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 Notchmediated 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. Conclusion: 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.

Differentiation of progenitors in the liver: a matter of local choice

“…Loss of Notch signaling in biliary development in mice, through genetic ablation of jagged 1 or haplosufficiency of Notch2, results in a reduction in biliary development and failure to pattern the biliary tree (57-60). The human congenital disease Alagille syndrome, which is caused by mutations in Notch pathway components, is characterized by a biliary paucity with failure to correctly resolve the ductal plate during development; this phenotype can also be observed in adult mice that harbor a fringe mutant in which Notch is inappropriately activated (61). Huppert and colleagues demonstrated that the Notch1 intracellular domain must act in a dose-dependent fashion, showing that overexpression of the Notch1 intracellular region during development results in a hyper-arborized biliary network, presumably at the cost of mature parenchyma (62).…”

Regulation of mammalian Notch signaling and embryonic development by the proteinO-glucosyltransferase Rumi

“…Rumi regulates Jag1-induced Notch signaling in a dosage-sensitive manner in the mouse liver To provide further in vivo evidence for the regulation of mouse Notch signaling by Rumi, we sought to determine whether decreasing the level of Rumi affects mouse Notch signaling in a Jag1 +/-haploinsufficient background, as these animals are especially sensitive to alterations in the gene dose of other Notch pathway components (Xue et al, 1999;McCright et al, 2001;McCright et al, 2002;Ryan et al, 2008). We crossed the Rumi +/-mice to animals heterozygous for the null allele Jagged1 dDLS (Xue et al, 1999) and analyzed liver sections of P0 animals double heterozygous for the null allele Jagged1 dDLS (Xue et al, 1999), and our Rumi allele and also their control littermates for binding to the Dolichos biflorus agglutinin (DBA) -a marker for bile duct epithelial cells (Watanabe et al, 1981).…”

Protein O-fucosyltransferase 1 (Pofut1) regulates lymphoid and myeloid homeostasis through modulation of Notch receptor ligand interactions

“…39 To determine whether Notch signaling in hematopoiesis is sensitive to Pofut1 heterozygosity when GDPfucose is made rate limiting as in FX Ϫ/Ϫ mice, 20,40 we crossed Pofut1 ϩ/Ϫ and FX Ϫ/Ϫ mice to generate Pofut1 ϩ/Ϫ /FX Ϫ/Ϫ and Pofut1 ϩ/ϩ /FX Ϫ/Ϫ mice. Mice of 8 week maintained on fucose-chow (0.5% weight/weight fucose) since birth were raised on standard chow without fucose supplementation for 1 month.…”