Osteoblast Differentiation and Gene Expression of Noncollagenous Proteins in the Developing Mandibula of Rat Fetuses

Abstract

We studied the differentiation of osteoblast precursor cells into osteoblasts and how this relates to the expression of noncollagenous proteins (NCPs), osteonectin (ON), bone sialoprotein (BSP), osteocalcin (OC), decorin, biglycan, and osteopontin (OPN) early in the formation of bone in the rat mandible by alkaline phosphatase (ALP) enzyme histochemistry and in situ hybridization. Mandibles of rat fetuses were collected on embryonic days 13.0 (E13.0) to E 15.0. Meckel's cartilage anlage and osteoblast precursor cells showing ALP activity appeared first at E 13.5 closely associated with nerve fibers in the developing mandible. Further differentiation in anlage was accompanied by increased expression of glycosaminoglycans and resulted in the formation of Meckel's cartilage. Osteoblast differentiation increased as the number of osteoblast precursor cells and their ALP activity increased in specimens from E 14.0 to E 15.0. At E 15, all NCPs were expressed by these ALP-positive cells, but their expression patterns differed: expression of NCPs other than OPN was observed in the majority of osteoblasts, which expressed ON and BSP intensely and OC, decorin, and biglycan weakly, whereas OPN was expressed intensely by only a few osteoblasts. These results indicate that the appearance of osteoblast precursor cells showing ALP activity is temporally and spatially related to that of Meckel's cartilage anlage and nerve fibers and precursor cells differentiate into osteoblasts at varying stages of differentiation at E 15. J Jpn Soc Periodontol, 44: 55-63, 2002.