Cell-autonomous and nonautonomous actions of endothelin-A receptor signaling in craniofacial and cardiovascular development

Craniofacial and cardiac development relies on the proper patterning of the neural crest-derived ectomesenchyme of the pharyngeal arches, from which many craniofacial and great vessel structures arise. One of the intercellular signaling molecules that is involved in this process, endothelin-1 (ET-1), is expressed in the arch epithelium and influences arch development by binding to its cognate receptor, the endothelin A (ET_A) receptor, found on ectomesenchymal cells. We have previously shown that absence of ET_A signaling in ET_A^-/- mouse embryos disrupts neural crest cell development, resulting in craniofacial and cardiovascular defects similar in many aspects to those in mouse models of DiGeorge syndrome. These changes may reflect a cell-autonomous requirement for ET_A signaling during crest cell development because the ET_A receptor is an intracellular signaling molecule. However, it is also possible that some of the observed defects in ET_A^-/- embryos could arise from the absence of downstream signaling that act in a non-cell-autonomous manner. To address this question, we performed chimera analysis using ET_A^-/- embryonic stem cells. We observe that, in almost all early ET_A ^-/- ↔ ^+/+ chimeric embryos, ET_A ^-/- cells are excluded from the caudoventral aspects of the pharyngeal arches, suggesting a cell-autonomous role for ET_A signaling in crest cell migration and/or colonization. Interestingly, in the few embryos in which mutant cells do reach the ventral arch, structures derived from this area are either composed solely of wild type cells or are missing, suggesting a second cell-autonomous role for ET_A signaling in postmigratory crest cell differentiation. In the cardiac outflow tract and great vessels, ET_A^-/- cells are excluded from the walls of the developing pharyngeal arch arteries, indicating that ET_A signaling also acts cell-autonomously during cardiac neural crest cell development.