Single-nucleus transcriptome of the gracile nucleus reveals multi-modular complex functional genes in excitatory projection neurons

The gracile nucleus (GR), conventionally regarded as a primary relay in the ascending somatosensory pathway, plays a pivotal role in processing fine-touch, vibration, and proprioceptive information originating from the lower body. The fidelity of this processing is fundamental to sensory perception and motor coordination. We employed single-nucleus RNA sequencing (snRNA-seq) to establish a high-resolution, comprehensive transcriptomic atlas of the adult mouse GR. We systematically dissected the cellular architecture of the GR. Our analysis delineated all major neuronal and non-neuronal populations, and revealed a rich diversity of excitatory projection neuron subtypes, each characterized by a unique transcriptomic signature and a distinct spatial organization. Functional gene enrichment analysis unveiled a striking dichotomy in the roles of these subtypes. We identified a cohort of "conduction-type" neurons, specialized for the rapid and high-fidelity transmission of core somatosensory information, thereby preserving the integrity of the somatosensory map. In contrast, a second cohort of "modulatory-type" neurons demonstrated enriched expression of a diverse repertoire of neuropeptides, including somatostatin and cholecystokinin. These neurons are positioned to exert state-dependent modulation over the principal sensory pathways, fine-tuning information throughput in response to behavioral context or internal states such as arousal and attention. Notably, our findings reveal that these excitatory neurons do not exist as discrete, static populations. Instead, they are organized along a continuous transcriptional spectrum, which appears to represent a trajectory of sensory learning and adaptation. One pole of this continuum, representing an "adapted" state, exhibited significant enrichment of activity-dependent immediate-early genes integral to synaptic plasticity, learning, and memory, such as Fos, Arc, and Npas4. By elucidating this intricate cellular architecture and intrinsic plasticity, our study provides novel insights into information processing within the somatosensory system and offers a valuable resource for investigating the pathophysiology of related disorders, including chronic pain and sensory neuropathies.

薄束核（gracile nucleus, GR）传统上被视作上行躯体感觉通路的初级中继站，在处理源自下半身的精细触觉、振动觉与本体感觉信息中发挥关键作用。此类信息处理的保真度是感觉感知与运动协调的核心基础。本研究采用单细胞核RNA测序（single-nucleus RNA sequencing, snRNA-seq）技术，构建了成年小鼠薄束核的高分辨率、全面转录组图谱。我们系统解析了薄束核的细胞构筑，明确了所有主要的神经元与非神经元群体，并揭示了丰富多样的兴奋性投射神经元亚型——每一种亚型均具有独特的转录组特征与专属的空间排布模式。功能基因富集分析揭示了这些亚型在功能上的显著二分性。我们鉴定出一类“传导型”神经元，其特化为快速且高保真地传递核心躯体感觉信息，从而维持躯体感觉图谱的完整性。与之相对的另一类“调节型”神经元则富集表达多种神经肽，包括生长抑素（somatostatin）与胆囊收缩素（cholecystokinin）。此类神经元可对主要感觉通路进行状态依赖性调节，根据行为情境或觉醒、注意力等内部状态，微调信息传递效率。值得注意的是，本研究发现这些兴奋性神经元并非以独立、静态的群体形式存在。相反，它们沿着一条连续的转录谱排布，这一谱式似乎代表了感觉学习与适应的轨迹。该连续谱的一端代表“适应态”，显著富集了与突触可塑性、学习记忆密切相关的活性依赖即刻早期基因，如Fos、Arc及Npas4。本研究通过解析这一复杂的细胞构筑与内在可塑性，为理解躯体感觉系统内的信息处理机制提供了全新视角，并为研究慢性疼痛、感觉神经病等相关疾病的病理生理学机制提供了宝贵的研究资源。