Kachar B, Reese T S
Laboratory of Neuro-otolaryngology, National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, Maryland 20205.
J Cell Biol. 1988 May;106(5):1545-52. doi: 10.1083/jcb.106.5.1545.
Electron microscopy of directly frozen giant cells of characean algae shows a continuous, tridimensional network of anastomosing tubes and cisternae of rough endoplasmic reticulum which pervade the streaming region of their cytoplasm. Portions of this endoplasmic reticulum contact the parallel bundles of actin filaments at the interface with the stationary cortical cytoplasm. Mitochondria, glycosomes, and other small cytoplasmic organelles enmeshed in the endoplasmic reticulum network display Brownian motion while streaming. The binding and sliding of endoplasmic reticulum membranes along actin cables can also be directly visualized after the cytoplasm of these cells is dissociated in a buffer containing ATP. The shear forces produced at the interface with the dissociated actin cables move large aggregates of endoplasmic reticulum and other organelles. The combination of fast-freezing electron microscopy and video microscopy of living cells and dissociated cytoplasm demonstrates that the cytoplasmic streaming depends on endoplasmic reticulum membranes sliding along the stationary actin cables. Thus, the continuous network of endoplasmic reticulum provides a means of exerting motive forces on cytoplasm deep inside the cell distant from the cortical actin cables where the motive force is generated.
对直接冷冻的轮藻巨型细胞进行电子显微镜观察，结果显示，粗面内质网的管道和扁平囊构成了一个连续的三维网络，相互吻合，遍布于其细胞质的流动区域。在与静止的皮层细胞质的界面处，内质网的部分区域与平行排列的肌动蛋白丝束相接触。内质网网络中交织着的线粒体、糖体和其他小的细胞质细胞器在流动时呈现布朗运动。在含有ATP的缓冲液中解离这些细胞的细胞质后，还可以直接观察到内质网沿着肌动蛋白丝的结合和滑动。与解离的肌动蛋白丝的界面处产生的剪切力会移动内质网和其他细胞器的大聚集体。快速冷冻电子显微镜以及对活细胞和解离细胞质的视频显微镜观察相结合，证明了细胞质流动依赖于内质网沿着静止的肌动蛋白丝滑动。因此，内质网的连续网络提供了一种对远离产生动力的皮层肌动蛋白丝的细胞深处的细胞质施加动力的方式。
