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Application de contraintes sur des systèmes complexes artificiels ou vivants : dégonflement de liposomes fonctionnalisés et réorganisation mécanosensible du cytosquelette de cellules Dictyostelium.

Abstract : During this work, 2 approaches have been explored.
First, I quantified the osmotic deswelling of liposomes filled with an agarose gel. The production of such artificial systems aims at mimicking cell behavior under the same constraints. Particularly, I observed that these functionnalized liposomes with a gel concentration between 0.07 and 0.18% w/w adopted crenated morphologies when strongly deswelled. These original shapes look like the ones of echinocytes sometimes seen with red blood cells. The gel is responsible for these shapes, does not affect deswelling kinetics but its elastic pressure stops more rapidly the osmotic deswelling compared to aqueous liposomes. This brings evidence for a water retention effect.
In a second approach, I studied the effect of hydrodynamical constraints on Dictyostelium amoebae adhering to a substrate. I quantified the mechanosensitive reorganization of the cytoskeleton of these living cells. To get relocalization kinetics of major cytoskeleton proteins in response to flow forces, I labeled actin and myosin-II with fluorescent proteins (GFP/mRFP) and designed a flow chamber enabling to rapidly change the flow direction. I showed that cells orient against flow forces and after a flow reversal reorient against new forces by inverting their polarity: first, actin depolymerizes, then actin rich protrusions are emitted against new mechanical forces and 15 sec later, the rear edge retracts with a myo-II crescent. Moreover, the actin-myosin contractility is dispensable to sense forces. Similar experiments by inverting the direction of a chemotactic gradient show that this cell reorientation process is not specific of flow experiments. This work proves the existence of a rapid inhibiting signal (leading to actin depolymerization) which is not taken into account in current models of chemotaxis. Finally, the visualization tools that I developped enable to study the role of proteins and cellular structures in mechanotransduction.
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https://tel.archives-ouvertes.fr/tel-00142229
Contributor : Jeremie Dalous <>
Submitted on : Tuesday, April 17, 2007 - 9:41:31 PM
Last modification on : Friday, November 6, 2020 - 4:08:55 AM
Long-term archiving on: : Wednesday, April 7, 2010 - 1:11:15 AM

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  • HAL Id : tel-00142229, version 1

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Jeremie Dalous. Application de contraintes sur des systèmes complexes artificiels ou vivants : dégonflement de liposomes fonctionnalisés et réorganisation mécanosensible du cytosquelette de cellules Dictyostelium.. Biophysique [physics.bio-ph]. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00142229⟩

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