How FGF Receptor Signaling Drives Homeostatic Neuroplasticity

细胞能够监测环境并调整其结构和功能，以便最好地维持支持其存在的所有生理属性(动态平衡)，这是所有生物系统的基本属性。动物神经系统中的细胞也不例外；它们需要不断地改变它们与大脑回路中其他细胞(突触)的信号连接，以响应正常环境变化和毒素等生理挑战，从而使大脑功能保持在生理上合适的范围内。然而，我们目前对影响大脑回路的细胞间通讯的动态平衡调节的基本生物学机制了解很少。该项目使用果蝇黑腹果蝇特有的遗传工具，结合电子记录、生化技术、显微镜突触成像和药物操作，了解果蝇肌肉中一种新发现的分子因子(称为无心/成纤维细胞生长因子受体酪氨酸激酶[HTL/FGFR])如何稳态控制导致这些肌肉收缩的运动神经细胞的活动水平。这项研究将准确地阐明是什么导致这种肌肉特异性分子变得具有生物学活性，以及它如何在这个回路中向后发出信号来影响控制肌肉的神经细胞的活动。这项研究计划还整合了多层次的各种教育活动，包括：1)与附近主要本科院校的教员进行持续的研究和教育合作；2)由首席研究员(PI)设计每年三天的夏季研讨会，以扩大PUI的神经科学研究资源；3)通过参观PI的实验室和PI及其研究生的学校访问，在爱荷华州开展K-12 STEM公共宣传；4)为本科生提供长期和短期的研究机会，包括参加爱荷华州大学SROP/McNair学者计划等项目的未被充分代表的少数族裔学生。稳态形式的突触可塑性指示突触和回路维持正常的输出范围，尽管他们一生可能会经历扰动。一个重要的未知因素是突触功能的动态平衡调节的分子基础。PI的实验室利用果蝇的黑腹神经肌肉接头(NMJ)作为模型来解决这个问题。在NMJ，受损的肌肉兴奋性通过抵消突触前神经递质释放的平衡增加而得到纠正。肌肉是如何传达增加神经递质释放的需求的，目前还不清楚。在哺乳动物的中枢和外周神经系统中也发现了类似的调节形式，但它们也不清楚。利用果蝇遗传学和电生理学，PI的实验室已经识别出新的分子，这些分子可以解释控制突触内稳态的信号事件。一个分子构成了这个项目的基础，一种成纤维细胞生长因子受体(FGFR)酪氨酸激酶。来自实验室的数据支持FGFR在肌肉中的特定作用。中心假设是，肌源性FGFR活动通过调节顺行(神经到肌肉)和逆行(肌肉到神经)细胞-细胞信号来调节突触强度。有两个具体目标。目标1将确定在执行体内平衡补偿过程中由FGFR触发的肌肉中的分子信号。这个目标包括识别直接目标的实验，以及由这些目标激活的逆行信号(S)。目标2将确定动态平衡FGFR信号是如何被激活和调节的。这两个目标都将结合电生理学、生物化学、突触成像和药理学。

The ability of cells to monitor the environment and adjust their structure and function in order to best maintain all of the physiological properties that support their existence (homeostasis) is a fundamental property of all biological systems. Cells in animal nervous systems are no exception; they need to constantly change their signaling connections with other cells (synapses) in brain circuits in response to both normal environmental changes and to physiological challenges such as toxins, so that brain function can be homeostatically maintained within a physiologically appropriate range. However, we currently have a very poor understanding of the basic biological mechanisms underlying the homeostatic regulation of cell-to-cell communication that affects brain circuitry. This project uses genetic tools uniquely available in the fruitfly Drosophila melanogaster together with electrical recordings, biochemical techniques, synapse imaging by microscopy, and drug manipulations to understand how a newly-identified molecular factor in fruitfly muscles (called Heartless/Fibroblast Growth Factor Receptor tyrosine kinase [Htl/FGFR]) homeostatically controls the level of activity in the motor nerve cells that cause these same muscles to contract. This research will precisely elucidate what causes this muscle-specific molecule to become biologically active, and how it signals its activity backwards in this circuit to affect the activity of the nerve cells that control muscles. This research plan also integrates a variety of educational activities at multiple levels, including: 1) an ongoing research and educational collaboration with a faculty member at a nearby primarily undergraduate institution (PUI); 2) a yearly three-day summer workshop designed by the principal investigator (PI) to expand neuroscience research resources for PUIs; 3) K-12 STEM public outreach in Iowa through tours of the PI's lab and school visits by the PI and his graduate students; and 4) long- and short-term research opportunities for undergraduates, including underrepresented minority students enrolled in programs such as the SROP/McNair Scholars Program at the University of Iowa.Homeostatic forms of synaptic plasticity direct synapses and circuits to maintain normal ranges of output, despite the perturbations they may experience throughout life. A significant unknown is the molecular underpinning of the homeostatic regulation of synapse function. The PI's lab addresses this problem utilizing the Drosophila melanogaster neuromuscular junction (NMJ) as a model. At the NMJ, impaired muscle excitability is corrected by offsetting, homeostatic increases in presynaptic neurotransmitter release. Precisely how the muscle communicates a need for increased neurotransmitter release is not understood. Similar forms of regulation have been found in the mammalian central and peripheral nervous systems, and they are not understood either. Using Drosophila genetics and electrophysiology, the PI's lab has identified new molecules that illuminate signaling events controlling synaptic homeostasis. One molecule forms the basis for this project, a Fibroblast Growth Factor Receptor (FGFR) tyrosine kinase. Data from the lab support muscle-specific roles for FGFR. The central hypothesis is that muscle-derived FGFR activity tunes synaptic strength by mediating both anterograde (nerve-to-muscle) and retrograde (muscle-to-nerve) cell-cell signals. There are two specific aims. Aim 1 will determine the molecular signals in the muscle triggered by FGFR during the execution of homeostatic compensation. This aim includes experiments that will identify direct targets, as well as the retrograde signal(s) activated by those targets. Aim 2 will determine how homeostatic FGFR signaling is activated and regulated. Both aims will employ a combination of electrophysiology, biochemistry, synapse imaging, and pharmacology.