Effect of CSF-1 on in vivo expression of c-fos in the dental follicle during tooth eruption.

It has been demonstrated that both colony-stimulating factor-one (CSF-1) and the transcription factor, c-fos are required for tooth eruption. Osteopetrotic mutant rats deficient in CSF-1 activity have unerupted teeth which can be induced to erupt by injections of CSF-1, and osteopetrotic mice deficient in c-fos, have unerupted teeth. Both CSF-1 and c-fos are expressed and translated in the dental follicle, the tissue that is required for eruption. Recent in vitro studies indicate that CSF-1 can enhance the expression of the c-fos gene in cultured dental follicle cells, but the effects in vivo are not known. In the present studies. postnatal rats were injected with 10(6) units of CSF-1 at different ages from birth to day 10 and sacrificed 30 min after injection. Isolation of total RNA from the follicle and reverse transcription PCR showed that CSF-1 injection enhanced the expression of c-fos over the non-injected controls. Chronologically, day 3 postnatally appeared to show the greatest increase of c-fos mRNA following CSF-1 injection. These results suggest that one of the functions of CSF-1 in tooth eruption is to enhance the early expression of c-fos. In turn, c-fos might act to promote fusion of monocytes into the osteoclasts needed for alveolar bone resorption and tooth eruption.