Regulation of secretion, exocytosis and membrane fusion by vesicular lipids

许多由细胞分泌的用于细胞间通讯的分子（例如激素）被包装成细胞内的小囊泡（每个小囊泡被包含大量胆固醇的脂质膜包围）。包装的信号分子从细胞中分泌涉及囊泡与细胞表面的融合（其也被脂质膜包围，其胆固醇密度约为囊泡膜的1/3）;该过程始于形成连接囊泡内部与细胞表面的非常小的孔。 我的实验室最近发现，当囊泡刚刚开始与细胞表面融合时，细胞中的胆固醇总量可以调节细胞中激素的缓慢流动。然而，我们不确定是否在囊泡膜或细胞表面的胆固醇在这种作用中发挥更突出的作用。 在这里，我们建议澄清这个问题，利用遗传操作，可以选择性地减少胆固醇的分泌囊泡膜，但不是细胞表面。 这项研究的结果将使我们更好地理解为什么细胞已经进化到在某些膜隔室自然积累胆固醇。 参与拟议研究的学员不仅将学习操纵细胞中胆固醇分子分布的遗传和分子工具，还将学习触发和监测单个细胞分泌的生物物理工具。

Many molecules (e.g. hormones) that are secreted by cells for communications between cells are packaged into small vesicles (each surrounded by a lipid membrane that includes lots of cholesterol) within the cell. The secretion of the packaged signaling molecules from a cell involves the fusion of the vesicle with the cell's surface (which is also surrounded by a lipid membrane whose density of cholesterol is about 1/3 that of the vesicular membrane); this process starts with the formation of a very small pore that connects the inside of a vesicle with the cell's surface. My lab recently discovered that total amount of cholesterol in cells can regulate the slow trickle of hormones from a cell when a vesicle just starts to fuse with the cell's surface. However we are uncertain whether the cholesterol in the membrane of the vesicle or the cell surface plays a more prominent role in this effect. Here we propose to clarify this issue by exploiting a genetic manipulation that can selectively reduce cholesterol in the membrane of the secretory vesicles, but not the cell surface. The results from the proposed study will allow us to better understand why cells have evolved to naturally accumulate cholesterol at certain membrane compartments. The trainees involved in the proposed study will learn not only the genetic and molecular tools to manipulate the distribution of cholesterol molecules in cells, but also the biophysical tools to trigger and monitor secretion from individual cells.