调控Emx2表达对椭圆囊毛细胞与传入神经定向连接作用的研究

The perception of hearing and balance depends on the correct connection between the inner ear hair cells and the innervated neurons, to relay the information to the central nervous system. Failure in the formation of proper connection leads to hearing loss and/or balance deficiency. In the utricle of the inner ear, the afferent neurons can be classified into two groups based on their central projection differences. The lateral neurons are projected to the cerebellum, while the medial ones go to the brainstem. The boundary of these two groups of neurons is intertwined closely with the line of polarity reversal (LPR) of the utricular hair cells. The LPR is an imaginary line drawn between two regions of hair cells that adapted opposite hair bundle polarity. However, the mechanism of how the hair cells selectively connected with the afferent neurons is still unknown. The former data from the applicant demonstrated the LPR in the maculae is established by the regional expression of Emx2 during development. Emx2 is a conserved homodomain transcription factor affects neuronal guidance and projection during cortical development. Based on these results, we proposed the project that focus on how the expression of Emx2 in the hair cells affecting the afferent neurons. Our group is producing transgenic mouse lines that specifically overexpress or knockout the Emx2 in the sensory epithelium, hair cells, or the neurons. Then, the hair cell polarity pattern, the morphology of synapses, the afferent neurons projection pattern, together with the behaviors of the transgenic mice will be examined. The outcomes from these tests will reveal the potential effects of the Emx2 expression in attracting the specific neurons to innervate the target sensory receptors, and establishes the correct hair cell-afferent neuron connection. These results will provide solid evidence to entangle the mechanism of connection formation between hair cells and afferent neurons, which will further build up the foundation for the formation and regeneration of proper functions in the inner ear.

听觉及前庭觉的感知依赖于内耳毛细胞与传入神经之间的正确连接。当传入神经不能够正确支配毛细胞时，会出现听力丧失和/或平衡障碍。在前庭系统椭圆囊中，两组传入神经分别投射到脑干和小脑，其分界与毛细胞纤毛极性的区域性密切相关。但椭圆囊毛细胞是如何定向连接相应神经的机制尚不明确。申请人前期实验证明了椭圆囊斑的纤毛极性区域性是由其外侧区表达的同源阈转录因子Emx2所确立的。基于此，我们提出Emx2的表达可能对椭圆囊传入神经定位分布有趋化作用。利用多种转基因小鼠特异性改变Emx2在感觉上皮、毛细胞及神经元内的表达谱，观察毛细胞极性、神经突触形态、传入神经的中枢投射模式以及小鼠前庭功能改变，来探索Emx2在椭圆囊中表达可以诱导特定神经元支配相应区域毛细胞并形成正确连接的机制。最终明确椭圆囊斑内传入神经与毛细胞建立连接的机制，并为进一步研究毛细胞与神经元连接的形成和再生提供理论基础。

听觉及前庭觉的感知依赖于内耳毛细胞与传入神经之间的正确连接。当传入神经不能够正 确支配毛细胞时，会出现听力丧失和/或平衡障碍。在前庭系统椭圆囊中，两组传入神经分别 投射到脑干和小脑，其分界与毛细胞纤毛极性的区域性密切相关。但椭圆囊毛细胞是如何定向连接相应神经的机制尚不明确。在前期实验椭圆囊斑的纤毛极性区域性是由其外侧 区表达的同源阈转录因子Emx2所确立的之上。通过进一步研究揭示了Emx2在斑马鱼神经丘以及椭圆囊的发育中影响一部分神经元与毛细胞的突触链接的建立。既往研究提出Emx2对神经元与感受器细胞链接的引导机制的研究中提示可能有上游基因Notch信号通路参与。Notch 信号通路的改变，也可以影响神经突触的选择性。因此我们进一步研究了Notch信号通路中下游基因Dll1在椭圆囊中的表达及谱系追踪，提出Dll1可能影响Emx2的表达和进一步功能。同时，为了更好地研究毛细胞与传入神经的链接，我们研发制备了Sall2小鼠，希望可以特异性标记部分前庭蜗神经，以便更好地分析神经的不同组群，进行进一步作用机制的研究。我们提出Emx2的表达可能对椭圆囊传入神经 定位分布有趋化作用。而该功能可能只主要被Notch调控。Emx2在椭圆囊中表达可以诱导特定神经元支配相应区域毛细胞并形成正确连接的机制。通过系列探索，希望能更好滴认识探索传入神经与毛细胞的突触建立和选择的机制。最终明确内耳内传入神经与毛细胞建立连接的机制，并为进一步研究毛细胞与神经元连接的形成和再生提供理论基础。