Regulation of axonal outgrowth in the developing spinal cord

脊髓发育中轴突生长的调节

• 批准号: 8132444
• 负责人: SAMANTHA J BUTLER
• 金额: $ 34.73万
• 依托单位: UNIVERSITY OF SOUTHERN CALIFORNIA
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-30 至 2013-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8132444
• 关键词: Actins; Address; Axon; Binding; Biochemical; Biological Assay; Bone Morphogenetic Proteins; Cells; Competence; Cues; Defect; Development; Disease; Dorsal; Electroporation; Embryo; Embryonic Development; Environment; Erinaceidae; Event; Floor; Freezing; Future; Genetic; Goals; Growth; Growth Cones; Health; In Vitro; Injury; Ligands; Mediating; Methods; Molecular; Mus; Natural regeneration; Neuraxis; Neurons; Pathway interactions; Perception; Phosphorylation; Phosphotransferases; Process; Protein Binding; Protein C; Recording of previous events; Regulation; Research; Role; Route; Series; Signal Transduction; Source; Specific qualifier value; Speed; Spinal Cord; Stereotyping; Synapses; Testing; Time; Tissue Grafts; To specify; Translating; Ventricular; Work; actin depolymerizing factor; axon growth; axon guidance; bone morphogenetic protein receptor type II; cofilin; in vitro Assay; in vivo; morphogens; novel; polymerization; repaired; response

DESCRIPTION (provided by applicant): Our research aim is to understand how neuronal networks are established during development with the long- term goal of determining how this process can be recapitulated to repair circuits damaged after injury or disease. To extend towards its target, an axon must process directional information in the embryonic environment, reach signals at the correct time in development and be competent to interpret the cue in the correct context. However, although the mechanisms that control directionality for axons have been extensively described, it remains unresolved how either the growth rate or competence of growth cones is regulated. We will examine these questions by determining how Bone Morphogenetic Proteins (BMPs) guide commissural (C) axons in the developing spinal cord. In our previous work, we identified a new class of guidance signals: morphogens that also induce specific cell fates. We showed that BMPs, secreted from the roof plate, provide directional signals for C axons by repelling their initial projections away from the dorsal midline. We have now identified two additional critical roles for BMP signaling in C axon guidance: regulating the rate of C axonal outgrowth and directing the responsiveness of C axons to subsequent guidance cues. To investigate these previously unrecognized activities, we will define the mechanism by which BMPs inhibit the rate of C axon outgrowth in Aim 1 and determine the developmental consequences of unregulated axon outgrowth in Aim 2. In Aim 3, we will assess an integrative mechanism regulated by BMP signaling that permits a C growth cone to change its response to signals over time. By advancing our understanding of the basic mechanisms of axon guidance during development, these studies will facilitate the regeneration of neuronal circuits in the CNS. Approach: We will use convergent in vitro and in vivo methods in these studies, combining biochemical and tissue grafting assays with mouse genetics and chick in ovo electroporation, in the following aims: Aim 1: Determine how BMP signaling regulates Limk1/cofilin to control the rate of C axon outgrowth. Hypothesis: BMPs regulate the rate of C axon outgrowth by upregulating Lim kinase 1 (Limk1) in C neurons and thereby inactivating cofilin, a direct regulator of actin polymerization. Aim 2. Determine the mechanism by which axon extension speed regulates the recognition of guidance cues Hypothesis: The timing of axon outgrowth determines the response of an axon to guidance cues. Guidance errors occur if the rate of C axon outgrowth is increased because either the response of accelerated C growth cones is intrinsically altered to guidance cues, or the extrinsic environment is not in place to guide them. Aim 3. Determine how BMP signaling regulates the response of C axons to Netrin1 Hypothesis: The activation of BMP signaling in C growth cones directs C axons to respond to Netrin1 as a repellent rather than an attractant. Thus, axons accumulate a history of signaling events that informs future guidance decisions, thereby permitting a few guidance cues to generate multiple distinct axon trajectories. PUBLIC HEALTH RELEVANCE: We are examining the mechanisms by which neurons send out projections, called axons, towards their synaptic targets during embryonic development. We have identified two previously undescribed processes within, or intrinsic to, neurons that control a) the rate at which axons grow and b) how axons regulate their response to signals in the embryonic environment. The identification of intrinsic regulators of axon outgrowth will be a significant advance for studies trying to re-establish axonal circuits after traumatic injury, given that regenerating axons in the central nervous system are unable to overcome the effect of inhibitory signals from the environment.

描述（由申请人提供）：我们的研究目的是了解神经元网络是如何在发育过程中建立的，长期目标是确定如何重现这一过程以修复损伤或疾病后受损的回路。为了向目标延伸，轴突必须在胚胎环境中处理方向信息，在发育的正确时间到达信号，并能够在正确的环境中解释线索。然而，尽管控制轴突方向性的机制已被广泛描述，但生长锥的生长速率或能力如何被调节仍未解决。我们将通过确定骨形态发生蛋白（BMP）如何指导发育中的脊髓中的连合（C）轴突来研究这些问题。在我们以前的工作中，我们确定了一类新的指导信号：也诱导特定细胞命运的形态发生素。我们发现，骨形态发生蛋白，分泌的顶板，提供定向信号的C轴突排斥其最初的预测远离背中线。我们现在已经确定了BMP信号传导在C轴突指导中的两个额外的关键作用：调节C轴突生长的速率和指导C轴突对随后的指导线索的反应。为了研究这些以前未被认识到的活动，我们将定义骨形态发生蛋白抑制目标1中C轴突生长速率的机制，并确定目标2中不受调节的轴突生长的发育后果。在目标3中，我们将评估由BMP信号调节的整合机制，该机制允许C生长锥随时间改变其对信号的响应。通过推进我们对发育过程中轴突引导的基本机制的理解，这些研究将促进CNS中神经元回路的再生。方法：我们将在这些研究中使用收敛的体外和体内方法，结合生物化学和组织移植试验与小鼠遗传学和鸡卵电穿孔，在以下目标：目的1：确定BMP信号如何调节Limk 1/cofilin控制C轴突生长的速率。假设：BMP通过上调C神经元中的Lim激酶1（Limk 1）来调节C轴突生长的速率，从而使cofilin（肌动蛋白聚合的直接调节剂）失活。目标2.确定轴突延伸速度调节对引导线索识别的机制假设：轴突生长的时间决定了轴突对引导线索的反应。如果C轴突生长的速率增加，则会发生指导错误，因为加速的C生长锥的反应本质上改变了对指导线索的反应，或者外部环境不适合指导它们。目标3.确定BMP信号如何调节C轴突对Netrin 1的反应假设：C生长锥中BMP信号的激活引导C轴突对Netrin 1作为排斥剂而不是引诱剂作出反应。因此，轴突积累了一个历史的信号事件，通知未来的指导决策，从而允许一些指导线索，以产生多个不同的轴突轨迹。公共卫生关系：我们正在研究神经元在胚胎发育过程中向其突触靶点发出投射（称为轴突）的机制。我们已经确定了两个以前未描述的过程，或内在的，神经元控制a）轴突生长的速度和B）轴突如何调节它们对胚胎环境中信号的反应。轴突生长的内在调节剂的鉴定将是创伤性损伤后试图重建轴突回路的研究的一个重大进展，因为中枢神经系统中再生的轴突无法克服来自环境的抑制信号的影响。