Expression of BMP-4 mRNA during distraction osteogenesis in rabbits

We characterized the presence and localization of bone morphogenetic protein 4 (BMP-4) mRNA in the regenerating tissues produced by distraction osteogenesis following tibial osteotomy in the rabbit. The findings are consistent with previous reports on the localization of BMP-4 mRNA expression during fracture repair. The BMP-4 gene is expressed by less differentiated osteoprogenitor cells (fibroblastic mesenchymal cells and preosteoblasts), and not by fully differentiated osteoblasts. BMP-4 gene expression is localized in callus-forming tissue (muscle, periosteum) during callus formation. Our observations suggest that the BMP-4 gene product is one of the local contributing factors in regulating bone and cartilage formation in distraction osteogenesis.