Structural Polarity Influences Terminal Placement and Competition in Formation of the Calyx of Held

描述（由申请人提供）：极性，在细胞过程和细胞内蛋白质和细胞器的排列中，对于人体多种组织的正常功能是必不可少的。在中枢神经系统中尤其如此，在那里极性决定细胞分裂过程中的命运，控制细胞迁移和核运动，并决定轴突和树突的位置。然而，极性在单个神经元上发展输入之间的竞争中的作用尚未得到检验。定义可能决定竞争的极性机制具有重要的临床意义，因为自闭症和精神分裂症等疾病被认为是由于在这一发育阶段末端修剪不足或过度而引起的。此外，极性缺陷已被证明与耳聋有关，并可能在与年龄相关的视网膜功能下降中发挥作用。最近，与梯形体（MNTB）内侧核连接的花萼（CoH）被认为是竞争的一个模式系统；它在整个开发过程中具有易于识别的输入，具有明确的单一终端作为竞争终点，并且从P3到P6的48-72小时的快速早期开发时间框架。我的初步数据表明，MNTB细胞也表现出核内极性，具有偏心位置的细胞核，面向细胞质的广泛的细胞核折叠，以及在远离偏心核的细胞表面优先生长的竞争性末端。这些特性使MNTB:CoH连接成为研究极性在竞争中的作用的理想选择。我假设MNTB神经元在CoH竞争过程中短暂地表达胞内极性，并且胞内极性延伸到体细胞表面，以确定竞争输入的定位和选择单一的获胜输入。为了证明这一点，我将利用串行块面扫描电子显微镜（SBEM），神经元结构的自动分割以及神经元及其内部结构的三维重建等新技术。条件转基因小鼠系将用于选择性地破坏MNTB神经元内的核偏心，以便与正常发育的动物进行比较。通过这些方法的结合，本研究将确定肌内极性对末端放置和竞争的贡献，这可能适用于发育中的神经系统的许多领域。此外，这些发现还可能为自闭症和精神分裂症等疾病的诊断、治疗和预防开辟新的研究途径。

DESCRIPTION (provided by applicant): Polarity, both in arrangement of cellular processes and intracellular proteins and organelles, is essential to the proper functioning of a wide array o tissues in the human body. This is particularly true in the central nervous system, where polarity dictates cell fate during division, controls cell migration and nuclear movement, and determines the location of axons and dendrites. However, the role of polarity in competition between developing inputs on a single neuron has yet to be examined. Defining the polarity mechanisms that may dictate competition is of significant clinical relevance, as disorders such as autism and schizophrenia are believed to arise from under- or over-pruning of terminals during this phase of development. Additionally, defects in polarity have been shown to be associated with deafness and may potentially play a role in age-related decline in retinal function. Recently, the calyx of Held (CoH) connection to the medial nucleus of the trapezoid body (MNTB) has emerged as a model system for competition; it possesses easily identifiable inputs throughout development, a well-defined single terminal as an endpoint for competition, and a rapid and early developmental timeframe of 48-72 hours from P3 to P6. My preliminary data demonstrates that MNTB cells also exhibit intrasomatic polarity, with an eccentrically located nucleus, extensive nuclear foldin where it faces the cytoplasm, and competing terminals that grow preferentially over the cell surface away from the eccentric nucleus. These qualities make the MNTB:CoH connection ideal for studying the role of polarity in competition. I hypothesize that MNTB neurons express intrasomatic polarity transiently during CoH competition and that intrasomatic polarity extends to the somatic surface to determine the positioning of competing inputs and selection of a single, winning input. To show this, I will utilize the novel technologies of serial block-face scanning electron microscopy (SBEM), automated segmentation of neuronal structures, and three-dimensional reconstruction of neurons and their internal structures. A conditional transgenic mouse line will be used to selectively disrupt nuclear eccentricity within MNTB neurons for comparison with normally developed animals. By combining these approaches, this research will establish the contribution of intrasomatic polarity to terminal placement and competition, which may be applicable to many areas of the developing nervous system. Additionally, these findings may also reveal new avenues of research for diagnosis, treatment and prevention of disorders such as autism and schizophrenia.