Mechanisms of Trigeminal Sensory Axon Guidance

这一提议的长期目标是了解三叉神经感觉系统中将轴突导向其靶区的机制。在这笔赠款的最后一个周期中，我们从分子上研究并确定了一种趋化活性，即上颌因子，它与三叉神经感觉轴突向外周投射的总体模式有关。在这里，我们建议使用单细胞基因差异筛选技术和基因芯片技术来研究三叉神经感觉神经元亚群选择更离散的通路的机制：(1)三叉神经三叉神经分支；(2)向触须垫个别触觉毛发的地形图投射；(3)大直径和小直径感觉神经元的中枢性分叉终末。该方法将识别在不同通路之间投射的三叉神经元亚群中差异表达的基因，并测试这些编码跨膜蛋白的基因中的任何一个参与轴突引导。长期目标是确定参与引导轴突沿着不同路径的跨膜受体，尽管实验还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路径选择的分子差异。此外，它在洞察离散轴突路径选择和局部轴突投射形成的机制方面应该具有更普遍的重要性，这是轴突引导中的两个基本问题，目前仍知之甚少。

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.