Regulation of distinct pools of intestinal stem cells

描述（由申请人提供）：小肠上皮每2至5天更新一次，使其成为最具再生性的哺乳动物组织之一。了解肠道干细胞（ISCs），燃料这种更新既是一个重要的基础科学问题，也是再生医学转化方法的一个重要起点。遗传诱导的命运映射（GIFM）研究已经确定了两个主要的上皮干细胞池在肠道。一个池由柱状Lgr 5表达细胞组成，其快速循环并主要存在于隐窝基底，另一个池由表达Bmi 1或其他标记物的细胞组成，其主要存在于隐窝基底上方。我们最近已经证明（Tian等人，Nature，2011），表达Bmi 1的ISC在正常生理条件下产生表达Lgr 5的ISC。重要的是，当我们特异性消融表达Lgr 5的ISCs时，表达Bmi 1的ISCs能够维持近端小肠的上皮稳态。这些结果已经被其他几个研究小组证实，表明表达Lgr 5和Bmi 1的ISC构成了两个不同的群体，尽管可能部分重叠。一个重要的问题是，哪些信号通路调节这些不同的干细胞群，越来越多的证据表明，Wnt和Notch信号传导指导表达Lgr 5和Bmi 1的干细胞自我更新。在本申请中，我们提出采用途径特异性阻断抗体来理解Wnt和Notch信号传导对ISCs中自我更新和谱系命运决定的差异和组合效应。这种独特的方法-结合抗体阻断和遗传命运映射-开辟了有趣的新途径，超越了传统的纯遗传方法。这些研究的结果将揭示ISCs自我更新和分化的机制，这将有助于了解这些ISCs在体内平衡和疾病中的作用，并将有助于为未来的器官再生尝试奠定基础。

DESCRIPTION (provided by applicant): The small intestine epithelium renews every 2 to 5 days, making it one of the most regenerative mammalian tissues. Understanding the intestinal stem cells (ISCs) that fuel this renewal is both an important basic science question and an essential starting point for translational approaches in regenerative medicine. Genetic inducible fate mapping (GIFM) studies have identified two principal epithelial stem cell pools in the intestine. One pool consists of columnar Lgr5-expressing cells that cycle rapidly and are present predominantly at the crypt base, and the other consists of cells expressing Bmi1 or other markers that largely reside above the crypt base. We have recently demonstrated (Tian et al, Nature, 2011) that Bmi1-expressing ISCs give rise to Lgr5- expressing ISCs under normal physiological conditions. Importantly, when we specifically ablated Lgr5- expressing ISCs, Bmi1-expressing ISCs were able to maintain epithelial homeostasis in the proximal small intestine. These results, which have been confirmed by several other groups, indicated that Lgr5- and Bmi1- expressing ISCs constitute two distinct, although possibly partially overlapping, populations. An important question is which signaling pathways regulate these different stem cell populations, and a growing body of evidence indicates that Wnt and Notch signaling guide both Lgr5- and Bmi1-expressing stem cell self-renewal. In this application, we propose to employ pathway-specific blocking antibodies to understand the differential and combinatorial effects of Wnt and Notch signaling on self-renewal and lineage fate decisions in ISCs. This unique approach - combining antibody blockade and genetic fate mapping - opens up interesting new avenues beyond the traditional purely genetic approaches. The results of these studies will shed important light on the mechanisms by which ISCs self-renew and differentiate, which will help to understand the roles of these ISCs in homeostasis and disease and will help to lay the groundwork for future attempts at organ regeneration.