Meltrin β expressed in cardiac neural crest cells is required for ventricular septum formation of the heart

The heart is divided into four chambers by membranous septa and valves. Although evidence suggests that formation of the membranous septa requires migration of neural crest cells into the developing heart, the functional significance of these neural crest cells in the development of the endocardial cushion, an embryonic tissue that gives rise to the membranous appendages, is largely unknown. Mice defective in the protease region of Meltrin β/ADAM19 show ventricular septal defects and defects in valve formation. In this study, by expressing Meltrin β in either endothelial or neural crest cell lineages, we showed that Meltrin β expressed in neural crest cells but not in endothelial cells was required for formation of the ventricular septum and valves. Although Meltrin β-deficient neural crest cells migrated into the heart normally, they could not properly fuse the right and left ridges of the cushion tissues in the proximal outflow tract (OT), and this led to defects in the assembly of the OT and AV cushions forming the ventricular septum. These results genetically demonstrated a critical role of cardiac neural crest cells expressing Meltrin β in triggering fusion of the proximal OT cushions and in formation of the ventricular septum.