title: Bile duct proliferation in Jag1/fringe heterozygous mice identifies candidate modifiers of the Alagille syndrome hepatic phenotype.
abstract: Alagille syndrome (AGS) is a heterogeneous developmental disorder associated with bile duct paucity and various organ anomalies. The syndrome is caused by mutations in JAG1, which encodes a ligand in the Notch signaling pathway, in the majority of cases and mutations in the NOTCH2 receptor gene in less than 1% of patients. Although a wide array of JAG1 mutations have been identified in the AGS population, these mutational variants have not accounted for the wide phenotypic variability observed in patients with this syndrome. The Fringe genes encode glycosyltransferases, which modify Notch and alter ligand-receptor affinity. In this study, we analyzed double heterozygous mouse models to examine the Fringe genes as potential modifiers of the Notch-mediated hepatic phenotype observed in AGS. We generated mice that were haploinsufficient for both Jag1 and one of three paralogous Fringe genes: Lunatic (Lfng), Radical (Rfng), and Manic (Mfng). Adult Jag1(+/-)Lfng(+/-) and Jag1(+/-)Rfng(+/-) mouse livers exhibited widespread bile duct proliferation beginning at 5 weeks of age and persisting up to 1 year. The Jag1(+/-)Mfng(+/-) livers showed a subtle, yet significant increase in bile duct numbers and bile duct to portal tract ratios. These abnormalities were not observed in the newborn period. Despite the portal tract expansion by bile ducts, fibrosis was not increased and epithelial to mesenchymal transition was not shown in the affected portal tracts.
  
  
  CONCLUSIONS
  Mice heterozygous for mutations in Jag1 and the Fringe genes display striking bile duct proliferation, which is not apparent at birth. These findings suggest that the Fringe genes may regulate postnatal bile duct growth and remodeling, and serve as candidate modifiers of the hepatic phenotype in AGS.
authors.affiliation: Division of Gastroenterology, Hepatology and Nutrition, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Ryan
authors.forename: Christina
authors.initials: C
authors.lastname: Bales
authors.forename: Anthony
authors.initials: A
authors.lastname: Nelson
authors.forename: Dorian M
authors.initials: DM
authors.lastname: Gonzalez
authors.forename: Lara
authors.initials: L
authors.lastname: Underkoffler
authors.forename: Michelle
authors.initials: M
authors.lastname: Segalov
authors.forename: Jeanne
authors.initials: J
authors.lastname: Wilson-Rawls
authors.forename: Susan E
authors.initials: SE
authors.lastname: Cole
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Moran
authors.forename: Pierre
authors.initials: P
authors.lastname: Russo
authors.forename: Nancy B
authors.initials: NB
authors.lastname: Spinner
authors.forename: Kenro
authors.initials: K
authors.lastname: Kusumi
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Loomes
mesh_terms: D016738:Alagille Syndrome / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D001652:Bile Ducts / Q000002:abnormalities / Q000378:metabolism / Q000473:pathology*; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D049109:Cell Proliferation; D004195:Disease Models, Animal; D005964:Glucosyltransferases; D016695:Glycosyltransferases / Q000235:genetics* / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D000072100:Jagged-1 Protein; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D000072099:Serrate-Jagged Proteins; D015398:Signal Transduction / Q000502:physiology
chemical_list: D002135:Calcium-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; C000606274:Jag1 protein, mouse; D000072100:Jagged-1 Protein; D008565:Membrane Proteins; D011506:Proteins; D000072099:Serrate-Jagged Proteins; D016695:Glycosyltransferases; D005964:Glucosyltransferases; C498392:Lfng protein, mouse; C486343:Mfng protein, mouse; C491317:Rfng protein, mouse