IMMUNOHISTOCHEMICAL LOCALIZATION OF CONNEXIN-43 IN THE DEVELOPING TOOTH GERM OF RAT

Distribution of gap junction protein in maxillary tooth germs of 1-day -old rats was examined by immunohistochemistry, using an affinity-puri fied antibody specific to residues 360-376 of rat connexin (CX) 43. In 1-day-old rats, the maxillary second molar formed the shape of the cu sp, but neither dentine nor enamel was formed between the cells of the dental papilla and the inner enamel epithelium. In the tooth germ, CX 43 was expressed in the cells of the stratum intermedium and the inne r enamel epithelium. Labelling in the stratum intermedium was extensiv e and showed an increasing gradient from peripheral to cuspal regions. CX 43 detected in the inner enamel epithelium was at cell surfaces fa cing the interface between the dental papilla and the inner enamel epi thelium. The cells of the dental papilla and the inner enamel epitheli um began differentiation as odontoblasts and secretory ameloblasts res pectively, in the cusps of the first molars, where predentine and dent ine were formed but enamel matrix was not secreted. CX 43 was present in the stratum intermedium, inner enamel epithelium, preodontoblasts, odontoblasts and subodontoblasts. The incisors showed the most advance d stage of development, where the enamel matrix and calcified dentine were formed in the labial part of the teeth. The CX 43 epitope was see n in the stratum intermedium, inner enamel epithelium, preameloblasts, preodontoblasts, odontoblasts, and subodontoblasts. Immunolabelling w as more extensive in the stratum intermedium and subodontoblasts than in preameloblasts, preodontoblasts, and odontoblasts. The immunolabell ing in preameloblasts and preodontoblasts was accumulated at cell surf aces facing the predentine. Further, the labelling in preameloblasts a nd preodontoblasts disappeared or was reduced at the initiation of ena mel matrix secretion and calcification of dentine matrix. The present results suggest that gap junctional cell communication has important r oles in tooth development. Further, the extensive CX 43 expression in the stratum intermedium and the subodontoblast layer suggests that gap junctions have an important role in amelogenesis and dentinogenesis.