Signaling Pathways Regulating Synaptic Vesicle Dynamics

神经元之间的通信主要是通过分泌化学神经递质来影响相邻细胞的电或生化活动。这些神经递质储存在被称为突触小泡的小器官中，这些小泡定位于突触前神经末梢。为了分泌神经递质，突触小泡必须与神经末梢的表面膜融合，从而允许神经递质扩散到附近的靶神经元。这种严格控制的融合过程是神经元间通讯的基础事件。最近的研究表明，囊泡融合是一种与与活动区对接的突触小泡数量有关的低概率事件，活动区是发生融合的部位。在具有融合能力的小泡和大多数保留的小泡之间存在着动态平衡；这种平衡是以钙离子依赖的方式调节的。这些依赖于钙离子的变化在大脑中的分子基础还不完全清楚，部分原因是数十亿个显微神经末梢分布在大脑各处，使得很难或不可能在一个完整的准备中同步神经末梢的活动。特纳博士提出的工作旨在研究使用突触小体调节突触囊泡动力学的信号通路。突触小体是组成相对统一的孤立神经末梢的修复。特纳博士的实验室将使用突触体来测量特定信号通路活动的生化变化，这些信号通路与调节突触小泡成熟有关，包括钙调节的激酶和已知的非单体GTP结合。同时，这些信号通路的相关性将通过测量更完整的准备材料中突触传递的强度来评估，该准备材料是从小脑获得的急性脑片。在这种准备材料中发现的与浦肯野细胞突触平行的纤维是一种特征良好的兴奋性突触，应该代表大脑所有部分发现的兴奋性突触。同时测量神经递质释放和伴随的胞浆信号通路的变化，将有助于更详细地理解突触强度依赖于钙的变化的机制，这些变化对大脑中的神经元间信号非常重要。这项工作的影响将广泛延伸到整个神经科学，因为突触传递在大脑信息处理中的基本重要性，包括感觉接收、运动控制、注意力和决策以及学习和记忆。此外，该项目将有助于启动一名年轻调查员的独立职业生涯。

Neurons communicate with one and other primarily by secreting chemicalneurotransmitters that influence the electrical or biochemical activities ofneighboring cells. These neurotransmitters are stored in small organellescalled synaptic vesicles that are localized to presynaptic nerve endings. Inorder for neurotransmitter to be secreted, a synaptic vesicle must fuse with thesurface membrane at the nerve terminal, which allows neurotransmitter to diffuseto the nearby target neurons. This tightly regulated fusion process is thefundamental event in interneuronal communication. Recent work has revealed thatvesicle fusion is a low probability event related to the number of synapticvesicles docked with the active zone, the site at which fusion occurs. A dynamicequilibrium exists between vesicles that are fusion-competent and the majorityof vesicles that are held in reserve; this equilibrium is regulated in aCa2+-dependent manner. The molecular basis for these Ca2+-dependent changes inthe brain is incompletely understood, in part because billions of microscopicnerve terminals are distributed throughout the brain, making it difficult ofimpossible to synchronize the activity of the nerve terminals in an intactpreparation. Work proposed by Dr. turner is designed to study thesignaling pathways that regulate synaptic vesicle dynamics using synaptosomes, apreparation of isolated nerve terminals that is relatively uniform incomposition. Dr. Turner's laboratory will use synaptosomes to measure biochemical changes inthe activities of specific signaling pathways that have been implicated inregulating synaptic vesicle maturation, including Ca2+-regulated kinases and amonomeric GTP-binding known as Ral. In parallel, the relevanceof these signaling pathways will be evaluatued by measuring the strength of synaptic transmission in a more intact preparation, the acute brain slice obtained from cerebellum.The parallel fiber to Purkinje cell synapse found in this preparation is a well-characterized excitatory synapse that should be representative ofexcitatory synapses found in all parts of the brain. Simultaneous measurementsof neurotransmitter release and the attendant changes in cytoplasmic signalingpathways will advance a more detailed understanding of the mechanisms that underlie Ca2+-dependent changes in synaptic strength important to interneuronal signaling in the brain. The impact of this work will extend broadly throughout neuroscience because of the fundamental importance of synaptic transmission in information processing by the brain, for features including sensory reception, motor control, attention and decision, and learning and memory. In addition, this project will help launch the independent career of a young investigator.