In vivo and in vitro effects of epidermal growth factor on its receptor gene expression in rat dental follicle cells

Epidermal growth factor receptor (EGFR) is known to be localized early postnatally in the follicle of rat mandibular molars and to decline later. Here, EGFR mRNA present early postnatally in the follicle was revealed by in situ hybridization and reverse transcription-polymerase chain reaction. Injections of epidermal growth factor (EGF) enhanced the expression of EGFR mRNA but not EGF mRNA through day 5 postnatally in the follicle. By day 7 postnatally, the amount of EGFR mRNA was dramatically reduced and EGF injection at that time or later did not enhance its expression. Cultured dental follicle cells were also shown to contain both EGFR mRNA and EGF mRNA, but only EGFR mRNA expression was enhanced after incubation of the cells with EGF. The EGFR mRNA was apparently translated, because the cultured cells could be immunostained for EGFR. This enhancement of EGFR mRNA in the dental follicle cells by EGF may be a necessary prelude to the mitogenic effect of EGF on the cultured cells because incubating the dental follicle cells in EGF over 6 days resulted in almost a doubling in their number as compared to controls. These results indicate that the tissue necessary for eruption to occur, the dental follicle, contains EGFR mRNA in the early postnatal days. In turn, this mRNA is enhanced by EGF, a molecule known to accelerate eruption if injected early postnatally. Whether or not the mitogenic effect of the EGF on the cultured dental follicle cells is a mechanistic factor that contributes to the subsequent tooth eruption is unknown.