Site-specific expression of mRNAs for osteonectin, osteocalcin, and osteopontin revealed by in situ hybridization in rat periodontal ligament during physiological tooth movement.

We investigated the gene expression for non-collagenous proteins in periodontal ligament (PDL) by in situ hybridization histochemistry with a non-radioisotopic probe with cRNAs for osteocalcin (Osc), osteonectin (Osn), and osteopontin (Opn) in rat maxillary dento-alveolar unit containing molars and intact PDL. A highly intense positive signal for Osn and Osc mRNAs was expressed at all distal surfaces of the interradicular septum of buccal roots of the upper second molar in 7-week-old Sprague-Dawley male rats. Cells showing positive signals for Osn and Osc mRNAs were osteoblasts and osteoprogenitor cells. The distribution of Opn mRNA-positive signal was demonstrable at the mesial surface of the interradicular septum of buccal roots, where physiological bone resorption was specifically restricted during physiological tooth movement. Opn mRNA was expressed in cells on the bone resorption surface, including osteoclasts, and osteocytes. A moderately intense positive signal for Osn mRNA was distributed in fibroblasts throughout the ligament. Odontoblasts and pre-mature odontoblasts exhibited a strong signal for Osn and Osc mRNA. Cementoblasts and cementocytes were positive for Osn, Osc, and Opn mRNAs. These findings suggest physiological roles of Osc, Osn, and Opn in bone remodeling, PDL remodeling, dentinogenesis, and cementogenesis.