Gene expression in the developing rat mandible: a gene array study.

To analyse the molecular events that occur in the developing mandible, gene arrays containing probes for 1176 known genes were used. Total RNA was extracted from the mandibles of 1- and 6-day-old rats. Radiolabeled probes were then synthesised and used to probe the DNA arrays. Of the 1176 genes examined, 306 were detectable, and the latter were analyzed by bioinformatics algorithms. K-means clustering grouped 72 genes into Up, 56 genes into Down and 178 genes into NO change. A large number of genes related to cell receptors (by ligands) were grouped into the Down cluster. Gene array technology appears to be a useful tool for studying the complex process of mandibular development.

Gene expression and immunohistochemical localization of osteonectin in association with early bone formation in the developing mandible.

We have compared the expression of osteonectin with that of osteocalcin and bone sialoprotein during bone formation in the rat mandible, using in situ hybridization and immunohistochemistry. Expression of osteonectin, osteocalcin and bone sialoprotein mRNAs were first observed in newly differentiated osteoblasts of the developing mandible at embryonic day 15 (E15) and subsequently increased with the number of osteoblasts through E20. Definitive osteonectin immunostaining was observed in newly differentiated osteoblasts, but not in the intercellular unmineralized matrix. Immunostaining for osteocalcin and bone sialoprotein was visible in osteoblasts and unmineralized matrix. Concomitant with the initiation of matrix mineralization at E16, mineralized bone matrix showed osteocalcin and bone sialoprotein immunostaining, but lacked osteonectin immunostaining. The same staining profile was observed during subsequent phases of bone formation at E17-20. However, sequential demineralization with ethanolic trimethylammonium EDTA and protease digestion of tissue sections demonstrated prominent osteonectin immunostaining of the mineralized bone matrix. Western blot analysis of osteonectin in extracts of fresh specimens at E18 and 20 revealed that an EDTA extract contains osteonectin having M, approximately 50 kDa. These results indicate that newly differentiated osteoblasts synthesize and secrete osteonectin, which is mainly incorporated into the mineralized bone matrix and becomes a specific component of developing manibula of foetal rats.