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Propulsion de liposomes géants par polymérisation d'actine: un modèle pour l'interaction dynamique cytosquelette-membrane dans la motilité

Abstract : Cell movement is organized by molecular processes which couple plasma membrane to actin cytoskeleton dynamics, in order to generate cell protrusions. I used a biomimetic approach to reconstitute in vitro site-directed actin polymerization against lipid membranes. To do so, I first synthesised giant unilamellar vesicles (GUVs) by electroformation and functionalized them with actin polymerization activators such as N-WASP. When placed in a reconstituted motility assay made of pure proteins, vesicle grow a branched actin network that propels them in the motility medium. I showed that actin-propelled GUVs undergo continuous or periodic saltatory movement, and that the transition between these two regimes is controlled by the concentration of Arp2/3 complex, which branches filaments by interacting with liposome-bound N-WASP. Phase contrast and fluorescence microscopy show that saltatory motion is linked to cycles in the distribution of N-WASP at the membrane, between a homogeneous and a segregated state. Comparison of the changes in the distributions of N-WASP, Arp2/3 and actin during propulsion demonstrates that actin filaments transiently bind to N-WASP, and that these transient bonds are mediated by the Arp2/3 complex. The interaction of N-WASP-Arp2/3 with the filaments drives segregation. The balance between segregation and free diffusion determines whether continuous movement can be sustained. Computed surface distributions of N-WASP, Arp2/3 complex, and actin, derived from a theoretical description of this mechanism, account satisfactorily for the measured density profiles.
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Submitted on : Friday, February 15, 2008 - 3:19:58 PM
Last modification on : Thursday, January 11, 2018 - 6:15:11 AM
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Vincent Delatour. Propulsion de liposomes géants par polymérisation d'actine: un modèle pour l'interaction dynamique cytosquelette-membrane dans la motilité. Biophysique [physics.bio-ph]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00256524⟩

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