Approches physiques de problématiques biologiques

Publications de l’équipe

Année de publication : 2004

Tatsiana Lobovkina, Paul Dommersnes, Jean-Francois Joanny, Patricia Bassereau, Mattias Karlsson, Owe Orwar (2004 May 14)

Mechanical tweezer action by self-tightening knots in surfactant nanotubes.

Proceedings of the National Academy of Sciences of the United States of America : 101 : 7949-7953 : DOI : 10.1073/pnas.0401760101 En savoir plus
Résumé

Entanglements and trefoil knots on surfactant nanotubes in the liquid phase were produced by a combination of network self-organization and micromanipulation. The resulting knots are self-tightening, and the tightening is driven by minimization of surface free energy of the surfactant membrane material. The formation of the knot and the steady-state knot at quasi-equilibrium can be directly followed and localized by using fluorescence microscopy. Knots on nanotubes can be used as nanoscale mechanical tweezers for trapping and manipulation of single nano- and micrometer-sized high-aspect ratio objects. Furthermore, we demonstrate that by controlling the surface tension, objects captured by a knot can be transported along given trajectories defined by the nanotube axes.

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Année de publication : 2003

Peter Lenz, Jean-François Joanny, Frank Jülicher, Jacques Prost (2003 Oct 4)

Membranes with rotating motors.

Physical review letters : 108104 En savoir plus
Résumé

We study collections of rotatory motors confined to two-dimensional manifolds. These systems show a nontrivial collective behavior since the rotational motion leads to a repulsive hydrodynamic interaction between motors. While for high rotation speed motors might exhibit crystalline order, they form at low speed a disordered phase where diffusion is enhanced by velocity fluctuations. These effects should be experimentally observable for motors driven by external fields and for dipolar biological motors embedded into lipid membranes in a viscoelastic solvent.

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Giovanni Cappello, Mathilde Badoual, Albrecht Ott, Jacques Prost, Lorenzo Busoni (2003 Oct 4)

Kinesin motion in the absence of external forces characterized by interference total internal reflection microscopy.

Physical review. E, Statistical, nonlinear, and soft matter physics : 021907 En savoir plus
Résumé

We study the motion of the kinesin molecular motor along microtubules using interference total internal reflection microscopy. This technique achieves nanometer scale resolution together with a fast time response. We describe the first in vitro observation of kinesin stepping at high ATP concentration in the absence of an external load, where the 8-nm step can be clearly distinguished. The short-time resolution allows us to measure the time constant related to the relative motion of the bead-motor connection; we deduce the associated bead-motor elastic modulus.

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Jean-François Joanny, Frank Jülicher, Jacques Prost (2003 May 7)

Motion of an adhesive gel in a swelling gradient: a mechanism for cell locomotion.

Physical review letters : 168102 En savoir plus
Résumé

Motivated by the motion of nematode sperm cells, we present a model for the motion of an adhesive gel on a solid substrate. The gel polymerizes at the leading edge and depolymerizes at the rear. The motion results from a competition between a self-generated swelling gradient and the adhesion on the substrate. The resulting stress provokes the rupture of the adhesion points and allows for the motion. The model predicts an unusual force-velocity relation which depends in significant ways on the point of application of the force.

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Année de publication : 2002

Imre Derényi, Frank Jülicher, Jacques Prost (2002 Jun 13)

Formation and interaction of membrane tubes.

Physical review letters : 238101 En savoir plus
Résumé

We show that the formation of membrane tubes (or membrane tethers), which is a crucial step in many biological processes, is highly nontrivial and involves first-order shape transitions. The force exerted by an emerging tube is a nonmonotonic function of its length. We point out that tubes attract each other, which eventually leads to their coalescence. We also show that detached tubes behave like semiflexible filaments with a rather short persistence length. We suggest that these properties play an important role in the formation and structure of tubular organelles.

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Année de publication : 2013

E Hannezo, J Prost, J-F Joanny (1970 Jan 1)

Growth, homeostatic regulation and stem cell dynamics in tissues.

Journal of the Royal Society, Interface / the Royal Society : 20130895 : DOI : 10.1098/rsif.2013.0895 En savoir plus
Résumé

The regulation of cell growth in animal tissues is a question of critical importance: most tissues contain different types of cells in interconversion and the fraction of each type has to be controlled in a precise way, by mechanisms that remain unclear. Here, we provide a theoretical framework for the homeostasis of stem-cell-containing epithelial tissues using mechanical equations, which describe the size of the tissue and kinetic equations, which describe the interconversions of the cell populations. We show that several features, such as the evolution of stem cell fractions during intestinal development, the shape of a developing intestinal wall, as well as the increase in the proliferative compartment in cancer initiation, can be studied and understood from generic modelling which does not rely on a particular regulatory mechanism. Finally, inspired by recent experiments, we propose a model where cell division rates are regulated by the mechanical stresses in the epithelial sheet. We show that pressure-controlled growth can, in addition to the previous features, also explain with few parameters the formation of stem cell compartments as well as the morphologies observed when a colonic crypt becomes cancerous. We also discuss optimal strategies of wound healing, in connection with experiments on the cornea.

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