title: Gradient of rigidity in the lamellipodia of migrating cells revealed by atomic force microscopy.
abstract: Changes in mechanical properties of the cytoplasm have been implicated in cell motility, but there is little information about these properties in specific regions of the cell at specific stages of the cell migration process. Fish epidermal keratocytes with their stable shape and steady motion represent an ideal system to elucidate temporal and spatial dynamics of the mechanical state of the cytoplasm. As the shape of the cell does not change during motion and actin network in the lamellipodia is nearly stationary with respect to the substrate, the spatial changes in the direction from the front to the rear of the cell reflect temporal changes in the actin network after its assembly at the leading edge. We have utilized atomic force microscopy to determine the rigidity of fish keratocyte lamellipodia as a function of time/distance from the leading edge. Although vertical thickness remained nearly constant throughout the lamellipodia, the rigidity exhibited a gradual but significant decrease from the front to the rear of the lamellipodia. The rigidity profile resembled closely the actin density profile, suggesting that the dynamics of rigidity are due to actin depolymerization. The decrease of rigidity may play a role in facilitating the contraction of the actin-myosin network at the lamellipodium/cell body transition zone.
authors.affiliation: Laboratory of Cell Biophysics, Ecole Polytechnique Fédérale, Lausanne, Switzerland. valerie.laurent@univ-paris5.fr
authors.forename: Valérie M
authors.initials: VM
authors.lastname: Laurent
authors.forename: Sandor
authors.initials: S
authors.lastname: Kasas
authors.forename: Alexandre
authors.initials: A
authors.lastname: Yersin
authors.forename: Tilman E
authors.initials: TE
authors.lastname: Schäffer
authors.forename: Stefan
authors.initials: S
authors.lastname: Catsicas
authors.forename: Giovanni
authors.initials: G
authors.lastname: Dietler
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Verkhovsky
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Meister
mesh_terms: D000199:Actins / Q000737:chemistry; D000818:Animals; D001703:Biophysics / Q000379:methods*; D002465:Cell Movement; D048429:Cell Size; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D000078404:Epidermal Cells; D005399:Fishes; D049452:Green Fluorescent Proteins / Q000737:chemistry; D018625:Microscopy, Atomic Force / Q000379:methods*; D008856:Microscopy, Fluorescence; D015233:Models, Statistical; D009218:Myosins / Q000737:chemistry; D016012:Poisson Distribution; D011554:Pseudopodia / Q000378:metabolism*
chemical_list: D000199:Actins; D049452:Green Fluorescent Proteins; D009218:Myosins