Epithelial tissue structures are indispensable for physiological functions of each organ. In the liver, cholangiocytes, one of liver epithelial cells, form tubular structures called bile ducts. The paucity of bile ducts and the uncontrolled expansion of the ducts result in cholestasis and polycystic disease, respectively. Therefore, it is important to regulate the proper size of the lumen during the development.

In this project, by using the three dimensional (3D) culture system of a liver progenitor cell line, we’d like to understand a general mechanism regulating the formation and maintenance of the luminal structures during organogenesis.

We have identified genes specifically expressed in cholangiocytes forming tubules. Among them, we found that a transcription factor, grainyhead like2 (Grhl2) regulates the formation of the lumen by establishing a molecular network among claudin 3, clauidn 4, and Rab25. We’ll further investigate the role of Grhl2 both in vitro and in vivo. We’re also going to investigate how other transcription factors are involved in the formation of the lumen.

It has been demonstrated that molecules regulating apico-basal polarity including small G-proteins and their regulators, and Par proteins are also involved in the formation of the apical lumen. However, during the development, other molecules must be involved in the formation of apico-basal polarity and lumen of tissue structures. By identifying novel molecules regulating the lumen size, we try to reveal molecular mechanisms governing the formation and maintenance of epithelial tissue structures. We hope our results will help us to understand how epithelial progenitors establish 3D tissue structures during the development.

Molecular mechanisms regulating the development of mature lumen structures

We’ll identify genes specifically upregulated in mature epithelial cells by comparing the gene expression patterns between progenitors (hepatoblasts) and epithelial cells (cholangiocytes). We’ll introduce a candidate gene into HPPL, a liver progenitor cell line, and perform three dimensional culture to examine whether the molecule affects the formation, maturation, and maintenance of the lumen structure.