Internal seminar - Cécile Sykes (LPENS)

By carefully choosing a limited number of purified proteins that reproduce cellular behaviours in simplified and controlled conditions, cellular functions such as motility and division can be studied thoroughly. Actin-based motility and protrusions dynamics are reproduced on liposome membranes with the exclusive contribution of cytoskeletal dynamics. I will present a few examples where physical models allow to describe these dynamics through phase diagrams depending on soft matter variables, such as membrane tension and the structural details of cytoskeleton architecture. I will show how inward and outward membrane deformations are generated by actin dynamics, and how liposomes covered with cytoskeletal actin shells undergo buckling or wrinkling of under osmotic deflation. Inspired by our experimental results of nuclei deformation during squeezed cell motility using microfluidic systems, I will present how we (think we) can distinguish the passive from the active contribution to nuclear movement and deformation. In particular, Stochastic Force Inference, applied to experimental nuclear trajectories and nuclear shape descriptors, results in equations that effectively describe the kinematics of this nuclear translocation phenomenon. Moreover, a careful observation of the re-organisation of proteins and cytoskeletal links in and around the nucleus gives a crucial information of which part of the nucleus is simply passively deformed and which part may contain an active contribution.