The Expression Of Fibroblast Growth Factor Receptors (FGFRs) In Odontoblasts

Objectives: It has been reported that one of fibroblast growth factors (FGFs), FGF 18, activates proliferation and differentiation of osteoblast lineage cells via FGFR2c during bone formation, and inhibits those of chondrocyte lineage cells via FGFR3c during cartilage formation. However little is known about possible contribution of FGF-FGFR pathway during tooth formation. To obtain further insight in the role of FGF-FGFR pathway during dentin formation, we performed in situ hybridization (ISH) studies to demonstrate the expressions of both FGFR2c and FGFR3 in the developing madibular first molar (M1) of the rat. Expression of DSP was also analyzed by ISH to clarify the activity of odontoblasts in matrix secretion.

Methods: Mandibles of the rat at 0-14-week-old were dissected and fixed. The specimens were processed for paraffin sectioning at the level of M1 after decalcification. ISH was performed utilizing digoxigenin (DIG) labeled probes to detect the transcripts of FGFR2c, FGFR3 (a consensus sequence for both R3b and R3c) and DSP. Finally, loci of the transcripts were immunohistochemically detected utilizing anti-DIG antibody.

Results: In the M1 of 0-day-old rat, the expression of FGFR2c and FGFR3 transcripts were detected in the odontoblasts secreting mantle dentin matrices, which were also expressing DSP transcripts. Transcripts of FGFR2c and FGFR3 were not observed in the undifferentiated DSP-negative cells facing the inner enamel epithelium. The expression of FGFR2c and FGFR3 in odontoblasts continued during the stages of crown and root formation, but became undetectable together with that of DSP in the animals at the age of 14-week-old.

Conclusion: Since the expression of DSP transcripts in the odontoblasts parallels with the secreting function of these cells, current data suggest an involvement of FGF-EGFR pathway in critical regulation of dentin matrix secretion by odontoblasts.