Membrane Protrusion Driven by Actin Polymerization





Protrusion of cell membranes, as occurs at the leading edge of a crawling cell, is considered to be driven by polymerization of actin.  Whether polymerization alone is sufficient to drive this process, however, has not been clear.  Here we demonstrate, in a simple system of a giant liposome containing actin monomers, that actin polymerization indeed pushes out the lipid membrane into several protrusions.  The observed growth rate of ~0.5 μm/s is comparable to the rate in living cells.  In the three movies, polymerization is initiated by KCl, which is introduced in the liposomes by electroporation.  Note, in the third movie, that the movement of small vesicles inside the lipsomes ceases when protrusive growth begins, presumably because actin filaments impede their motion.
                                          Miyata, H. et al.  Proc. Natl. Acad. Sci. USA 96, 2048-2053 (1999)