Deficient GATA6-ACKR3/CXCR7 signaling leads to bicuspid aortic valve

The cardiac outflow tract (OFT) transiently links the ventricles to the aortic sac and gives rise to the arterial valves. Abnormalities of the arterial valves, mainly bicuspid aortic valve (BAV), are the commonest congenital anomalies. Gata6 inactivating mutations cause cardiac OFT defects and BAV, but the cellular and molecular mechanisms are poorly understood. We find that Gata6 ^STOP/+ mice, generated by CRISPR-Cas9, display highly penetrant BAV (70%), and a membranous ventricular septal defect (43%). OFT development in Gata6 ^STOP/+ mice is characterized by decreased proliferation and increased presence of ISL1-positive progenitor cells, suggestive of aberrant cardiovascular differentiation. In support, conditional Gata6 deletion with the Mef2c ^{AHF − Cre} driver line recapitulates Gata6 ^STOP/+ phenotypes, indicating a cell-autonomous requirement for Gata6 in the SHF. Gata6 ^STOP/+ mice display dramatic reductions in OFT length and caliber, associated with deficient cardiac neural crest cells (cNCCs) contribution in the mutant OFT, potentially underlying the valvulo-septal defects. RNA-seq analysis of Gata6 ^STOP/+ OFT reveal multiple depleted pathways linked to cell proliferation and migration, and highlight ACKR3/CXCR7 as a candidate gene regulating migratory effects downstream of GATA6. Consistently, mesenchymal cell migration and invasion are drastically reduced in explanted Gata6 ^STOP/+ OFT tissue. Supplementing wild type OFT explants with CXCR7 agonists decreases mesenchymal cell migration and increases invasion, these effects are suppressed in the Gata6 ^STOP/+ explants, suggesting that CXCR7-mediated migration and invasion is Gata6-dependent. These findings demonstrate a requirement for CXCR7 downstream of Gata6 in OFT development and suggest that the cellular defects associated with BAV in GATA6-deficient mice can be ascribed, in part, to reduced CXCR7 function.