PAX3 and synovial sarcoma: Cre/LoxP-driven mouse synovial sarcoma (SS) most readily forms in a Myf5-expressing skeletal muscle-specific lineage, whereas fusion oncogene expression in early myogenic precursors (Pax3/Pax7) was fatal and myofiber expression (Myf6) caused myopathy (Haldar et al., 2007; Haldar et al., 2009; Jones et al., 2016).