Lasek R J, Paggi P, Katz M J
Bio-architectonics Center, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
J Cell Biol. 1992 May;117(3):607-16. doi: 10.1083/jcb.117.3.607.
Pulse-labeling studies of slow axonal transport in many kinds of axons (spinal motor, sensory ganglion, oculomotor, hypoglossal, and olfactory) have led to the inference that axonal transport mechanisms move neurofilaments (NFs) unidirectionally as a single continuous kinetic population with a diversity of individual transport rates. One study in mouse optic axons (Nixon, R. A., and K. B. Logvinenko. 1986. J. Cell Biol. 102:647-659) has given rise to the different suggestion that a significant and distinct population of NFs may be entirely stationary within axons. In mouse optic axons, there are relatively few NFs and the NF proteins are more lightly labeled than other slowly transported slow component b (SCb) proteins (which, however, move faster than the NFs); thus, in mouse optic axons, the radiolabel of some of these faster-moving SCb proteins may confuse NF protein analyses that use one dimensional (1-D) SDS-PAGE, which separates proteins by size only. To test this possibility, we used a 2-mm "window" (at 3-5 mm from the posterior of the eye) to compare NF kinetics obtained by 1-D SDS-PAGE and by the higher resolution two-dimensional (2-D) isoelectric focusing/SDS-PAGE, which separates proteins both by their net charge and by their size. We found that 1-D SDS-PAGE is insufficient for definitive NF kinetics in the mouse optic system. By contrast, 2-D SDS-PAGE provides essentially pure NF kinetics, and these indicate that in the NF-poor mouse optic axons, most NFs advance as they do in other, NF-rich axons. In mice, greater than 97% of the radiolabeled NFs were distributed in a unimodal wave that moved at a continuum of rates, between 3.0 and 0.3 mm/d, and less than 0.1% of the NF population traveled at the very slowest rates of less than 0.005 mm/d. These results are inconsistent with the proposal (Nixon and Logvinenko, 1986) that 32% of the transported NFs remain within optic axons in an entirely stationary state. As has been found in other axons, the axonal transport system of mouse optic axons moves NFs and other cytoskeletal elements relentlessly from the cell body to the axon tip.
对多种轴突（脊髓运动轴突、感觉神经节轴突、动眼神经轴突、舌下神经轴突和嗅神经轴突）进行的慢轴突运输脉冲标记研究表明，轴突运输机制以单一连续动力学群体的形式单向移动神经丝（NFs），且个体运输速率具有多样性。一项针对小鼠视神经轴突的研究（尼克松，R.A.，和K.B.洛维年科。1986年。《细胞生物学杂志》102:647 - 659）提出了不同的观点，即相当数量且独特的神经丝群体可能在轴突内完全静止。在小鼠视神经轴突中，神经丝相对较少，且神经丝蛋白的标记比其他缓慢运输的慢组分b（SCb）蛋白（然而，其移动速度比神经丝快）更淡；因此，在小鼠视神经轴突中，一些移动速度较快的SCb蛋白的放射性标记可能会干扰使用一维（1 - D）SDS - PAGE进行的神经丝蛋白分析，一维SDS - PAGE仅根据大小分离蛋白质。为了验证这种可能性，我们使用一个2毫米的“窗口”（在距眼球后部3 - 5毫米处）来比较通过一维SDS - PAGE和分辨率更高的二维（2 - D）等电聚焦/SDS - PAGE获得的神经丝动力学，二维等电聚焦/SDS - PAGE根据蛋白质的净电荷和大小分离蛋白质。我们发现一维SDS - PAGE不足以确定小鼠视神经系统中的神经丝动力学。相比之下，二维SDS - PAGE提供了基本纯净的神经丝动力学，这些结果表明，在神经丝较少的小鼠视神经轴突中，大多数神经丝的移动方式与其他神经丝丰富的轴突相同。在小鼠中，超过97%的放射性标记神经丝以单峰波的形式分布，移动速率连续，介于3.0和0.3毫米/天之间，且不到0.1%的神经丝群体以小于0.005毫米/天的极慢速率移动。这些结果与（尼克松和洛维年科，1986年）提出的32%的运输性神经丝在视神经轴突内完全静止的观点不一致。正如在其他轴突中所发现的那样，小鼠视神经轴突的轴突运输系统将神经丝和其他细胞骨架成分持续不断地从细胞体运输到轴突末端。
