Macdonald R, Scholes J, Strähle U, Brennan C, Holder N, Brand M, Wilson S W
Developmental Biology Research Centre, Randall Institute, Kings College London, UK.
Development. 1997 Jun;124(12):2397-408. doi: 10.1242/dev.124.12.2397.
No-isthmus (Noi) is a member of the zebrafish Pax family of transcriptional regulators that is expressed in restricted domains of the developing CNS. In the developing eye and optic nerve, the Noi+ cells are primitive glial cells that line the choroid fissure and optic stalk/nerve to its junction with the optic tract. This pattern of Noi expression is retained in the adult, defining the optic nerve astroglia, which wrap the left and right nerves separately at the midline, thus forming the bodily crossed optic chiasm found in fish. In embryos carrying mutations in the noi gene, the choroid fissure fails to close, glial cells of the optic nerve fail to differentiate and optic axons exhibit abnormal trajectories exiting the eye and at the midline of the diencephalon. Optic axons select inappropriate pathways into the contralateral optic nerve, rostrally towards the anterior commissure and along the ipsilateral optic tract. Noi+ cells also border the pathway of axons in the postoptic commissure, which is located adjacent to the optic chiasm. These postoptic commissural axons are defasciculated and also exhibit pathfinding defects in noi- embryos. These results indicate that Noi is required in cells that line the pathways taken by optic and non-optic commissural axons for guidance across the midline of the diencephalon. We find that expression of two members of the Netrin family of axon guidance molecules and the signalling protein Sonic hedgehog is disturbed in noi- embryos, whereas several members of the Eph family of receptors and ligands show no obvious alterations in expression at the diencephalic midline.
无峡部（Noi）是斑马鱼转录调节因子Pax家族的成员，在发育中的中枢神经系统的特定区域表达。在发育中的眼睛和视神经中，Noi+细胞是原始神经胶质细胞，它们排列在脉络膜裂和视神经柄/神经与视束的交界处。Noi的这种表达模式在成体中得以保留，确定了视神经星形胶质细胞，它们在中线处分别包裹左右神经，从而形成鱼类中发现的身体交叉的视交叉。在携带noi基因突变的胚胎中，脉络膜裂无法闭合，视神经的神经胶质细胞无法分化，视神经轴突在离开眼睛和间脑中线时表现出异常轨迹。视神经轴突选择了不适当的路径进入对侧视神经，向前朝向胼胝体联合，并沿着同侧视束走行。Noi+细胞也与视交叉后连合中轴突的路径相邻，视交叉后连合位于视交叉附近。这些视交叉后连合轴突发生了轴突分离，并且在noi-胚胎中也表现出路径寻找缺陷。这些结果表明，在排列视神经和非视神经连合轴突穿过间脑中线的引导路径的细胞中，Noi是必需的。我们发现，轴突引导分子Netrin家族的两个成员和信号蛋白音猬因子的表达在noi-胚胎中受到干扰，而Eph家族受体和配体的几个成员在间脑中线的表达没有明显变化。
