Mechanics and growth of the actin cytoskeleton probed by magnetic micro-objects
Julien Heuvingh (PMMH, ESPCI)
The ability of cells to perform essential processes such as migration or deformation relies on their cytoskeleton, and especially on the structures and networks formed by the actin polymer and its associated proteins. Understanding the dynamics and the mechanics of the actin filaments and its multiple partner is a major goal at the frontier of biology and physics. Our team developed a new experimental setup to study the mechanics of in vitro reconstituted actin networks, with an unprecedented throughput. This technique is based on self-organized chains of micron-size magnetic beads or cylinders where the controlled attractive dipolar force between the colloids deforms the actin networks. We characterized for the first time the mechanics of actin networks reconstituted with different concentrations of purified proteins, leading to networks of different architectures, and drew conclusions on the origin of the elasticity on these networks (Pujol et al PNAS 2012). We are now measuring mechanical properties of networks reconstituted from yeast extract which allows comparison between a wild type containing hundred different actin binding proteins to mutants lacking some of them. Our experimental setup was decisively improved by the fabrication of magnetic micro-objects of cylindrical or cubic shape (Tavacoli et al. Soft Matter 2013) allowing the deformation of actin networks between two flat surfaces. In this way, we can access properties of dense branched networks such as non-linear elasticity and Poisson modulus, which are required to test theoretical models of fiber networks (Mikado). We are currently studying the growth velocity of the actin gel as a function of an applied mechanical stress and the architecture of the networks. I will also present other applications of our magnetic methods to probe the mechanics of whole cells.