The extrahepatopancreatic ducts as a novel source of hepatic progenitors

项目摘要 虽然前肠内胚层的研究主要集中在肝脏的发育和再生上， 胰腺和肠道，相对较少的注意力集中在这些器官之间的联系上。 连接在一起。哺乳动物和斑马鱼肝胰管外系统(EHPD)的功能是管状的 连接肝、胰腺、胆和十二指肠的网络。广泛的遗传和 人和斑马鱼EHPD之间的形态发生保守不仅使斑马鱼有资格成为实用的 这种组织的遗传模型，但也表明EHPD在简单的运输之外发挥着更关键的作用 肝脏胆汁和胰酶。我们在这里建议利用斑马鱼脊椎动物模型严格地 探索EHPD细胞作为肝脏发育祖细胞的新的和重要的来源的功能， 动态平衡和再生。 使用斑马鱼模型，表现为阿拉格尔综合征(ALGS)的肝胆管细胞丢失，我们发现 肝内胆管(IHD)细胞的发育不全，由于Notch配体的一过性丢失，可导致 在EHPD内，肝脏外有强大的细胞反应。具体地说，EHPD细胞对肝管起反应 细胞过度增殖造成的细胞损失，主要是再生的IHD细胞和肝细胞 还有。这些意想不到的发现表明，EHPD系统中有多能祖细胞，可以 对肝脏有贡献。我们在EHPD中发现的多能祖细胞导致了根本的新 问题：在发育过程中，EHPD细胞对肝脏的贡献程度和机制是什么？ 动态平衡和再生？这些祖细胞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初始来源。我们假设 EHDP前体细胞具有很高的增殖能力，并保持在未分化的静止状态 通过成纤维细胞生长因子信号。此外，我们假设这些EHPD细胞准备好扩增和迁移到 分布在整个肝脏，最终采用胆管细胞或肝细胞的特性 发育和动态平衡，在更大程度上，是对特定类型的肝损伤的反应。不足 EHPD祖细胞可能导致不同的再生机制，如转分化。测试 这些假设可能导致一个统一的、动态的肝脏再生模型，由此EHPD的可用性 祖细胞是一个重要的决定因素，再生机制占主导地位。 发现EHPD细胞在肝脏再生生物学中的更基本作用将促进我们的 肝病的认识和治疗，包括ALGS和其他胆管疾病，以及肝细胞 精神错乱。EHPD在肝脏再生中的核心作用也将使其成为 肝脏疗法。我们建议研究EHPD细胞在肝脏发育过程中的谱系贡献。 动态平衡和再生，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.