[Expression of c-myc and N-myc in mouse embryos during craniofacial development]

To analyze the role of c- and N-myc on the craniofacial development during the midgestation of mouse embryo, the temprospatial expression in the mandible and the tooth germ was examined by in situ hybridization. In the mandible, c-myc RNA was strongly expressed in the mesenchymal condensation surrounding the ossification center in which a high-level expression of osteopontin was detected with the basal-level expression of c-myc in the corresponding area. In tooth germs, the strong expression of c-myc was detected uniformly in the epithelia of bud stage and then gradually localized in the inner enamel epithelia from cap to bell stages. In contrast, the expression of N-myc was weakly detected in the undifferentiated mesenchymal cells of the dental papilla but was not detected in the regions where c-myc was highly expressed. To study the correlation of myc expression and growth activity, the incorporation of BrdU was examined immunohistochemically. The results revealed that levels of BrdU incorporation were similar between the regions where c-myc was highly expressed and the regions where basal-levels of c- and N-myc expression were detected, suggesting that levels of myc expression are not necessarily correlated to the growth activity. These results indicated that c- and N-myc genes are differentially expressed and further raise the possibility that c- and N-myc may play a major role in differentiation rather than proliferation in the early stage of these organogenesis.