Disruption of spinal circuit early development after silencing En1/Foxp2 interneurons

摘要 节律性自发活动发作，称为自发网络活动(SNA)，发生在 第一个突触连接建立时的中枢神经系统(CNS)。在此期间 早期的连接体是通过这些早期连接的后期成熟和精炼而形成的 具有成熟功能的成人突触回路出现。因此，这一早期的发展首先 当遗传或环境因素破坏SNA时，连通性对后来的成人功能网络至关重要 由此产生的成人神经回路是畸形的和功能失调的。例如，SNA机制在 胎儿酒精谱障碍会导致海马区神经回路的异常发育。同样， 许多神经发育障碍，如自闭症谱系中的那些，表现出与运动障碍相关的 刚出生的。SNA在一些中枢神经系统区域(视网膜、视觉通路、海马体)和 涉及的确切细胞相互作用、SNA网络的组装和分解及其意义 对于正确连接的成人回路的成熟是众所周知的。令人惊讶的是，人们对SNA知之甚少 脊髓运动回路，尽管这是研究SNA机制的早期模型。目前， 关于参与SNA脊髓网络的神经元的确切类型，文献给出了相互矛盾的结论 SNA对脊髓神经回路发育的意义尚不清楚。这些是我们的关键差距 在病因不明的新生儿中有大量运动综合征的知识。这种探索性的 这一建议源于一项偶然发现的严重共济失调和肢体不协调的小鼠幼鼠 表达转录因子Engraile1(EN1)和叉头盒P2的脊髓抑制中间神经元 (Foxp2)在整个胚胎发育过程中长期沉默。这表明大脑中存在严重的功能障碍 成人控制肢体的脊髓运动回路和初步结果表明早期SNA在 胚胎。因此，这种遗传模型可以提供一个新的切入点，以询问细胞机制在 脊髓SNA的网络驱动(目标1)以及SNA功能障碍对后者的影响 组织关键的脊髓马达电路(目标2)。对于第二个目标，我们将使用最基本的 由伸肌和屈肌运动神经元组成的运动回路，Ia相互抑制的中间神经元(许多 它们是EN1-Foxp2)和Renshaw细胞。该电路显示了特定的组织结构 已经被广泛研究多年的联系，因此提供了一个明确的模型 测试SNA在建立特定连通性方面的作用。我们假设它的基本组织是 被异常的早期SNA干扰，因为参与SNA网络的主要中间神经元(Renshaw 细胞和Ia抑制中间神经元)也参与了这一成人环路。我们希望能拿出第一批证据 这一模型的实用性，这可能会导致未来的提案侧重于更彻底的分析 细胞机制，以更好地了解一些新生儿运动综合征的可能来源。

ABSTRACT Rhythmic spontaneous activity episodes, known as spontaneous network activity (SNA), occur throughout the central nervous system (CNS) at the time in which the first synaptic connections are established. During this time an early connectome is form and it is through later maturation and refinement of these early connections that adult synaptic circuitries with mature functionalities emerge. Therefore, the early development of this first connectivity is critical for later adult functional networks and when genetic or environmental factors disrupt SNA the resulting adult circuits are malformed and dysfunctional. For example, SNA mechanisms are disturbed in fetal alcohol spectrum disorders resulting in anomalous circuit development in the hippocampus. Similarly, many neurodevelopmental disorders like those in the autism spectrum display associated motor deficits in the newborn. SNA has been intensely studied in some CNS regions (retina, visual pathways, hippocampus) and the exact cellular interactions involved, the assembly and disassembly of the SNA network and its significance for maturation of correctly connected adult circuits are well known. Surprisingly, less is known about SNA in spinal cord motor circuits, despite this being an early model for the study of SNA mechanisms. Currently, the literature offers contradictory conclusions on the exact types of neurons involved in the SNA spinal network and the significance of SNA for spinal circuit development remains unexplored. These are critical gaps in our knowledge given the large number of motor syndromes in newborns with unknown etiology. This exploratory proposal stems from the serendipitous finding of profound ataxia and limb discoordination in mouse pups in which spinal inhibitory interneurons expressing the transcription factors engrailed 1 (En1) and forkhead box P2 (Foxp2) were chronically silenced throughout embryonic development. This suggests major dysfunction in adult spinal motor circuits controlling limbs and preliminary results suggest disruption of early SNA in the embryo. This genetic model could therefore offer a new entry point to interrogate cellular mechanisms in the network driving SNA in the spinal cord (Aim 1) and the consequences of SNA dysfunction for the later organization of key spinal motor circuits (Aim 2). For the second aim we will use as model the most basic of motor circuits composed by extensor and flexor motoneurons, Ia reciprocal inhibitory interneurons (many of which are En1-Foxp2) and Renshaw cells. This circuit displays a well-defined organization of specific connections that has been extensively studied for many years and therefore offers an unambiguous model to test the role of SNA in establishing specific connectivity. We hypothesize that its basic organization will be disrupted by anomalous early SNA given that the principal interneurons involved in the SNA network (Renshaw cells and Ia inhibitory interneurons) are also participants in this adult circuit. We hope to generate first evidence for the usefulness of this model, and this could lead to future proposals focusing on more thorough analyses of cellular mechanisms to better understand possible origins of some newborn motor syndromes.