ROLE OF ENDOTHELIN-1 ENDOTHELIN-A RECEPTOR-MEDIATED SIGNALING PATHWAYIN THE AORTIC-ARCH PATTERNING IN MICE/

The intercellular signaling mediated by endothelins and their G protei n-coupled receptors has recently been shown to be essential for the no rmal embryonic development of subsets of neural crest cell derivatives . Endothelin-l (ET-1) is proteolytically generated from its inactive p recursor by endothelin-converting enzyme-1 (ECE-1) and acts on the end othelin-A (ETA) receptor. Genetic disruption of this ET-1/ECE-1/ETA pa thway results in defects in branchial arch-derived craniofacial tissue s, as well as defects in cardiac outflow and great vessel structures, which are derived from cephalic (cardiac) neural crest. in this study, in situ hybridization of ETA(-/-) and ECE-1(-/-) embryos with a cardi ac neural crest marker, cellular retinoic acid-binding protein-1, show s that the migration of neural crest cells from the neural tube to car diac outflow tract is not affected in these embryos. Immunostaining of an endothelial marker, platelet endothelial cell adhesion molecule CD -31, shows that the initial formation of the branchial arch arteries i s not disturbed in ETA-/- or ECE-1(-/-) embryos. To visualize the subs equent patterning of arch vessels in detail, we generated ETA-/- or EC E-1(-/-) embryos that expressed an SM22 alpha-lacZ marker transgene in arterial smooth muscle cells. Whole-mount X-gal staining of these mut ant embryos reveals that the abnormal regression and persistence of sp ecific arch arteries results in disturbance of asymmetrical remodeling of the arch arteries. These defects include abnormal regression of ar ch arteries 4 and 6, enlargement of arch artery 3, and abnormal persis tence of the bilateral ductus caroticus and right dorsal aorta. These abnormalities eventually lead to various types of great vessel malform ations highly similar to those seen ire neural crest-ablated chick emb ryos and human congenital cardiac defects. This study demonstrates tha t ET-1/ETA-mediated signaling plays an essential role in a complex pro cess of aortic arch patterning by affecting the postmigratory cardiac neural crest cell development.