Fig. 1

Post-mortem muscle biopsy processing workflow. Example of a larger muscle biopsy that was split transversely across the long (L) axis of fibres into two new biopsy segments, referred to as L-splits (e.g., L1 and L2). From each segment, six 20 μm serial sections were collected for homogenate DNA analysis. This was followed by collection of four 10 μm serial sections onto a glass slide: three grouped for quadruple immunofluorescence (QIF) staining, and a fourth used as a no-primary control (NPC). The original biopsy was measured along its longitudinal axis prior to splitting, and the resulting segments were mounted by their splitting faces, leaving the original extremities exposed for cryosectioning. Consequently, for L-split biopsies, the anatomical distance between sections used for mitochondrial DNA and QIF analyses is known. Smaller biopsies were directly mounted and cut in the same way.