Morphogenesis of liposomes encapsulating actin depends on the type of actin-crosslinking

To study the morphogenesis of cells caused by the organization of their int ernal cytoskeletal network, we characterized the transformation of liposome s encapsulating actin and its crosslinking proteins, fascin, alpha-actinin, or filamin, using real-time high-intensity dark-field microscopy. With inc reasing temperature, the encapsulated G-actin polymerized into actin filame nts and formed bundles or gels, depending on the type of actin-crosslinking protein that was co-encapsulated, causing various morphological changes of liposomes. The differences in morphology among transformed liposomes indic ate that actin-crosslinking proteins determine liposome shape by organizing their specific actin networks. Morphological analysis reveals that the cro sslinking manner, i.e. distance and angular flexibility between adjacent cr osslinked actin filaments, is essential for the morphogenesis rather than t heir binding affinity and stoichiometry to actin filaments. (C) 1999 Academ ic Press.