Morphological changes of giant liposomes caused by cytoskeletal proteins, surfactants, or optical tweezers

1)脂质体是由脂质双层膜构成的微室，其特性与生物膜非常相似。为了形成人造细胞样结构，我们制造了含有细胞骨架亚基蛋白的脂质体：肌动蛋白及其相关蛋白。球形脂质体通过包封肌动蛋白聚合转化成圆盘状或哑铃状。双极性或细胞样形状的脂质体是由包裹的肌动蛋白及其交联蛋白（束状蛋白、-肌动蛋白或丝蛋白）在内部肌动蛋白网络组织产生的机械力作用下组装而成的。利用高强度暗场光显微镜观察脂质体形态转化的动态过程。转化脂质体的形态差异表明，肌动蛋白交联蛋白通过组织其特定的肌动蛋白网络来决定脂质体的形状。形态学分析表明，交联方式，即相邻交联肌动蛋白丝之间的距离和角柔韧性，对形态发生至关重要。2)膜囊泡的融合、分裂等拓扑结构变化在细胞活动中起着重要作用。为了研究这些过程的机制，我们利用高强度暗场显微镜直接实时观察了脂质体在脂质体膜与源自流感血凝素、蜂毒素或表面活性剂的促聚变肽相互作用下发生的拓扑转变。结果，发现了各种新颖的拓扑变换，包括脂质体的开放，内部囊泡的直接排出，间歇性地震和由内到外的拓扑反转。这些新发现揭示了脂质双分子层本身具有进行拓扑转化的能力。

1)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 : actin, and its associating proteins. Spherical liposomes were transformed into disk-or dumbbell-shapes by the polymerization of encapsulated actin. Bipolar-or cell-like-shaped liposomes were developed by the assembly of encapsulated actin and its crosslinking proteins, fascin, -actinin, or filamin, by mechanical forces generated by the organization of internal actin-networks. Dynamic processes of morphological transformations of liposomes were visualized by high intensity dark-field light microscopy. The differences in morphology among transformed liposomes indicate that actin-crosslinking proteins determine liposome shape by organizing their specific actin networks. Morphological analysis reveals that the crosslinking manner, i.e. distance and angular flexibility between adjacent crosslinked actin filaments, is essential for the morphogenesis.2)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 the liposomes undergoing topological transformation induced by interactions between liposomal membranes and fusogenic peptides derived from influenza hemagglutinin, melittin, or surfactants with direct, real-time observation using high-intensity dark-field microscopy. As the results, a variety of novel topological transformations were found, including the opening-up of liposomes, the direct expulsion of inner vesicles, intermittent quakes, and inside-out topological inversion. These novel findings reveal that the lipid bilayer itself possesses the ability to undergo topological transformation.