Growth Factor Signaling in Intestinal Development

描述（由申请人提供）：上皮，如胃肠道上皮，能够进行持续的自我更新，因为它们含有大量未分化的干细胞，这些干细胞具有很大的自我更新能力，也可以产生子细胞，这些子细胞能够分化为上皮层正常功能所需的所有成熟细胞类型。在正常胃肠道发育过程中，介导这种上皮分层组织建立的信号的性质尚未明确。成纤维细胞生长因子（FGFs）是一个由至少23个相关的间质衍生肽生长因子组成的家族，它们调节各种组织正常个体发育过程中发生的一系列形态发生和分化事件。我们最近发现，一种FGF受体基因FGFR- 3的表达仅限于肠隐窝上皮下三分之二的未分化细胞，并在隐窝形态发生期间最大限度地表达。此外，FGFR3-/-小鼠肠道发育的初步研究表明，FGFR-3调节哺乳小鼠肠道中新生隐窝形成的速度和复制隐窝转运细胞的数量。该建议的中心假设是，在正常肠道个体发生过程中，通过FGFR-3信号传导调节多能上皮干细胞的命运和/或增殖。目的1是确定fgfr -3介导的信号传导是否通过影响干细胞增殖和/或程序性细胞死亡直接调节正常肠道发育过程中上皮干细胞群的扩增。FGFR3受体基因靶向突变的小鼠将被用于确定FGFR3介导的信号传导对不同发育时间点克隆干细胞数量和凋亡的影响。Aim 2将研究FGFR3对隐窝形态发生的影响是否通过β -catenin/TCF-4依赖机制介导。文献证据表明HMG转录因子TCF-4和left -1是隐窝上皮增殖和凋亡事件的重要下游调节介质。细胞培养和动物模型都将用于确定通过FGFR3的信号传导是否可以调节TCF-4活性。目的3的目的是确定FGFR3用于调节肠道发育过程中形态发生事件的中间信号级联。肠上皮细胞系中的FGFR3信号通路，特别是那些影响TCF-4的信号通路，将采用生物化学和分子方法相结合的方法进行研究。

DESCRIPTION (provided by applicant): Epithelia, such as those lining the gastrointestinal tract, are able to undergo continuous self-renewal because they contain a population of undifferentiated stem cells that have a large capacity for self renewal and can also give rise to daughter cells which are able to differentiate into all of the mature cell types needed for normal function of the epithelial layer. The nature of the signals that mediate the establishment of this hierarchical organization of the epithelium during normal gastrointestinal development has not yet been defined. Fibroblast growth factors (FGFs) are a family of at least 23 related mesenchymally derived peptide growth factors that modulate a wide array of morphogenic and differentiation events occurring during normal ontogeny of a variety of tissues. We have recently found that expression of one FGF receptor gene, FGFR- 3, is restricted to undifferentiated cells in the lower two-thirds of the intestinal crypt epithelium and is maximally expressed during crypt morphogenesis. Additionally, preliminary studies of intestinal development in FGFR3-/- mice, demonstrate that FGFR-3 regulates both the rate of nascent crypt formation and the number of replicating crypt transit cells in the suckling mouse intestine. The central hypothesis of this proposal is that signaling through FGFR-3 regulates the fate and/or proliferation of the multipotent epithelial stem cells during normal intestinal ontogeny. Aim 1 is to determine whether FGFR-3-mediated signaling directly regulates expansion of the epithelial stem cell population during normal intestinal development through effects on stem cell proliferation and/or programmed cell death. Mice with targeted mutations in the FGFR3 receptor gene will be used to determine the effects of FGFR3 mediated signaling on the number of clonogenic stem cells and on apoptosis at various developmental time points. Aim 2 will examine whether the effects of FGFR3 on crypt morphogenesis are mediated through a beta-catenin/TCF-4 dependent mechanism. Evidence in the literature suggests that the HMG transcription factors TCF-4 and Lef-1 are important downstream regulatory mediators of proliferative and apoptotic events in the crypt epithelium. Both cell culture and animal models will be used to determine whether signaling through FGFR3 can modulate TCF-4 activity. The goal of aim 3 is to define the intermediate signaling cascades that FGFR3 uses to regulate morphogenic events during intestinal development. The operant FGFR3 signaling pathways in intestinal epithelial cell lines, especially those impinging on TCF-4, will be investigated using a combination of biochemical and molecular approaches.