Zelina Pavol, Avci Hasan X, Thelen Karsten, Pollerberg G Elisabeth
Department of Developmental Neurobiology, University of Heidelberg, 69120 Heidelberg, Im Neuenheimer Feld 232, Germany.
Development. 2005 Aug;132(16):3609-18. doi: 10.1242/dev.01934. Epub 2005 Jul 20.
We investigated the role of the cell adhesion molecule NrCAM for axonal growth and pathfinding in the developing retina. Analysis of the distribution pattern of NrCAM in chick embryo retina sections and flat-mounts shows its presence during extension of retinal ganglion cell (RGC) axons; NrCAM is selectively present on RGC axons and is absent from the soma. Single cell cultures show an enrichment of NrCAM in the distal axon and growth cone. When offered as a substrate in addition to Laminin, NrCAM promotes RGC axon extension and the formation of growth cone protrusions. In substrate stripe assays, mimicking the NrCAM-displaying optic fibre layer and the Laminin-rich basal lamina, RGC axons preferentially grow on NrCAM lanes. The three-dimensional analysis of RGC growth cones in retina flat-mounts reveals that they are enlarged and form more protrusions extending away from the correct pathway under conditions of NrCAM-inhibition. Time-lapse analyses show that these growth cones pause longer to explore their environment, proceed for shorter time spans, and retract more often than under control conditions; in addition, they often deviate from the correct pathway towards the optic fissure. Inhibition of NrCAM in organ-cultured intact eyes causes RGC axons to misroute at the optic fissure; instead of diving into the optic nerve head, these axons cross onto the opposite side of the retina. Our results demonstrate a crucial role for NrCAM in the navigation of RGC axons in the developing retina towards the optic fissure, and also for pathfinding into the optic nerve.
我们研究了细胞粘附分子NrCAM在发育中的视网膜轴突生长和路径寻找中的作用。对鸡胚视网膜切片和整装片上NrCAM分布模式的分析表明，在视网膜神经节细胞（RGC）轴突延伸过程中它是存在的；NrCAM选择性地存在于RGC轴突上，而在胞体中不存在。单细胞培养显示NrCAM在轴突远端和生长锥中富集。当作为层粘连蛋白之外的底物提供时，NrCAM促进RGC轴突延伸和生长锥突起的形成。在底物条带试验中，模仿展示NrCAM的视神经纤维层和富含层粘连蛋白的基膜，RGC轴突优先在NrCAM条带上生长。对视网膜整装片中RGC生长锥的三维分析显示，在NrCAM抑制条件下，它们会增大并形成更多从正确路径延伸开的突起。延时分析表明，与对照条件相比，这些生长锥会更长时间地停顿以探索周围环境，前进的时间跨度更短，并且回缩更频繁；此外，它们经常偏离正确路径朝向视裂。在器官培养的完整眼中抑制NrCAM会导致RGC轴突在视裂处走错路；这些轴突不是潜入视神经乳头，而是穿过到视网膜的另一侧。我们的结果证明了NrCAM在发育中的视网膜中RGC轴突朝向视裂的导航以及进入视神经的路径寻找中起着关键作用。
