PROX1 Controls Cellular Patterning, Innervation and Differentiation in the Mouse Organ of Corti

The organ of Corti is divided into functional compartments responsible for hearing or cochlear amplification. A medial compartment containing inner hair cells innervated by Type I spiral ganglion neurons and a lateral compartment containing outer hair cells innervated by Type II spiral ganglion neurons. Supporting cells also differ, with lateral compartment pillar cells and Deiters cells developing specialized cellular structures to support outer hair cell electromotility. We bred organ of Corti-restricted Prox1 conditional knockout mice to study lateral compartment development because PROX1 is the first transcription factor expressed strictly in lateral compartment supporting cells. In the absence of Prox1, supporting cell numbers increased without corresponding changes in outer hair cells, and they appear incompletely differentiated based on morphological criteria. Outer hair cell number was not impacted but innervation was disrupted with many afferent neurons turning incorrectly towards the cochlear apex. RNAseq revealed no changes in gene expression that could account for the innervation phenotype. Therefore, we propose that PROX1 promotes pillar and Deiters cell differentiation and organization that has secondary effects on innervation but is not required for compartment specification. RNA-seq profiling of micro-dissected organ of Corti from wildtype and conditional Prox1 knock-out (Emx2-cre; floxed-Prox1) mice at P0柯蒂氏器（organ of Corti）可被划分为负责听觉感知与耳蜗放大的两类功能分区：内侧分区包含受I型螺旋神经节神经元支配的内毛细胞，外侧分区则包含受II型螺旋神经节神经元支配的外毛细胞。两类分区的支持细胞亦存在显著差异，外侧分区的柱细胞与戴特细胞（Deiters cells）会形成特化细胞结构，以支撑外毛细胞的电运动特性。为研究外侧分区的发育机制，我们构建了柯蒂氏器特异性的Prox1条件性敲除小鼠——这是因为PROX1是首个仅在外侧分区支持细胞中特异性表达的转录因子。实验结果显示，在Prox1缺失的小鼠中，支持细胞数量异常增加，但外毛细胞数量未发生相应改变；通过形态学标准判断，此类支持细胞似乎未完成完全分化。此外，外毛细胞数量未受影响，但神经支配过程遭到破坏：大量传入神经元错误地朝向耳蜗顶方向生长。RNA测序（RNA-seq）分析未发现可解释该神经支配表型的差异基因表达。据此我们提出，PROX1可促进柱细胞与戴特细胞的分化与组织构建，该过程会对神经支配产生间接影响，但并非柯蒂氏器分区特化所必需的调控因子。本研究对出生后第0天（P0）的野生型小鼠与Prox1条件性敲除（Emx2-cre; floxed-Prox1）小鼠的显微解剖柯蒂氏器样本开展了RNA-seq测序分析。