Mechanisms of Trigeminal Sensory Axon Guidance

这项建议的长期目标是了解在三叉神经感觉系统中将轴突定向到其目标区域的机制。在本基金的最后一个周期，我们研究并确定了分子的趋化活性，上颌因子，这是牵连在指导三叉神经感觉轴突投射到周边的总模式。在此，我们拟利用单细胞cDNA差异筛选技术和cDNA微阵列技术研究三叉神经感觉神经元亚群选择更为离散的通路形成（1）三叉神经三支、（2）触须垫对单个触觉毛的拓扑投射和（3）大直径和小直径感觉神经元分叉的中枢终末的机制。该方法将确定在三叉神经元亚群中差异表达的基因，这些基因在不同的通路之间投射，并测试参与编码跨膜蛋白的任何这些基因的轴突引导。长期的目标是确定跨膜受体参与引导轴突沿着不同的途径，尽管实验也应该揭示神经元之间的其他分子差异，包括调节轴突引导受体表达的转录因子的表达。这项工作将有助于确定调节三叉神经感觉轴突不同通路选择的分子差异。此外，它应该是更普遍的重要性，通过离散轴突通路的选择和地形轴突投影形成的机制，轴突指导的两个基本问题，仍然知之甚少提供洞察。

The long-term aim of this proposal is to understand the mechanisms that direct axons to their target fields in the trigeminal sensory system. In the last cycle of this grant, we studied and identified molecularly a chemotropic activity, Maxillary Factor, that was implicated in directing the gross pattern of trigeminal sensory axon projections to the periphery. Here, we propose to use single-cell cDNA differential screening technology and cDNA microarray technology to study the mechanisms responsible for the more discrete pathway choices made by subsets of trigeminal sensory neurons to form (1) the three trigeminal nerve branches, (2) the topographic projections to individual tactile hairs of the whisker pad, and (3) the divergent central terminations of large and small diameter sensory neurons. The approach will be to identify genes that are differentially expressed in subpopulations of trigeminal neurons projecting among distinct pathways, and to test the involvement in axon guidance of any of these genes that encode transmembrane proteins. The long-term aim is to define transmembrane receptors involved in guiding axons along different pathways, though the experiments should also reveal other molecular differences among the neurons, including in expression of transcription factors that regulated axon guidance receptor expression. This work will help define the molecular differences that regulate the distinct pathway choices of trigeminal sensory axons. In addition, it should be of more general importance in providing insight into the mechanisms through which discrete axonal pathway choices and topographic axonal projections are formed, two fundamental issues in axon guidance that are still poorly understood.