Genetic Control of Neural Stem Cell Homeostasis

描述（由申请人提供）：实现神经干细胞（NSC）谱系内的稳态对神经系统的发育和维持至关重要。它需要在NSC自我更新和分化之间取得微妙的平衡。调控NSC内稳态的分子和细胞机制尚不清楚。阐明这些机制将为神经系统的发育和维持提供新的见解，并为由NSC内稳态失败引起的疾病（包括脑肿瘤、神经发育、精神和神经退行性疾病）的分子靶向治疗提供关键。我们建议以果蝇幼虫脑II型神经母细胞（NBs）为模型，阐明NSC稳态遗传控制的基本机制。果蝇NBs在发现信号分子（如Numb和Notch）和细胞机制（如不对称细胞分裂）方面发挥了重要作用，它们在NSC稳态中起着重要作用。与哺乳动物NSCs一样，果蝇II型NBs也能产生中转扩增的中间祖细胞（IPs），这有助于产生大量分化的后代。Notch信号对于维持II型NBs的“干性”至关重要。Notch信号的抑制导致NB命运不能正常维持，而异常的Notch激活导致异位NB形成和脑肿瘤发生。Notch在哺乳动物中调控NSC稳态的功能似乎是保守的。然而，关于Notch的作用机制及其与Numb在体内的关系仍有很多未解之谜和争议。我们发现典型的Notch信号对于Notch导向的NSC调控是必要的，但不是充分的，并且一个新的非典型Notch信号通路也参与其中。我们的主要假设是，非规范Notch信号与规范Notch信号协调作用，介导NSC稳态控制的不同方面，而Numb调节这两种途径。提出了许多基本的问题：规范和非规范通路调节什么细胞程序？这些途径的关键分子靶点是什么？我们能否通过操纵这些关键靶点来重现Notch的效果？麻木在这两种途径中扮演什么角色？三个具体目标将有助于解决这些问题。目的1将从遗传和生化角度阐明调节NSC稳态的非规范Notch信号通路。目的2将验证非规范Notch通路和规范通路协同作用以维持NSC稳态的假设。目的3将验证一种假设，即Numb在一种新的蛋白质复合物中起作用，以调节规范和非规范Notch通路中的关键下游介质。在成功完成这些目标后，我们将对Notch和Numb对NSC内稳态的控制产生新的机制见解。我们期望这将为研究Numb和Notch在NSC生物学和癌症生物学中的基础作用开辟全新的方向。

DESCRIPTION (provided by applicant): Achieving homeostasis within neural stem cell (NSC) lineages is essential for nervous system development and maintenance. It requires an exquisite balance between NSC self-renewal and differentiation. The molecular and cellular mechanisms underlying the control of NSC homeostasis remain poorly understood. Elucidation of these mechanisms will provide novel insights into the development and maintenance of the nervous system as well as offer the keys to molecularly targeted therapy for diseases resulting from NSC homeostasis failure, including brain tumors and neurodevelopmental, psychiatric, and neurodegenerative disorders. We propose to elucidate the basic mechanisms underlying the genetic control of NSC homeostasis, using Drosophila larval brain type II neuroblasts (NBs) as a model. Drosophila NBs have been instrumental in discovering signaling molecules such as Numb and Notch, and cellular mechanisms such as asymmetric cell division, that are centrally involved in NSC homeostasis. Like mammalian NSCs, fly type II NBs generate transit-amplifying intermediate progenitors (IPs), which help to generate a vast number of differentiated progenies. Notch signaling is critical for maintaining the "stemness" of type II NBs. Inhibition of Notch signaling results in NB fate not being properly maintained, whereas aberrant Notch activation causes ectopic NB formation and brain tumorigenesis. The function of Notch in regulating NSC homeostasis appears to be conserved in mammals. However, there is much to be learned about the mechanisms of action of Notch and its in vivo relationship with Numb, which remains enigmatic and controversial. We have found that canonical Notch signaling is necessary but not sufficient for Notch-directed NSC regulation and that a novel non-canonical Notch signaling pathway is also involved. Our main hypothesis is that non-canonical Notch signaling acts coordinately with canonical Notch signaling to mediate distinct aspects of NSC homeostasis control, and that Numb regulates both of these two pathways. Many fundamental questions are raised: What cellular programs do the canonical and the non-canonical pathways regulate? What are the key molecular targets of these pathways? Can we recapitulate the effect of Notch by manipulating these key targets? What roles does Numb play in these two pathways? Three specific aims will help address these questions. Aim 1 will genetically and biochemically elucidate a non-canonical Notch signaling pathway that regulate NSC homeostasis. Aim 2 will test the hypothesis that the non-canonical Notch pathway and the canonical pathway act coordinately to maintain NSC homeostasis. Aim 3 will test the hypothesis that Numb acts in a novel protein complex to regulate key downstream mediators in the canonical and non-canonical Notch pathways. Upon successful completion of these Aims, we will generate new mechanistic insights into the control of NSC homeostasis by Notch and Numb. We anticipate that this will open up entirely new directions for studying the fundamental roles of Numb and Notch in NSC biology and cancer biology.