Molecular, Cellular, and Developmental Organization of the Mouse Vomeronasal organ at Single Cell Resolution

We have generated single cell transcriptomic atlases of vomeronasal organs (VNO) from juvenile and adult mice. Combined with spatial molecular imaging, we uncover a distinct, previously unidentified class of cells that express the vomeronasal receptors and a population of canonical olfactory sensory neurons in the VNO. High resolution trajectory and cluster analyses reveal the lineage relationship, spatial distribution of cell types, and a putative cascade of molecular events that specify the V1r, V2r, and OR lineages from a common stem cell population. The expression of vomeronasal and olfactory receptors follow power law distributions, but there are high variabilities in average expression levels between individual receptor and cell types. Substantial co-expression is found between receptors across clades, from different classes, and between olfactory and vomeronasal receptors, with nearly half from pairs located on the same chromosome. Interestingly, the expression of V2r, but not V1r, genes is associated with various transcription factors, suggesting distinct mechanisms of receptor choice associated with the two cell types. We identify association between transcription factors, surface axon guidance molecules, and individual VRs, thereby uncovering a molecular code that guides the specification of the vomeronasal circuitry. Our study provides a wealth of data on the development and organization of the accessory olfactory system at both cellular and molecular levels to enable a deeper understanding of vomeronasal system function.我们构建了幼年及成年小鼠犁鼻器（vomeronasal organ, VNO）的单细胞转录组图谱。结合空间分子成像技术，我们在犁鼻器中发现了一类独特的、此前未被鉴定的表达犁鼻器受体的细胞群，以及一群经典的嗅觉感觉神经元。高分辨率轨迹分析与聚类分析揭示了细胞类型的谱系关系、空间分布特征，以及一套推测的分子事件级联——该级联可指导来自共同干细胞群的V1r、V2r及嗅觉受体（olfactory receptor, OR）谱系的特化。犁鼻器受体与嗅觉受体的表达均遵循幂律分布，但不同受体及细胞类型间的平均表达水平存在显著差异。不同进化枝、不同类别间的受体，以及嗅觉受体与犁鼻器受体之间均存在大量共表达现象，其中近半数共表达受体对位于同一染色体上。值得注意的是，V2r基因（而非V1r基因）的表达与多种转录因子相关，这提示两类细胞对应的受体选择机制存在差异。我们鉴定出转录因子、细胞表面轴突导向分子与单个犁鼻器受体之间的关联，进而揭示了一套指导犁鼻器神经环路特化的分子编码。本研究从细胞与分子层面为辅助嗅觉系统的发育与组织结构提供了海量数据，有助于更深入地解析犁鼻器系统的功能。