Inactivation of Fam20B in the dental epithelium of mice leads to supernumerary incisors.

Tooth formation is tightly regulated by epithelial-mesenchymal interactions via hierarchic cascades of signaling molecules. The glycosaminoglycan (GAG) chains covalently attached to the core protein of proteoglycans (PGs) provide docking sites for signaling molecules and their receptors during the morphogenesis of tissues and organs. Although PGs are believed to play important roles in tooth formation, little is known about their exact functions in this developmental process and the relevant molecular basis. Family with sequence similarity member 20-B (FAM20B) is a newly identified kinase that phosphorylates the xylose in the common linkage region connecting the GAG with the protein core of PGs. The phosphorylation of xylose is essential for elongation of the common linkage region and the subsequent GAG assembly. In this study, we generated a Fam20B-floxed allele in mice and found that inactivating Fam20B in the dental epithelium leads to supernumerary maxillary and mandibular incisors. This finding highlights the pivotal role of PGs in tooth morphogenesis and opens a new window for understanding the regulatory mechanism of PG-mediated signaling cascades during tooth formation.