Morphology of mitochondria in spatially restricted axons revealed by cryo-electron tomography
Fig 5
Mitochondrial membranes display distinct morphological features at the boundaries of varicosities and axons with limited physical dimensions.
(A–C) To highlight the membrane organization of the mitochondria shown in Fig 3A–3C, the cristae and inner and outer membranes of the 3D reconstructions were segmented. (A) IMMs and OMMs remain in close apposition within the narrowed portion of this mitochondrion resident in the axon. (B) OMM is separated from the inner membrane, creating a distinct “matrix-free” compartment in this portion of the mitochondria residing in the axon. (C) Three mitochondria near the varicosity/axon junction show distinct internal membrane organization. The left mitochondrion shows a portion of outer membrane separated from the inner membrane, while the top right mitochondrion is narrowed near the axon junction, but the inner and outer membranes remain in apposition. A short tip of a third mitochondrion is partially captured at the edge of the tomogram that also shows inner and outer membranes together. Plasma membrane (dark blue), OMM (dark green), mitochondrial IBM (orange), cristae (pink). IBM, inner boundary membrane; IMM, inner mitochondrial membrane; OMM, outer mitochondrial membrane.