SITE-SPECIFIC EXPRESSION OF MESSENGER-RNAS 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 pe riodontal ligament (PDL) by in situ hybridization histochemistry with a non-radioisotopic probe with cRNAs for osteocalcin (Osc), osteonecti n (Osn), and osteopontin (Opn) in rat maxillary dento-alveolar unit co ntaining molars and intact PDL. A highly intense positive signal for O sn and Osc mRNAs was expressed at all distal surfaces of the interradi cular septum of buccal roots of the upper second molar in 7-week-old S prague-Dawley male rats. Cells showing positive signals for Osn and Os c mRNAs were osteoblasts and osteoprogenitor cells. The distribution o f Opn mRNA-positive signal was demonstrable at the mesial surface of t he interradicular septum of buccal roots, where physiological bone res orption was specifically restricted during physiological tooth movemen t. Opn mRNA was expressed in cells on the bone resorption surface, inc luding osteoclasts, and osteocytes. A moderately intense positive sign al for Osn mRNA was distributed in fibroblasts throughout the ligament . Odontoblasts and pre-mature odontoblasts exhibited a strong signal f or 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.