LIM-HD/bHLH Combinatorial Code in Motoneurons

我们的长期目标是理解在发育过程中的组合转录调控网络 中枢神经系统(CMS)，它扮演着重要的角色，指定大量不同的神经元和 神经胶质细胞类型。LIM同源结构域(LIM-HD)和碱性螺旋-环-螺旋(BHLH)蛋白相对较好 描述了胚胎CMS中调节细胞类型规范的转录因子。然而，这两个 这些因子调节基因表达及其靶基因同一性的分子机制 人们对此仍然知之甚少。我们希望通过特别关注这些重要问题在 产生脊髓运动神经元(MN)。我们的结果表明，LIM-HD因子Lhx3和Isl1指定 胚胎脊髓的两个截然不同的神经元以组合的方式。Lhx3和LIM余因子NLI(用于 核LIM-中介体)形成V2-中间神经元(IN)特异性四聚体。相比之下，Lhx3和NLI形成了一个 当与Isl1共表达时，MN指定六聚体。在MN规范过程中，bHLH蛋白Ngn2/Neurm 与六角体在功能上是同步的，尽管这本小说背后的分子机制 人们对相声的理解还不完全。我们最近的筛选工作导致发现了具有 NLI：LSL1：Lhx3六聚体结合位点，其中许多与候选MN基因连锁。这些结果导致我们的 这一建议的中心假设：六聚体与bHLH一起直接调节多个MN基因 影响MN规格的因素。我们将剖析这一假说，以揭示指导 响应转录因子的组合表达的MN规范。具体地说，研究是 建议探索六聚体/bHLHs及其候选靶基因的不同功能。 总体而言，拟议的研究应为适当地形成 神经系统和治疗各种神经性损伤和疾病的实用信息。值得注意的是， LIM-HD/bHLH因子也与指定发育中中枢神经系统其他区域的细胞命运有关(例如， 视网膜和前脑)以及非中枢器官，如心脏、胰腺和脑下垂体，这突出了 拟议研究的总体重要性。

Our long-term goal is to understand the combinatorial transcriptional regulatory networks in the developing central nervous system (CMS), which play essential roles to specify a large number of distinct neuronal and glial cell types. LIM homeodomain (LIM-HD) and basic helix-loop-helix (bHLH) proteins are relatively well characterized transcription factors regulating cell type specification in the embryonic CMS. However, both the molecular mechanism by which these factors regulate gene expression and the identity of their target genes remain poorly understood. We wish to explore these important issues by specifically focusing on their role in generating spinal motoneurons (MNs). Our results demonstrate that LIM-HD factors Lhx3 and Isl1specify two distinct neurons of the embryonic spinal cord in a combinatorial manner. Lhx3 and the LIM cofactor NLI(for nuclear LIM-interactor) form a V2-interneuron (IN)-specifying tetramer. In contrast, Lhx3 and NLI form a MN-specifying hexamerwhen coexpressed with Isl1. During MN specification, bHLH proteins Ngn2/NeuroM are functionally synchronized with the hexamer, although the molecular mechanism underlying this novel crosstalk is not fully understood. Our recent screening effort led to the finding of genomic fragments with the NLI:lsl1 :Lhx3 hexamer binding sites, many of which are linked to candidate MN genes. These results led to our central hypothesis of this proposal: the hexamer directly regulates multiple MNgenes in conjunction with bHLH factors to effect MN specification. We will dissect this hypothesis to uncover the molecular basis that directs MN specification in response to a combinatorial expression of transcription factors. Specifically, studies are proposed to explore the diverse functional aspects of the hexamer/bHLHs with their candidate target genes. Overall, the proposed studies should provide critical insights into the basic principles for the proper formation of the nervous system and practical information to treat a variety of neuronal injuries and diseases. Of note, LIM-HD/bHLH factors are also involved with specifying cell fates in other regions of the developing CNS (e.g., retina and forebrain) as well as non-CNS organs such as heart, pancreas and pituitary, which highlights the general importance of the proposed studies.