An autoradiographic study on the effect of epidermal growth factor on cell proliferation in erupting mouse incisors

Epidermal growth factor (EGF) is a small polypeptide that induces precocious eyelid opening and incisor eruption in newborn mice; it stimulates cell proliferation in various cell types in vitro and in vivo. EGF was injected twice daily into newborn mice (0.4 microgram/g) and tritiated thymidine was injected subcutaneously 6 h before killing the mice. Longitudinal sections of the lower incisors showed significantly more thymidine-labelled mitoses in the pre-odontoblast and pre-ameloblast layers at the basal ends of incisors in EGF-treated mice than in control mice. Although these results indicate that the EGF-induced precocious tooth emergence is associated with a stimulation of cell proliferation in the root sheath, this tissue may not be the target for the actions of EGF. Earlier studies have shown that root growth is not a factor in the generation of the eruptive force and, as neither the pre-ameloblasts nor pre-odontoblasts express EGF-receptors, the stimulation of cell proliferation in the root-sheath region appears to be a result and not a cause of accelerated tooth eruption, i.e. the increase in root growth may meet the need to maintain the tooth positionally during the accelerated eruptive process.