Fig. S1. Gli3 expression in diastema and molar regions. Radioactive in situ hybridisation on sagittal sections showed that Gli3 expression was prominent in mesenchyme of the diastema region in wild type at E14.5 (arrow).

Fig. S2. Cilia in Wnt1-Cre/polaris^flox/flox mice. In Wnt1-Cre/polaris^flox/flox mice at E14.5, acetylated α-tubulin positive cells (immunohistochemistly) are found in mesenchymal cell adjacent to tooth epithelium (arrowheads). Tooth epithelium outlined in blue (A). Nuclei are shown in blue by DAPI (B).

Fig. S3. p21 expression in diastema and molar regions. Radioactive in situ hybridisation on sagittal sections showed that p21 was expressed in epithelial buds in the diastema region in wild type (arrowhead in A), whereas expression was absent in diastemal epithelial buds in Tg737^orpk embryos at E13.5 (arrowhead in B).

Fig. S4. Incisor and molar gene expression in Tg737^orpk mutants. Radioactive in situ hybridisation on sagittal sections of newborn Tg737^orpk mutants. Arrowheads indicate supernumerary teeth. The molar marker gene Barx1 was expressed in supernumerary tooth (B), whereas expression of incisor marker genes dHAND (C) and Islet1 (D) could not be detected.