Fate specification of corticospinal neurons by cell autonomous signaling

描述（由申请人提供）：本提案的目标是确定指导皮质脊髓运动神经元（CSMN）命运规范和谱系特异性发育的分子信号。这些神经元是临床相关的群体，在人类中，选择性地死于神经退行性疾病，包括肌萎缩侧索硬化症（ALS）、遗传性痉挛性截瘫（HSP）和原发性侧索硬化症（PLS）。它们也是永久性损伤的细胞，并负责脊髓损伤（SCI）的瘫痪。在神经系统中，由于组织具有惊人的细胞异质性，再加上无法将一种神经元类型与其他神经元类型分离开来并进行纯化，旨在调查单个神经元类型的出生、存活和连接的分子控制的研究一直是出了名的困难。在我的博士后工作中，我直接在皮层中解决了这个问题，并且已经确定并开始在功能上描述第一个基因系列，这些基因以组合的方式独特地识别CSMN，因为这种神经元类型发展为[1]。与目前的建议最相关的是，我们发现转录因子Fezf2是CSMN诞生所必需的“主基因”（即CSMN在Fezf2-/-小鼠的皮层中缺失），并且至少在一定程度上足以指导皮层祖细胞的命运规范CSMN（即升高的Fezf2水平可以诱导注定形成上层神经元的祖细胞向形成CSMN和深层神经元的“命运开关”）[2]。在此，我以先前的工作和我自己实验室的新数据为基础，直接研究这一建议的核心问题：(1)：什么分子信号指导皮质祖细胞的命运规范和早期发展为CSMN？（目的1和目的2）(2)：不同皮质类型的有丝分裂后神经元是否在Fezf2反应中维持产生CSMN的能力，或者更确切地说，神经元谱系规范决定仅在祖细胞阶段做出并被调节？（目的3）我们提出了先前发表的工作和大量新数据，支持这些实验的可行性，并将结果与开发替代CSMN治疗神经退行性和皮质脊髓回路创伤性疾病的新治疗策略直接相关。

DESCRIPTION (provided by applicant): The goal of this proposal is to determine the molecular signals that instruct the fate specification and the lineage-specific development of corticospinal motor neurons (CSMN). These neurons are a clinically relevant population that, in humans, selectively dies in neurodegenerative diseases, including Amyotrophic Lateral Sclerosis (ALS), Hereditary Spastic Paraplegia (HSP), and Primary Lateral Sclerosis (PLS). They are also the cells permanently injured and responsible for paralysis in spinal cord injury (SCI). In the nervous system, studies aimed at investigating the molecular controls over birth, survival and connectivity of individual neuron types have been notoriously difficult, owing to the astonishing cellular heterogeneity of the tissue, combined with the inability to distinguish and purify one neuron type in isolation from others. In my postdoctoral work, I addressed this issue directly in the cortex, and have identified and begun to functionally characterize the first series of genes that in a combinatorial fashion uniquely identify CSMN as this neuron type develops [1]. Most relevant to the present proposal, we discovered that the transcription factor Fezf2 is a "master gene" that is both necessary for the birth of CSMN (i.e. CSMN are absent from the cortex of Fezf2-/- mice), and is at least in part sufficient to instruct the fate-specification of cortical progenitors to CSMN (i.e. elevated levels of Fezf2 can induce a "fate-switch" in progenitors destined to form upper layer neurons towards forming CSMN and deep layer neurons) [2]. Here, I build on this prior work and on new data from my own laboratory to directly investigate the central questions of this proposal: (1): What are the molecular signals that instruct the fate-specification and early development of cortical progenitors into CSMN? (Aim 1 and Aim 2) (2): Do postmitotic neurons of a different cortical type maintain the ability to generate CSMN in response to Fezf2 or, rather, are neuron lineage-specification decisions made and only modulated at the progenitor stage? (Aim 3) We present prior published work and substantial new data that support the feasibility of these experiments, and the direct relevance of the results to the development of novel therapeutic strategies to replace CSMN in neurodegenerative and traumatic diseases of the corticospinal circuitry. PUBLIC HEALTH RELEVANCE: Different neurodegenerative diseases of the CNS are typically characterized by the progressive death of specific neuron types. Corticospinal motor neuron (CSMN) degeneration and injury is a key component of motor neuron disease (including ALS), and of spinal cord injury. Here we propose to determine the molecular signals that instruct the birth of this clinically relevant neuron type, and to investigate the extent to which CSMN can be regenerated for therapeutic application.