Axonal Connectivity in the Murine Olfactory System

描述（申请人提供）：近年来，小鼠嗅觉和犁鼻系统已成为研究哺乳动物大脑神经元连接的有用模型。这些系统以大脑嗅球激活的焦点模式的形式传递环境中化学刺激的信息。在哺乳动物中，化学检测是由一大家族的气味和犁鼻受体介导的，这些受体在化学感觉神经元中表达。目前的理解是，气味和犁鼻受体是部分的，但不是唯一的，负责连接的感觉轴突投射到嗅球。在寻找其他引导分子的过程中，neuropilin-2 （NP2）被确定为在建立这些连接方面具有独特的作用。然而，这些研究提出的主要问题与NP2的配体有关。本研究的第一个重点是梳理sema3B、sema3C、sema3F对NP2轴突引导功能的贡献。这将通过从小鼠基因组中遗传地切除这些NP2配体，分析由此产生的寻路错误，并将这些数据与观察到的NP2突变小鼠轴突寻路缺陷相关联来完成。在感觉神经支配建立的同时，主嗅球内的二尖瓣细胞和簇状细胞向前脑腹侧发出初级轴突，形成外侧嗅道（LOT）。与感觉轴突不同，二尖瓣细胞和丛状细胞通过广泛的侧支支配其众多的靶区。然而，这一过程在小鼠中的确切时间仍然是一个悬而未决的问题。这些研究的第二个目标是通过转基因荧光标记二尖瓣和簇状细胞轴突来跟踪LOT在体内的发展。由于这个过程与感觉神经支配同时发生，一个问题是LOT的形成是否独立于嗅觉上皮的感觉神经支配。这个问题将通过将荧光标记LOT与已知影响感觉神经支配的突变相结合来解决。体内荧光成像和基因消融的结合将为研究嗅觉系统和大脑其他区域的轴突引导提供有力的工具。

DESCRIPTION (provided by applicant): In recent years, the mouse olfactory and vomeronasal systems have emerged as useful models for studying neuronal connectivity in the mammalian brain. These systems relay information about chemical stimuli in their environment in the form of focal patterns of activation in the olfactory bulb of the brain. In mammals, chemical detection is mediated by a large family of odorant and vomeronasal receptors expressed in chemosensory neurons. Current understanding is that odorant and vomeronasal receptors are partially, yet not solely, responsible for the connectivity of sensory axonal projections to the olfactory bulb. In the search for additional guidance molecules, neuropilin-2 (NP2) was identified as having distinct roles in setting up these connections. The major questions raised by these studies, however, concern the ligands for NP2. The first focus of this study is to sort out the contributions of sema3B, sema3C, and sema3F to the axon guidance function of NP2. This will be done by genetically ablating these NP2 ligands from the mouse genome, assaying the resulting pathfinding errors, and correlating these data with observed axon pathfinding defects in NP2 mutant mice. Concurrent to the establishment of sensory innervation, mitral and tufted cells within the main olfactory bulb send out primary axons to the ventral forebrain forming the lateral olfactory tract (LOT). In contrast to sensory axons, mitral and tufted cells innervate their numerous target areas through extensive collateral branching. Yet, the exact timing of this process in mouse remains an open question. The second goal of these studies is to follow the development of the LOT in vivo through genetically-modified fluorescently-labeled mitral and tufted cell axons. Because this process occurs concomitant with sensory innervation, one question raised is the independence of LOT formation from sensory innervation by the olfactory epithelium. This question will be addressed by combining the fluorescently tagged LOT with mutations known to affect sensory innervation. The combination of in vivo fluorescent imaging and genetic ablation will provide powerful tools for investigating axonal guidance in the olfactory systems as well as other areas of the brain.