REPULSIVE CUES AND THE DEVELOPING VISUAL SYSTEM

视网膜定位图的准确形成对我们的视觉能力至关重要。在这个过程中，视网膜轴突被引导形成大脑中连接的精确地形图，从而允许视觉空间被感知。这些引导机制的分子基础尚不清楚。这一建议的长期目标是了解排斥线索如何作用于引导轴突形成视网膜定位图。最近发现的各种排斥性线索引导轴突形成视网膜定位图。最近发现的各种令人厌恶的线索改变了我们对轴突如何引导的理解。现在是时候解决这些信号如何在体内发挥作用了。排斥性引导分子(RGM)和肾上腺素A5在低等脊椎动物顶盖视网膜顶盖投射形成过程中的高后低前梯度表达。目前的研究进展对这两个线索如何在体内作用于塑造视网膜顶盖地图提出了具体的假设：1)RGM引导最初的视网膜顶盖轴突生长。2)肾上腺素-A5阻止视网膜轴突离开顶盖，并在最初的轴突生长完成后调节侧支。拟议中的实验将检验这些假设。我们将观察在体扰动RGM和eaffin-A5对视网膜顶盖投射的影响。我们将研究鸡胚和斑马鱼胚胎；它们的特性都很好，每一个都为实现我们的目标提供了独特的优势。在视网膜顶盖MAP形成过程中，RGM和Ephin-A5的急性和局部失活将通过发色团辅助激光灭活(CALI)在轴突生长初期和后来的侧枝过程中实现。感染重组逆转录病毒会在雏鸡的顶盖产生慢性错误表达的ePhin-A5。视网膜顶盖项目的变化将通过高分辨率轴突追踪和实时成像进行评估。这两种方法的结合将提供强有力的互补性信息，以检验拟议的假设。由于RGM和ewitin-A5可能用于轴突引导和形成局部秩序，因此拟议的实验具有重要的临床意义。

Accurate formation of the retinotopic map is critical for our ability to see. During this process, retinal axons are guided to form a precise topographic map of connections in the brain that allow visual space to be perceived. The molecular basis of these guidance mechanisms is not yet known. The long term objective of this proposal is to understand how repulsive cues act to guide axons to form the retinotopic map. The recent discovery of a variety of repulsive cues act to guide axons to form the retinotopic map. The recent discovery of a variety of repulsive cues has modified our understanding of how axons re guided. It is timely to address how these cues function in vivo. Repulsive guidance molecule (RGM) and ephrin-A5 are expressed in high posterior to low anterior gradients in the tectum of lower vertebrates during the formation of the retinotectal projection. Current advances have suggested specific hypotheses of how these two cues act in vivo to shape the retinotectal map: 1) RGM guides initial retinotectal axon outgrowth. 2) Ephrin-A5 prevents retinal axons from exiting the tectum and modulates lateral branching after initial axon outgrowth is completed. The proposed experiments will test these hypotheses. The changes in retinotectal projects caused by perturbing RGM and ephrin-A5 in vivo will be observed. Chick and zebrafish embryos will be studied; they are well characterized and each offers distinct advantages to achieve our goals. Acute and local inactivation of RGM and ephrin-A5 during retinotectal map formation will be achieved by chromophore-assisted laser inactivation (CALI) during initial axon outgrowth and later during lateral branching. Infection with recombinant retrovirus will generate chronic misexpression of ephrin-A5 in the chick tectum. The changes in retinotectal projects will be assessed by high resolution axon tracing and live imaging. The combination of these two approaches will provide strong complementary information that will test the proposed hypotheses. As RGM and ephrin-A5 are likely used for axon guidance and formation of topographic order, the proposed experiments are of significant clinical relevance.