Molecular mechanisms of motor neuron terminal identity

运动神经元(MN)功能或存活缺陷会导致严重的人类病理，如肌营养不良 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。 目前还没有有效的治疗MN疾病的方法，部分原因是对MN疾病缺乏了解 允许不同的MN亚型获得和维持其功能定义的分子机制 属性。因此，需要对线虫、苍蝇和老鼠等模式生物进行基础研究，以揭示 这样的机制。末端同源基因的差异表达赋予了MN亚型功能。 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、黏附分子)，从发育的最后几步到 成年期，从而定义特定MN亚型的独特功能特征。因此，揭示了 诱导(在发育期间)和(在整个生命中)维持末端表达的分子机制 身份基因将帮助我们理解MN如何变得并保持功能，这是MN领域的一个关键目标 发展和疾病。所有胆碱能MN都有非常丰富的终末身份标志物 线虫控制运动的神经索的亚型，提供了一个独特的模型系统来阐明 跨国公司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)UNC-3是ALL持续发挥功能所必需的 这些胆碱能MN亚型，这种结果是由UNC-3依赖的诱导和 MN亚型特异性末端识别基因的维持。通过公正的基因筛查，我们最近 确定了几个保守的调节因子(6个TF，2个染色质因子)，它们控制着 个别MN亚型。有趣的是，我们的初步结果表明，虽然UNC-3激活了 所有MN亚型特异的末端标识基因，这些调节因子中和激活功能 通过压制特定MN亚型中的UNC-3目标。这些观察结果表明了一个普遍的原则 用于控制MN末端的身份，其中广泛作用的激活剂(UNC-3)的转录靶标 被不同的转录因子和染色质因子以MN亚型特有的方式抑制。为了检验这一假说 在5年R01时间框架内，这项提案将侧重于一项Tf(BNC-1/哺乳动物BNC1-2)和一项 染色质因子(PBRM-1/哺乳动物BAF180)，在不同的MN亚型中抵消UNC-3。具体来说， 我们试图：(A)确定这两个因素是否在一生中都是确保亚型身份所必需的 (目标1)，(B)确定BNC-1抑制物活性的潜在机制(目标2)，和(C)破译 通过确定其下游目标来发挥PBRM-1的作用(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终端身份的范例，其可以服务于 作为一个有价值的切入点，以了解哺乳动物的MN是如何变得和保持功能的。

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.