Tissue Distribution of N‐myc Expression in the Early Organogenesis Period of the Mouse Embryo: N‐myc/mouse embryo/in situ hybridization/neural/crest/sclerotome

N‐myc expression in the mouse embryo was examined in its organogenesis period. Northern blot analysis of total RNA of embryos from 9.5 days to 17.5 days of gestation indicated that N‐myc mRNA level was the highest at 9.5 days and decreased as development proceeded. Tissue distribution of N‐myc expression in 9.5 day embryos was histologically analyzed by in situ hybridization of the transcripts and immunofluorescent staining of N‐myc protein. In addition to the central nervous system indicated in previous studies on embryos of different stages, we found N‐myc expression in various developing tissues. Neural crest‐derived tissues generally expressed N‐myc transcripts and proteins to significant levels, e.g. facial primordia, visceral arches and dorsal root ganglia. Among mesodermal tissues, N‐myc expression was especially high in the migrating sclerotomes derived from caudal halves of the somites, primitive nephric tubules, and mesenchymes condensed around the digestive tract and in the limb buds. Expression in endodermal tissues, however, was very low. In situ hybridization and immunohistology gave consistent results, confirming the authenticity of the detection of N‐myc expression.