Investigation of putative receptors for diffusible axon-guidance molecules

背根神经节（DRG）轴突的初始轨迹是由周围组织的化学排斥形成的。先前的研究表明，发育中的脊索、皮肌节和腹侧脊髓分泌排斥背根神经节（DRG）神经突的可扩散轴突导向分子（Keynes等（1997）Neuron 18，889-897; Nakamoto和滋贺（1998）发育生物学202，304-314）。然而，DRG神经突上的化学排斥物及其受体都是未知的。在这里，我们调查是否细胞粘附分子的免疫球蛋白/纤连蛋白III型亚家族（IgFnIII CAMs）和neuropilin-1，这两者都是本地化的DRG神经突需要介导的化学排斥从这些组织。我们在胶原凝胶中将背根神经节与来自鸡或小鼠胚胎的脊索、皮肌节或腹侧脊髓外植体共培养。我们发现针对轴突素-1/SC2的抗体减弱了来自脊索的化学排斥活性的影响，而针对N-CAM、Ng-CAM和Nr-CAM的抗体没有影响。我们还发现，neuropilm-1缺陷小鼠的DRG完全失去了对真皮肌节衍生的化学排斥的反应性，而那些显著但不完全减少了对脊索衍生的化学排斥的反应性。未观察到腹侧脊髓源性化学排斥反应的变化。因此，本研究揭示了差异化学排斥系统参与介导DRG轴突的化学排斥。

Initial trajectories of dorsal root ganglion (DRG) axons are shaped by chemorepulsion of surrounding tissues. Previous studies have suggested that the developing notochord, dermamyotome and ventral spinal cord secretes diffusible axon guidance molecules that repel dorsal root ganglion (DRG) neurites (Keynes et al. (1997) Neuron 18, 889-897; Nakamoto and Shiga (1998) Developmental Biology 202, 304-314). Neither chemorepellents nor their receptors on DRG neurites are, however, known. Here we investigated whether cell adhesion molecules of the immunoglobulin/fibronectin type III sub family (IgFnIII CAMs) and neuropilin-1 both of which are localized on DRG neurites are required for mediating the chemorepulsion from these tissues. We cocultured DRGs with notochord, dermamyotome or ventral spinal cord explants from either chick or mouse embryos in a collagen gel. We found that an antibody against axonin-l/SC2 diminished the effects of the chemorepulsive activity from the notochord, whereas antibodies against N-CAM, Ng-CAM and Nr-CAM had no effect. We also found that DRGs from neuropilm-1-deficient mice lost completely the responsiveness for the dermamyotome-derived chemorepulsion, whereas those diminished significantly but incompletely the responsiveness for the notochord-derived chemorepulsion. No changes were observed for the responsiveness for the ventral spinal cord-derived chemorepulsion. Thus, the present study revealed the differential chemorepulsion systems are involved in mediating the chemorepulsion for DRG axons.