Converting stochastic olfactory receptor expression to stereotypic axon guidance programs

总结 哺乳动物的嗅觉系统具有非凡的能力，可以检测和识别天文数字的气味。 挥发性化学物质，称为气味剂。嗅觉感受器（ORs）是嗅觉器官中的一种， 感觉神经元（OSNs），将化学信息转化为电信号传输到嗅觉 球（OB）。约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。 在主嗅上皮（莫伊）中，具有相同OR的OSNs的轴突会聚成不同的， 在OB处的称为肾小球的刻板的神经细胞结构。因为每个OR标识由 相应的肾小球，气味结合到不同的OR库激活气味特异性组合， 肾小球，提供气味感知的基础。在这里，我们研究的分子机制，转化为 在莫伊中单个OR的随机表达与刻板的和高度协调的轴突靶向程序相比， OB。以前的工作表明OR序列在这个轴突中起着重要的调节作用 在某种程度上，通过指导参与轴突导向和细胞增殖的基因的表达程序， 粘连我们发现，OR身份可能通过引发不同水平的内质网来告知这一过程。 内质网（ER）应激，其反过来影响控制轴突靶向特异性的转录程序。与 产生一种翻译荧光报告基因，定量ER应激诱导的Perk 信号，我们证明OSN根据OR的身份具有不同水平的ER应激 快车此外，通过对转录网络进行去卷积，我们确定了转录因子， 将ER压力水平转化为不同的轴突指导输出。基于这些初步发现，我们建议 实验将破译ER应激反应转录因子的功能，并将确定 细胞外条形码对应于各种水平的ER应激。此外，我们提出的实验将 解开OR身份和OSN起源对ER应激细胞水平的贡献，并将识别OR 在这个过程中起主要作用的蛋白质序列。我们的实验有望提供新的见解， 几十年来一直不为人知的迷人问题。此外，这项工作将揭示 负责将神经元的细胞和分子身份转换为精确轴突的可推广机制 指导特异性，具有巨大的基础和翻译分支。

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.