Generation of neuronal diversity by temporal mechanisms in the developing spinal cord

在脊椎动物的脊髓中，不同类别的神经元形成了神经元回路，允许我们移动和感知我们的环境。在发育过程中，这些不同类别的神经元是对空间线索的反应而产生的，空间线索沿着胚胎神经管的背腹轴排列。然而，这种细分不足以解释脊髓中观察到的神经元的复杂性-相反，每种神经元类别可以根据分子和功能特征进一步划分为不同的亚型。协调这些神经元亚型的规范并将其正确整合到具有特定功能的电路中的信号和基因调控网络在很大程度上仍不清楚。我最近的工作发现了脊髓中神经元亚型规范的一个时间维度，这取决于早期、中期或晚出生神经元特有的转录因子(TF)群。在这里，我认为这个时间性TF程序是必要的，并与定义不同神经元类别的身份的空间TF一起工作，以建立神经元多样性和脊髓中神经元连接的正确模式。为了验证这一假设，我计划将体外干细胞分化与基因组分析、体内遗传追踪和功能扰动方法相结合。这一建议的主要目的是：1.描述控制脊髓神经元时间分层的信号和基因调控网络；2.研究时空转录因子共同建立神经元亚型特异性基因表达模式的分子逻辑；3.描述胚胎中暂时转录因子的表达如何影响成年脊髓神经元的多样性和连通性。我的提议的预期结果将提供一个详细的理解，即空间和时间模式系统如何联合指定神经元多样性，并为小鼠脊髓中神经元回路的正确形成奠定基础。最终，这种对细胞命运和连通性的机械性理解将为开发新的疾病模型和治疗神经退行性运动障碍和脊柱损伤奠定基础。

In the vertebrate spinal cord different classes of neurons form the neuronal circuits that allow us to move and perceive our environment. During development, these distinct classes of neurons are generated in response to spatial cues that pattern the embryonic neural tube along its dorsal-ventral axis. This subdivision however is not sufficient to account for the complexity of neurons observed in the spinal cord - instead each neuronal class can be further divided into distinct subtypes based on molecular and functional characteristics. The signals and gene regulatory networks that orchestrate the specification of these neuronal subtypes and underlie their correct incorporation into circuits with specific functions are still largely unclear.My recent work uncovered a temporal dimension to neuronal subtype specification in the spinal cord, which depends on cohorts of transcription factors (TFs) that are specific for early, intermediate, or late-born neurons. Here, I propose that this temporal TF program is essential and works in combination with the spatial TFs that define the identity of the distinct neuronal classes to establish neuronal diversity and the correct patterns of neuronal connectivity in the spinal cord. To test this hypothesis, I plan to combine in vitro stem cell differentiation with genomic assays, in vivo genetic tracing and functional perturbation approaches. The key aims of this proposal are to:1. Characterize the signals and gene regulatory networks orchestrating the temporal stratification of neurons in the spinal cord,2. Investigate the molecular logic by which spatial and temporal TFs jointly establish neuronal subtype-specific patterns of gene Expression, 3. Delineate how temporal TF expression in the embryo underlies neuronal diversity and connectivity in the adult spinal cord. The expected results of my proposal will provide a detailed understanding how spatial and temporal patterning systems jointly specify neuronal diversity and underlie the correct formation of neuronal circuitry in the mouse spinal cord. Ultimately, such mechanistic understanding of cell fate and connectivity will underpin the development of novel disease models and therapies for neurodegenerative movement disorders and spinal injuries.