Reduced satellite cell number and proliferation in Pparδ -cKO mice. (A) Freshly isolated extensor digitorum longus (EDL) muscle fibers were stained with paired-box transcription factor 7 (Pax7) antibody to label satellite cells. Nuclei were counterstained with 4', 6-diamidino-2-phenylindole (DAPI). Scale bar = 25 μm for all panels in parts (A) and (B). (B) Soleus (SOL) muscle fibers were cultured for 72 hours, and the proliferating satellite cells on the fibers were fixed and stained with Pax7 and myogenic differentiation antigen 1 (MyoD) antibodies. Nuclei were counterstained with DAPI. Satellite cell status is classified as self-renewed cells (Pax7+), proliferating cells (Pax7+/MyoD+) and differentiating cells (MyoD+). (C) Quantification of the number of Pax7+ satellite cells per single fiber isolated from the EDL and SOL muscles (N = 360 fibers each from the SOL and EDL muscles). **P < 0.0001. (D) Relative expression of the Pax7 gene in tibialis anterior (TA) muscles by quantitative PCR (N = 3). (E) Quantification of the number of self-renewed, proliferating and differentiating cells on SOL fibers after culture for 72 hours (N = 20 fibers for each group).