EFFECT OF CSF-1 ON IN-VIVO EXPRESSION OF C-FOS IN THE DENTAL FOLLICLEDURING TOOTH ERUPTION

It has been demonstrated that both colony-stimulating factor-one (CSF- 1) and the transcription factor, c-fos, are required for tooth eruptio n. Osteopetrotic mutant rats deficient in CSF-1 activity have unerupte d teeth which can be induced to erupt by injections of CSF-1, and oste opetrotic mice deficient ir c-fos, have unerupted teeth, Both CSF-1 an d c-fos are expressed and translated in the dental follicle, the tissu e that is required for eruption. Recent in vitro studies indicate that CSF-1 can enhance the expression of the c-Sos gene in cultured dental follicle cells, but the effects in in vivo are not known. In the pres ent 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 injec tion. Isolation of total RNA from the follicle and reverse transcripti on PCR showed that CSF-1 injection enhanced the expression of c-fos ov er the non-injected controls, Chronologically, day 3 postnatally appea red to show the greatest increase of c-fos mRNA following CSF-1 inject ion. 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 f or alveolar bone resorption and tenth eruption.