Studying <i>in vitro</i> the effect of actin dynamics on membrane tubes

Living cells change their shape in biological processes like division, motility or intracellular trafficking. These morphological changes rely on a dynamic network of biopolymers, the actin cytoskeleton that interacts with membranes. In particular, intracellular transport implies the formation of tubular membrane intermediates, with a radius of 10-100nm, finally destabilised into vesicles. In vivo examples of actin-dependent formation, stabilisation or scission of such tubes have been reported, but the underlying physical mechanisms remain unclear.

To address this issue, I use in vitro reconstituted systems with a minimal number of compounds to control the growth of a branched actin sleeve at the surface of preformed tubes. These tubes can be formed using an optically trapped bead. The presence of a tube affects the amplitude of bead fluctuations at long time scale while an actin sleeve surrounding the tube modifies its short time fluctuations. Furthermore, depending on network cohesiveness, actin either entirely or locally stabilise membrane tubes under extension. On a single tube, different tube radii coexist over several minutes, and may provide enough time and curvature geometries for other proteins to act on tube stability.