Morphological and topological transformation of membrane vesicles.

Liposomes are micro-compartments made of lipid bilayer membranes withcharacteristics quite similar to those of biological membranes. To formartificial cell-like structures, we generated liposomes that containedsubunit proteins of cytoskeletons: tubulin or actin. Spherical liposomeswere transformed into bipolar or cell-like shapes by mechanical forcesgenerated by the polymerization of encapsulated subunits of microtubules.Disk- or dumbbell-shaped liposomes were developed by the polymerizationof encapsulated actin. Dynamic processes of morphological transformationsof liposomes were visualized by high intensity dark-field lightmicroscopy.Topological changes, such as fusion and division of membrane vesicles,play an essential role in cellular activities. To investigate themechanism of these processes, we visualized in real time the liposomesundergoing topological transformation. A variety of novel topologicaltransformations were found, including the opening-up of liposomes and thedirect expulsion of inner vesicles.