Pax3CreKI/+; RosanTnG/+ E12.5 PPFs, cultured for 1 d (A, C) or 5 d (B, D) in F10 with FBS and FGF (A, B) or F12/DMEM with FBS and FGF (C, D). F10 media is only suitable to expand PPF fibroblasts, as indicated by the predominance of Tomato+ PPF fibroblasts and reduced numbers of GFP+ myogenic cells by 5 d in culture (n = 3) (B). F12/DMEM allows expansion of both GFP+ muscle progenitors and Tomato+ PPF fibroblasts as numbers of GFP+ cells increased in 3 of 4 PPF cultures in this media (D). Scale bars are 100 μm.