Molecular mechanism of CPG15 mediated activity-dependent synaptic plasticity

)：皮质功能依赖于由多种细胞类型和数百万个连接突触组成的复杂神经元电路。在发育后期，未成熟的皮质网络通过一个称为突触修剪的过程逐渐优化。在此期间，神经元对外界刺激特别敏感，依赖于活动的信号通过选择性稳定或消除特定突触连接来指导电路改进。阐明依赖活性的突触选择的分子机制是理解大脑发育和可塑性这一基本方面的关键。活性调节基因是调节神经元活性对突触形成和消除的影响的主要分子。一个例子是应用可塑性基因15(Cpg15)，它编码一种附着在细胞表面的小糖基磷脂酰肌醇(GPI)连接蛋白。Cpg15参与了轴突和树突的生长以及兴奋性突触的成熟。新的初步结果显示，cpg15基因敲除减少了突触后密度蛋白95(PSD95)向新形成的锥体神经元树突棘的募集，从而降低了脊柱的稳定性。这一发现在力学上令人费解，因为cpg15是细胞外的，而PSD95是细胞内的，两种蛋白都不具有跨膜结构域。最近，对AMPA型谷氨酸受体蛋白质组的研究发现，cpg15是与AMPA受体亚单位共沉淀的蛋白质复合体的一部分。为了测试cpg15在脊柱稳定中的作用，我们的目标是研究cpg15与AMPA受体的直接相互作用，以介导PSD95重新招募到新形成的兴奋性突触。通过体外和体内相结合的方法，我们的数据可以首次以前所未有的详细信息揭示AMPAR和PSD95招募的时间和序列，并阐明控制神经网络形成和持续适应的分子信号。对cpg15基因敲除小鼠的体外和体内分析可以很容易地转化为任何神经发育或神经退行性疾病的KO模型，并提供体内成像、分子工具开发和复杂数据分析方面的关键培训，所有这些都适用于我作为独立研究员的未来工作。Nedivi博士是我的赞助人，也是突触可塑性和活体双光子成像领域的国际公认专家，他的培训非常适合拟议的项目和我在培训计划中概述的职业目标。作为麻省理工学院和波士顿充满活力的神经科学社区的活跃成员，我将帮助我与该领域的领导者和博士后研究员建立科学关系，他们将成为我未来的同事。Nedivi实验室、皮考尔学习与记忆研究所和麻省理工学院在神经科学和工程学的交界处培养了创新的工作，这非常适合我的学术成长。这种出色的博士后培训环境将有助于我作为一名独立调查员成功地开始职业生涯。

): Cortical function relies on complex neuronal circuits composed of multiple cell types and millions of connecting synapses. During late development, immature cortical networks are progressively optimized via a process known as synaptic pruning. During this period, neurons are particularly sensitive to external stimuli, and activity- dependent signals guide circuit refinement through selective stabilization or elimination of specific synaptic connections. Elucidating the molecular mechanisms underlying activity-dependent synapse selection is key to understanding this fundamental aspect of brain development and plasticity. Activity-regulated genes are prime molecular applicants for mediating the effects of neuronal activity on synapse formation and elimination. One example is applicant plasticity gene 15 (CPG15), which encodes a small glycosylphosphatidylinositol (GPI)- linked protein attached to the cell surface. CPG15 has been previously implicated in axonal and dendritic growth and the maturation of excitatory synapses. New preliminary results reveal that CPG15 knockdown reduces recruitment of the postsynaptic density protein 95 (PSD95) to newly formed dendritic spines of pyramidal neurons, thus reducing spine stabilization. This finding is mechanistically puzzling given that CPG15 is extracellular while PSD95 is intracellular, and neither protein possesses a transmembrane domain. Recently, investigation of the AMPA-type glutamate receptor proteome identified CPG15 as part of the protein complex that co-precipitates with AMPA receptor subunits. To test the role of CPG15 in spine stabilization, our goal is to investigate the effect of CPG15 direct interaction with AMPA receptors to mediate the recruitment of PSD95 to newly formed excitatory synapses. With the power of combined in vitro and in vivo approaches, our data can reveal, for the first time and in unprecedented detail, the timing and sequence of AMPAR and PSD95 recruitment and shed light onto molecular signals that control the formation and continuous adaptation of neuronal networks. The in vitro and in vivo analyses of the CPG15 knockout mouse could easily be translated to a KO model for any neurodevelopmental or neurodegenerative disorder and provide crucial training in in vivo imaging, molecular tool development, and sophisticated data analysis, all applicable to my future work as an independent researcher. Training with Dr. Nedivi, my sponsor and an internationally recognized expert in the field of synaptic plasticity and in vivo 2-photon imaging, is an ideal fit for the project proposed and for my career goals as outlined in the training plan. Being an active member of the vibrant neuroscience community at MIT and Boston, will help me establish scientific relationships with leaders in the field and postdoctoral fellows who will become my colleagues in the future. The Nedivi lab, the Picower Institute for Learning and Memory, and MIT foster innovative work at the interface of neuroscience and engineering, an ideal fit for my academic growth. This outstanding postdoctoral training environment will facilitate my success in launching a career as an independent investigator.