The extrahepatopancreatic ducts as a novel source of hepatic progenitors

项目摘要 虽然前肠内胚层研究主要集中在肝脏的发育和再生， 胰腺和肠，相对较少的注意力放在这些器官之间的联系上， 连接.哺乳动物和斑马鱼的肝外胰管（extrahepatopancreatic duct，EHPD）系统是一个管状系统 连接肝脏、胰腺和胆囊以及十二指肠的网络。广泛的遗传和 人类和斑马鱼EHPDs之间的形态发生保守性不仅使斑马鱼有资格成为一种实用的 这种组织的遗传模型，但也表明EHPDs除了简单的运输外， 肝胆汁和胰腺酶。我们在这里建议利用斑马鱼脊椎动物模型， 探索EHPD细胞作为肝脏发育祖细胞的新的重要来源的功能， 体内平衡和再生 使用斑马鱼模型，表型模仿Alagille综合征（ALGS）中的肝胆管细胞丢失，我们发现 由于Notch配体Jagged的短暂缺失，肝内胆管（IHD）细胞的发育不全可导致 在肝外EHPD内有强烈的细胞反应具体来说，EHPD细胞对肝管反应， 过度增殖导致的细胞丢失，主要导致再生的IHD细胞和肝细胞 also.这些意想不到的发现表明EHPD系统含有多能祖细胞， 有助于肝脏。我们在EHPD中发现了多能祖细胞，这导致了一个新的基础。 问题：在发育过程中，EHPD细胞对肝脏的贡献程度如何，作用机制如何， 体内平衡和再生这些祖先是如何形成和维持的？ 我们假设EHPD是几乎所有肝脏祖细胞的最初来源。我们断定 EHDP祖细胞具有高增殖能力并维持在未分化的静止状态 FGF信号。此外，我们假设这些EHPD细胞准备扩增和迁移， 分布在整个肝脏，最终采用胆管细胞或肝细胞的身份， 发展和稳态，并在更大程度上，在响应特定类型的肝损伤。不足 EHPD祖细胞可能导致替代的再生机制，如转分化。测试 这些假设可能会导致一个统一的，动态的肝再生模型， 祖细胞是再生机制占主导地位的重要决定因素。 揭示EHPD细胞在肝脏再生生物学中更基本的作用将推动我们的研究。 了解和治疗肝脏疾病，包括ALGS和其他胆管疾病，以及肝细胞 紊乱EHPD在肝再生中的核心作用也将暗示它是一种新的靶组织， 肝脏治疗我们建议研究EHPD细胞在肝脏发育过程中的谱系贡献， 体内平衡和再生，以及驱动这一复杂过程的遗传和细胞机制。

Project Summary While foregut endoderm research has primarily focused on the development and regeneration of the liver, pancreas, and intestine, relatively little attention have been placed on the nexus by which these organs are connected. The mammals and zebrafish the extrahepatopancreatic duct (EHPD) system functions as a tubular network joining the liver, pancreas, and gall bladder together with the duodenum. Extensive genetic and morphogenetic conservation between human and zebrafish EHPDs not only qualifies the zebrafish as a practical genetic model for this tissue, but also suggests more critical roles for the EHPDs beyond simply transporting hepatic bile and pancreatic enzymes. We propose here to leverage the zebrafish vertebrate model to rigorously explore the function of EHPD cells as a novel and significant source of progenitors for liver development, homeostasis, and regeneration. Using a zebrafish model that phenocopies hepatic biliary cell loss in Alagille Syndrome (ALGS), we found that agenesis of intrahepatic duct (IHD) cells, due to transient loss of the Notch ligand Jagged, can lead to a robust cellular response outside the liver, within the EHPD. Specifically, the EHPD cells react to the liver duct cell loss by proliferating excessively and contributing primarily to the regenerated IHD cells and hepatocytes also. These unexpected findings suggest that the EHPD system harbors multipotent progenitors that can contribute to the liver. Our discovery of multipotent progenitors residing in the EHPD leads to fundamental new questions: To what extent and by what mechanisms do the EHPD cells contribute to the liver during development, homeostasis, and regeneration? And how are these progenitors formed and maintained? We hypothesize that the EHPDs act as the initial source of nearly all progenitors for the liver. We posit that EHDP progenitors have high proliferative capacity and are maintained in an undifferentiated, quiescent state by FGF signaling. Further, we hypothesize that these EHPD cells are poised for expansion and migration to become distributed throughout the liver, ultimately adopting cholangiocyte or hepatocyte identity during development and homeostasis, and to a greater degree, in response to specific types of liver damage. Insufficient EHPD progenitors may lead to alternative mechanisms of regeneration such as transdifferentiation. Testing these hypotheses may lead to a unifying, dynamic liver regeneration model, whereby the availability of EHPDs progenitors is a significant determinant of which regenerative mechanism predominates. Uncovering a more fundamental role for the EHPD cells in liver regenerative biology will advance our understanding and treatment of liver diseases including ALGS and other cholangiopathies, as well as hepatocyte disorders. A central role for the EHPD in liver regeneration would also implicate it as a novel target tissue for liver therapies. We propose to investigate the lineage contribution of EHPD cells during liver development, homeostasis, and regeneration, and the genetic and cellular mechanisms driving this complex process.