Osr2 acts downstream of Pax9 and interacts with both Msx1 and Pax9 to pattern the tooth developmental field

► Generation of new Pax9 conditional and Pax9Osr2 knockin mouse strains. ► Expression of Osr2 from Pax9 locus rescued tooth development in Osr2−/− mice. ► Pax9 is required for maintenance of Osr2 expression in developing tooth mesenchyme. ► Pax9−/−Osr2−/− mutant mice show tooth developmental arrest similar to Pax9−/− mice. ► Osr2 forms protein interaction complexes with Msx1 and Pax9 in vivo.