Mammalian Dlx homeobox gene control of craniofacial and inner ear morphogenesis

The Dir homeobox gene family is of ancient origin, with apparent ancestral developmental functions in both nervous system regionalization and appendag e (limb) outgrowth. Additional roles in inner ear and craniofacial developm ent were likely acquired by the Dir gene family during the course of animal evolution. Loss-of-function genetic mutations generated in the mouse have revealed a striking role for Dir genes in patterning of the mammalian centr al nervous system, craniofacial structures and inner ear. Interestingly, no ne of the individual murine Dir gene mutations to date have resulted in lim b defects, suggesting a potentially significant developmental overlap of Di r activity in this embryonic structure. (C) 1999 Wiley-Liss, Inc.