MRC Centre for Developmental Neurobiology, King's College London, London, SE1 1UL, UK.
J Comp Neurol. 2012 Jun 1;520(8):1629-49. doi: 10.1002/cne.23003.
Motoneurons are key points of convergence within motor networks, acting as the "output channels" that directly control sets of muscles to maintain posture and generate movement. Here we use genetic mosaic techniques to reveal the origins and architecture of the leg motoneurons of Drosophila. We show that a small number of leg motoneurons are born in the embryo but most are generated during larval life. These postembryonic leg motoneurons are produced by five neuroblasts per hemineuromere, and each lineage generates stereotyped lineage-specific projection patterns. Two of these postembryonic neuroblasts generate solely motoneurons that are the bulk of the leg motoneurons. Within the largest lineage, lineage 15, we see distinct birth-order differences in projection patterns. A comparison of the central projections of leg motoneurons and the muscles they innervate reveals a stereotyped architecture and the existence of a myotopic map. Timeline analysis of axonal outgrowth reveals that leg motoneurons reach their sites of terminal arborization in the leg at the time when their dendrites are elaborating their subtype-specific shapes. Our findings provide a comprehensive description of the origin, development, and architecture of leg motoneurons that will aid future studies exploring the link between the assembly and organization of connectivity within the leg motor system of Drosophila.
运动神经元是运动网络中的关键汇聚点，作为“输出通道”，直接控制肌肉群以维持姿势和产生运动。在这里，我们使用遗传嵌合技术来揭示果蝇腿部运动神经元的起源和结构。我们表明，一小部分腿部运动神经元在胚胎中产生，但大多数是在幼虫期产生的。这些胚胎后的腿部运动神经元由每个半神经节的五个神经母细胞产生，每个谱系产生特定的刻板投射模式。这两个胚胎后的神经母细胞仅产生大量的腿部运动神经元。在最大的谱系 15 中，我们看到了投射模式的明显出生顺序差异。腿部运动神经元的中央投射和它们支配的肌肉的比较揭示了一种刻板的结构和肌节图的存在。轴突生长的时间线分析表明，腿部运动神经元在其树突发育出其特定亚型的形状时，到达腿部末端分支的位置。我们的发现提供了腿部运动神经元起源、发育和结构的全面描述，将有助于未来探索果蝇腿部运动系统中连接的组装和组织之间的联系的研究。
