NEUROTROPHINS IN ODONTOGENESIS

Neurotrophins (NTFs) are a family of structurally related proteins wit h specific effects on the developing nervous system and a wide range o f non-neuronal differentiating cells. To date, four NTFs have been cha racterized: nerve growth factor (NGF), brain-derived neurotrophic fact or (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). To perfor m their biological effects, the NTFs must bind to appropriate receptor s on the surface of responsive cells. High- and low-affinity receptors for NTFs have been identified. The high-affinity receptors are member s of the trk protein tyrosine kinase receptor family. The low-affinity neurotrophin receptor gp75(NTFR) is a common receptor for all NTFs. H ere we summarize some of our previous findings on the expression patte rns of NGF, gp75(NTFR), TrkB, and TrkC in the developing molar tooth o f the rat. Both NGF and gp75(NTFR) are localized in dental epithelium and mesenchyme but often their expression patterns differ. Concomitant expression of NGF and gp75(NTFR) in mesenchyme is correlated with odo ntoblast differentiation. The trkB and trkC receptors show distinct ce ll-specific expression patterns in developing tooth, suggesting that o ther NTFs, apart from NGF, may be involved in odontogenesis. These dat a demonstrate that NTFs participate in the cascade of molecular events that direct tooth development, and support the notion that NTFs may h ave multiple and distinct roles in dental tissues.