However, in osteoblast precursor-specific p53-deleted mice using Osx-cre (Osx-cre; p53fl/fl), nearly 100% of the sarcomas that developed in most individuals were OS (68, 73, 74, 76), suggesting that the OS cells of origin are enriched in Osx-positive cells (Figure 1B). The gene discussed is SP7; the disease is sarcoma.