Mechanisms of axon guidance during development

发育过程中轴突引导的机制

• 批准号: 10263026
• 负责人: edward giniger
• 金额: $ 91.39万
• 依托单位: NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10263026
• 关键词: Actins; Animals; Axon; Back; Biochemistry; Biological Assay; Biophysics; Cell physiology; Computer Simulation; Cues; Development; Drosophila genus; Epithelial; Epithelium; Filopodia; Genetic; Growth; Growth Cones; Image; Image Analysis; Individual; Length; Literature; Maintenance; Methods; Microscopy; Modeling; Molecular; Monitor; Morphogenesis; Morphology; Motion; Nerve; Neurodegenerative Disorders; Neurons; Output; Paper; Pathway interactions; Pattern; Phenotype; Plant Roots; Polymerase; Production; Proteins; Proto-Oncogene Proteins c-abl; Regulation; Reporting; Resolution; Role; Sampling; Signal Pathway; Signal Transduction; Structure; Surface; Testing; Time; Vertebrates; axon growth; axon guidance; cell motility; experimental study; genetic manipulation; imaging modality; in vivo; molecular modeling; neural circuit; notch protein; novel; polymerization; receptor; temporal measurement

Abl tyrosine kinase is a master regulator of axon growth and guidance throughout the animal kingdom. It is a key regulator of actin structure and dynamics, and a key point of integration of signals from many guidance cue receptors in axonal growth cones. As we reported in two back-to-back papers this year, we can now trace the mechanism by which Abl controls actin structure, and thereby growth cone motility, all the way back to its roots in actin biophysics. In brief, our previous genetics and biochemistry showed that Abl controls the ratio of linear actin polymerization to actin branching (through its antagonistic regulation of the actin polymerase, Enabled, and of the Rac GEF, Trio). Now, by performing high-resolution, quantitative, live imaging of actin in a growth cone advancing in vivo, we have revealed the significance of this regulation. The intermediate level of actin branching maintained by Abl allows a mass of actin in the core of the growth cone to oscillate in length, but only within narrow limits consistent with maintenance of order in the actin distribution. The role of guidance cue receptors is to locally favor actin extension or branching (respectively), which we show introduces a spatial bias to the oscillations of actin, and thus causes the actin mass to advance along a predictable trajectory. Motion of the actin, in turn, favors filopodial assembly in places where the axon is destined to extend, and disassembly of filopodia in places the growth cone is destined to vacate. Over time, this mechanism produces net motion of the dynamic core of the growth cone along the trajectory defined by guidance cues. This molecular model is entirely without precedent in the literature of axon growth and guidance, but in addition to explaining our own observations, it can account for the effects of a wide range of actin modulatory proteins, and also provides simple explanations for numerous longstanding mysteries in the mechanism of axon guidance. Ongoing experiments are performing further tests of our model, both by imaging the phenotypes observed upon genetic manipulation of other Abl pathway components, and by generating detailed computational simulations of the consequences of altering various parameters of actin dynamics. In addition, together with collaborators we are (1) developing novel methods of advanced microscopy that increase the spatial and temporal resolution with which we can monitor growth cone structure and dynamics in live samples, (2) developing novel methods of image analysis to automate tracing of axon images, and (3) investigating the implications that uncontrolled excursions of Abl activity have for the production and maintenance of neural circuits in the context of neurodegenerative disease.

ABL酪氨酸激酶是整个动物王国轴突生长和指导的主要调节剂。它是肌动蛋白结构和动力学的关键调节剂，也是轴突生长锥中许多引导提示受体集成信号的关键点。正如我们在今年的两篇背靠背论文中报道的那样，我们现在可以追踪ABL控制肌动蛋白结构的机制，从而可以追溯到生长锥运动，一直回到其在肌动蛋白生物物理学中的根源。简而言之，我们以前的遗传学和生物化学表明，ABL控制线性肌动蛋白聚合与肌动蛋白分支的比率（通过其对肌动蛋白聚合酶的拮抗作用，启用肌动蛋白聚合酶，以及RAC GEF，Trio）。现在，通过在体内前进的生长锥中肌动蛋白的高分辨率，定量，实时成像，我们揭示了这种调节的意义。 ABL维持的肌动蛋白分支的中间水平使生长锥核心的大量肌动蛋白的长度振荡，但仅在狭窄的限制内与肌动蛋白分布中的顺序保持一致。引导提示受体的作用是分别在局部偏爱肌动蛋白的扩展或分支，我们表明，这引入了肌动蛋白振荡的空间偏置，因此使肌动蛋白质量沿着可预测的轨迹前进。反过来，肌动蛋白的运动有利于轴突注定要延伸的地方，而在生长锥体注定要撤离的地方的丝状运动。随着时间的流逝，这种机制会沿指导线索定义的轨迹产生生长锥动力核心的净运动。该分子模型在轴突生长和指导的文献中完全没有先例，但是除了解释我们自己的观察结果外，它还可以解释广泛的肌动蛋白调节蛋白的影响，并且还为轴突指导机制中的许多长期谜团提供了简单的解释。 正在进行的实验正在对我们的模型进行进一步的测试，这是通过对其他ABL途径组件的基因操纵时观察到的表型的成像，并通过生成改变肌动蛋白动力学各种参数的后果的详细计算模拟。 In addition, together with collaborators we are (1) developing novel methods of advanced microscopy that increase the spatial and temporal resolution with which we can monitor growth cone structure and dynamics in live samples, (2) developing novel methods of image analysis to automate tracing of axon images, and (3) investigating the implications that uncontrolled excursions of Abl activity have for the production and maintenance of neural circuits in the context of neurodegenerative 疾病。