Development of hemopoietic bone marrow within the ectopic bone induced by bone morphogenetic protein.

Neogenesis of hemopoietic bone marrow was observed in the ectopic bone induced by implantation of bone morphogenetic protein (BMP) into the muscle of mice. A bone rudiment-like cartilage was formed first, which was then replaced by bone through an endochondral ossification process. Bone marrow formation occurred after the invasion of blood vessels into the cartilage, with accumulations of small lymphocyte-like cells and the appearance of large hemopoietic stem cells around the blood vessels. The stem cells proliferated and differentiated to form hemopoietic bone marrow. This process was similar to the embryogenesis of bone and bone marrow, but the hemopoietic activity of the BMP-induced bone was transient. The bone marrow was converted to fatty tissue within 2 weeks of its appearance. This study showed that implantation of BMP in the ectopic sites offers a useful model to investigate the neogenesis of ectopic bone marrow and the regulation of its activity.