Electron micrographs of HSA-Cre EDL muscles of 3-month-old mice showed that mitochondria are almost exclusively positioned at the two sides of Z lines in EDL fibers from control mice (black arrows). On the other hand, in Lipin1 deficient EDL fibers mitochondria are more often clustered and display electron-dense contact sites (white arrows). Scale bars: 0.20 μm. 