Laboratoire Matière et Systèmes Complexes

Modelling Cell Mechanics with Active Gel Theory

Andrew Callan-Jones

Abstract: In essentially all living cells there is a polymer network called the actin-myosin cytoskeleton. It is involved in a remarkably vast number of living processes, such as cell division, left-right symmetry breaking, wound repair, cancer metastasis, to name just a few. From a physicist’s point of view, it is a network of semi-flexible filaments, cross-linked by protein molecules. In addition, the cytoskeleton is an active system: by converting the chemical energy of ATP into useful work, molecular motors behave as walking cross-linkers, maintaining the gel out of equilibrium. It is thus an internally driven system, and has much in common with other such systems, synthetic and living, ranging from active colloids to bird flocks.

In this talk, I will first present a formalism – known as active gel theory – to describe cytoskeletal phenomena at scales of roughly 100 nm and up (greater than the network mesh size). This theory is based on conservation laws, symmetries, and out-of-equilibrium thermodynamics, and gives rise to a set of phenomenological equations, akin to the Navier-Stokes equation. Although biological systems are tremendously complex, active gel theory provides a semi-quantitative description of numerous biological phenomena.

I will illustrate the usefulness of this theory to understand two biological applications: spontaneous polarization of cells and cell migration. These processes occur during embryonic development, for example, but can also be observed in in vitro experiments. In collaborations with three experimental teams, we were able to measure cytoskeletal flows and to relate these to polarization and migration using models based on active gel theory. Experiments and theory, developed hand-in-hand, offer a very promising approach to uncover the physics behind cell biology.

6 Avril 2017 à 13:00 en salle 646A