Identification of phospholipid translocase and its role in cell polarity formation.

众所周知，生物膜中的磷脂不对称地分布在脂质双层的内外小叶之间。虽然最近的研究表明，跨双层脂质不对称是由一系列特定的脂质运输蛋白产生和控制的，但这种脂质不对称的生理作用在很大程度上仍不清楚。在过去的十年里，我们已经建立了一系列磷脂结合探针和哺乳动物细胞突变株，这些突变株在磷脂生物合成方面存在缺陷。这些探针和突变体为研究膜磷脂的分子运动和细胞功能提供了有用的工具。在细胞分裂的最后阶段，胞质分裂收缩并随后封闭两个子细胞之间的质膜。收缩是由肌动蛋白的收缩环驱动的，断裂涉及细胞膜脂质双层的融合或重排。使用我们拥有的…基因的磷脂特异结合探针在过去的十年中，我们发现通常存在于双层内小叶的脂质磷脂酰乙醇胺(PE)暴露在卵裂沟的外小叶上。随后使用磷脂结合探针和PE合成缺陷突变细胞的分析表明，在细胞质分裂过程中，PE在卵裂沟上的这种表面暴露是协调肌动蛋白细胞骨架和质膜重组所必需的。为了确定参与脂-细胞骨架协调的分子，我们分离了在磷脂跨双层运动方面存在缺陷的芽生酵母突变株。一个名为ROS3的基因被鉴定为PE在质膜上跨双层定位的调节基因。ROS3编码一种存在于质膜上的新的跨膜蛋白。ROS3的破坏导致皮质肌动蛋白斑块的形态和形成的缺陷。Ros3p的过表达导致了多芽的形成。由于Ros3p同源物在一些哺乳动物组织中强烈表达，如脑和上皮细胞，Ros3p可能在细胞骨架和膜脂之间可能的交叉对话中发挥普遍作用，细胞骨架和膜脂是细胞分裂和细胞极性形成所必需的。较少

It is well established that phospholipids in biological membranes are distributed asymmetrically between the inner and outer leaflets of the lipid bilayer. Although recent studies have shown that the transbilayer lipid asymmetry is generated and controlled by a family of specific lipid transport proteins, the physiological role of the lipid asymmetry remains largely unknown. Over the past decade, we have established a series of phospholipid-binding probes and mammalian cell mutants defective in phospholipid biosynthesis. These probes and mutants have provided useful tools to study the molecular motion and the cellular function of membrane phospholipids.In the final stage of cell division, cytokinesis constricts and then seals the plasma membrane between the two daughter cells. The constriction is powered by a contractile ring of actin, and scission involves a fusion or rearrangement of the lipid bilayer of the cell membrane. Using phospholipid-specific binding probes that we have gener … More ated over the past decade, we found that the lipid phosphatidylethanolamine (PE), which normally resides in the inner leaflet of the bilayer, was exposed onto the outer leaflet of the cleavage furrow. Subsequent analyses, using the phospholipid-binding probes and mutant cells defective in PE synthesis, have shown that this surface exposure of PE on the cleavage furrow is needed to coordinate the reorganization of the actin cytoskeleton and the plasma membrane during cytokinesis.To identify the molecules involved in the lipid-cytoskeleton coordination, we have isolated budding yeast mutants that have a defective in the transbilayer movement of phospholipids. A gene, designated as ROS3, was identified as a regulator of transbilayer relocation of PE on plasma membrane. ROS3 encodes a novel transmembrane protein present on plasma membrane. Disruption of ROS3 resulted in defects in morphology and formation of cortical actin patch. Overexpression of Ros3p led to multibud formation. Since Ros3p homologue is strongly expressed in some mammalian tissues such as brain and epithelial cells, Ros3p may play a general role in possible cross-talks between the cytoskeleton and membrane lipids that are required for proper cell division as well as cell polarity formation. Less