Morphological and topological transformation of membrane vesicles

Liposomes are micro-compartments made of lipid bilayer membranes with characteristics quite similar to those of biological membranes. To form artificial cell-like structures, we generated liposomes that contained subunit proteins of cytoskeletons: tubulin or actin. Spherical liposomes were transformed into bipolar or cell-like shapes by mechanical forces generated by the polymerization of encapsulated subunits of microtubules. Disk- or dumbbell-shaped liposomes were developed by the polymerization of encapsulated actin. Dynamic processes of morphological transformations of liposomes were visualized by high intensity dark-field light microscopy. Topological changes, such as fusion and division of membrane vesicles, play an essential role in cellular activities. To investigate the mechanism of these processes, we visualized in real time the liposomes undergoing topological transformation. A variety of novel topological transformations were found, including the opening-up of liposomes and the direct expulsion of inner vesicles.