RETINOIC ACID AND RETINOIC ACID RECEPTORS IN CRANIOFACIAL DEVELOPMENT

Interest in retinoids and craniofacial development originated independ ently from nutritional and teratological studies; however the site of action of retinoids in normal development remains contentious. Recent transgenic strategies have shown that retinoic acid and nuclear retino id receptors are required for the morphogenetic specification of crani al neural crest cells and their mesenchymal derivatives during craniof acial development. Interestingly, while some aspects of the RA teratog enicity have been shown to be receptor-mediated, there is as yet no cl ear evidence that this is the case for the embryonic head and face. Ho x genes are one important set of targets for RA in the developing neur al primordium and cranial neural crest, but it remains unclear as to h ow retinoid-mediated regulation of such targets is realized as the mor phogenetic specification of cell fate.