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Fig. 1 | Skeletal Muscle

Fig. 1

From: Development of the excitation-contraction coupling machinery and its relation to myofibrillogenesis in human iPSC-derived skeletal myocytes

Fig. 1

Myofibrillogenesis and SR-TT junctions in differentiating human iPSC-derived skeletal myocytes. A1–A5 Day 4 post-differentiation. Immunofluorescence labeling of α-actinin (A1) and electron micrographs of ultrathin longitudinal cell sections (A2–A5). Nascent myofibrils with Z-bodies (A2–A3); the boxed area is enlarged in A3 for further details. A4–A5 SR-TT junctions from different cells. Whenever possible, the SR is highlighted by artificial post-coloring. Note that T-tubules (T) are surrounded and/or associated with numerous caveolae. B1–B6 Day 5 post-differentiation. Transition from Z-bodies to Z-bands as revealed by α-actinin labeling (B1) and confirmed by electron microscopy (B2–B4). Upper and lower boxed areas in B2 are enlarged in B3 and B4, as indicated. B5–B6 SR-TT junctions from different cells; feet-like structures are visible and caveolae surround the T-tubules. C1–C5 Day 7 post-differentiation. A significant increase in the number of α-actinin+ cells with prevalent Z-bands (C1). C2–C3 Myofibrils with well-defined A-I banding pattern; the boxed area is enlarged in C3. C4–C5 Large and multiple SR-TT junctions from different cells with noticeable rows of feet-like structures in the interspace. D1–D4 Mature stages (> 3 weeks post-differentiation). D1 Alpha-actinin labeling at day 26 post-differentiation showing large skeletal myocytes with clear-cut Z-lines. D2–D3 Ultrastructure of 29-day-old myocytes showing parallel bundles of myofibrils (D2) with fully mature and aligned banding pattern including H-bands and M-lines as can be seen from subsequent enlargement of the boxed areas in D3 and D4. SR-TT junctions (arrows in D4) are enlarged in boxes on the right. Notice the smaller size of these structures and their proximity to the myofibrils compared with earlier stages

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