Pax3 is essential for normal cardiac neural crest morphogenesis but is not required during migration nor outflow tract septation.

Systemic loss-of-function studies have demonstrated that Pax3 transcription factor expression is essential for dorsal neural tube, early neural crest and muscle cell lineage morphogenesis. Cardiac neural crest cells participate in both remodeling of the pharyngeal arch arteries and outflow tract septation during heart development, but the lineage specific role of Pax3 in neural crest function has not yet been determined. To gain insight into the requirement of Pax3 within the neural crest, we conditionally deleted Pax3 in both the premigratory and migratory neural crest populations via Wnt1-Cre and Ap2α-Cre and via P0-Cre in only the migratory neural crest, and compared these phenotypes to the pulmonary atresia phenotype observed following the systemic loss of Pax3. Surprisingly, using Wnt1-Cre deletion there are no resultant heart defects despite the loss of Pax3 from the premigratory and migratory neural crest. In contrast, earlier premigratory and migratory Ap2α-Cre mediated deletion resulted in double outlet right ventricle alignment heart defects. In order to assess the tissue-specific contribution of neural crest to heart development, genetic ablation of neural crest lineage using a Wnt1-Cre-activated diphtheria toxin fragment-A cell-killing system was employed. Significantly, ablation of Wnt1-Cre-expressing neural crest cells resulted in fully penetrant persistent truncus arteriosus malformations. Combined, the data show that Pax3 is essential for early neural crest progenitor formation, but is not required for subsequent cardiac neural crest progeny morphogenesis involving their migration to the heart or septation of the outflow tract.