FGFs-1 and -2, and TGF beta 1 as inductive signals modulating in vitro odontoblast differentiation

We have studied the expression of FGF1 and FGF2 during mouse odontogenesis by immunohistochemistry. FGF1 was detected in differentiated odontoblasts and at the secretory pole of ameloblasts. Localization of FGF2 was mainly observed within the basement membrane interposed between dental epithelium and dental mesenchyme. These findings indicate that FGF1 and FGF2 may participate in the control of odontoblast and ameloblast differentiation. Thereafter, we studied the ability of FGF1 and FGF2, alone or in combination with TGF beta 1, to induce polarization and/or functional differentiation of preodontoblasts. Dental papillae (DP) obtained from first lower molars of 17-day-old mouse embryo were cultured in the presence or the absence of growth factors. DP cultured with FGF1 + TGF beta 1 showed gradients of odontoblast-like cell differentiation, which displayed alkaline phosphatase reactivity. DP treated with FGF2 + TGF beta 1 exhibited pre-odontoblast cell polarization, and the cell bodies displayed long cytoplasm processes. However, following this treatment we did not observe extracellular matrix secretion, and alkaline phosphatase activity was completely inhibited. In summary, our results show that exogenous addition of FGF1 to pre-odontoblasts induces their terminal differentiation, by synergistically acting with TGF beta 1. In contrast, FGF2 may regulate the effect of TGF beta 1, permitting cell polarization but restraining pre-odontoblast functions.