The PAX3-FOXO1 fusion cDNA was subcloned into the lentiviral doxycycline-inducible pINDUCER10 vector (provided by Dr. J. Luo). A single-guide RNA (sgRNA) targeting the 5′ PAX3 region was designed (Table S1) and cloned into the lentiCRISPR v2 plasmid (provided by Dr. J. Luo) [13 (link)–15 (link)]. Oligonucleotides were purchased from Integrated DNA Technologies. Lentiviral particles were prepared in HEK293T cells with the HIV-based pPACK-H1 Packaging Plasmid Mix (System Biosciences).