Laying down the jaw

The Dlx gene family has been linked to the evolution of the gnathostome (jawed vertebrate) skull. In the 22 August ScienceXpress, Depew et al. describe the affect of deleting Dlx5 and Dlx6 genes on the development of the mouse jaw (Sciencexpress, 22 August 2002, DOI:10.1126/science.1075703). They performed extensive in situ hybridization analysis of mutant embryos to study the expression of genes involved in branchial arch development. In the absence of Dlx5/6 they observed a 'homeotic' transformation of the lower jaw into an upper jaw. Depew et al. propose that the establishment of a pattern of nested expression of Dlx genes in the branchial arches contributed to the transition from jawless to jawed vertebrates.