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

描述(申请人提供)：支配对哺乳动物至关重要的行为的神经回路，如运动和呼吸，依赖于脊髓内的运动神经元(MN)与特定的外周和中央突触目标建立选择性连接的能力。沿着神经管的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的其他神经元类型区分开来。随后MN的多样化依赖于大约20个Hox转录因子的作用，这些转录因子似乎在MN分化的不同阶段都是必需的。虽然HOX基因对MN命运的指定是必不可少的，但其活动的靶点尚不清楚，也不清楚它们是如何实现MN特异性的，因为它们在沿喙尾轴的模式中扮演着相对广泛的角色。此外，决定HOX蛋白在MNS中表达模式的因素还不清楚。在目标1中，我们将描述HOX蛋白的直接靶标，评估它们如何在运动柱中被调控，并确定它们是否以及如何与MN特异的基因程序相交。在AIM2中，我们将剖析HOX蛋白特异性控制MN身份的各个方面的机制，重点是Hoxc9蛋白，MN柱状组织的中心决定因素。在AIM 3中，我们将测试这一假设，即依赖于HOX的MN亚型的组织依赖于多梳蛋白的分级活性，以确保适当的有丝分裂后HOX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的见解，并应允许设计从未分化的细胞产生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.