Comparative analysis of TGF beta s, BMPs, IGF1, msxs, fibronectin, osteonectin and bone sialoprotein gene expression during normal and in vitro-induced odontoblast differentiation.

Immobilized TGF beta 1 and BMP2 are able to promote the differentiation of odontoblast-like cells in isolated mouse dental papillae cultured in vitro. These cells polarize and accumulate predentin-like matrix at their apical pole. Immobilized IGF1 mainly promoted polarization with disturbed matrix accumulation. In situ hybridization demonstrated that TGF beta 1 combined with heparin mirrored the physiological processes of odontoblast differentiation. Normal odontoblast and in vitro induced odontoblast-like cells expressed transcripts encoding for TGF beta 1 and 3, BMP2 and 4, bone sialoprotein and osteonectin whereas either ubiquitous expression or no expression could be detected for TGF beta 2, IGF1 or fibronectin mRNAs. Odontoblast-like cells obtained in the presence of IGF-1 combined with heparin did not express TGF beta 1 transcripts and expressed weakly TGF beta 3 transcripts. Our results suggest that in vivo an epithelial-derived member of the TGF beta family trapped by basement membrane-associated components interacts with competent preodontoblasts and promotes the polarization by triggering the transcription of growth factor gene(s) like TGF beta itself and/or selector gene(s) like msx2.