Stem cells in the epithelial tubular tissues are essential for provision of epithelial cells during not only development but also regeneration. Thus, in order to understand how epithelial tubular tissues are formed and maintained, molecular mechanisms underlying maintenance and differentiation of stem cells should be revealed. In this study, we focus on hepatoblasts that act as hepatic stem cells in the developing liver and challenge to clarify extracellular signals and transcription factor networks that regulate maintenance and differentiation of hepatoblasts. Moreover, we try to induce formation of bile duct-like structures from biliary epithelial cells generated from hepatoblasts in culture.

Hepatic stem cells are defined as clonogenic cells that can differentiate into both hepatocytes and biliary epithelial cells, renew themselves and are essential for liver development, regeneration and carcinogenesis. We have developed a strategy to isolate hepatoblasts from the developing mouse liver using flow-cytometry. Cells separated into various cell subpopulations were severally sorted out and clonally cultured (1 cell/well) to precisely examine the potential for proliferation and differentiation of each cell. This clonal analysis of isolated cells allowed us to identify and enrich cells with hepatic stem cell capacity, including bi-lineage differentiation, self-renewing cell division and liver tissue reconstitution. In this study, we examine the molecular mechanism regulating maintenance and differentiation of isolated hepatoblasts and induce their differentiation into biliary epithelial cells and formation of bile duct-like structures in vitro.

Our study will be helpful to understand a common mechanism that regulates a process from differentiation of tissue-specific stem cells into epithelial cells to formation of tubular tissues by differentiated epithelial cells during development and regeneration. Our future findings may contribute to the development of regenerative therapies for refractory diseases and provide information on a mechanism of malformation of epithelial tubular tissues.