Structural and functional diversity of homeodomain genes of the orthodenticle and empty spiracles classes in Craniata

Despite extensively divergent morphologies, the patterning of the embryonic brain is controlled by highly conserved genetic networks. Orthodenticle and empty spiracles-related homeodomain genes, which are expressed in insects as in vertebrates in anteriormost neuromeres of the embryonic brain, provide examples of such conservations. In gnathostomes, they form small multigene families, each containing three well-characterised orthology classes. In mice, paralogous genes play very different roles in the development of cephalic regions. Some of these roles are probably ancient and conserved in all chordates, while others, like the morphogenesis of gnathostomespecific characters, correspond to much more diversified functions. Genetic analyses in mice together with comparative analyses in a broad range of vertebrates provide new possibilities to investigate the molecular mechanisms which underlie these functional diversifications.