Fehrenbacher K L, Davis D, Wu M, Boldogh I, Pon Liza A
Department of Anatomy and Cell Biology, Columbia University, College of Physicians and Surgeons, New York, New York 10032, USA.
Mol Biol Cell. 2002 Mar;13(3):854-65. doi: 10.1091/mbc.01-04-0184.
The endoplasmic reticulum (ER) in Saccharomyces cerevisiae consists of a reticulum underlying the plasma membrane (cortical ER) and ER associated with the nuclear envelope (nuclear ER). We used a Sec63p-green fluorescent protein fusion protein to study motility events associated with inheritance of cortical ER and nuclear ER in living yeast cells. During M phase before nuclear migration, we observed thick, apparently rigid tubular extensions emanating from the nuclear ER that elongate, undergo sweeping motions along the cell cortex, and shorten. Two findings support a role for microtubules in this process. First, extension of tubular structures from the nuclear ER is inhibited by destabilization of microtubules. Second, astral microtubules, structures that undergo similar patterns of extension, cortical surveillance and retraction, colocalize with nuclear ER extensions. During S and G(2) phases of the cell cycle, we observed anchorage of the cortical ER at the site of bud emergence and apical bud growth. Thin tubules of the ER that extend from the anchored cortical ER display undulating, apparently random movement and move into the bud as it grows. Finally, we found that cortical ER morphology is sensitive to a filamentous actin-destabilizing drug, latrunculin-A, and to mutations in the actin-encoding ACT1 gene. Our observations support 1) different mechanisms and cytoskeletal mediators for the inheritance of nuclear and cortical ER elements and 2) a mechanism for cortical ER inheritance that is cytoskeleton dependent but relies on anchorage, not directed movement.
酿酒酵母中的内质网（ER）由位于质膜下方的网状结构（皮质内质网）和与核膜相关的内质网（核内质网）组成。我们使用Sec63p-绿色荧光蛋白融合蛋白来研究活酵母细胞中与皮质内质网和核内质网遗传相关的运动事件。在核迁移前的M期，我们观察到从核内质网发出的粗大、明显刚性的管状延伸物，这些延伸物会伸长，沿着细胞皮质进行扫描运动，然后缩短。两项发现支持微管在此过程中发挥作用。第一，微管的去稳定化会抑制核内质网管状结构的延伸。第二，星体微管，即经历类似延伸、皮质监测和收缩模式的结构，与核内质网延伸物共定位。在细胞周期中的S期和G2期，我们观察到皮质内质网在芽出现的部位和顶端芽生长处锚定。从锚定的皮质内质网延伸出的内质网细管呈现出起伏的、明显随机的运动，并随着芽的生长而移入芽中。最后，我们发现皮质内质网形态对丝状肌动蛋白去稳定药物latrunculin-A以及肌动蛋白编码基因ACT1的突变敏感。我们的观察结果支持：1）核内质网和皮质内质网元件遗传的不同机制和细胞骨架介质；2）一种皮质内质网遗传机制，该机制依赖于细胞骨架，但依赖于锚定，而非定向运动。
