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），发生在整个 在第一次建立突触连接时，中枢神经系统（CNS）。在此 一个早期的连接体形成的时间，是通过这些早期连接的后期成熟和完善 成熟功能的成年突触回路出现。因此，早期开发这一第一 当遗传或环境因素破坏SNA时，连通性对成年后的功能网络至关重要 所产生的成人电路是畸形的和功能失调的。例如，国民账户体系机制受到干扰， 胎儿酒精谱系障碍导致海马体异常回路发育。同样地， 许多神经发育障碍，如自闭症谱系中的神经发育障碍， 新生儿SNA已经在一些CNS区域（视网膜、视觉通路、海马）中被深入研究， 涉及的确切的细胞相互作用，SNA网络的组装和拆卸及其意义 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， 脊髓运动回路，尽管这是SNA机制研究的早期模型。目前 关于SNA脊髓网络中涉及的神经元的确切类型，文献提供了相互矛盾的结论 SNA对脊髓神经回路发育的意义尚不清楚。这些都是我们的关键差距 鉴于大量新生儿运动综合征病因不明，这项探索性 这项提议源于一个偶然的发现，即在老鼠幼崽中发现了严重的共济失调和肢体不协调， 脊髓抑制性中间神经元表达转录因子enrailed 1（En 1）和forkhead box P2， Foxp 2基因在胚胎发育过程中长期沉默。这表明， 控制四肢的成人脊髓运动回路，初步结果表明， 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， 在脊髓中驱动SNA的网络（目的1）以及SNA功能障碍对脊髓的影响 关键脊髓运动回路的组织（目标2）。对于第二个目标，我们将使用最基本的模型 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En 1-Foxp 2）和Renshaw细胞。该电路显示了一个明确的组织， 多年来已被广泛研究的连接，因此提供了一个明确的模型， 测试SNA在建立具体连接方面的作用。我们假设它的基本组织将是 由于SNA网络中涉及的主要中间神经元（Renshaw）， 细胞和Ia抑制性中间神经元）也参与该成人回路。我们希望能找到第一手证据 这可能导致今后的建议侧重于更透彻地分析 细胞机制，以更好地了解一些新生儿运动综合征的可能起源。

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.