APC and Retinoids in Zebrafish Enterocyte Development

描述（由申请人提供）：APC突变被认为通过促进增殖和阻止结肠细胞的适当分化来启动结肠肿瘤的发展。在之前的资助期内，我们有效地利用斑马鱼作为遗传模型系统，证明了视黄酸对肠道发育和分化至关重要，APC通过控制视黄酸的产生来控制肠道细胞分化。我们发表的研究表明，APC调节视黄醇脱氢酶的表达，并首次证明了视黄醇脱氢酶在脊椎动物组织发育中的重要作用和动态调控。此外，我们的工作已经确立了APC和维甲酸在促进肠细胞分化中的新作用。作为连接APC和维甲酸的纽带，我们证明了APC控制转录共抑制因子c端结合蛋白（CtBP）的稳定性，CtBP可以直接抑制视黄醇脱氢酶和肠细胞分化。此外，我们已经证明CtBP和维甲酸产生的失调先于Wnt信号的激活。这一观察结果表明，维甲酸的丧失是Apc突变后的起始事件，而不是Wnt的失调。与该模型一致，我们最新发表的初步数据定义了APC、视黄酸和一种新型DNA去甲基化酶系统之间的意外联系，该系统似乎使携带APC突变的斑马鱼的肠道细胞维持在祖细胞样状态。在这一竞争性更新中，我们在之前的研究基础上，确定了Apc、维甲酸和新型DNA去甲基酶系统在控制肠道细胞命运和分化中的相互作用机制。我们假设APC肿瘤抑制因子通过控制维甲酸的产生在正常肠细胞分化中起重要作用。维甲酸反过来通过抑制一种新型DNA去甲基化酶的活性来调节肠道祖细胞内DNA甲基化的重塑。去甲基化酶的下调允许肠道分化所需的关键基因的甲基化依赖性沉默。

DESCRIPTION (provided by applicant): Mutations in APC are thought to initiate colon tumor development by promoting proliferation and preventing proper differentiation of colonocytes. In the previous funding period, we effectively employed zebrafish as a genetic model system to show that retinoic acid is essential for intestinal development and differentiation and that APC controls intestinal cell differentiation by controlling the production of retinoic acid. Our published studies indicate that APC regulates the expression of retinol dehydrogenases and were the first to demonstrate an essential role for, and dynamic regulation of, retinol dehydrogenases in vertebrate tissue development. Moreover, our work has established novel roles for APC and retinoic acid in promoting enterocyte differentiation. As a link between APC and retinoic acid, we demonstrated that APC controls the stability of the transcriptional co-repressor, C-terminal binding protein (CtBP) which can directly repress retinol dehydrogenases and intestinal cell differentiation. Further, we have demonstrated that dysregulation of CtBP and retinoic acid production precedes activation of Wnt signaling. This observation points to loss of retinoic acid as the initiating event following Apc mutation rather than dysregulation of Wnt. Consistent with this model, our most recent published and preliminary data define an unexpected connection between APC, retinoic acid and a novel DNA demethylase system that appears to maintain intestinal cells in a progenitor-like state in zebrafish harboring Apc mutations. In this competitive renewal, we build upon our previous studies to define the mechanistic interplay between Apc, retinoic acid and the novel DNA demethylase system in governing intestinal cell fate and differentiation. We hypothesize that the APC tumor suppressor plays an essential role in normal enterocyte differentiation by controlling the production of retinoic acid. Retinoic acid, in turn, regulates remodeling of DNA methylation within intestinal progenitor cells by suppressing the activity of a novel DNA demethylase. Downregulation of the demethylase allows methylation-dependent silencing of key genes required for intestinal differentiation.