Role of Calsyntenin in Axon Guidance

描述（由申请人提供）：为了建立一个功能性的神经系统，轴突沿着已建立的通路投射很远的距离，以达到它们适当的连接。影响轴突生长和引导的因素对大脑的正常发育至关重要，但这些因素在体内发挥作用的机制尚不清楚。我们正在使用光学透明的胚胎斑马鱼来研究和可视化感觉神经元是如何在自然环境中被引导的。斑马鱼的感觉神经元具有两种轴突的刻板形态，它们表现出不同的投射模式和行为。一个细胞的轴突表现出如此不同行为的机制尚不清楚。近年来，转录因子已被证明部分控制某些轴突的特定投射模式。在斑马鱼的感觉神经元中，抑制lim同源结构域（LIM-HD）转录因子会导致外周轴突的丧失，而对中枢轴突没有影响。这一发现表明LIM-HD转录因子对中枢和外周感觉神经元的形成有不同的作用。我们使用微阵列来鉴定lim - hd的下游靶标。在这里，我的目的是了解这些目标之一的功能，我们的微阵列鉴定，一个跨膜蛋白钙合蛋白。钙调蛋白的体内功能尚不清楚，然而，它已被证明可以调节淀粉样蛋白前体蛋白（APP）的运输，并在细胞培养中介导囊泡货物与酪蛋白-1的结合。这些功能提示Calsyntenin可能参与运输和选择性靶向神经元成分-对轴突生长和引导至关重要的过程。钙调蛋白在神经系统发育过程中被表达，此时轴突被引导到它们的目标，然而，它在神经元发育中的作用尚不清楚。我们的初步数据表明，钙调蛋白对外周感觉轴突的投射有特定的影响，而对中枢轴突没有影响。这种表型与LIM-HD抑制相似，进一步表明Calsyntenin是LIM-HD的下游靶点。在拟议的实验中，我将进一步表征Calsyntenin对感觉轴突生长的影响（目的1），确定Calsyntenin是否被不同地输送到感觉轴突的中枢和外周成分（目的2），并确定Calsyntenin的哪些功能域负责选择性外周轴突表型（目的3）。

DESCRIPTION (provided by applicant): To establish a functional nervous system, axons project long distances along established pathways to reach their proper connections. Factors that influence the growth and guidance of axons are critical for the proper development of the brain, but the mechanisms by which these factors function in vivo are not well understood. We are using the optically transparent embryonic zebrafish to study and visualize how sensory neurons are guided in their natural environment. Zebrafish sensory neurons have a stereotyped morphology with two types of axons which exhibit distinct projection patterns and behaviors. Mechanisms by which axons from one cell can exhibit such different behaviors are not known. Recently, transcription factors have been shown to partially control the specific projection patterns of some axons. In zebrafish sensory neurons, inhibition of LIM-homeodomain (LIM-HD) transcription factors causes a loss of peripheral axons, without an effect on central axons. This finding suggests that LIM-HD transcription factors act differently on the formation of central and peripheral sensory neurons. We performed a microarray to identify downstream targets of LIM-HDs. Here, I aim to understand the function of one of these targets as identified by our microarray, a transmembrane protein Calsyntenin. The in vivo function of Calsyntenin is not known, however, it has been shown to regulate the trafficking of Amyloid Precursor Protein (APP) and to mediate vesicular cargo binding to kinesin-1 in cell culture. These functions suggest that Calsyntenin may be involved in trafficking and selective targeting of neuronal components - processes that are vital for axon outgrowth and guidance. Calsyntenin is expressed during the development of the nervous system at a stage when axons are guided to their targets, however, its role in neuronal development is not known. Our preliminary data suggest that Calsyntenin exerts a specific effect on the projections of peripheral sensory axons, without an effect on central axons. This phenotype is similar to that of LIM-HD inhibition, further suggesting that Calsyntenin is a downstream target of LIM-HD. In the proposed experiments, I will further characterize the effect of Calsyntenin on sensory axon growth (Aim 1), determine whether Calsyntenin is differentially trafficked to central vs. peripheral components of sensory axons (Aim 2), and identify which functional domains of Calsyntenin are responsible for the selective peripheral axon phenotype (Aim 3).