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)的溶解度几乎是恒定的(约20%)，与细胞体的距离无关。在损伤的神经中，由于轴突的瓦勒变性，损伤部位远端的神经丝蛋白在损伤后1周消失。在新生的轴突中，核因子-H的溶解度较高，其C末端的磷酸化程度较低。相反，轴突运输标记的损伤部位近端的神经丝动力学分析表明，随着NF-H溶解度的增加，NF-L的含量相对减少。越靠近细胞体，其变化就越大。这些结果表明，神经细丝的结构和稳定性除了由其N末端的磷酸化-去磷酸化控制的普通聚合-解聚变化外，还受到核因子-H亚基的选择性释放的调节。轴突微管的…表征冷稳定亚群比例较高。为了阐明其稳定的分子机制，利用视频增强差示干涉显微镜对培养的大鼠背根神经节细胞突起内稳定的微管进行了直接观察，获得了以下结果。通过裂解质膜暴露神经细胞微管后，一小部分细胞保持聚合状态超过30min。结果1.植入后1周，这些稳定的微管在神经突起中的比例不到10%。稳定的微管在激光切割后立即从两端开始解聚，这表明它们并不是沿整个长度稳定的。当弯曲的微管被横切时，它会直线弹跳，这表明微管是被强迫弯曲的。在横断后稳定的微管解聚过程中，常在附着颗粒结构处停顿一段时间。在某些情况下，在没有任何可见结构的情况下，可能会出现停机。这些停止点被认为是微管稳定的位置，对稳定的分子机制的分析目前正在进行中。较少

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