(A) Representative immunofluorescence images of muscle cross sections from mice of the indicated genotype at 14 dpi. Sections were stained with antibodies targeting fiber-type-specific myosin heavy chains, including Myh7 (type I, purple), Myh2 (type IIa, red), Myh4 (type IIb, blue), Myh1 (type IIx, red), Myh3 (embryonic, red), and Myh8 (neonatal, red). Myofiber borders were visualized with laminin staining (green). Scale bar: 50 μm. (B) Quantification of fiber types (as a percentage of total regenerating fibers) in wild-type and mfn2^–/– animals at 14 and 42 dpi. (C) Levels of H3K9me3, H3K27me3, and a number of KDM family members in 14-dpi myofibers. Molecular weight markers (in kDa) are indicated. Histone 2B (H2B) and histone 3 (H3) are shown as loading controls. (D) Heatmaps representing normalized H3K9me3 ChIP-seq intensities of identified genome-wide peaks in 14-dpi myofibers of the indicated genotype, after k-means clustering. Peaks were ranked according to their ChIP-seq intensity in wild-type samples. n = 3 mice per group. (E) Heatmaps representing normalized H3K27me3 ChIP-seq intensities of identified genome-wide peaks in 14 dpi myofibers of the indicated genotype, after k-means clustering. Peaks were ranked according to their ChIP-seq intensity in wild-type samples. n = 3 mice per group. (F) Representative snapshots for H3K9me3 and H3K27me3 ChIP-seq analyses performed in 14-dpi myofibers of the indicated genotype, focusing on the myosin heavy chain locus. Increased deposition of H3K27me3 at the Myh8 gene is highlighted (red box). (G) Representative snapshots of H3K9me3 and H3K27me3 deposition at the Myh8 gene in 14-dpi myofibers of the indicated genotype. For each ChIP-seq data set, 3 biological replicates were analyzed. Box-and-whisker plots indicate median (horizontal line) and interquartile ranges (bounds of the boxes) from the indicated number of biological replicates; whiskers were plotted using Tukey’s method.