Cytosolic SOD1 proteins can be transported into mitochondria of skeletal muscle.

<p>(<b>A</b>) Western blot to show the expression of human SOD1<sup>G93A</sup> in the skeletal muscle of G93A mice. C-SOD1 antibody recognizes both mouse and human SOD1. Lane 1: Control muscle; Lane 2-4: G93A muscle (2,3 and 4-month old). Note the skeletal muscle of G93A mice expresses human SOD1<sup>G93A</sup> at all ages. (<b>B</b>) Intact normal muscle fibers expressing SOD1-GFP or SOD1<sup>G93A</sup>-GFP. Note, in addition to the cytosolic expression, both SOD1-GFP and SOD1<sup>G93A</sup>-GFP show mitochondrial targeting. (<b>C</b>) After cell membrane permeabilization, the cytosolic GFP was lost. The overlay of TMRE and remaining GFP signals indicate the expression of SOD1-GFP or SOD1<sup>G93A</sup>-GFP inside mitochondria. Bar: 10 µm. </p>