Eph Signaling Auditory Brainstem Development

描述(由申请人提供)： 这项拟议的研究解决了听觉脑干中形成精确突触连接的潜在分子机制。申请人之前已经证明，在鸟类听觉脑干核团中，在突触连接形成过程中沿着中线表达了Eph受体酪氨酸激酶家族的几个成员。这些受体在轴突生长过程中调节细胞与细胞之间的相互作用，而Eph受体及其配体的梯度是在视觉系统中形成精确地形图所必需的。其具体目的是测试Eph受体信号在听觉脑干投射发育中的作用。每组实验既包括对发育表达的描述性研究，也包括使用实验操作的功能研究。INovo微电穿孔技术将用于错误表达Eph受体，体外标记方法将用于评估由此产生的轴突投射。来自雏鸡的发现的一般性将在发育中的小鼠脑干中进行检验。具体目的1提出实验，以研究Eph受体和肾上腺素的梯度是否对从V11神经轴突到鸟类耳蜗核的紧张性投射的发育是必要的。《特定目标2》将这些研究扩展到哺乳动物。Eph受体EphA4在发育中的小鼠耳蜗核中表达不均匀。EphA4在建立从VIIIth神经到耳蜗核的同源投射中的作用将在缺乏EphA4的突变小鼠中进行评估。大细胞核支的轴突投射使同侧分支在靶区板层核的背侧区域突触，而对侧分支横跨背侧中线生长并与对侧板层核腹侧区域接触。具体目标3中概述的实验将评估Eph受体在鸟类脑干中线的耳蜗核轴突引导中的作用。这些实验将测试Eph信号是否被广泛用于听觉脑干的通路发育，并将解决Eph受体在建立突触特异性方面的作用是否在不同模式和不同物种中相似。

DESCRIPTION (provided by applicant): The proposed research addresses potential molecular mechanisms underlying the formation of precise synaptic connections in the auditory brainstem. The applicant has previously shown that several members of the Eph family of receptor tyrosine kinases are expressed in avian auditory brainstem nuclei and along the midline during the formation of synaptic connections. These receptors mediate cell-cell interactions during axon outgrowth, and gradients of Eph receptors and their ligands, the ephrins, are required for the formation of precise topographic maps in the visual system. The Specific Aims are to test the roles of Eph receptor signaling in the development of auditory brainstem projections. Each group of experiments includes both descriptive studies of developmental expression and functional studies using experimental manipulations. Inovo microelectroporation will be used to misexpress Eph receptors and an in vitro labeling method will be used to evaluate resulting axonal projections. The generality of findings from chicks will be examined in developing mouse brainstem. Specific Aim 1 proposes experiments to investigate whether gradients of Eph receptors and ephrins are essential for the development of the tonotopic projection from VllIth nerve axons to the avian cochlear nucleus, n. magnocellularis. Specific Aim 2 extends these studies to mammals. The Eph receptor EphA4 is expressed nonuniformly in the developing mouse cochlear nuclei. The role of EphA4 in the establishment of a homologous projection from the VIIIth nerve to the cochlear nucleus will be evaluated in mutant mice that lack EphA4. Axonal projections from n. magnocellularis branch so that an ipsilateral branch synapses in the dorsal region of the target, n. laminaris, while the contralateral branch grows across the dorsal midline and contacts the ventral region of contralateral n. laminaris. Experiments outlined in Specific Aim 3 will evaluate the role of Eph receptors in the guidance of cochlear nucleus axons at the midline in the avian brainstem. These experiments will test whether Eph signaling is extensively used in the development of pathways in the auditory brainstem, and will address whether the roles for Eph receptors in establishing synaptic specificity are similar across modalities and across species.