Defective growth and proliferation of primary myoblast cells derived from Pparδ -cKO muscles. (A) and (B) Representative images of Ki67 staining that specifically labeled proliferating primary myoblasts: Ki67 staining (red) and 4', 6-diamidino-2-phenylindole (DAPI) staining (blue). Scale bar = 50 μm. (C) Relative Ki67 signal intensity in wild-type and mutant myoblast cultures. The intensity of Ki67 and DAPI staining and the number of pixels were measured using Photoshop software (Adobe Systems Inc, San Jose, CA, USA). The ratio of Ki67 intensity values to DAPI intensity values was also quantified using Photoshop (N = 3). (D) Growth curve of wild-type and mutant myoblasts after nine days in culture (N = 3).