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斥力形成的。先前的研究表明，发育中的脊索、皮肌节和腹侧脊髓分泌可扩散的轴突引导分子，从而排斥背根神经节(DRG)神经突起(Keynes等人。(1997)神经元18,889-897；Nakamoto和Shiga(1998)发育生物学202,304-314)。然而，无论是化学反应物还是它们在DRG轴突上的受体都是已知的。在这里，我们研究了定位于DRG神经突起上的免疫球蛋白/纤维连接蛋白III型亚家族的细胞黏附分子(IgFnIII CAMs)和神经粘连蛋白-1是否需要介导这些组织的化学排斥。我们从鸡胚胎或小鼠胚胎中将背根节与脊索、皮肤肌肉或腹侧脊髓外植体在胶原凝胶中共同培养。我们发现，抗轴索素-L/sC_2的抗体可减弱脊索的化学排斥作用，而抗N-CAM、Ng-CAM和Nr-CAM的抗体则不起作用。我们还发现，神经鞘-1缺陷小鼠的DRG完全失去了对皮肌节衍生的化学排斥的反应性，而那些显著但不完全降低了对脊索衍生的化学排斥的反应性。没有观察到腹侧脊髓派生的化学排斥反应的变化。因此，本研究揭示了不同的化学排斥系统参与了对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.