Transitory expression of and in maxillary arch Dlx 5 Dlx 6 precursors is essential for upper jaw morphogenesis

Asymmetric, articulated jaws support active predation in vertebrates; they derive from the first pharyngeal arch (PA1) which generates both maxillary and mandibular components. PA1 is colonized by cranial neural crest cells (CNCCs) which give rise to most bones and tendons of the jaws. The elements formed by different CNCCs contingents are specified by the combinatorial expression of genes. and are predominantly expressed by Dlx Dlx5 Dlx6 mandibular CNCCs. Analysis of the phenotype of and double mutant Dlx5 Dlx6 mice has suggested that they are necessary and sufficient to specify mandibular identity. Here, using 3D reconstruction, we show that inactivation of and does not only affect the mandibular arch, but results in the Dlx5 Dlx6 simultaneous transformation of mandibular and maxillary skeletal elements which assume a similar morphology with gain of symmetry. As and Dlx5Dlx6 -expressing cells are not found in the maxillary bud, we have examined the lineage of -expressing progenitors using an genetic approach. We Dlx5 in vivo find that a contingent of cells deriving from precursors transiently expressing participate in the formation of the maxillary arch. These cells are mostly Dlx5 located in the distal part of the maxillary arch and might derive from its lambdoidal junction with the olfactory pit. Our findings extend current models of jaw morphogenesis and provide an explanation for the maxillary defects of Dlx5 and mutants. Our results imply that Dlx5 and Dlx6 model the upper and Dlx6 the lower PA1 components through different morphogenetic mechanisms which are, however, coordinated as they give rise to functional, articulated jaws. Referee Status: