Transcriptional Control of Motor Neuron Identity and Connectivity. - Renewal - 1

描述（由申请人提供）：控制哺乳动物重要行为的神经回路，如运动和呼吸，依赖于脊髓内运动神经元（MNs）与专门的外周和中枢突触靶点建立选择性连接的能力。沿神经管背腹轴作用的信号通路已被证明决定了MNs的早期身份，并将这类神经元与脊髓内其他类型的神经元区分开来。随后MN的分化取决于大约20个Hox转录因子的作用，这似乎是MN分化的不同阶段所必需的。虽然Hox基因对MN的命运调控至关重要，但它们的活动目标尚不清楚，也不清楚它们是如何实现MN特异性的，因为它们在沿背尾轴的模式中具有相对广泛的作用。此外，决定MNs中Hox蛋白表达模式的因素定义不清。在目的1中，我们将描述Hox蛋白的直接靶标，评估它们在运动柱中是如何调节的，并确定它们是否以及如何与mn特异性基因程序相交。在目的2中，我们将剖析Hox蛋白特异性在MN身份控制方面的机制，重点关注Hoxc9蛋白，这是MN柱状组织的核心决定因素。在目的3中，我们将验证这样的假设，即Hox依赖性MN亚型的组织依赖于Polycomb蛋白的分级活性，以确保有丝分裂后Hox的正确表达模式。这些研究将为Hox蛋白影响MN分化的机制提供基本见解，并允许设计从未分化细胞产生MN亚型的策略。

DESCRIPTION (provided by applicant): The neural circuits that govern behaviors vital to mammals, such as locomotion and respiration, rely on the ability of motor neurons (MNs) within the spinal cord to establish selective connections with dedicated sets of peripheral and central synaptic targets. Signaling pathways acting along the dorsoventral axis of the neural tube have been shown to determine the early identity of MNs and distinguish this class from other neuronal types within the spinal cord. The subsequent diversification of MNs depends on the actions of approximately 20 Hox transcription factors, which appear to be required at distinct phases of MN differentiation. While Hox genes are essential for MN fate specification, the targets of their activities are not known, nor is it understood how they achieve MN-specificity, given their relatively broad roles in patterning along the rostrocaudal axis. Moreover the factors that determine the expression patterns of Hox proteins in MNs are poorly defined. In aim1 we will characterize the direct targets of Hox proteins, assess how they are regulated in motor columns, and determine if and how they intersect with MN-specific gene programs. In aim2 we will dissect the mechanisms of Hox protein specificity in controlling facets of MN identity, focusing on the Hoxc9 protein, a central determinant of MN columnar organization. In aim3 we will test the hypothesis that the organization of Hox-dependent MN subtype relies on graded activities of Polycomb proteins that ensure proper postmitotic Hox expression patterns. These studies will provide basic insights into the mechanisms through which Hox proteins influence MN differentiation, and should allow for the design of strategies to generate MN subtypes from undifferentiated cells.