The Role of the Eda Pathway in the Morphogenesis of Molar Roots

Abstract

The role of the Eda gene during the formation of ectodermal appendages such as nail, hair, teeth, and sweat glands have been unveiled through many studies. Mutation in the Eda pathway (Eda, Edar, Edaradd) results in Hypohydrotic Ectodermal Dysplasia (HED) with patients showing hypodontia and abnormally shaped teeth. The role of the Eda pathway in tooth crown development has been widely studied using the mouse as a model but the role of the Eda pathway during root formation is not well known. I have used computerised tomography (CT) and histological sections of Eda ‐/‐ (tabby) and Edar ‐/‐ (downless) mice to investigate possible root defects in these mice.My analysis shows a clear variation in the size, shape, and number of roots in mutants (tabby and downless) compared to wild type littermates. In particular the mutant teeth showed late or no bifurcation of roots (Taurodontism), indicating disruption in the development of the cells that create the roots (Hertwig epithelial root sheath, HERS). In situ analysis also indicated that Shh expression was reduced in these cells. The results show that the Eda pathway has a role in root morphogenesis and we are now further investigating the mechanisms by which loss of the Eda pathway affects root formation.