Resolving heterogeneity in liver development

项目摘要 最后的内胚层(DE)在原肠形成过程中以上皮层的形式出现。这个单元格工作表，它 产生整个肠管和相关器官，被图案化并分化为器官域 对邻近中胚层组织提供的诱导提示的反应。在诱导过程中，肝脏 前体细胞，即肝母细胞，从DE中出现，作为一组表达肝脏标志物的增厚细胞。 新生的肝母细胞形成一个肝芽，它将侵入邻近的中胚层组织。一旦入侵是 完整，可见单个中线喙叶和两个较小的两侧对称的尾叶。 尽管肝母细胞及其相关的中胚层都被认为是统一的群体，但我们 在这两个方面都发现了显著的异质性。首先，肝母细胞起源于两个空间上不同的DE 每个种群都对肝芽有独特的贡献。腹侧中线祖细胞主要贡献 位于前肝芽的肝母细胞，而两侧对称的外侧祖细胞 产生对后肝芽有贡献的肝母细胞。令人惊讶的是，每个祖先都有独特的 对这一过程的需求，每个都与诱导时不同的支持性间充质相关联。 例如，成纤维细胞生长因子信号是诱导与静脉窦结合的前肝母细胞所必需的，而 横隔间充质结合的后肝母细胞需要BMP信号的诱导 此外，本组最近绘制的命运图显示，前肝母细胞主要是 肝细胞主要分布在尾叶，而后肝母细胞主要分布在吻叶。终于 未发表的组织学和分子数据表明，支持吻部和尾部的间质 小叶是不同的组织。总而言之，这些观察表明，正常的发育遵循两条路线 产生肝母细胞。我们假设在肝脏发育早期产生的异质性 对于正常的肝功能是必不可少的，并且它有助于产生最近在 成年肝细胞和胆管细胞种群。在概述的新发展框架的指导下 如上所述，我们提案的目的是利用我们在胚胎学方面的专业知识和老鼠遗传学的力量来进一步 描述这种异质性，并确定它对正常发育的贡献。在Aim1中，我们建议 使用条件性基因敲除策略评估成纤维细胞生长因子和骨形态发生蛋白信号在成肝细胞诱导中的作用 活着。在AIM2中，我们使用体外方法和体内新颖的小鼠记者来揭示发育 吻叶和尾叶间充质的来源和成人贡献以及分子测定 吻叶和尾叶肝母细胞的特征。长期目标是了解如何 发育异质性有助于关键的成人反应，如动态平衡和再生，以及 利用这些发育洞察力在体外培养出具有功能的肝组织。

Project Summary The definitive endoderm (DE) emerges during gastrulation as an epithelial sheet. This single cell sheet, which produces the entire gut tube and associated organs, is patterned and differentiates into organ domains in response to inductive cues provided by adjacent mesoderm-derived tissues. During induction, the hepatic progenitor, the hepatoblast, emerges from the DE as a group of thickened cells that express hepatic markers. The nascent hepatoblasts form a liver bud that will invade adjacent mesodermal tissue. Once invasion is complete, a single midline rostral lobe and two smaller bilaterally symmetric caudal lobes are evident. Although hepatoblasts and their associated mesoderm have each been regarded as uniform populations, we have discovered remarkable heterogeneity in both. Firstly, hepatoblast arise from two spatially distinct DE populations that each contributes uniquely to the liver bud. The ventral midline progenitors contribute mainly to the hepatoblasts that populate the anterior liver bud while the bilaterally symmetric lateral progenitors produce hepatoblasts that contribute to the posterior liver bud. Surprisingly, each progenitor has unique requirements for this process and is each associated with different supportive mesenchyme upon induction. For example, FGF signals are required to induce the sinus venosus bounded anterior hepatoblasts, while the septum transversum mesenchyme bounded posterior hepatoblasts require BMP signaling to be induced Furthermore, recent fate mapping from our group demonstrates that the anterior hepatoblasts mainly contribute to the caudal lobes while posterior hepatoblasts mainly contribute to the rostral lobe. Finally unpublished histological and molecular data suggests that the mesenchyme supporting the rostral and caudal lobes are distinct tissues. Together these observations suggest that normal development follows two routes for generating hepatoblasts. We hypothesize that the heterogeneity generated during early hepatic development is essential for normal liver function and that it aids in generating the heterogeneity recently identified in adult hepatocyte and cholangiocyte populations. Guided by the new developmental framework outlined above, the aims of our proposal use our expertise in embryology and the power of mouse genetics to further delineate this heterogeneity and to identify how it contributes to normal development. In Aim1 we propose to use conditional knock-out strategies to assess how FGF and BMP signals contribute to hepatoblast induction in vivo. In Aim2, we use an ex vivo approach and novel mouse reporters in vivo to uncover the developmental origin and adult contribution of the rostral and caudal lobe mesenchyme as well as determine the molecular signature of the rostral and caudal lobe hepatoblasts. The long-term goals are to understand how developmental heterogeneity contributes to key adult responses such as homeostasis and regeneration and to use these developmental insights to produce functional hepatic tissues in vitro.