How do neurons in the brain decide to refine their synaptic connections in vivo?

大脑中的神经元如何决定在体内完善其突触连接？

• 批准号: 9383862
• 负责人: Hisashi Umemori
• 金额: $ 68.63万
• 依托单位: BOSTON CHILDREN'S HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-16 至 2022-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9383862
• 关键词: Alpha Cell; Autistic Disorder; Axon; Brain; CD47 gene; Cell Adhesion Molecules; Cerebral hemisphere; Complement; Cues; Data; Defect; Development; Disease; Dominant-Negative Mutation; Electrophysiology (science); Electroporation; Emotional; Etiology; Functional disorder; Gene Expression; Genetic; Goals; Hippocampus (Brain); Image; JAK2 gene; Knock-out; Knockout Mice; Limbic System; Maintenance; Mediating; Memory; Mental disorders; Microglia; Molecular; Mus; Neurons; Pathway interactions; Phagocytosis; Phosphotransferases; Physiological; Play; Population; Presynaptic Receptors; Process; Protein Tyrosine Kinase; Regulation; Role; Schizophrenia; Signal Transduction; Signaling Molecule; Social Behavior; Synapses; System; Testing; Time; Work; cingulate cortex; design; gene complementation; in utero; in vivo; insight; mutant; nervous system disorder; neural circuit; neuropsychiatric disorder; neurotransmitter release; novel; optogenetics; overexpression; postsynaptic neurons; prevent; relating to nervous system; response; transgene expression

Formation of functional neural circuits is critical for proper functioning of the brain. To establish the most efficient synaptic circuits, synaptic connections must be refined by neural activity during development. In this proposal, we will determine the molecules and manner by which functional circuits are established by neural activity, focusing on the limbic system (including the hippocampus and cingulate cortex), which is implicated in emotional processing, memory formation and social behavior. Using a mouse genetic system in which restricted populations of hippocampal neurons can be conditionally inactivated, we found that hippocampal axons are refined through activity-dependent competition, where active neuronal connections stay (maintained) while inactive ones leave (eliminated). We further found that a cell adhesion molecule SIRP from postsynaptic neurons stabilizes active synapses through its presynaptic receptor CD47, serving as a "Stay" signal. To identify the signaling molecules that play critical roles in inactive axon elimination ("Go" signal), we generated a new system in which neural activity and gene expression can be conditionally controlled in vivo, using in utero electroporation. When neurotransmitter release is blocked in a subset of neurons in the cingulate cortex, their callosal projections (the major connections between the cerebral hemispheres) are eliminated during development. Using this system, we screened for signaling molecules that are upregulated in inactive neurons right before their axons start to leave and identified the Ca2+-dependent tyrosine kinase Pyk2. Inactive axons were not eliminated when a kinase-dead mutant of Pyk2 was expressed, indicating that Pyk2 activity is necessary for inactive axons to leave. We further identified that a Pyk2-interacting kinase, JAK2, is also necessary for inactive axon elimination. Consistently, Pyk2 and JAK2 are activated in inactive neurons. Finally, we found that overexpression of Pyk2 or JAK2 induces axonal elimination even when axons are active. We propose that the Pyk2-JAK2 pathway is the "Go" signal and serves as the determinant of axon refinement. To further characterize this pathway and to understand how the "Go" and "Stay" pathways regulate activity- dependent axon/synapse refinement, we propose to: Aim 1: Investigate the role of Pyk2 and JAK2 for axon/synapse refinement in physiological conditions. Aim 2: Analyze the electrophysiological consequences of Pyk2/JAK2 inactivation during synapse refinement using conditional KO mice. Aim 3: Examine whether the Pyk2-JAK2 pathway provides cues for microglial clearance of inactive axons in vivo. Aim 4: Investigate the interaction between the Stay (SIRP-CD47) and Go (Pyk2-JAK2) pathways in axon/synapse refinement in vivo. Our project will molecularly delineate how neurons decide to establish functional synaptic connections in the mammalian brain. Pyk2 and JAK2 are associated with various neuropsychiatric disorders. Many forms of mental illness including autism and schizophrenia are associated with abnormal alterations in the limbic circuitry. Thus, our studies should also yield novel insights into the etiology and treatment of such disorders.

功能性神经回路的形成对于大脑的正常功能至关重要。建立最大的 有效的合成回路，突触连接必须通过发育过程中的神经活动来完善。在这个 提案，我们将确定通过神经建立功能电路的分子和方式 活动，专注于边缘系统（包括海马和扣带皮质），该活动已在 情绪处理，记忆形成和社会行为。使用小鼠遗传系统 海马神经元的受限种群可能有条件地灭活，我们发现海马 轴突是通过活动依赖性竞争来完善的，在该竞争中，活跃的神经元连接停留（维持） 当不活动的人离开时（被淘汰）。我们进一步发现细胞粘合分子sirp 突触后神经元通过其突触前受体CD47稳定活性突触，作为“留下” 信号。确定在消除无效轴突中起关键作用的信号传导分子（“ GO”信号），我们 产生了一个新系统，其中神经活动和基因表达可以在体内有条件地控制， 在子宫电穿孔中使用。当神经递质释放被阻塞在扣带中的神经元中 皮层，他们的callosal项目（大脑半球之间的主要连接）被消除 在开发过程中。使用此系统，我们筛选了在非活动中上调的信号分子 神经元在轴突开始离开并鉴定出Ca2+依赖性酪氨酸激酶Pyk2。不活动 当表达Pyk2的激酶死亡突变体时，未消除轴突，表明Pyk2活性为 不活动轴突离开所必需的。我们进一步确定PYK2相互作用激酶JAK2也是 消除无活性轴突所必需的。一致地，PYK2和JAK2在非活性神经元中被激活。最后， 我们发现，即使轴突活跃，PYK2或JAK2的过表达也会诱导轴突消除。我们 建议PYK2-JAK2途径是“ GO”信号，并作为轴突改进的确定。到 进一步描述了这一途径，并了解“ go”和“ arter”途径如何调节活动 - 依赖的轴突/突触改进，我们建议：目标1：调查PYK2和JAK2的作用 轴突/突触在身体条件下的细化。目标2：分析电生理后果 PYK2/JAK2使用条件KO小鼠在突触细化过程中失活。目标3：检查是否 PYK2-JAK2途径为体内非活性轴突的小胶质清除提供了线索。目标4：调查 轴突/突触细化中的住宿（sirp-cd47）与GO（pyk2-jak2）途径之间的相互作用 体内。我们的项目将分子描述神经元如何决定建立功能突触连接 哺乳动物的大脑。 PYK2和JAK2与各种神经精神疾病有关。多种形式 包括自闭症和精神分裂症在内的精神疾病与边缘的异常改变有关 电路。这也是我们的研究还应对此类疾病的病因和治疗产生新的见解。