Regulation of Cytoskeletal Protein Dynamics in the Axon and Its Changes with Growth, Aging and Regeneration

在正常大鼠坐骨神经中，神经丝亚单位H（NF-H）的溶解度几乎不变（约20%），与离细胞体的距离无关。在损伤神经中，损伤部位远端神经丝蛋白在轴突沃勒氏变性损伤后1周消失。NF-H在新生轴突中的溶解度高，其c端区磷酸化程度低。相反，通过轴突运输标记对损伤部位近端神经丝动力学分析显示NF-L量的相对减少与NF-H溶解度的增加平行。离细胞体越近，其变化越大。这些结果表明，神经丝的结构和稳定性除了受其N端区磷酸化-去磷酸化控制的普通聚合-解聚变化外，还受NF-H亚基的选择性释放调节。轴突微管的特点是冷稳定亚群的比例较高。为了阐明其稳定的分子机制，利用视频增强对比差示干涉显微镜直接观察培养大鼠背根神经节细胞神经突内的稳定微管，得到如下结果。通过裂解质膜暴露神经性微结节后，一小部分仍保持聚合超过30分钟。这些稳定的微管在神经突中所占比例在1周内小于10%。稳定微管在激光束切割后立即从两端开始解聚，表明它们不是沿整个长度稳定的。当弯曲的微管被横切时，它会弹直，这表明微管是被迫弯曲的。稳定微管在横断后解聚过程中，往往会在附着颗粒结构处停留一段时间。在。在某些情况下，停止可能发生在没有任何可见结构的点上。这些停止点被认为是微管稳定化的位置，目前正在进行稳定化的分子机理分析。少

In normal rat sciatic nerve, the solubility of neurofilament subunit H(NF-H) is almost constant(about 20%) irrespective of the distance from the cell body. In injured nerve, neurofilament protein distal to the injured site disappears by 1 week after injury by Wallerian degeneration of the axon. The solubility of NF-H is high in the newly regenerating axon, and the phosphorylation in its C-terminal region is low. In contrast, the analysis of neurofilament dynamics in proximal portion to the injured site by labeling with axonal transport reveals the relative decrease of NF-L amount in parallel with the increase of NF-H solubility. The closer to the cell body, the greater its change is. These results suggest that the structure and stability of neurofilament is also regulated by selective release of NF-H subunit in addition to ordinary polymerization-depolymerization change controlled by phosphorylation-dephosphorylation of its N terminal region.Axonal micotubules are characterized by the … More high proportion of cold stable subpopulation. To elucidate the molecular mechanism of their stabilization, stable microtubules within the neurites of cultured rat dorsal root ganglion cells are directly observed by video-enhanced contrast differential interference microscope, and the following results are obtained.1. After exposing neuritic microtules by lysing plasma membrane, a small population remains polymerized for more than 30min. The proportion of these stabilized microtubules in neurites I week after plating is less than 10%.2. Stable microtubules starts depolymerizing from both ends immediately after cutting with laser beam, suggesting that they are not stabilized along entire length.3. When curved microtubule is transected, it springs straight, indicating that the microtubules are forced to be curved.4. In the course of depolymerization of stable microtubule after transection, it often halts for a while at a point of attached granular structure. In .some cases halting may occur such a point without any visible structure. These stop points are considered to be the locations of microtubile stabilization, and the analysis about molecular mechanism of stabilization is now under progress. Less