Next seminar : Séminaire du LPTMS: Cécile Sykes (Institut Curie)

Tuesday, April 21 2020 at 11:00:00

Active deformation of the cell membrane through actin assembly, and how we may infer nucleus deformation

Cécile Sykes (Institut Curie)

In all cell functions, a common observation is that cytoskeleton assembly correlates with membrane deformation based on active forces. The exact role, in particular, of the actin cytoskeleton in cell membrane deformation, with pushing or pulling forces, is what we address both experimentally and theoretically. We conceive stripped-down experimental systems that reproduce cellular behaviours in simplified conditions: cytoskeleton dynamics are reproduced on liposome membranes. Actin polymerization through the growth of a branched actin network is able to initiate membrane tubules and spikes by pushing or pulling, and mimics cellular deformations. By changing experimentally membrane tension and the structural details of the cytoskeleton architecture, we displace the system within a phase diagram where inward or outward deformations are favoured [1]. Moreover, shells of branched actin networks grown around liposomes display buckling and wrinkling under osmotic deflation, thereby confirming their elastic properties. The time during which we let the network grow around liposomes allows us to vary the shell thickness, and to specify the length scale of buckling versus wrinkling [2]. Our results illustrate the generic mechanism of buckling and wrinkling found in various systems spanning from pollen grains to the development of the gut or the brain. Inspired by actin forces exerted on membranes and organelles, we address now how the nucleus, which is the most rigid cell organelle, is deformed by the actin cytoskeleton during cell translocation. When cells move through narrow spaces that are smaller than their nuclei, we find that proteins of the nuclear membrane, such as nesprins, accumulate at the nucleus front and pull the nucleus forward [3]. We want to address in the future how we could characterize this active process and infer its molecular details. References: [1] Simon et al., Nature Physics (2019) [2] Kusters et al., Soft Matter (2019) [3] Davidson et al., in revision

Last Highlight : Comment une barrière peut être plus haute et plus facile à franchir

Que ce soit en physique, en chimie ou en biologie, les vitesses de réaction sont très souvent limitées par des barrières énergétiques à franchir grâce à l'activation thermique. Des travaux menés par le LPTMS et le LPS d'Orsay en collaboration avec l'Université de Cambridge,  démontrent que l'on peut jouer sur le profil d'une barrière pour en accélérer le franchissement par un objet Brownien : l'optimisation des profils conduit aux barrières les plus élevées.

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