Differential Expression of c-myc and N-myc during Oral Organogenesis of the Mouse Embryo

The expressions of the c- and N-myc proto-oncogenes during oral development of midgestational mouse embryos were examined by in situ hybridization in order to analyze their roles. In the mandibular rudiment, c-myc RNA was strongly expressed in the mesenchymal condensation around the ossification center in which high-level expression of 2 ar (osteopontin) was detected. In tooth germs, c-myc was strongly expressed in the epithelia at the bud stage, and its expression gradually became restricted to the inner enamel epithelia from the cap to bell stages. In contrast, N-myc expression was detected in the undifferentiated mesenchymal cells of the dental papilla. Incorporation of BrdU was examined immunohistochemically to study the relationship between the expressions of c- and N-myc and cell proliferation. Unexpectedly, the distribution of BrdU labelled regions was not coincident with the expressions of c- and N-myc. These results suggest that the level of myc expression is not necessarily related to cell proliferation.