:physiology* / Q000648:ultrastructure; D018625:Microscopy, Atomic Force / Q000379:methods; D017686:Oncorhynchus mykiss; D011554:Pseudopodia / Q000502:physiology* / Q000648:ultrastructure; D013314:Stress, Mechanical; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology