Honig Marcia G, Camilli Suzanne J, Xue Qing-Shan
Department of Anatomy and Neurobiology, University of Tennessee College of Medicine, The Health Science Center, Memphis, Tennessee 38163, USA.
Dev Biol. 2002 Mar 1;243(1):137-54. doi: 10.1006/dbio.2001.0556.
In the developing chick hindlimb, sensory axons, which grow together in bundles as they extend distally, and the motoneuron axons they encounter express the cell adhesion molecule L1. Following injection of function-blocking anti-L1 antibodies into the limb at stage 25, some sensory axons choose inappropriate peripheral nerves even though motoneuron pathfinding is unaffected. Here, to further elucidate L1's role, we assessed the effects of this perturbation using pathway tracing, immune labeling, confocal microscopy, and electron microscopy. After L1 blockade, sensory axons were still bundled and closely apposed. However, clear signs of decreased adhesion were detectable ultrastructurally. Further, sensory axons grew into the limb more slowly than normal, wandering more widely, branching more frequently, and sometimes extending along inappropriate peripheral nerves. Sensory axons that ultimately projected along different cutaneous nerves showed increased intermixing in the spinal nerves, due to errors in pathfinding and also to a decreased ability to segregate into nerve-specific fascicles. These results suggest that, in the highly complex in vivo environment, as in tissue culture, L1 stimulates axon growth and enhances fasciculation, and that these processes contribute to the orderly, timely, and specific growth of sensory axons into the limb.
在发育中的鸡后肢中，感觉轴突在向远端延伸时成束生长，它们遇到的运动神经元轴突表达细胞粘附分子L1。在第25阶段向肢体注射功能阻断性抗L1抗体后，尽管运动神经元的路径寻找未受影响，但一些感觉轴突选择了不适当的外周神经。在这里，为了进一步阐明L1的作用，我们使用路径追踪、免疫标记、共聚焦显微镜和电子显微镜评估了这种扰动的影响。L1阻断后，感觉轴突仍然成束且紧密相邻。然而，在超微结构上可检测到粘附力下降的明显迹象。此外，感觉轴突向肢体生长的速度比正常情况慢，游走范围更广，分支更频繁，有时还沿着不适当的外周神经延伸。最终沿着不同皮神经投射的感觉轴突在脊神经中混合增加，这是由于路径寻找错误以及分离成神经特异性束的能力下降所致。这些结果表明，在高度复杂的体内环境中，如同在组织培养中一样，L1刺激轴突生长并增强束化，并且这些过程有助于感觉轴突有序、及时且特异性地向肢体生长。
