Motor and sensory functions of the spinal cord are mediated by populations of cardinal neurons arising from separate progenitor lineages. However, each cardinal class is composed of multiple neuronal types with distinct molecular, anatomical, and physiological features, and there is not a unifying logic that systematically accounts for this diversity. We reasoned that the expansion of new neuronal types occurred in a stepwise manner analogous to animal speciation, and we explored this by defining transcriptomic relationships using a top-down approach. We uncovered orderly genetic tiers that sequentially divide groups of neurons by their motor-sensory, local-long range, and excitatory-inhibitory features. The genetic signatures defining neuronal projections were tied to neuronal birth date and conserved across cardinal classes. Thus, the intersection of cardinal class with projection markers provides a unifying taxonomic solution for systematically identifying distinct functional subsets.

脊髓的运动和感觉功能由来自不同祖细胞谱系的基数神经元群介导。然而，每个基本类别都由具有不同分子、解剖学和生理学特征的多种神经元类型组成，并且没有统一的逻辑来系统地解释这种多样性。我们推断新神经元类型的扩张以类似于动物物种形成的逐步方式发生，我们通过使用自上而下的方法定义转录组关系来探索这一点。我们发现了有序的遗传层，它们按运动感觉、局部长距离和兴奋抑制特征依次划分神经元组。定义神经元投射的遗传特征与神经元出生日期相关，并在基数类中保守。因此，