Neurotrophin receptor regulation of taste development

描述(申请人提供)：在发育过程中，味蕾的感觉神经支配受到两种神经营养因子-脑源性神经营养因子(BDNF)和神经营养因子-4(NT4)的严格调控。虽然这两个因素都调节味觉神经支配，但它们的具体功能是不同的。BDNF在味觉上皮细胞中表达，并决定味觉神经元在发育过程中是否定位和支配味觉安慰剂，而NT4不表达。BDNF和NT4对味觉神经元和味蕾数量均有调节作用，但在发育的不同时期有不同程度的影响。这项研究的长期目标是了解在发育过程中调节味蕾神经支配和维持的细胞和分子机制。建议的研究集中在这两种神经营养因子BDNF和NT4通过相同的受体TrkB和p75影响神经支配的各个方面的机制。这项拟议的研究利用基因敲除小鼠的细胞计数、轨迹追踪、免疫组织化学和扫描电子显微镜来确定TrkB和p75在味觉发育的特定方面是必需的，包括轴突延伸到舌头、目标选择和膝曲神经元/味蕾存活。此外，这些研究将这些解剖学方法与复杂的遗传工具相结合，允许在体内阻断TrkB受体蛋白上单个磷酸化位点的功能。这些实验将确定哪些TrkB细胞内信号通路是轴突延伸到舌头、目标选择和膝状神经元/味蕾存活所必需的。这些研究共同验证了这样的假设，即TrkB同时介导BDNF和NT4的作用，但这些神经营养因子的每一种功能都需要不同的细胞内信号通路。而p75‘S更微妙的作用是通过神经营养因子调节味觉发育。由于这些实验研究了神经营养因子如何通过Trk受体调节神经元存活和轴突靶向的基本机制，因此该项目对这些信号机制在控制神经元存活和再生期间轴突靶向的治疗应用具有重要意义。公共卫生相关性：味觉系统是检查损伤后轴突再生的理想和常用系统。我们正在研究两个因素(神经营养因子)的信号机制，这两个因素在发育过程中影响轴突靶向和神经元存活。通过了解这些信号机制的正常功能，可以开发出在神经再生过程中操纵这些重要信号因子的技术，这将改善神经系统损伤后的神经再支配和功能。

Description (provided by applicant): During development, sensory innervation to taste buds is tightly regulated by the actions of two neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT4). Although both of these factors regulate gustatory innervation, their specific functions are different from one another. BDNF is expressed in gustatory epithelium and determines whether gustatory neurons will locate and innervate taste placodes during development, while NT4 does not. Both BDNF and NT4 regulate gustatory neuron and taste bud number, but they have their influences at different times during development. The long range goal of this research is to understand the cellular and molecular mechanisms that regulate the neural innervation to and the maintenance of taste buds during development. The proposed studies focus on mechanisms by which these two neurotrophins, BDNF and NT4, can influence various aspects of neural innervation through the same receptors, TrkB and p75. The proposed studies use cell counting, tract tracing, immunohistochemistry and scanning electron microscopy in gene knockout mice to determine when TrkB and p75 are required for specific aspects of gustatory development, including axonal extension into the tongue, target selection, and geniculate neuron/taste bud survival. Furthermore, these studies combine these anatomical approaches with sophisticated genetic tools allowing the function of single phosphorylation sites on the TrkB receptor protein to be blocked in vivo. These experiments will determine which TrkB intracellular signaling pathways are required for axonal extension into the tongue, target selection, and geniculate neuron/taste bud survival. Together these studies test the hypotheses that TrkB mediates the effects of both BDNF and NT4, but that each function of these neurotrophins requires a different intracellular signaling pathway. While p75's, more subtle role, is to modulate the regulation of gustatory development by neurotrophins. Because these experiments examine the fundamental mechanisms of how neurotrophins regulate neuronal survival and axon targeting via Trk receptors, this project has important implications for the therapeutic use of these signaling mechanisms in controlling neuron survival and axon targeting during regeneration. PUBLIC HEALTH RELEVANCE: The taste system is an ideal and commonly used system for examining axon regeneration following injury. We are examining the signaling mechanisms for two factors (neurotrophins) that influence axon targeting and neuron survival during development. By understanding of how these signaling mechanisms normally function, techniques can be developed to manipulate these important signaling factors during nerve regeneration which will improve reinnervation and function following nervous system injury.