Frontal sections through the head of E18.5 Ednra+/+;R26R;Wnt1-Cre (A,C,E,G) and Ednra−/−;R26R;Wnt1-Cre (B,D,F,H) embryos. (A,B) Labeled cells are observed in the head mesenchyme, premaxilla (pm), mandible (md), Meckel’s cartilage (mc) and dental papilla of the upper and lower incisors (in) of Ednra+/+;R26R;Wnt1-Cre embryos (A). A similar pattern is observed in Ednra−/−;R26R;Wnt1-Cre embryos, though the recessed lower jaw is not observed (B). (C,D) In sections through the lower incisors, labeled cells are observed in the dental papilla and mandible of Ednra+/+;R26R;Wnt1-Cre embryos (C). In Ednra−/− ;R26R;Wnt1-Cre embryos (D), labeled cells are present in the dental papilla and small amount of mandible that is present (arrow). (E,F) Labeled cells in Ednra+/+;R26R;Wnt1-Cre embryos are observed in the maxilla (mx), dental papilla of upper (um) and lower (lm) molars and lower incisor (in) and surrounding mesenchyme (E). A similar pattern is observed in Ednra−/−;R26R;Wnt1-Cre embryos (F), though the lower molars are proximal to this plane of section due to the mandibular hypoplasia. (G,H) In sections proximal to those in (E,F), labeled cells in wild type embryos are observed in the mandible and palatine bones (pl), dental papilla of the upper and lower molars and surrounding mesenchyme (G). In Ednra−/−;R26R;Wnt1-Cre embryos, a similar contribution of labeled cells is observed, including the dysmorphic bone in the lower jaw that has previously been shown to have undergone homeosis to a maxilla-like structure (pseudo-maxilla, mx*). (I,J) In Ednra+/+;R26R;Wnt1-Cre embryos, the malleus (m), incus (i), Meckel’s cartilage (mc) and tympanic ring (ty) are all populated by labeled cells (I). In Ednra−/−;R26R;Wnt1-Cre embryos, aberrant cartilage (*) containing labeled cells have replaced the malleus and incus (J). Labeled cells are also present in the greater horns (h) of the hyoid, which are aberrantly present near the otic capsule (oc). or, oral cavity; t tongue; *vib, ectopic vibrissae.