Microtrabecular structure of the axoplasmic matrix: visualization of cross-linking structures and their distribution.
Microtrabecular structure of the axoplasmic matrix: visualization of cross-linking structures and their distribution.
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DOI：
10.1083/jcb.87.2.464
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发表时间：
1980-11
期刊：
影响因子：
--
通讯作者：
Porter KR
中科院分区：
文献类型：
--
作者：
Ellisman MH;Porter KR
轴浆运输是细胞质运动的一个引人注目的例子。轴质的成分迁移远达400 mm/d或约5微米/s。薄切片研究已经确定了轴浆内的主要形态元素是微管，神经丝（100-A丝），光滑内质网（SER）的互连和细长的静脉曲张组件，更扩张和囊泡状的细胞器类似于SER的部分，多泡体，线粒体，最后，基质中的小管，细丝和囊泡悬浮。在普通的薄切片图像中，基质是由细小的碎片组成的，这些碎片没有明显地联系在一起，给人的印象只是蛋白质均匀溶液的浓缩物。然而，用高压显微镜在厚（0.5微米）切片上观察，我们注意到所谓的细丝状碎片是三维晶格的一部分。我们认为，这种晶格不是醛固定的人工制品，我们的论点是支持它的可见性后，快速冷冻和冷冻取代。这种轴浆的网格或微小梁基质被发现由微管、神经丝、SER池和质膜之间的有组织的交叉桥系统组成。我们建议，该系统的形成和变形参与快速轴突运输。为便于电镜观察轴浆各成分间的小梁连接，采用了三种技术：首先，在固定液中加入单宁酸，OsO_4后固定，然后用醋酸双氧铀整体染色，用于常规透射电镜（TEM）;第二步，将组织包埋于聚乙二醇中进行薄切片，将包埋剂从切片和块中溶出，临界点干燥（J. J. Wolosewick，1980，J.CellBiol.，86：675-681.），然后用TEM观察无基质切片或用扫描电子显微镜观察块;第三，快速冷冻固定的组织，然后冷冻蚀刻和旋转阴影，用TEM观察复制品。所有这些程序产生的图像之间的神经丝和轴浆细胞器的交联元素。这些改进的可视化应使我们能够检查分布的小梁连接的运动轴突细胞器。
Axoplasmic transport is a dramatic example of cytoplasmic motility. Constituents of axoplasm migrate as far as 400 mm/d or at approximately 5 micron/s. Thin-section studies have identified the major morphological elements within the axoplasm as being microtubules, neurofilaments (100-A filaments), an interconnected and elongated varicose component of smooth endoplasmic reticulum (SER), more dilated and vesicular organelles resembling portions of SER, multivesicular bodies, mitochondria, and, finally, a matrix of ground substance in which the tubules, filaments, and vesicles are suspended. In the ordinary thin-section image, the ground substance is comprised of wispy fragments which, in not being noticeably tied together, do not give the impression of representing more than a condensation of what might be a homogeneous solution of proteins. With the high-voltage microscope on thick (0.5-micron) sections, we have noticed, however, that the so- called wispy fragments are part of a three-dimensional lattice. We contend that this lattice is not an artifact of aldehyde fixation, and our contention is supported by its visability after rapid-freezing and freeze-substitution. This lattice or microtrabecular matrix of axoplasm was found to consist of an organized system of cross-bridges between microtubules, neurofilaments, cisternae of the SER, and the plasma membrane. We propose that formation and deformation of this system are involved in rapid axonal transport. To facilitate electron microscope visualization of the trabecular connections between elements of axoplasm, the following three techniques were used: first, the addition of tannic acid to the primary fixative, OsO4 postfixation, then en bloc staining in uranyl acetate for conventional transmission electron microscope (TEM); second, embedding tissue in polyethylene glycol for thin sectioning, dissolving out the embedding medium from the sections and blocks, critical-point-drying (J. J. Wolosewick, 1980, J. Cell Biol., 86:675-681.), and then observing the matrix-free sections with TEM or the blocks with a scanning electron microscope; and third, rapid freezing of fixed tissue followed by freeze-etching and rotary- shadowing with replicas observed by TEM. All of these procedures yielded images of cross-linking elements between neurofilaments and organelles of the axoplasm. These improvements in visualization should enable us to examine the distribution of trabecular links on motile axonal organelles.