SEGMENTAL IDENTITY CAN CHANGE INDEPENDENTLY IN THE HINDBRAIN AND RHOMBENCEPHALIC NEURAL CREST

In this study we tested whether the segmental identities of the hindbr ain and its derived neural crest are necessarily linked or, instead, i f they can be altered independently. Using morphological criteria, we show that the hindbrains of Hoxa-2 mutant mice, in which the second ar ch skeletal derivatives assume first arch characteristics (Gendron-Mag uire et al. [1993] Cell 75:1317-1331; Rijli et al. [1993] Cell 75:1333 -1349), retain normal segmental identities. Also, by phenotypic analys is, we show that, with retinoic acid, changes can be induced in the id entity of the preotic hindbrain without effects in its derived neural crest. Our data thus indicate that identity changes in the hindbrain a nd branchial arch neural crest can occur independently. Moreover, if H oxa-2 is concomitantly induced by retinoic acid in the first branchial arch, the proximal derivatives of this arch are also affected. We pro pose a model for the patterning of the branchial region, according to which the segmental identity in this area is provided mainly by the br anchial arches. (C) 1997 Wiley-Liss, Inc.