Ectodysplasin receptor-mediated signaling is essential for embryonic submandibular salivary gland development

Hypohidrotic (anhidrotic) ectodermal dysplasia (HED), the most common of the approximately 150 described ectodermal dysplasias, is a disorder characterized by abnormal hair, teeth, sweat glands, and salivary glands. Mutations in the EDA (ectodysplasin-A) and EDAR (ectodysplasin-A receptor) genes are responsible for X-linked and autosomal HED, respectively. Abnormal phenotypes similar to HED are seen in Tabby (Eda(Ta)) and downless (Edar(dl)) mutant mice. Although recent studies have focused on the role of Eda/Edar signaling during hair and tooth development, very little is known about its role during embryonic submandibular salivary gland (SMG) development. To this end, we analyzed the SMG phenotypes in Tabby (Ta) and downless (dl) mutant mice and determined that Ta SMGs are hypoplastic, whereas dl SMGs are severely dysplastic. The absence of SMG ducts and acini in dl SMGs suggests that Eda/Edar signaling is essential for lumina formation and glandular histodifferentiation. Our localization of Eda and Edar proteins at sites of lumen and acini formation supports this conclusion. Moreover, the presence of SMGs in both Ta and dl mutant mice, as well as the absence of immunodetectable Eda and Edar protein in Initial Bud and Early Pseudoglandular stage SMGs, indicate that Eda/Edar-mediated signaling is important for branching morphogenesis and histodifferentiation, but not for initial gland formation. To initially delineate the morphoregulatory role of Eda/Edar-mediated signaling during embryonic SMG development, we cultured embryonic day 14 SMGs with enhanced or abrogated Eda/Edar signaling. Eda supplementation induced a significant increase in SMG branching, and enhanced activation of NF-kappaB. Abrogating Eda/Edar signaling by adding the soluble form of Edar to bind endogenous ligand in embryonic SMGs results in a significant dose-dependent decrease in branching morphogenesis. Taken together, our results suggest that the Eda/Edar/NF-kappaB pathway exerts its effect on SMG epithelial cell proliferation, lumina formation, and histodifferentiation.