Irradiation increases total engraftment into skeletal muscle. The number of Y-1_positive nuclei per square millimeter was quantified in recipient mice irradiated before transplantation, or not irradiated, and sacrificed 3 weeks after transplantation (3-wk IRRAD and 3-wk NON, respectively; n = 5 of each). The number of Y-1_positive nuclei per square millimeter was also quantified in recipient mice irradiated before transplantation and sacrificed 3 months after transplantation (3-mo IRRAD; n = 4). The 3-week irradiated group showed a significantly higher number of Y-1_positive nuclei per square millimeter compared with the 3-week nonirradiated group (Kruskal-Wallis test followed by Dunn’s multiple-comparison test, P < 0.05).