Kim Minkyung, Fontelonga Tatiana, Roesener Andrew P, Lee Haeram, Gurung Suman, Mendonca Philipe R F, Mastick Grant S
Department of Biology, University of Nevada, Reno, NV, USA.
Department of Biology, University of Nevada, Reno, NV, USA.
Dev Biol. 2015 Mar 1;399(1):68-79. doi: 10.1016/j.ydbio.2014.12.014. Epub 2014 Dec 18.
Motor neurons differentiate from a ventral column of progenitors and settle in static clusters, the motor nuclei, next to the floor plate. Within these cell clusters, motor neurons receive afferent input and project their axons out to muscle targets. The molecular mechanisms that position motor neurons in the neural tube remain poorly understood. The floor plate produces several types of guidance cues with well-known roles in attracting and repelling axons, including the Slit family of chemorepellents via their Robo receptors, and Netrin1 via its DCC attractive receptor. In the present study we found that Islet1(+) motor neuron cell bodies invaded the floor plate of Robo1/2 double mutant mouse embryos or Slit1/2/3 triple mutants. Misplaced neurons were born in their normal progenitor column, but then migrated tangentially into the ventral midline. Robo1 and 2 receptor expression in motor neurons was confirmed by reporter gene staining and anti-Robo antibody labeling. Mis-positioned motor neurons projected their axons longitudinally within the floor plate, and failed to reach their normal exit points. To test for potential counteracting ventral attractive signals, we examined Netrin-1 and DCC mutants, and found that motor neurons shifted dorsally in the hindbrain and spinal cord, suggesting that Netrin-1/DCC signaling normally attracts motor neurons closer to the floor plate. Our results show that motor neurons are actively migrating cells, and are normally trapped in a static position by Slit/Robo repulsion and Netrin-1/DCC attraction.
运动神经元由腹侧一列祖细胞分化而来，并定居在紧邻底板的静态细胞簇即运动核中。在这些细胞簇内，运动神经元接收传入输入，并将其轴突投射到肌肉靶标。但对于将运动神经元定位在神经管中的分子机制，我们仍知之甚少。底板产生几种类型的引导信号，它们在吸引和排斥轴突方面具有众所周知的作用，包括通过Robo受体发挥作用的Slit化学排斥因子家族，以及通过其DCC吸引受体发挥作用的Netrin1。在本研究中，我们发现Islet1(+)运动神经元细胞体侵入了Robo1/2双突变小鼠胚胎或Slit1/2/3三突变体的底板。错位的神经元在其正常的祖细胞列中产生，但随后沿切线方向迁移到腹侧中线。通过报告基因染色和抗Robo抗体标记证实了运动神经元中Robo1和2受体的表达。位置错误的运动神经元在底板内纵向投射其轴突，无法到达其正常的出口点。为了测试潜在的对抗腹侧吸引信号，我们检查了Netrin-1和DCC突变体，发现运动神经元在后脑和脊髓中向背侧移位，这表明Netrin-1/DCC信号通常会吸引运动神经元更靠近底板。我们的结果表明，运动神经元是活跃迁移的细胞，通常通过Slit/Robo排斥和Netrin-1/DCC吸引被困在一个静态位置。
