The role of notch signaling in the development of intrahepatic bile ducts.
OBJECTIVE
Mutations in Jagged1 , a Notch ligand, cause Alagille syndrome (AGS), a disorder characterized by a paucity of intrahepatic bile ducts (IHBD). The mechanism underlying the contribution of the Notch signaling pathway to IHBD formation, however, remains unknown. Here we investigated the role of Notch signaling in IHBD development.


METHODS
The expression patterns of Jagged1, Notch2, and Hes1 during mouse liver development were analyzed by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR), immunoblot, and immunohistochemistry. The hepatocyte maturation level and IHBD development were studied in Hes1 null mice in comparison with wild-type mice. The effect of Jagged1 on biliary differentiation was assessed by using an in vitro 2-cell coculture system with WB-F344 cells, a cell line derived from normal adult rat liver.


RESULTS
Jagged1 was expressed in the portal mesenchyme during the neonatal period. During the same period, Notch2 and Hes1 expression was observed in the biliary epithelial cells adjacent to the Jagged1-positive cells. During ductal plate remodeling, Notch2 and Hes1 were up-regulated exclusively in the biliary epithelial cells that form tubular structures. In contrast, the tubular formation of IHBD was completely absent in Hes1 null mice. Coculture with Balb3T3 cells stably overexpressing Jagged1 induced transactivation of the Hes1 promoter and increased expression of biliary lineage markers, such as cytokeratin-19 and gamma-glutamyl transpeptidase, in WB-F344 cells.


CONCLUSIONS
Our results suggest that Notch signaling has an important role in the differentiation of biliary epithelial cells and is essential for their tubular formation during IHBD development.
Kodama
Yuzo
Y
Department of Gastroenterology and Hepatology, Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan.
Hijikata
Makoto
M
Kageyama
Ryoichiro
R
Shimotohno
Kunitada
K
Chiba
Tsutomu
T
D016738:Alagille Syndrome / Q000235:genetics* / Q000503:physiopathology; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001653:Bile Ducts, Intrahepatic / Q000196:embryology*; D002135:Calcium-Binding Proteins; D018507:Gene Expression Regulation, Developmental; D018257:Helix-Loop-Helix Motifs; D018398:Homeodomain Proteins / Q000235:genetics* / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins; D000072100:Jagged-1 Protein; D008099:Liver / Q000196:embryology; D008565:Membrane Proteins / Q000235:genetics* / Q000494:pharmacology; D051379:Mice; D051883:Receptor, Notch2; D011956:Receptors, Cell Surface / Q000235:genetics*; D012097:Repressor Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000072099:Serrate-Jagged Proteins; D015398:Signal Transduction; D000072056:Transcription Factor HES-1
D051792:Basic Helix-Loop-Helix Proteins; D002135:Calcium-Binding Proteins; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D000072100:Jagged-1 Protein; D008565:Membrane Proteins; D051883:Receptor, Notch2; D011956:Receptors, Cell Surface; D012097:Repressor Proteins; D000072099:Serrate-Jagged Proteins; D000072056:Transcription Factor HES-1; C000606273:JAG1 protein, human; C000606274:Jag1 protein, mouse; C000606275:Jag1 protein, rat; C497765:Notch2 protein, mouse; C078493:HES1 protein, human