Morphological changes of liposomes caused by actin assembly : the effect of actin binding proteins and surfactants.

1.为了研究细胞内部骨架网络的组织化所引起的细胞形态发生，我们用实时高强度暗视野显微镜表征了包裹肌动蛋白及其交联蛋白（fascin、α-actinin或filamin）的脂质体的转化。包封的G-肌动蛋白聚合成肌动蛋白丝并形成束或凝胶，这取决于共包封的肌动蛋白交联蛋白的类型，从而引起脂质体的各种形态变化。转化脂质体之间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，相邻交联肌动蛋白丝之间的距离和角度灵活性是其形态发生的关键。2.凝溶胶蛋白（Gelsolin）是已知的肌动蛋白结合蛋白之一，其活性受钙离子调控。我们发现，血浆凝溶胶蛋白可以磷酸化，通过使用从有丝分裂的HeLa细胞分离的激酶馏分。磷酸化后，凝溶胶蛋白的活性不再需要Ca ^2+：它切断肌动蛋白丝并随后将其封端，并在无Ca ^2+的溶液中使肌动蛋白丝成核。3.利用高强度暗视野显微镜直接、实时观察脂质体膜与表面活性剂相互作用引起的脂质体动力学行为。表面活性剂对脂质体的溶解被认为是类似于肥皂泡在空气中爆炸的灾难性事件;然而，实际过程尚未澄清。我们通过实验研究了这一过程，发现暴露于各种表面活性剂的脂质体表现出新颖的行为，即伴随间歇性震动的连续收缩、包裹的脂质体的释放、打开和由内而外的拓扑反转。

1.To study the morphogenesis of cells caused by the organization of their internal cytoskeletal network, we characterized the transformation of liposomes encapsulating actin and its crosslinking proteins, fascin, α-actinin, or filamin, using real-time high-intensity dark-field microscopy. The encapsulated G-actin polymerized into actin filaments 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 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.Gelsolin is one of the best known actin-binding proteins with activities regulated by calcium. We found that plasma gelsolin can be phosphorylated by using the kinase fraction isolated from mitotic HeLa cells. After this phosphorylation, gelsolin no longer requires Ca^<2+> for activity : it severs and subsequently caps actin filaments, and nucleates filament formation in Ca^<2+>-free solutions.3.Dynamic behaviors of liposomes caused by interactions between liposomal membranes and surfactant were studied by direct, real-time observation using high-intensity dark-field microscopy. Solubilization of liposomes by surfactants is thought to be a catastrophic event akin to the explosion of soap bubbles in the air ; however, the actual process has not been clarified. We studied this process experimentally and found that liposomes exposed to various surfactants exhibited novel behavior, namely continuous shrinkage accompanied by intermittent quakes, release of encapsulated liposomes, opening-up, and inside-out topological inversion.