Intrahepatic bile ducts develop according to a new mode of tubulogenesis regulated by the transcription factor SOX9.
OBJECTIVE
A number of diseases are characterized by defective formation of the intrahepatic bile ducts. In the embryo, hepatoblasts differentiate to cholangiocytes, which give rise to the bile ducts. Here, we investigated duct development in mouse liver and characterized the role of the SRY-related HMG box transcription factor 9 (SOX9).


METHODS
We identified SOX9 as a new biliary marker and used it in immunostaining experiments to characterize bile duct morphogenesis. The expression of growth factors was determined by in situ hybridization and immunostaining, and their role was studied on cultured hepatoblasts. SOX9 function was investigated by phenotyping mice with a liver-specific inactivation of Sox9.


RESULTS
Biliary tubulogenesis started with formation of asymmetrical ductal structures, lined on the portal side by cholangiocytes and on the parenchymal side by hepatoblasts. When the ducts grew from the hilum to the periphery, the hepatoblasts lining the asymmetrical structures differentiated to cholangiocytes, thereby allowing formation of symmetrical ducts lined only by cholangiocytes. We also provide evidence that transforming growth factor-beta promotes differentiation of the hepatoblasts lining the asymmetrical structures. In the absence of SOX9, the maturation of asymmetrical structures into symmetrical ducts was delayed. This was associated with abnormal expression of CCAAT/Enhancer Binding Protein alpha and Homolog of Hairy/Enhancer of Split-1, as well as of the transforming growth factor-beta receptor type II, which are regulators of biliary development.


CONCLUSIONS
Our results suggest that biliary development proceeds according to a new mode of tubulogenesis characterized by transient asymmetry and whose timing is controlled by SOX9.
Antoniou
Aline
A
Université catholique de Louvain, de Duve Institute, Brussels, Belgium.
Raynaud
Peggy
P
Cordi
Sabine
S
Zong
Yiwei
Y
Tronche
François
F
Stanger
Ben Z
BZ
Jacquemin
Patrick
P
Pierreux
Christophe E
CE
Clotman
Frederic
F
Lemaigre
Frederic P
FP
D000818:Animals; D001653:Bile Ducts, Intrahepatic / Q000196:embryology* / Q000254:growth & development; D002454:Cell Differentiation; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D008099:Liver / Q000196:embryology / Q000254:growth & development; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D009024:Morphogenesis / Q000235:genetics; D011247:Pregnancy; D011336:Probability; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055758:SOX9 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology
D055758:SOX9 Transcription Factor; D004815:Epidermal Growth Factor