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. 2012 Jun 1;23(11):2057–2065. doi: 10.1091/mbc.E12-02-0120

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© 2012 Wang et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

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FIGURE 5: — Ultrastructure of PwMhc2 control and E701K mutant IFM over time. Longitudinal sections through pupal PwMhc2 (A) and E701K IFM (C). Control sarcomeres are highly organized, showing a characteristic pattern of straight myofilaments running parallel to each other and perpendicular to straight M-lines surrounded by denser-staining Z-disks. Mutant myofibrils show assembly defects. E701K sarcomeres are less organized than control, display cracking between myofilaments, and have jagged M-lines and Z-disks. Transverse sections through pupal PwMhc2 (B) and E701K (D) IFM myofibrils. Control myofibrils are round, with a consistent pattern of hexagonally packed hollow thick filaments each surrounded by six thin filaments. Mutant myofibrils lack round shape and show disrupted hexagonal packing between thick and thin filaments. Bars, 1 μm in A and B. Longitudinal sections through 2-h-old adult PwMhc2 (E) and E701K (G) IFM. Mutant sarcomeres lack visible M-lines and are disorganized. Myofilaments are losing their parallel relationship to one another and appear broken. Transverse sections through 2-h-old adult PwMhc2 (F) and E701K (H) IFM myofibrils. Thin and thick filaments are dissociated in approximately half of the myofibril surface area. Longitudinal sections through 2-d-old adult PwMhc2 (I) and E701K (K, M–P) IFM. Sarcomeric structure in mutants is nearly absent. E701K myofibrils show Z-disk streaming and loss of Z-disk spacing and thick filaments. Thin filaments were observed in the sarcoplasm in the absence of any sarcomeric structures. Transverse sections through 2-d-old adult PwMhc2 (J) and E701K (L) IFM myofibrils. Hexagonal packing is absent in mutants; sarcoplasmic reticulum is broken down into vesicles surrounded by a soup of thick and thin filaments. Mutant fibers also display rimmed vacuoles fused with additional membranes (M, N), suggesting the formation of type 2 autophagic vacuoles (Fernandez et al., 2005). Bar, 1 μm in N. Cylindrical spiral membranes (O, P) found in E701K fibers appear similar to sarcolemmal inclusions in human skeletal myopathy (Carpenter and Karpati, 1979). Bar, 0.1 μm in P. Magnification is the same in A, C, E, G, I, K, and O. Magnification is the same in B, D, F, H, J, L, and M.