Shape Changes of Self-Assembled Actin Bilayer Composite Membranes

We report the self-assembly of thin actin shells beneath the membranes of giant vesicles. Ion-carrier mediated influx of $\mathrm{Mg}{}^{2+}$ induces actin polymerization in the initially spherical vesicles. Buckling of the vesicles and the formation of blisters after thermally induced bilayer expansion are demonstrated. Bilayer flickering is dominated by tension generated by its coupling to the actin cortex. Quantitative flicker analysis suggests that the bilayer and the actin cortex are separated by 0.4 to $0.5\mu \mathrm{m}$ due to undulation forces.