RESUMO
UNLABELLED: 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. 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.
Assuntos
Síndrome de Alagille/patologia , Ductos Biliares/patologia , Proteínas de Ligação ao Cálcio/genética , Glicosiltransferases/genética , Peptídeos e Proteínas de Sinalização Intercelular/genética , Fígado/patologia , Proteínas de Membrana/genética , Proteínas/genética , Síndrome de Alagille/genética , Síndrome de Alagille/metabolismo , Animais , Ductos Biliares/anormalidades , Ductos Biliares/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Proliferação de Células , Modelos Animais de Doenças , Glucosiltransferases , Glicosiltransferases/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Proteína Jagged-1 , Fígado/metabolismo , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Mutação/genética , Fenótipo , Proteínas/metabolismo , Proteínas Serrate-Jagged , Transdução de Sinais/fisiologiaRESUMO
Mutations in the Notch1 receptor and delta-like 3 (Dll3) ligand cause global disruptions in axial segmental patterning. Genetic interactions between members of the notch pathway have previously been shown to cause patterning defects not observed in single gene disruptions. We examined Dll3-Notch1 compound mouse mutants to screen for potential gene interactions. While mice heterozygous at either locus appeared normal, 30% of Dll3-Notch1 double heterozygous animals exhibited localized, segmental anomalies similar to human congenital vertebral defects. Unexpectedly, double heterozygous mice also displayed statistically significant reduction of mandibular height and decreased length of the [corrected] maxillary hard palate. Examination of somite-stage embryos and perinatal anatomy and histology did not reveal any organ defects, so we used microarray-based analysis of Dll3 and Notch1 mutant embryos to identify gene targets that may be involved in notch-regulated segmental or craniofacial development. Thus, Dll3-Notch1 double heterozygous mice model human congenital scoliosis and craniofacial disorders.
