Histology from a nontransgenic recipient mouse that received a transplant via intramedullary injection of TBM from a 3.6-blue donor and expanded calvarial progenitor cells from a 3.6-green or 2.3-green donor. The recipient mice were injected with XO 2 days prior to being killed. (A) Full-length section of bone transplanted with calvarial progenitor cells from a 2.3-green donor mouse and TBM from a 3.6-blue donor. The needle tract (NT) is less obvious with the 2.3-green marker gene because it only visualizes mature osteoblasts. Distal engraftment is apparent in the femoral neck (FN) region. (B) Full-length section of bone transplanted with calvarial progenitor cells from a 3.6-green donor mouse and TBM from a 3.6-blue donor. The needle tract (NT) is composed of newly formed trabeculae and a core of fibroblastic-shaped progenitor cells. Bone lining cells of donor origin are present at sites distal to the injected cells such as the femoral neck region.