Reactivation of Delta-Notch signaling after injury: Complementary expression patterns of ligand and receptor in dental pulp

The evolutionarily conserved Notch-mediated intercellular signaling pathway is essential for proper embryonic development of many tissues and organs. Recent data suggest that Notch receptors and their membrane-bound ligands D elta and Serrate are involved in both patterning and cell fate determinatio n during odontogenesis. It remains, however, uncertain if Notch signaling i s important for tooth homeostasis and regeneration. Here we report on the e xpression of Notch receptors and the Delta1 ligand in dental pulp of normal and injured adult rat teeth, Notch receptors were absent from normal adult dental tissues, whereas expression was upregulated after injury, In injure d teeth, Notch2 was expressed in mesenchymal cells of the pulp both close t o the site of injury (i.e., in the dental crown) and at a distance from it (i.e., in the dental roots), Notch3 expression was mainly associated with v ascular structures, while Notch1 expression was restricted to few pulpal ce lls close to the lesion. None of them was expressed in odontoblasts. Expres sion of Delta1 was upregulated in odontoblasts of the injured teeth, as wel l as in vascular structures, These results demonstrate the reactivation of the Notch signaling pathway during wound healing and, furthermore, highligh t the similarity between developmental and regenerative processes. (C) 1999 Academic Press.