The polymerization of the protein, actin, appears to be the source of the propulsive force for eukaryotic cell motion. While the alphabet soup of proteins that initiate and control actin polymerization is being scrupulously characterized, it is not clear how this generates a force to push. I will describe experiments in which we have reconstructed motility using phospholipid vesicles as model cell membranes in order to probe the polymerization forces.
Vorticella, one of the most powerful cellular machines, is a single celled organism with a cell body attached to a substrate by a slender stalk which contains a rod-like polymeric structure – the spasmoneme. Vorticella motility is characterized by an extremely rapid contraction which is powered by the collapse of the spasmoneme. We have conducted high-speed imaging experiments to study the dynamics of contraction.