Kinetics of bone engraftment after transplantation. Robust GFP⁺ osteoblast engraftment was detected at 2 and 4 weeks after transplantation with significant declines thereafter: 6 weeks (P = .02), 8 weeks (P = .04), 24 weeks (P = .01). GFP⁺ osteocyte engraftment showed a different kinetic profile characterized by a significant increase at 4 weeks (P = .04), a plateau phase and a significant decrease to a negligible level at 52 weeks (P = .004). To quantify the engraftment of donor GFP + cells in bone, we scored 20 random 400× fields in both the epiphysis and the metaphysis of 10 bone sections taken from each mouse at different times after transplantation (n ≥ 4 mice per group). Experiments were performed in triplicate. The reported values are mean (+SD) percentages of GFP⁺ cells per 400× microscopic field.