The roles of regional specialization, mechanical forces and epigenetic memory after perturbation and injury of the intestinal stem cell microenvironment

项目总结/摘要 小肠上皮每2至5天更新一次，使其成为最具再生能力的哺乳动物之一。 组织中了解肠道干细胞（ISCs）的燃料这种更新是一个重要的基础科学 问题和再生医学转化方法的一个重要起点。遗传 诱导性命运作图（GIFM）研究已经鉴定了肠中的两个主要上皮干细胞库。 一个池由表达Lgr 5的柱状细胞组成，这些细胞周期迅速，主要存在于细胞周期的第一阶段。 另一种由表达Bmi 1或其他标记物的细胞组成，这些标记物主要位于隐窝上方 基地我们最近已经证明（Tian等，Nature，2011）表达Bmi 1的ISC产生Lgr 5- 在正常生理条件下表达ISCs。重要的是，当我们专门消融Lgr 5时， 表达ISCs，Bmi 1表达ISCs能够维持近端小血管中的上皮稳态。 肠子这些结果已经被其他几个小组证实，表明Lgr 5-和Bmi 1- 表达ISC的细胞群构成两个不同的，尽管可能部分重叠的群体。一个重要 问题是哪些信号通路调节这些不同的干细胞群，以及越来越多的干细胞。 有证据表明Wnt和Notch信号传导引导表达Lgr 5和Bmi 1的干细胞自我更新。 在本申请中，我们建议采用通路特异性阻断抗体来理解差异表达。 以及Wnt和Notch信号传导对ISCs自我更新和谱系命运决定的组合作用。这 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 超越传统的纯基因方法的途径。这些研究的结果将为我们了解 关于ISCs自我更新和分化的机制，这将有助于理解这些机制的作用。 ISCs在体内平衡和疾病中的作用，将有助于为未来的器官再生尝试奠定基础。

PROJECT SUMMARY/ABSTRACT 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.