Development of the Primary Olfactory Pathway

描述（由申请人提供）：该项目的长期目标是确定参与建立初级嗅觉通路复杂地形的轴突引导分子。我们之前确定了发育中的关键时间点，轴突的行为表明引导分子在起作用。嗅觉感觉神经元（OSN）轴突在胚胎早期发育过程中从嗅觉位点向端脑泡生长。轴突穿透端脑，形成假定的嗅觉神经层（pONL）。一小部分轴突生长到心室表面，这被认为是诱导嗅球（OB）形成的原因。大多数轴突被限制在pONL上长达4天，可能被分类成分子定义的亚群。4天后，一些轴突深入OB，开始肾小球形成。了解嗅觉通路形成的一个关键问题是，在肾小球形成之前，OB中存在哪些线索阻止轴突向内生长？回答这个关键问题的一种方法是检查候选指导分子在发展途径中的分布。我们假设pONL内轴突的停滞可能是由于OB发育中的抑制性引导分子。OB中抑制性线索的一个潜在来源是细胞外基质（ECM）的成分。我们已经确定腱素和硫酸软骨素蛋白聚糖（CSPGs）的成员是调节轴突长入和肾小球形成的抑制线索的良好候选者。本研究的具体目的是：1)验证ECM成分在嗅觉通路发育过程中是OSN轴突时空动态的关键调节因子的假设，并在体外对这些分子抑制OSN神经突生长的能力进行功能测试；2)验证整合素和非整合素ECM受体在发育中的嗅觉系统中促进细胞表面-基质相互作用的假设，并在体外功能测试它们在ECM基质上调节OSN神经突生长的能力；3)验证基质金属蛋白酶在嗅觉系统发育过程中对ECM环境的塑造起重要作用的假设。这些研究将极大地增强我们对轴突如何在嗅觉系统中建立连接的认识，并可能对诸如卡尔曼综合征之类的疾病产生影响。此外，这些结果将广泛适用于其他CNS区域，其中的工作继续朝着理解边界和地形图的形成。

DESCRIPTION (provided by applicant): The long term aim of this project is to identify axon guidance molecules involved in establishing the complex topography of the primary olfactory pathway. We previously identified critical time points in development where axon behavior indicates that guidance molecules are acting. Olfactory sensory neuron (OSN) axons grow from the olfactory placode to the telencephalic vesicle in early embryonic development. Axons penetrate the telencephalon, forming a presumptive olfactory nerve layer (pONL). A small subset of axons grow to the ventricular surface which has been suggested to induce the formation of olfactory bulb (OB). The majority of axons remain restricted to the pONL for up to 4 days, presumably sorting out into molecularly defined subsets. After 4 days, some axons grow deeper into the OB, initiating glomerular formation. A pivotal question in understanding olfactory pathway formation is which cue(s) are present in the OB that prevent(s) axon ingrowth prior to glomerular formation? One way to answer this key question is to examine the distributions of candidate guidance molecules within the developing pathway. We hypothesize that the stalling of axons within the pONL may be due to inhibitory guidance molecules within the developing OB. One potential source of inhibitory cues in the OB are components of the extracellular matrix (ECM). We have identified members of the tenascin and chondroitin sulfate proteoglycans (CSPGs) as good candidates for the inhibitory cues that regulate axon ingrowth and glomerular formation. The specific aims of the current proposal are to: 1) test the hypothesis that components of the ECM are key regulators of OSN axon spatio-temporal dynamics in the developing olfactory pathway, and to functionally test the ability of these molecules to inhibit OSN neurite outgrowth in vitro; 2) to test the hypothesis that both integrin and non-integrin ECM receptors facilitate cell surface - matrix interactions in the developing olfactory system and to functionally test their ability to modulate OSN neurite outgrowth on ECM substrates in vitro; 3) to test the hypothesis that the matrix metallooroteases play an important role in sculpting the ECM environment during development of the olfactory system. These studies will greatly enhance our knowledge of how axons establish connections in the olfactory system and may have implications for diseases such as Kallman's syndrome. Moreover these results will be broadly applicable to other CNS regions where work continues towards understanding the formation of boundaries and topographic maps.