Growth factors in the development and physiology of geniculate taste neurons

项目总结/摘要 味觉始于味蕾，味蕾是一群感觉细胞，它们传递化学感觉 信息传递到其细胞体位于膝状体和结状体/岩神经节中的传入神经元。 膝状神经节（GG）口腔感觉神经元通过鼓索（CT）神经投射以支配味觉 分布在舌前部的菌状乳突中的芽。重要的是，真菌状 乳头是多模式的，因为CT神经纤维对所有五种味觉品质、触觉刺激和味觉刺激都有反应。 舌头表面和温度。我们对感觉神经元不同亚型的理解， 将这些不同的刺激传达给大脑，以及它们在进食和感知味道中的作用， 基本的同样地，负责这些GG口服给药的细胞命运特化的分子机制也不清楚。 感觉亚群，以及在整个生命过程中维持其功能性连接， 明白神经营养因子信号通路，沿着下游转录因子，是关键的 其他感觉系统中神经元多样性的出现。为了确定细胞命运的具体途径， 味觉系统，我们使用核糖体分析来鉴定在GG口腔中特异性富集的基因， 感觉神经元从该筛选中，我们鉴定了生长因子受体间变性淋巴瘤激酶（ALK）， 其在其它内脏神经元如交感神经元中表达。我们还鉴定了 早期生长反应因子4（EGR 4），证实ALK和EGR 4在GG口服液中表达。 感觉神经元我们将检验ALK受体复合物是口腔感觉神经元所必需的这一假设。 通过检查Alk-/-小鼠在整个生命周期中的分化、靶神经支配和维持。我们将 还确定与Alk+/+小鼠相比，Alk-/-小鼠是否具有对化学物质的受损应答， 以及使用CT的电生理记录对舌头进行触觉刺激。同样， 将通过以下分析来评估EGR 4在膝状体口腔感觉神经元的细胞命运特化中的作用： Egr 4-/-小鼠。Egr 4-/-小鼠对味觉和触觉刺激的CT反应是否受损 将评估，沿着是否BDNF，一种对GG神经元发育至关重要的神经营养因子， 是启动EGR 4表达的信号。最后，我们鉴定了一群GG口腔感觉神经元， 是机械感觉的并且选择性地表达受体Ret。利用交叉遗传学，我们将 区分Ret+ GG神经元在菌状乳头中的投射与混合的三叉神经投射。我们将 还确定哪些Ret配体支持这些口腔机械感觉神经元的神经支配模式。 将该亚群与细胞命运途径联系起来，我们将确定Ret+ GG的出现是否与Ret+ GG的表达有关。 神经元需要EGFR 4和/或ALK复合物。这些实验将使人们更好地了解 组织和维持周围味觉系统，并可能揭示治疗策略， 由神经退行性疾病、癌症治疗、病毒感染和衰老引起的味觉障碍。

Project Summary/Abstract The sense of taste starts with taste buds, clusters of sensory cells, that communicate chemosensory information to afferent neurons whose cell bodies are located in the geniculate and nodose/petrosal ganglia. Geniculate ganglion (GG) oral sensory neurons project via the chorda tympani (CT) nerve to innervate taste buds located in fungiform papillae that are distributed across the anterior tongue. Importantly, fungiform papillae are multimodal in that CT nerve fibers respond to all five taste qualities, tactile stimulation of the tongue surface, and temperature. Our understanding of the different subtypes of sensory neurons that communicate these varied stimuli to the brain, and their role in feeding and the perception of flavor, is rudimentary. Likewise, the molecular mechanisms responsible for cell fate specification of these GG oral sensory subpopulations, and the maintenance of their functional connections throughout life, are poorly understood. Neurotrophic factor signaling pathways, along with downstream transcription factors, are critical for the emergence of neuronal diversity in other sensory systems. To identify cell fate specification pathways in the taste system, we used ribosomal profiling to identify genes that were enriched specifically in GG oral sensory neurons. From this screen we identified the growth factor receptor anaplastic lymphoma kinase (ALK), which is expressed in other visceral neurons such as sympathetic neurons. We also identified the transcription factor early growth response 4 (EGR4), and both ALK and EGR4 were confirmed to be expressed in GG oral sensory neurons. We will test the hypothesis that the ALK receptor complex is required for oral sensory neuron differentiation, target innervation and maintenance throughout the lifespan by examining Alk-/- mice. We will also determine whether whether Alk-/- mice, as compared to Alk+/+ mice, have impaired responses to chemical and tactile stimulation of the tongue using electrophysiological recordings of the CT. Likewise, the function of EGR4 in the cell fate specification of geniculate oral sensory neurons will be evaluated through the analysis of Egr4-/- mice. Whether Egr4-/- mice have impaired CT responses to taste and tactile stimulation of the tongue will be evaluated, along with whether BDNF, a neurotrophic factor critical for the development of GG neurons, is the signal that initiates EGR4 expression. Lastly, we identified a population of GG oral sensory neurons that are mechanosensory and selectively express the receptor Ret. Using intersectional genetics, we will distinguish Ret+ GG neuron projections in fungiform papillae from intermingled trigeminal projections. We will also determine which Ret ligands support the innervation pattern of these oral mechanosensory neurons. Linking this subpopulation to cell fate pathways, we will determine whether the emergence of Ret+ GG neurons requires EGR4 and/or ALK complexes. These experiments will provide a greater understanding of the organization and maintenance of the peripheral gustatory system, and may reveal therapeutic strategies for taste impairments caused by neurodegerative disorders, cancer treatments, viral infections and aging.