Grand Séminaire d'Institut

Vendredi 1^er Décembre 2017 à 11h00.

Grab-and-pull: from molecular motors to tissue dynamics

''Cells sense the rigidity of their environment through local pinching, which are exerted by myosin motors contracting over bundles of actin filaments. Recent experiments have shown that: (i) these motorsare surprisingly efficient, exerting forces larger than the usually reported value of a few piconewtons per motors, (ii) these motors move collectively in a stepwise fashion, with 2.5nm steps - i.e. half the 5nm actin period [1]. Our new molecular motor model encompasses both observations and explains why efficient motors move by steps. Motivated by recent experiments showing that the stochastic activity of motors controls the cell nucleus deformations, we investigate the role of active fluctuations on the stochastic dynamics of an inclusion embedded in a viscous gel. We show that non-equilibrium stress fluctuations give rise to an effective attraction towards the boundaries of a confining domain. Our theory rationalizes the counter-intuitive experimental observation that actin polymerization can either reduce or increase the amplitude of nuclear fluctuations, depending on the cell shape [2]. Moving further to larger length scales, we consider the role of myosin motor contractility in organ formation. We model how, during embryogenesis, muscle segments of the zebrafish acquire a V-shape, which is characteristic of most swimming species [3]. [1] Wolfenson, H. et al. Nature Cell Biol., 18(1), 33–42 (2015). [2] J.-F. Rupprecht, A. Singh, G. V. Shivashankar, M. Rao, J. Prost, arXiv:1703.04395 (2017). [3] J-F Rupprecht, S. Tlili, J Yin, J Prost, TE Saunders, Mechanisms of Development, 145 (2017).''