Effects of epidermal growth factor (EGF) and colony-stimulating factor-1 (CSF-1) on expression of c-fos in rat mandibular molars: implications for tooth eruption.

The c-fos gene is expressed in the dental follicle of the first mandibular molar of rats. Molecules that accelerate tooth eruption, epidermal growth factor (EGF) and colony-stimulating factor-1 (CSF-1), enhance the expression of the c-fos gene in vitro in both a time- and concentration-dependent manner. In vivo, EGF enhances c-fos expression in the follicle from day 0-7 postnatally, but by day 9 the follicle is refractory to this stimulus. Immunostaining reveals that the c-fos gene is translated in the cultured dental follicle cells, with staining seen in the nucleus and the perinuclear region of the cytoplasm. In vivo, immunostaining for c-fos is prominent in the dental follicle early postnatally, with little or no staining seen in the stellate reticulum and dental pulp. By day 10 postnatally, staining for c-fos is greatly reduced in the dental follicle. Thus, the presence of c-fos early postnatally in the tissue required for eruption, the dental follicle, as well as the enhancement of c-fos gene expression in the follicle by EGF or CSF-1, suggests that c-fos plays a role in tooth eruption. That role may be either to promote differentiation of mononuclear cells into osteoclasts needed for eruption or to recruit the mononuclear cells into the follicle.