Developmental profiling of spiral ganglion neurons reveals insights into auditory circuit assembly

The sense of hearing depends on the faithful transmission of sound information from the ear to the brain by spiral ganglion (SG) neurons. However, how SG neurons develop the connections and properties that underlie auditory processing is largely unknown. We catalogued gene expression in mouse SG neurons at six developmental stages, ranging from embryonic day 12 (E12), when SG neurons first extend projections, up until postnatal day 15 (P15), after the onset of hearing. For comparison, we also analyzed the closely-related vestibular ganglion (VG) at the same time points. To identify genes involved in SG axon guidance and branching, target selection, synaptogenesis, synaptic refinement, and synaptic function, we collected SG at E12 and E13, E16, P0, P6, and P15. We also collected VG at the same time points. For E12 and E13 time points, SG and VG were microdissected from Rnx-cre; Z/EG embryos, which express GFP in the VG. E16-P15 VG was also isolated by microdissection from Rnx-cre; Z/EG animals. E16-P15 SG neurons were isolated by FACS sorting dissociated cochlea from Mafb-GFP animals.听觉依赖螺旋神经节（spiral ganglion, SG）神经元将声音信息从耳部精准传递至大脑。然而，螺旋神经节神经元如何形成支撑听觉处理的连接与特性，目前仍尚未明确。本研究对小鼠螺旋神经节神经元在六个发育阶段的基因表达进行了系统性编目，涵盖从螺旋神经节神经元首次伸出突起的胚胎期12天（E12），直至听觉功能启动后的出生后第15天（P15）。为开展对照分析，我们同时在上述相同时间点对亲缘关系密切的前庭神经节（vestibular ganglion, VG）进行了检测。为筛选参与螺旋神经节神经元轴突导向与分支、靶区选择、突触发生、突触重塑及突触功能的相关基因，我们分别在E12、E13、E16、P0、P6及P15六个时间点采集了螺旋神经节样本。我们亦在上述相同时间点采集了前庭神经节样本。针对E12与E13阶段的样本，我们从Rnx-cre; Z/EG胚胎中显微解剖获得螺旋神经节与前庭神经节，该品系的前庭神经节可表达绿色荧光蛋白（green fluorescent protein, GFP）。E16至P15阶段的前庭神经节同样通过显微解剖从Rnx-cre; Z/EG动物中分离得到。而E16至P15阶段的螺旋神经节神经元，则通过对Mafb-GFP转基因动物解离的耳蜗组织进行荧光激活细胞分选（fluorescence-activated cell sorting, FACS）分离获取。