Wadsworth W G, Hedgecock E M
Department of Pathology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Bioessays. 1996 May;18(5):355-62. doi: 10.1002/bies.950180505.
During embryogenesis, the basic axon scaffold of the nervous system is formed by special axons that pioneer pathways between groups of cells. To find their way, the pioneer growth cones detect specific cues in their extracellular environment. One of these guidance cues is netrin. Observations and experimental manipulations in vertebrates and nematodes have shown that netrin is a bifunctional guidance cue that can simultaneously attract and repel axons. During the formation of this basic axon scaffold in Caenorhabditis elegans, the netrin UNC-6 is expressed by neuroglia and pioneer neurons, providing hierarchical guidance cues throughout the animal. Each cue has a characteristic role depending on the cell type, its position and the developmental stage. These roles include activities as global, decussation and labeled-pathway cues. This hierarchical model of UNC-6 netrin-mediated guidance suggests a method by which guidance cues can direct formation of basic axon scaffolds in developing nervous systems.
在胚胎发育过程中，神经系统的基本轴突支架由特殊的轴突形成，这些轴突开辟了细胞群之间的通路。为了找到路径，先驱生长锥会检测细胞外环境中的特定信号。其中一种引导信号是网蛋白。对脊椎动物和线虫的观察及实验操作表明，网蛋白是一种双功能引导信号，它可以同时吸引和排斥轴突。在秀丽隐杆线虫形成这种基本轴突支架的过程中，网蛋白UNC-6由神经胶质细胞和先驱神经元表达，在整个动物体内提供分级引导信号。每个信号根据细胞类型、其位置和发育阶段具有特定的作用。这些作用包括作为全局、交叉和标记通路信号的活动。UNC-6网蛋白介导的这种分级引导模型提示了一种引导信号在发育中的神经系统中指导基本轴突支架形成的方法。
