The unfolded protein response as a mechanism for cellular identity in the developing olfactory system

项目摘要 在神经发育中，遗传程序赋予每个神经元独特的细胞身份。这个身份 包括细胞表面的一系列分子，这些分子决定了神经元对环境的反应 在投射形成神经回路的过程中所遇到的东西。大量的研究集中在 细胞表面识别分子和细胞外空间中的配体之间的相互作用引导神经投射，然而， 哺乳动物是如何产生令人惊叹的神经元身份多样性的， 这些错综复杂的连接网络。哺乳动物的嗅觉系统提供了一个完美的缩影 问题在这里，发育中的嗅觉感觉神经元（OSN）选择表达单一的嗅觉受体（OR）， 从老鼠基因组中大约1,500种可能性中。OR选择设置OSN蜂窝身份的组件 直接靶向，赋予OSN细胞表面分子的“条形码”， 在嗅球（OB）中，所有选择OR的细胞都会投射到OB。该条形码的组成是 神经纤毛蛋白是已知的并且包括神经活性非依赖性分子（神经纤毛蛋白-1/脑信号蛋白-3A，神经纤毛蛋白-1/脑信号蛋白-3A）。 2/脑信号蛋白-3F）以及活性依赖性分子（Kirrel 2 -3、Ephrin-A5及其受体、非典型的 原钙粘蛋白）。然而，将OR选择映射到特定身份条形码的机制是不完全的。 明白我们以前报道过OSN发育过程中OR的选择触发了未折叠蛋白 反应（UPR），一个全基因组的mRNA表达调控程序，对完整的神经元细胞的生长至关重要。 成熟和稳定的OR表达。初步数据表明，UPR在OSN中的活性不同 取决于他们选择的手术室值得注意的是，这些差异与表达模式密切相关 对于OSN细胞表面轴突靶向条形码的几种神经元活性依赖性组分，以及 三个转录因子在组织条形码中可能起作用。这些结果表明， UPR在轴突引导的背景下作为神经元身份的分子决定因素的作用。我们将测试 这一假设有三个具体目标。在aim 1中，我们将使用两种小鼠遗传学方法来证明 UPR的差异激活因果地影响OSN细胞特性和轴突靶向。目标2将 通过鉴定主调节因子，确定连接UPR与这些身份分子的分子级联 转录因子（mrTF）控制UPR介导的细胞身份。最后，目标3将确定 普遍定期审议中依赖或不依赖或有等级的作用如何共同作用，形成整体 OSN身份。我们预计，这些实验将揭示普遍定期审议以前没有描述的作用， 一种与嗅觉系统中轴突引导相关的神经元身份的分子决定因素，提供了一种新的 研究健康和疾病背景下神经发育的范式。

PROJECT SUMMARY In neural development, genetic programs endow each neuron with a distinct cellular identity. This identity includes a repertoire of molecules on the cell surface that dictate how that neuron will respond to the environment it encounters as it projects to form neural circuits. A large body of work has focused on how the interactions between cell surface identity molecules and ligands in the extracellular space guide neural projections, yet it remains comparatively unclear how mammals generate the stunning diversity of neuronal identities that underly these intricate networks of connectivity. The mammalian olfactory system offers a perfect microcosm of this question. Here, developing olfactory sensory neurons (OSN) chose to express a single olfactory receptor (OR) from roughly 1,500 possibilities in the mouse genome. OR choice sets the components of OSN cellular identity that direct targeting, endowing an OSN with a “barcode” of cell surface molecules that specifies a precise location in the olfactory bulb (OB) to which all cells choosing that OR will project. The composition of this barcode is known and includes neural activity-independent molecules (Neuropilin-1/Semaphorin-3A, Neuropilin- 2/Semaphorin-3F) as well as activity-dependent molecules (Kirrel2-3, Ephrin-A5 and its receptor, non-canonical Protocadherins). However, the mechanisms mapping OR choice to a specific identity barcode are incompletely understood. We previously reported that OR choice during OSN development triggers the unfolded protein response (UPR), a genome-wide mRNA translation-regulatory program essential for complete neuronal maturation and stable OR expression. Preliminary data suggests that the UPR is differentially active in OSNs depending on the OR that they chose. Remarkably, these differences are intimately linked to expression patterns for several neuronal activity-dependent components of the OSN cell surface axon targeting barcode, as well as three transcription factors with possible roles in organizing the barcode. These results suggest an entirely novel role for the UPR as a molecular determinant of neuronal identity in the context of axon guidance. We will test this hypothesis in three specific aims. In aim 1, we will use two mouse genetic approaches to demonstrate that differential activation of the UPR causally affects OSN cellular identity and axon targeting. Aim 2 will define the molecular cascade linking the UPR to these identity molecules by identifying master regulator transcription factors (mrTFs) controlling UPR-mediated cellular identity. Finally, aim 3 will determine how hierarchical OR-dependent and OR-independent roles for the UPR work together to shape the whole of OSN identity. We anticipate that these experiments will unveil a previously undescribed role for the UPR as a molecular determinant of neuronal identity relevant for axon guidance in the olfactory system, offering a new paradigm with which to study neural development in the context of health and disease.