Analysis of the molecular mechanism of the novel topological transformation of membrane vesicle and the construction of the cell-model

(1)脂质体操作。活细胞的形态是以细胞骨架和膜的机械特性为基础的。为了研究脂膜在形态发生中的作用，我们用双光束激光镊子操纵包裹了两个聚苯乙烯小球的巨型脂质体。当机械力施加到微珠上，从内部推动脂质体薄膜时，随着张力的增加，球形脂质体转变为柠檬形状，随后在柠檬状脂质体的末端产生管状膜突起。在柠檬形状的伸长阶段，转化所需的力变得更大。就在膜管产生之前，力达到了最大强度。然而，在膜管发展后，力突然减小，并保持恒定的强度，与管的长度无关。这些结果表明，只要简单地施加机械力，脂膜就可以形成膜管。(2)利用巨型脂质体建立细胞模型。众所周知，许多肌动蛋白结合蛋白在活细胞中肌动蛋白网络的组织中起着调节作用。为了研究这种组织作用，我们研究了将肌动蛋白与其交联蛋白、法菌素、α-肌动蛋白或细丝蛋白包裹在一起的脂质体的变化。随着肌动蛋白的聚合，脂质体的形态发生了变化。形态上的差异表明，肌动蛋白-交联蛋白实际上是通过组织它们特定的肌动蛋白网络来决定脂质体的形状。

(1) Liposome manipulation. The morphologies of living cells are based on the mechanical characteristics of cytoskeleton and membrane. To investigate the role of lipid membrane in the morphogenesis, we manipulated the giant liposomes that encapsulated two polystyrene beads by using double beam laser tweezers. As mechanical force was applied onto the beads to push a liposome membrane from inside, a spherical liposome transformed into a lemon shape with increasing the tension, and subsequently a tubular membrane projection was generated at the end of the lemon-shaped liposome. In an elongation stage of the lemon shape, the force required for the transformation became larger. Just before a membrane tube was generated, the force reached the maximum strength. However, after the membrane tube was developed, the force suddenly decreased, and kept constant strength independently from the tube length. These results indicate that lipid membrane can form the membrane tube by simple applying of mechanical force.(2) Cell model developed with giant liposome. It is well established that many kinds of actin binding proteins play regulatory roles in the organization of actin networks in living cells. To study such organization roles, we characterized the transformation of liposomes encapsulating actin with its crosslinking proteins, fascin, a-actinin or filamin. As the actin polymerized, which caused various morphological changes of liposomes. The differences in morphology indicate that the actin-crosslinking proteins actually determine liposome shape by organizing their specific actin networks.