CSF-1 and ODF Expression During Tooth Eruption in Mice

Introduction: Tooth eruption is a tightly regulated and complex process that is precisely timed during normal development. The c-fos knock-out mouse model provides a powerful tool for studying deviations from the normal process of tooth eruption. Homozygous c-fos knockout mice present with fully formed teeth that do not erupt. Tooth eruption relies heavily on osteoclast recruitment and their interactions with certain key factors, osteoblasts and the dental follicle. Key factors including CSF-1 (colony stimulating factor-1) and ODF (osteoclast differentiation factor) are required for the recruitment, formation, differentiation and proliferation of osteoclasts and the subsequent onset of osteoclastogenesis and tooth eruption (Wise et al., 2002; Wise and Yao, 2003; Proff et al., 2006). Purpose: This study was conducted to evaluate the spatial and temporal distribution of factors CSF-1 and ODF at two specific stages of tooth eruption. Materials and Methods: Two ages corresponding to the pre-eruption stage (21 and 24 days of development) and the pre-functional stage of tooth eruption (28 and 30 days of development) were collected. Hemi-mandibles were obtained from both heterozygous and homozygous mice and fixed in 95% ethanol. Specimens were embedded in paraffin wax, sectioned and placed on slides. Finally, monoclonal antibodies against CSF-1 and ODF were stained for using immunohistochemistry. Results: Positive staining was observed for CSF-1 and ODF in pre-eruption and pre-functional heterozygous study groups. Staining for the pre-eruption group was mainly visible in the mucosa, muscle tissue and dental lamina. Conversely, the pre-functional study groups presented with a similar staining pattern with the addition of the dental papilla. No positive staining for CSF-1 and ODF was observed in the 28 day homozygous knock-out study group. Conclusion: The expression of CSF-1 and ODF is present in heterozygous animals whereas homozygous animals do not seem to express these key factors.