Increased apoptosis in plt skeletal muscle and skeletal myocytes. (A) Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining was performed on sections from wild-type (WT) and plt skeletal muscle. Arrows point to TUNEL-positive nuclei. There was a qualitative increase in TUNEL-positive fibers in plt muscle (experiment repeated with sections from three different mice per condition). (B) TUNEL staining was performed on myocytes. There was a significant increase in TUNEL-positive cells in plt myocytes vs WT myocytes. Data reflect fraction of 4′,6-diamidino-2-phenylindole-positive nuclei that were also TUNEL-positive. Numbers were 0.28 ± 0.06 for plt and 0.17 ± 0.05 for WT (P = 0.006). One hundred cells per experiment were counted, and each experiment was repeated five times (once for each culture derived with cells isolated from five different mice per condition).