SummaryThe sense of smell is intricately linked to essential animal behaviors necessary for individual survival and species preservation. During vertebrate evolution, odorant receptors (ORs), responsible for detecting odor molecules, have evolved to adapt to changing environments, transitioning from aquatic to terrestrial habitats and accommodating increasing complex chemical environments. These evolutionary pressures have given rise to the largest gene family in vertebrate genomes. Vertebrate ORs are phylogenetically divided into two major classes; class I and class II. Class I OR genes, initially identified in fish and frog, have persisted across vertebrate species. On the other hand, class II OR genes are unique to terrestrial animals, accounting for ~90% of mammalian OR genes. In mice, each olfactory sensory neuron (OSN) expresses a single functional allele of a single OR gene from either the class I or class II OR repertoire. This one neuron‐one receptor rule is established through two sequential steps: specification of OR class and subsequent exclusive OR expression from the corresponding OR class. Consequently, OSNs acquire diverse neuronal identities during the process of OSN differentiation, enabling animals to detect a wide array of odor molecules. This review provides an overview of the OSN differentiation process through which OSN diversity is achieved, primarily using the mouse as a model animal.

中文翻译：

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嗅觉感觉神经元分化和类别选择的分子机制

摘要嗅觉与个体生存和物种保护所必需的基本动物行为有着错综复杂的联系。在脊椎动物进化过程中，负责检测气味分子的气味受体（OR）已经进化到适应不断变化的环境，从水生栖息地过渡到陆地栖息地，并适应日益复杂的化学环境。这些进化压力催生了脊椎动物基因组中最大的基因家族。脊椎动物 OR 在系统发育上分为两大类：I 类和 II 类。I 类 OR 基因最初在鱼类和青蛙中发现，现已在脊椎动物物种中持续存在。另一方面，II 类 OR 基因是陆生动物所独有的，约占哺乳动物 OR 基因的 90%。在小鼠中，每个嗅觉感觉神经元 (OSN) 表达来自 I 类或 II 类 OR 库的单个 OR 基因的单个功能等位基因。这一神经元受体规则是通过两个连续步骤建立的：指定 OR 类以及随后来自相应 OR 类的异或表达式。因此，OSN 在 OSN 分化过程中获得了不同的神经元身份，使动物能够检测到各种气味分子。这篇综述概述了 OSN 分化过程，通过该过程实现了 OSN 多样性，主要使用小鼠作为模型动物。