Immunofluorescence staining

Muscle sections were blocked with 2% FBS in 1 × PBS for 30 min. The sections were incubated with primary antibodies against human-specific spectrin (1:50 mouse monoclonal IgG2b NCL-spec1, Novocastra; Leica Biosystems, Wetzlar, Germany) human-specific lamin A/C (1:300 mouse monoclonal IgG1 Ab40567; Abcam, Cambridge, UK), or laminin (1:400 diluted, Z0097, Dako) for 1 h and further incubated with appropriate secondary antibodies for 1 h. When necessary, β-gal detection was performed using a chicken antibody (Invitrogen AB9361; 1:1,000; 1 h). Pax7 staining was performed using a mouse monoclonal antibody (1:20; Developmental Studies Hybridoma Bank, Iowa City, IA) after a 10-min fixation with 4% paraformaldehyde. Fiber type composition was obtained using an anti-MYHC-I antibody (A4.840, 1:50; Developmental Studies Hybridoma Bank) and an anti-MYHC-II antibody (A4.74, 1:50; Developmental Studies Hybridoma Bank). Macrophages and neutrophils were stained with the F4/80 antibody (MCA497BB, 1:50; Bio-Rad) and Ly6g antibody (Ab25377, 1:100; Abcam), respectively, after a 10-min fixation with 4% paraformaldehyde. Finally, the sections were incubated for 10 min with Hoechst (0.5 μg/mL, Hoechst No. 33258; Sigma-Aldrich) and mounted with a mounting medium (Cytomation fluorescent mounting medium, S3023, Dako; Agilent Technologies, France).