An in situ hybridization study of decorin and biglycan mRNA in mouse osteoblasts in vivo.

In situ hybridization of decorin and biglycan mRNA, principal members of small leucine-rich proteoglycan, was performed using [35S]-labeled RNA probes, in the context of the hypothesis that they show different expression patterns associated with osteoblast differentiation in mice. We adopted two ossifying sites that can clearly follow the developmental process of bone formation: ossifying tympanic ring and developing bone collar of mandibular condylar cartilage. Decorin mRNA was expressed in osteoblasts of developing tympanic ring at E14.0, as well as of developing bone collar at E15.0, but biglycan mRNA was not, indicating decorin mRNA was expressed earlier in newly differentiating osteoblasts than biglycan. With maturation of osteoblasts, biglycan mRNA became expressed and maintained its expression both in the outer region (periosteum) and in the interior region (endosteum) of bone. By contrast, decorin mRNA expression was maintained in the outer region but diminished in the interior region. These results indicate that decorin and biglycan show differential expression patterns in differentiating osteoblasts and play specific roles in bone formation.

Expression, localization and synthesis of small leucine-rich proteoglycans in developing mouse molar tooth germ.

The gene expression and protein synthesis of small leucine-rich proteoglycans (SLRPs), including decorin, biglycan, fibromodulin, and lumican, was analyzed in the context of the hypothesis that they are closely related to tooth formation. In situ hybridization, immunohistochemistry, and organ culture with metabolic labeling of [35S] were carried out in mouse first molar tooth germs of different developmental stages using ICR mice at embryonic day (E) 13.5 to postnatal day (P) 7.0. At the bud and cap stage, decorin mRNA was expressed only in the surrounding mesenchyme, but not within the tooth germ. Biglycan mRNA was then expressed in the condensing mesenchyme and the dental papilla of the tooth germ. At the apposition stage (late bell stage), both decorin and biglycan mRNA were expressed in odontoblasts, resulting in a switch of the pattern of expression within the different stages of odontoblast differentiation. Decorin mRNA was expressed earlier in newly differentiating odontoblasts than biglycan. With odontoblast maturation and dentin formation, decorin mRNA expression was diminished and localized to the newly differentiating odontoblasts at the cervical region. Simultaneously, biglycan mRNA took over and extended its expression throughout the new and mature odontoblasts. Both mRNAs were expressed in the dental pulp underlying the respective odontoblasts. At P7.0, both mRNAs were weakly expressed but maintained their spatial expression patterns. Immunostaining showed that biglycan was localized in the dental papillae and pulp. In addition, all four SLRPs showed clear immunostaining in predentin, although the expressions of fibromodulin and lumican mRNAs were not identified in the tooth germs examined. The organ culture data obtained supported the histological findings that biglycan is more predominant than decorin at the apposition stage. These results were used to identify biglycan as the principal molecule among the SLRPs investigated. Our findings indicate that decorin and biglycan show spatial and temporal differential expressions and play their own tissue-specific roles in tooth development.