Genetic Control of Neural Stem Cell Homeostasis

描述(由申请人提供)：在神经干细胞(NSC)谱系内实现动态平衡对于神经系统的发育和维护至关重要。它需要在NSC自我更新和差异化之间取得微妙的平衡。控制神经干细胞稳态的分子和细胞机制仍然知之甚少。这些机制的阐明将为神经系统的发育和维持提供新的见解，并为分子靶向治疗由NSC稳态失调引起的疾病提供关键，包括脑肿瘤和神经发育、精神和神经退行性疾病。我们建议以果蝇幼虫脑II型神经母细胞(NBS)为模型，阐明遗传控制NSC动态平衡的基本机制。果蝇NBS在发现Numb和Notch等信号分子以及不对称细胞分裂等细胞机制方面发挥了重要作用，这些机制与NSC的动态平衡密切相关。与哺乳动物神经干细胞一样，苍蝇II型神经干细胞产生转运性放大中间祖细胞(IP)，帮助产生大量分化的后代。Notch信号对于保持II型NBS的“干性”至关重要。Notch信号的抑制导致NB的命运不能被正确地维持，而Notch的异常激活导致了异位NB的形成和脑肿瘤的发生。在哺乳动物中，Notch在调节NSC动态平衡方面的功能似乎是保守的。然而，关于Notch的作用机制以及它与Numb的体内关系还有很多需要了解的地方，这仍然是一个谜，也是有争议的。我们发现规范的Notch信号对于Notch导向的NSC调控是必要的，但不是充分的，并且还涉及一条新的非规范的Notch信号通路。我们的主要假设是，非典范Notch信号与典范Notch信号协同作用，调节NSC内稳态调控的不同方面，而NSC信号调节这两条途径。许多基本问题被提出：规范和非规范途径调节哪些细胞程序？这些途径的关键分子靶点是什么？我们能通过操纵这些关键目标来概括Notch的效果吗？Numet在这两条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将从遗传学和生物化学的角度阐明一种非规范的Notch信号通路，该信号通路调节NSC的稳态。目的2验证非典型性Notch途径和典型性途径协同作用以维持NSC内环境平衡的假设。目的3将验证Numb在一种新的蛋白质复合体中作用的假说，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，我们将通过Notch和Numb对NSC动态平衡的控制产生新的机械性见解。我们预计这将为研究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.