Eph-eprhin Signaling in Mapping Auditory Midbrain Circuitry

描述（由申请人提供）：听觉系统的功能组织地形图保留了空间表示和外围接收的信号属性。最佳频率的音调分布图是所有听觉结构的主要组织特征。在分层的tonotopic安排，二级“nucleotopic”地图存在马赛克形式，离散的神经元区室或模块接收不同的输入阵列。这些输入的图案化和精确对准定义了处理其他刺激特征所需的功能区。考虑到地形图的重要性和定义功能性听觉回路所需的空间精度，令人惊讶的是，对在发育早期指导这种连接的机制知之甚少。我们试图确定的分子机制的模式形成的听觉中脑，或下丘（IC），经验之前。IC接收许多收敛的输入终止在一个单一的地形框架，使其成为一个很好的模型，研究目标问题。本实验室以往的研究表明，在听力发作前，IC的中央核和外侧皮层（分别为CNIC和LCIC）形成了多种传入模式。我们假设，建立这种早期地形登记所需的空间分辨率需要通过膜系的引导分子进行密切的细胞间信号传导。受体酪氨酸激酶的Eph家族及其相应的配体肝配蛋白表现出已知影响这种空间复杂连接映射的吸引（粘附）或排斥（去粘附）结合行为。最近，我们报道了分级和模块化表达模式（EphA 4，ephrin-B2，ephrin-B3在CNIC和LCIC），时间和空间上与分离投影模式相关。利用已建立的对照（C57 BL/6 J）和Eph/ephrin突变小鼠集落（EphA 4lacZ、ephrin-B2 lacZ、ephrin-B3 lacZ、ephrin-B3-/-），本研究的重点是：从外侧上级橄榄核（LSO）和外侧丘系背核（DNLL）向CNIC的分层输入，以及从LSO和CNIC向LCIC的模式化输入。计划的实验将测试三个假设：1）在Eph/肝配蛋白缺陷小鼠的CNIC和LCIC中发生地形图映射错误，2）体外条纹测定揭示EphA 4/肝配蛋白-B2，-B3信号传导在生长的听觉轴突的指导下，以及3）改变的地形图投射导致Eph/肝配蛋白突变体的生理（听觉脑干反应，ABR）和行为（声惊吓）效应。了解听觉网络中的早期指导机制将为评估刺激范式的潜在成本/效益提供基础，从而为听力受损和耳鸣患者提供新的治疗策略。 公共卫生相关性：听力由听觉系统执行，是一种重要的感觉，对言语和语言习得至关重要。尽管听力损失的发生率很高，并且有创新的治疗策略（例如植入设备），但关于听觉回路发育和组织的基本问题仍然没有得到解决。该项目的目标是：1）确定一个信号分子家族（Eph受体和ephrins）如何引导模式化的听觉回路形成，2）测试它们的功能重要性，3）将学到的机制应用于可塑性，恢复和再生领域。

DESCRIPTION (provided by applicant): The auditory system's functionally organized topographic maps preserve spatial representations and signal attributes received by the periphery. Tonotopic maps of best-frequency are the principal organizational feature exhibited by all auditory structures. Within layered tonotopic arrangements, secondary "nucleotopic" maps exist in mosaic form where discrete neuronal compartments or modules receive varying input arrays. Patterning and accurate alignment of these inputs define functional zones necessary for processing other stimulus features. Given the significance of topographic maps and the spatial precision necessary in defining functional auditory circuits, surprisingly little is known about th mechanisms that guide such connections early in development. We seek to determine the molecular mechanisms of pattern formation in the auditory midbrain, or inferior colliculus (IC), prior to experience. The IC receives numerous converging inputs terminating within a single topographical framework, making it an excellent model for studying targeting questions. Previous studies in our laboratory showed shaping of multiple afferent patterns in the central nucleus and lateral cortex of the IC (CNIC and LCIC, respectively) prior to hearing onset. We hypothesize that the spatial resolution necessary to establish this early topographic registry requires close cell-to-cell signaling via membrane- tethered guidance molecules. The Eph family of receptor tyrosine kinases, and their corresponding ligands, the ephrins, exhibit attractant (adhesive) or repulsive (de-adhesive) binding behaviors known to influence such spatially complex connection mapping . Recently, we reported graded and modular expression patterns (EphA4, ephrin-B2, and ephrin-B3 in CNIC and LCIC) that correlate temporally and spatially with segregating projection patterns. Utilizing established control (C57BL/6J) and Eph/ephrin mutant mouse colonies (EphA4lacZ, ephrin-B2lacZ, ephrin-B3lacZ, ephrin-B3-/-), the proposed work focuses on: layered inputs to the CNIC from the lateral superior olivary nuclei (LSO) and the dorsal nuclei of the lateral lemniscus (DNLL), as well as patterned inputs to the LCIC from the LSO and the CNIC. The planned experiments will test three hypotheses: 1) that topographic mapping errors occur in the CNIC and LCIC in Eph/ephrin-deficient mice, 2) that in vitro stripe assays reveal EphA4/ephrin-B2, -B3 signaling in the guidance of growing auditory axons, and 3) that altered topographic projections cause physiological (auditory brainstem responses, ABR) and behavioral (acoustic startle) effects in Eph/ephrin mutants. Understanding early guidance mechanisms in auditory networks will provide the foundation for assessing potential costs/benefits of stimulation paradigms, thus guiding new treatment strategies for the hearing impaired and those suffering from tinnitus. PUBLIC HEALTH RELEVANCE: Hearing, performed by the auditory system, is a vital sense and critical for speech and language acquisition. Despite significant incidences of hearing loss and innovative treatment strategies (e.g. implantation devices), fundamental questions remain unaddressed concerning auditory circuit development and organization. The goals of this project are to: 1) determine how a family of signaling molecules (Eph receptors and ephrins) guides patterned auditory circuit formation, 2) test their functional importance, and 3) apply mechanisms learned to fields of plasticity, recovery, and regeneration.