Expression of CSF-1 receptor on TRAP-positive multinuclear cells around the erupting molars in rats

Bone resorption overlying a developing tooth is a necessary event in the cr eation of an eruption pathway. The formation and function of osteoclasts, w hich play a major role in bone resorption, are controlled by several factor s. Although CSF-1 and its mRNA are expressed in dental follicle cells requi red for eruption, little is known about the contribution of CSF-1 to osteoc last formation on the bony crypt around the tooth germ. The receptor protei n of the CSF-1 encoded proto-oncogene c-fms was identified on multinucleate d cells adjacent to the dental follicle, in conjunction with TRAP staining as a marker enzyme for osteoclasts in rat, c-Fms was highly expressed in TR AP-positive multinuclear cells at 3 days postnatal and the number of e-Fms- expressing cells was reduced thereafter. Administration of IL-1 alpha, whic h enhances formation and function of osteoclasts, caused an increase in the number of c-Fms and TRAP-positive cells in rat. On the contrary, injection of calcitonin, which depresses osteoclast formation, caused a decrease in the number. It is obvious that the receptor of CSF-1 is expressed on the su rface of osteoclasts around the tooth germ, on the dental follicle. These f indings suggested that CSF-1 directly enhances the influx of osteoclasts ad jacent to the erupting tooth: resulting in the formation of an eruption pat hway.