Expression and localization of connexin 43 in rat incisor odontoblasts

We have examined the expression and localization of connexin 43 (CX43) in r at incisor odontoblasts using reverse transcriptase polymerase chain reacti on, in situ hybridization and immunohistochemistry. The CX43 gene was expre ssed in odontoblasts, and levels of gene expression increased throughout th e course of development. In contrast, CX43 was down-regulated at an incisal segment. In situ hybridization analysis showed no positive signal for CX43 RNA in the cytoplasm of differentiating dental papilla cells, but faint po sitive signals for CX43 RNA were observed in early pre-odontoblasts. Those signals were more intense in young and in old odontoblasts, but were less i n short odontoblasts. CX43 could not be detected in differentiating dental papilla cells or in early pre-odontoblasts by immunohistochemical localizat ion, but a positive reaction was found in the late pre-odontoblast stage wh ere predentin had been produced. The positivity gradually increased during odontoblast maturation, and was highest in the layer of old odontoblasts. T hese results indicate that odontoblasts that secrete actively dentin matrix components are tightly in contact with each other by gap junctions as sugg ested by the intense CX43.