Over-activation of BMP signaling in neural crest cells precipitates heart outflow tract septation

Establishment of separated pulmonary and systemic circulations in vertebrates relies on the key role of neural crest cells (NCC) for the septation of the embryonic cardiac outflow tract (OFT). Absence of NCCs induces OFT septation defects, analogous to a loss of Bone Morphogenetic Proteins (BMPs) activity, though it remains unclear how BMPs control cardiac NCC differentiation and behaviour. To address this question, we monitored cardiac NCC state upon gain in BMP signaling, caused by the deletion of Dullard , using 3D-imaging and single cell transcriptomics. Specific loss of Dullard in the NCC results in premature OFT septation, pulmonary artery obstruction and embryonic death. This is caused by uncontrolled NCC convergence towards the endocardium and asymmetrical myocardial differentiation, promoted by elevated levels of the guiding cue Sema3c and decreased levels in mesenchymal trait markers. Furthermore, we unraveled the molecular basis of the zipper-like OFT septation where graded Sema3c expression follow a gradient of BMP activation in NCC along the OFT length.