Converting stochastic olfactory receptor expression to stereotypic axon guidance programs

摘要 哺乳动物的嗅觉系统具有非凡的能力来探测和识别天文数字的 挥发性化学物质，称为气味物质。气味是由嗅觉纤毛上的嗅觉感受器(ORs)检测到的 感觉神经元(OSN)，将化学信息转化为电信号传输到嗅觉 灯泡(OB)。~1000个OR基因中的每一个都以单基因、单等位基因和看似随机的方式表达 在主嗅觉上皮(MOE)中，具有相同OR的OSN的轴突会聚为不同的AND OB的典型神经束结构称为肾小球。因为每个OR标识由 相应的肾小球，气味结合到不同的或曲目激活气味特定的组合 肾小球，提供气味感知的基础。在这里，我们研究了转化细胞的分子机制 单一OR在MOE中的随机表达到刻板和高度协调的轴突靶向程序 妇产科医生。以往的工作表明，OR序列在该轴突中起着重要的调节作用 引导过程，部分是通过引导参与轴突引导和细胞的基因的表达程序 粘附力。我们发现，OR同一性可能通过引发不同水平的内质网来影响这一过程 网状(ER)应激，进而影响控制轴突靶向性的转录程序。使用 量化内质网应激诱导的PERK水平的翻译荧光报告的产生 信号，我们证明了OSN根据OR的身份有不同的ER应激水平 快递。此外，通过去卷积转录网络，我们确定了转录因子 将内质网应激水平转换为不同的轴突引导输出。基于这些初步发现，我们建议 将破译内质网应激反应转录因子的功能并将识别 胞外条形码对应于不同水平的内质网应激。此外，我们提出的实验将 解开OR身份和OSN来源对内质网应激细胞水平的贡献，并将识别OR 蛋白质序列在这一过程中起着主要作用。我们的实验承诺提供新的洞察 这是一个几十年来一直鲜为人知的有趣问题。此外，这项工作将揭示 负责将神经元的细胞和分子同一性转化为精确轴突的通用机制 指导的特殊性，具有巨大的基本和翻译分支。

Summary The mammalian olfactory system has the remarkable ability to detect and identify an astronomical number of volatile chemicals, termed odorants. Odorants are detected by olfactory receptors (ORs) at the cilia of olfactory sensory neurons (OSNs), which transform chemical information into electrical signals transmitted to the olfactory bulb (OB). Each one of the ~1000 OR genes is expressed in a monogenic, monoallelic, and seemingly stochastic fashion in the main olfactory epithelium (MOE), yet axons from OSNs with the same OR converge to distinct and stereotypic neuropil structures at the OB called glomeruli. Because each OR identity is represented by corresponding glomeruli, odor binding to distinct OR repertoires activates an odor-specific combination of glomeruli, providing the basis of odor perception. Here, we investigate molecular mechanisms that transform the random expression of a single OR in the MOE to stereotypic and highly coordinated axon targeting programs in the OB. Previous work revealed that the OR sequence plays an essential regulatory function in this axon guidance process, in part, by directing the expression programs of genes involved in axon guidance and cell adhesion. We reveal that the OR identity may inform this process by eliciting distinct levels of endoplasmic reticulum (ER) stress, which in turn, influence transcriptional programs controlling axon targeting specificity. With the generation of a translational fluorescent reporter that quantifies the levels of ER stress-induced Perk signaling, we demonstrate that OSNs have distinct levels of ER stress according to the identity of the OR they express. Furthermore, by deconvoluting transcriptional networks, we identified transcription factors that transform ER stress levels into distinct axon guidance outputs. Based on these preliminary findings, we propose experiments that will decipher the function of ER stress-responsive transcription factors and will identify extracellular barcodes corresponding to various levels of ER stress. Moreover, we propose experiments that will untangle the contribution of OR identity and OSN origin to the cellular levels of ER stress and will identify OR protein sequences with a major role in this process. Our experiments promise to provide novel insight into a fascinating problem that has remained poorly understood for decades. Moreover, this work will uncover generalizable mechanisms responsible for converting cellular and molecular identity of neurons into precise axon guidance specificity, with immense basic and translational ramifications.