Molecular mechanisms of motor neuron terminal identity

运动神经元（MN）功能或存活的缺陷导致严重的人类病理学，例如肌萎缩性侧索硬化症。 脊髓侧索硬化症和脊髓性肌萎缩症，不同的MN亚型对疾病的易感性不同。 目前对于MN病症没有有效的治疗，部分原因是缺乏对MN病症的理解。 允许不同MN亚型获得并维持其功能定义的分子机制 特性.因此，需要对线虫、苍蝇和小鼠等模式生物进行基础研究，以揭示 这样的机制。MN亚型功能由末端身份基因的差异表达赋予。 这些基因编码蛋白质（例如，离子通道，神经递质受体，神经肽，跨膜 受体，粘附分子），从发育的最后阶段到 成年期，并由此定义给定MN亚型的独特功能特征。因此，揭示 诱导（在发育期间）和维持（在整个生命期间）终末表达的分子机制 身份基因将帮助我们了解MN如何成为和保持功能，这是MN领域的一个关键目标 发展和疾病。一个显着的财富的终端身份标记是可用于所有胆碱能MN C.线虫控制运动的神经索，提供了一个独特的模型系统来阐明 MN如何获得和保持其功能特征。利用这些工具，我们发现， 保守的Collier/Olf/Ebf型转录因子（TF）β-3是所有转录因子的连续功能所必需的。 这些胆碱能MN亚型，这种结果来自于β-3依赖性诱导， MN亚型特异性末端同一性基因的维持。通过无偏见的基因筛选，我们最近 鉴定了几个保守的调控因子（6个TF，2个染色质因子），它们控制着 单个MN亚型。有趣的是，我们的初步研究结果表明，虽然BMP3激活了 所有MN亚型特异性末端同一性基因，这些调节因子抵消激活剂的功能， 通过抑制特定MN亚型中的IL-3靶标来抑制IL-3。这些观察表明了一个普遍的原则 对于MN末端身份的控制，其中广泛作用的激活剂（β-3）的转录靶点 被不同的TF和染色质因子以MN亚型特异性方式抑制。为了验证这一假设 在未来5年的研究性试验计划（R01）的时间框架内，该计划的重点将放在一个TF（BNC-1/哺乳动物BNC-1 - 2）和一个 染色质因子（PBRM-1/哺乳动物BAF 180），其在不同MN亚型中抵消α-3。具体地说， 我们试图：（a）确定这两个因素是否在整个生命过程中都需要，以确保亚型的身份 (Aim 1），（B）定义BNC-1（Aim 2）阻遏物活性的潜在机制，和（c）破译 PBRM-1的功能，通过识别其下游目标（目标3）。拟议的实验将建立一个 在遗传模型系统中诱导和维持MN末端身份的范例，这可以为 作为一个有价值的切入点，了解哺乳动物MN如何成为和保持功能。

Defects in motor neuron (MN) function or survival result in severe human pathologies, such as amyotrophic lateral sclerosis and spinal muscular atrophy, with distinct MN subtypes differing in susceptibility to disease. There is currently no effective treatment for MN disorders in part due to a lack of understanding of the molecular mechanisms that allow distinct MN subtypes to acquire and maintain their function-defining properties. Thus, basic research in model organisms such as nematodes, flies, and mice is needed to reveal such mechanisms. MN subtype function is endowed by the differential expression of terminal identity genes. Such genes encode proteins (e.g., ion channels, neurotransmitter receptors, neuropeptides, trans-membrane receptors, adhesion molecules) that are expressed continuously, from the last steps of development through adulthood, and thereby define the unique functional features of a given MN subtype. Hence, revealing the molecular mechanisms that induce (during development) and maintain (throughout life) expression of terminal identity genes will help us understand how MNs become and remain functional, a key goal in the fields of MN development and disease. A remarkable wealth of terminal identity markers is available for all cholinergic MN subtypes of the C. elegans nerve cord that control locomotion, providing a unique model system to elucidate how MNs acquire and maintain their functional features. Leveraging these tools, we discovered that the conserved Collier/Olf/Ebf-type transcription factor (TF) UNC-3 is required for the continuous function of all these cholinergic MN subtypes, and that this outcome arises from UNC-3-dependent induction and maintenance of MN subtype-specific terminal identity genes. Through unbiased genetic screens, we recently identified several conserved regulatory factors (6 TFs, 2 chromatin factors) that control the terminal identity of individual MN subtypes. Intriguingly, our preliminary results suggest that while UNC-3 activates expression of all MN subtype-specific terminal identity genes, these regulatory factors counteract the activator function of UNC-3 by repressing UNC-3 targets in specific MN subtypes. These observations suggest a general principle for the control of MN terminal identity, in which the transcriptional targets of a broadly acting activator (UNC-3) are repressed in a MN subtype-specific fashion by distinct TFs and chromatin factors. To test this hypothesis within the 5-year R01 timeframe, this proposal will focus on one TF (BNC-1/mammalian BNC1-2) and one chromatin factor (PBRM-1/mammalian BAF180) that counteract UNC-3 in different MN subtypes. Specifically, we seek to: (a) determine whether these two factors are required throughout life to secure subtype identity (Aim 1), (b) define the mechanism underlying the repressor activity of BNC-1 (Aim 2), and (c) decipher the function of PBRM-1 by identifying its downstream targets (Aim 3). The proposed experiments will establish a paradigm for induction and maintenance of MN terminal identity in a genetic model system, which could serve as a valuable entry point to understand how mammalian MNs become and remain functional.