title: Disrupted Slit-Robo signalling results in membranous ventricular septum defects and bicuspid aortic valves.
abstract: OBJECTIVE
  The mesenchymal cushions lining the early embryonic heart undergo complex remodelling to form the membranous ventricular septum as well as the atrioventricular and semilunar valves in later life. Disruption of this process underlies the most common congenital heart defects. Here, we identified a novel role for Slit-Robo signalling in the development of the murine membranous ventricular septum and cardiac valves.
  
  
  RESULTS
  Expression of Robo1 and Robo2 receptors and their ligands, Slit2 and Slit3, was present in or adjacent to all cardiac cushions/valves. Loss of Robo1 or both Robo1 and Robo2 resulted in membranous ventricular septum defects at birth, a defect also found in Slit3, but not in Slit2 mutants. Additionally, Robo1;Robo2 double mutants showed thickened immature semilunar and atrioventricular valves as well as highly penetrant bicuspid aortic valves. Slit2 mutants recapitulated the semilunar phenotype, whereas Slit3 mutants displayed thickened atrioventricular valves. Bicuspid aortic cushions were already observed at E12.5 in the Robo1;Robo2 double mutants. Expression of Notch- and downstream Hey and Hes genes was down-regulated in Robo1 mutants, suggesting that reduced Notch signalling in mice lacking Robo might underlie the defects. Luciferase assays confirmed regulation of Notch signalling by Robo.
  
  
  CONCLUSIONS
  Cardiac defects in mutants for Robo or Slit range from membranous ventricular septum defects to bicuspid aortic valves. These ligands and receptors have unique functions during development of specific cardiac cushion derivatives, and the Slit-Robo signalling pathway likely enforces its role by regulating Notch signalling, making these mutants a valuable new model to study cardiac valve formation.
authors.affiliation: Department of Cell and Developmental Biology, University College London, 21 University Street, London WC1E 6DE, UK m.mommersteeg@ucl.ac.uk.
authors.forename: Mathilda T M
authors.initials: MT
authors.lastname: Mommersteeg
authors.affiliation: Department of Cell and Developmental Biology, University College London, 21 University Street, London WC1E 6DE, UK.
authors.forename: Mason L
authors.initials: ML
authors.lastname: Yeh
authors.affiliation: Department of Cell and Developmental Biology, University College London, 21 University Street, London WC1E 6DE, UK.
authors.forename: John G
authors.initials: JG
authors.lastname: Parnavelas
authors.affiliation: Department of Cell and Developmental Biology, University College London, 21 University Street, London WC1E 6DE, UK.
authors.forename: William D
authors.initials: WD
authors.lastname: Andrews
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000002:abnormalities* / Q000503:physiopathology; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000502:physiology; D000082882:Bicuspid Aortic Valve Disease; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology; D004195:Disease Models, Animal; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology; D006330:Heart Defects, Congenital / Q000235:genetics* / Q000503:physiopathology; D006349:Heart Valve Diseases / Q000235:genetics* / Q000503:physiopathology; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics* / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics* / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000502:physiology; D011971:Receptors, Immunologic / Q000235:genetics* / Q000502:physiology; D051880:Receptors, Notch / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology; D000072056:Transcription Factor HES-1; D054088:Ventricular Septum / Q000473:pathology; D000097905:Roundabout Proteins; D000098552:Slit Homolog 2 Protein
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018797:Cell Cycle Proteins; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011971:Receptors, Immunologic; D051880:Receptors, Notch; D000072056:Transcription Factor HES-1; D000097905:Roundabout Proteins; D000098552:Slit Homolog 2 Protein; C489734:Hes1 protein, mouse; C120420:Hey1 protein, mouse; C498888:Robo2 protein, mouse; C432251:Slit3 protein, mouse
keywords: Bicuspid aortic valves; Heart development; Membranous ventricular septum defect; Notch signalling pathway; Slit-Robo signalling pathway