DIFFERENTIAL AND OVERLAPPING EXPRESSION DOMAINS OF DLX-2 AND DLX-3 SUGGEST DISTINCT ROLES FOR DISTAL-LESS HOMEOBOX GENES IN CRANIOFACIAL DEVELOPMENT

During the development of the vertebrate head, cranial neural crest ce lls migrate into the branchial arches to form many of the structures o f the facial skeleton. These cells follow defined developmental pathwa ys and their fates are determined early. We have isolated and characte rized the murine Distal-less homeobox gene Dlx-3 and have performed a comparative analysis of Dlx-3 and Dlx-2 expression during craniofacial development. In contrast to Dlx-2 and other vertebrate Distal-less ge nes, Dlx-3 is not expressed in the central nervous system and is expre ssed in a highly restricted region of the branchial arches. Dlx-2 and -3 display temporal and spatial differences in expression in the arche s and their derivatives. In later development, these two genes are exp ressed in both complementary and partially overlapping domains in regi ons whose development is dependent on epithelial-mesenchymal interacti ons, such as the developing middle and inner ear, teeth and whisker fo llicles. The differential expression of Dlx genes in the branchial reg ion suggests that they play key roles in craniofacial patterning and m orphogenesis.