SPATIAL-DISTRIBUTION OF EPIDERMAL GROWTH-FACTOR TRANSCRIPTS AND EFFECTS OF EXOGENOUS EPIDERMAL GROWTH-FACTOR ON THE PATTERN OF THE MOUSE DENTAL LAMINA

The initiation of odontogenesis is characterized by the site-specific proliferation of mandibular epithelium in the formation of the dental lamina. The epidermal growth factor (EGF) gene is expressed in the developing mandible immediately before the appearance of the dental lamina. This expression is necessary for the formation of the dental lamina and subsequent development of teeth. Previous work has demonstrated that retinoids and EGF may interact in the establishment of the pattern of the dentition. In the present study explanted mandibles that were treated with exogenous EGF (40 ng/ml of medium) contained supernumerary buds of mandibular epithelium in the diastema region. These pattern changes were the same as in previous retinoid-treated explants. These results, in addition to the previously reported effects of retinoids on the expression of the EGF gene, support the hypothesis that retinoids and EGF interact in controlling, at least in part, the pattern of the dentition by affecting the pattern of the dental lamina. The spatial distribution of EGF transcripts was also characterized. The location of EGF transcripts in the mesenchyme adjacent to the mandibular epithelium suggests a paracrine mechanism in the stimulation of epithelial proliferation in the formation of the dental lamina.