Regulation of distinct pools of intestinal stem cells

描述（申请人提供）：小肠上皮每2 - 5天更新一次，是最具再生能力的哺乳动物组织之一。理解肠道干细胞（ISCs）促进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重要起点。遗传诱导命运定位（GIFM）研究已经确定了肠中两个主要的上皮干细胞池。一个池由表达lgr5的柱状细胞组成，这些细胞周期快，主要存在于隐窝基部，另一个池由表达Bmi1或其他标记的细胞组成，这些细胞主要位于隐窝基部上方。我们最近证明（Tian et al ., Nature, 2011），在正常生理条件下，表达bmi1的ISCs会产生表达Lgr5的ISCs。重要的是，当我们特异性切除表达Lgr5-的ISCs时，表达bmi1的ISCs能够维持小肠近端上皮稳态。这些结果已经被其他几个研究小组证实，表明表达Lgr5-和Bmi1-的ISCs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信号通路指导表达Lgr5-和bmi1的干细胞自我更新。在这项应用中，我们建议使用途径特异性阻断抗体来了解Wnt和Notch信号在ISCs自我更新和谱系命运决定中的差异和组合作用。这种独特的方法-结合抗体阻断和遗传命运定位-开辟了超越传统纯遗传方法的有趣的新途径。这些研究的结果将揭示ISCs自我更新和分化的机制，这将有助于理解这些ISCs在体内平衡和疾病中的作用，并将有助于为未来器官再生的尝试奠定基础。

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.