Because many of the radiation-induced tumors in our model are UPS tumors and because we and others have previously used Pax7-CreER mice to show that mouse sarcomas that mimic human UPS can arise from Pax7+ myogenic progenitor cells (7, 35), we examined the fate of satellite cells in mice with temporary p53 KD during irradiation. This evidence concerns the gene PAX7 and sarcoma.