Fig. 2

Pax9 in developing mouse dentary coronoid process. a, b Parasagittal section through proximal mouse mandible at E14.5 to show domain of Pax9 expression. Pax9 ^LacZ reporter mouse (a) and in situ hybridisation for Pax9 (b) show gene expression in the condensed mesenchyme surrounding the coronoid process. This expression domain is continuous with the Pax9 expressing mesenchyme of the dental field (d.m. in a); c Sox9 protein, detected by immunofluorescence, is expressed in the same domain around the ossified coronoid process as Pax9; d, g haematoxylin and eosin staining of the coronoid process at E14.5 after conditional deletion of Pax9 in Wnt1-positive neural crest lineage. The ossified dentary is pseudo-coloured. An ossified coronoid process is observed in wildtype mice (d), but not in conditional mutant mice (g). f, i Sirius red/alcian blue trichrome staining shows that the coronoid process fails to develop by E17.5. Loss of Pax9 expression does not result in loss of the temporalis muscle (d, f, g, i). e, h in situ hybridisation staining for Scleraxis (Scx) mRNA. The connection between the temporalis muscle and dentary bone is maintained via Scx expressing tendon cells which form around an outgrowth of periosteal tissue in place of the coronoid process (double dagger in g–i); cp coronoid process; temp temporalis muscle; dm dental mesenchyme; Scale bar in b–i is 100 µm