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 Delta and Serrate are involved in both patterning and cell fate determination during odontogenesis. It remains, however, uncertain if Notch signaling is important for tooth homeostasis and regeneration. Here we report on the expression 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 injured teeth, Notch2 was expressed in mesenchymal cells of the pulp both close to 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 vascular structures, while Notch1 expression was restricted to few pulpal cells close to the lesion. None of them was expressed in odontoblasts. Expression of Delta1 was upregulated in odontoblasts of the injured teeth, as well as in vascular structures. These results demonstrate the reactivation of the Notch signaling pathway during wound healing and, furthermore, highlight the similarity between developmental and regenerative processes. Copyright 1999 Academic Press.