Define Interneuron Subpopulations in the Mouse Spinal Cord during Development

神经回路的精确组织确保了中枢神经系统(CNS)的正常运作。组装这些电路需要对发育过程中定义的神经元群体进行正确的规范。我研究的一个目标是了解脊髓神经元功能群形成背后的发育过程。胚胎脊髓中不同的祖细胞结构域形成运动神经元(MN)和不同的中间神经元(IN)，每一类都有独特的分子特征。不同类型的脊髓INs出现在这些前体结构域中，最近发现，其中一些经历了进一步的细分，形成了不同的种群。然而，到目前为止，人们对支配这种细分的分子机制知之甚少。 我的实验室专注于一个被称为V3s的IN组，作为一个模型系统来研究脊柱INs在发育过程中的细分。V3 INS起源于腹侧前体区p3，在有丝分裂后早期表达Sim1转录因子。V3 INS具有谷氨酸能和连合作用。在小鼠中，整个V3种群的基因缺失阻止了动物表现出健壮和稳定的步态。我们最近证实，至少有两个V3亚群，腹侧和背侧，存在于成熟的脊髓中，每个亚群都有不同的生理和解剖学特性。然而，确定这些亚群及其功能所需的分子标记仍然不可用。此外，在NSERC基金的支持下，我们最新的研究表明，V3亚群表现出的不同生理特性存在于胚胎中，SIM1可能在调节它们的建立中发挥不同的作用。因此，我们建议定义V3亚群的分子标记和Sim1在发育过程中的作用机制。为此，我们将使用转基因小鼠追踪野生型对照小鼠和胚胎发育过程中Sim1缺陷小鼠的V3 INS。我们将结合电生理学、免疫组织化学、原位杂交和微阵列/RNA测序筛选进行以下研究： 目的1.定义胚胎阶段的生理V3亚群，以建立一个时间表，显示V3亚群何时开始表现出独特的生理特性。 目的II.确定V3亚群的特异分子标记，特别是特异的转录因子，以确定不同V3亚群的分子图谱。 目的III.研究Sim1调节V3亚群形成的分子途径，以确定在胚胎发育过程中哪些下游分子因子受Sim1转录因子的调控。 这些研究的成功完成将使我们能够区分V3亚群并确定它们在脊髓环路中的功能。我们的工作也可能为旨在评估其他IN亚群形成的研究铺平道路。

Precise organization of neural circuits ensures proper functioning of the central nervous system (CNS). Assembly of these circuits requires correct specification of neuronal populations defined during development. One goal in my research is to understand developmental processes underlying formation of functional groups of spinal neurons. Different progenitor domains in the embryonic spinal cord give rise to the motoneurons (MNs) and different interneuron (IN) classes, each with a unique molecular profile. Distinct types of spinal INs emerge from these progenitor domains, and, as recently revealed, some undergo further subdivision to form heterogeneous populations. As yet, however, little is known about molecular mechanisms that govern such subdivision. My lab focuses on an IN group known as V3s as a model system to study subdivision of spinal INs during development. V3 INs arise from a ventral progenitor domain, p3, and express the Sim1 transcription factor at early postmitotic stages. V3 INs are glutamatergic and commissural. In mice, genetic deletion of the entire V3 population prevents animals from exhibiting robust and stable gait. We recently demonstrated that at least two V3 subpopulations, ventral and dorsal, reside in mature spinal cord, each with distinct physiological and anatomical properties. Nevertheless, molecular markers required to define these subpopulations and their function remain unavailable. Moreover, our most recent studies, supported by NSERC funding, suggest that differing physiological properties displayed by V3 subpopulations are present embryonically and that Sim1 may play different roles in regulating their establishment. Therefore, we propose to define molecular markers of V3 subpopulations and mechanisms underlying Sim1 function during development. To do so, we will use transgenic mice to trace V3 INs in wild-type control and Sim1-deficient mice during embryogenesis. We will combine electrophysiology, immunohistochemistry, in situ hybridization and microarray/RNA sequencing screening to conduct the following studies: Aim I. Define physiological V3 subpopulations at embryonic stages to establish a timeline showing when V3 subpopulations start to display distinctive physiological properties. Aim II. Identify specific molecular markers, especially specific transcription factors, of V3 subpopulations to define molecular profiles for different V3 subpopulations. Aim III. Investigate molecular pathways that regulate the V3 subpopulation formation by Sim1 to determine which downstream molecular factors are regulated by the Sim1 transcription factor during embryonic development. Successful completion of these studies will allow us to distinguish V3 subpopulations and determine their function in spinal circuits. Our work could also pave the way for studies designed to assess formation of other IN subpopulations.