Abstract
In this study, histological and in situ hybridization methods were applied to investigate ectopic hard tissue formation induced by bone morphogenetic protein (BMP)-collagen composites. The BMP-collagen composites were implanted into dorsal subcutaneous tissue of mice, and examined at 3 days,1 week, and 2 weeks after implantation. Formation of cartilage-like tissue mainly composed of ovoid chondrocyte-like cells was observed at 3 days after implantation. Maturation of the cartilage-like tissue and presence of a number of hypertrophic chondrocyte-like cells were observed at 1 week after implantation. Bone-like tissue formation occurred at 2 weeks after implantation. The localization of type Ⅰ and Ⅱ collagen mRNAs was examined during the ectopic hard tissue formation by the composites and compared with that of endochondral ossification in tibial growth plate of mice. In the ectopic hard tissue, both type Ⅰ and Ⅱ collagen mRNAs were detected in chondrocytelike cells and hypertrophic chondrocyte-like cells. Whereas in the chondrocytes and hypertrophic chondrocytes of the tibial growth plate, only type Ⅱ collagen mRNA was detected. These results indicated that ectopic hard tissue formation induced through this process was histologically similar to normal endochondral ossification, but different from it in aspects of expression pattern of type Ⅰ and Ⅱ collagen genes. It was suggested that the chondrocyte-like cells in the ectopic cartilage-like tissue have both characters of chondrocytes and osteoblasts.
