In mouse U23674 and U21459 cells (established from Myf6Cre+/−,Pax3:Foxo1+/+,p53−/− mouse sarcomas), expression of P3F is directed by the Pax3 promoter and coupled to an eYFP fluorescent marker, which is activated as a second cistron downstream from an encephalomyocarditis virus–derived IRES (17). The gene discussed is FOXO1; the disease is sarcoma.