Figure 1.

Isolated mouse skeletal myofibrils imaged using electron cryotomography

(A) Projection image of mouse skeletal muscle, with Z-disc, I-, M-, and A-bands visible (green, light blue, dark blue, and purple, respectively). A schematic diagram is shown below, highlighting the lateral organization and cross-links in different zones. Mitochondria (Mito) and sarcoplasmic reticulum (SR) can be identified between sarcomeres. Scale bar, 1 μm.

(B) Slice through an electron cryo-tomogram spanning A- to M-band. Its representative position on a sarcomere is marked as the black box in (A) (not same sarcomere). In this region, myosin heads bound to the thin filament, myosin tails emanating from the thick filament (dark blue insets) and obscure protein densities at the M-band (purple inset) can be discerned. Scale bar, 100 nm.

(C) Slice through an electron cryo-tomogram spanning I-band and Z-disc. Its representative position on a sarcomere is marked as the white box in (A) (not same sarcomere). The tail-feather-like arrangement of α-actinin molecules cross-linking thin filaments in a zig-zag manner is visible (green inset). Thin filaments in the I-band have regularly-spaced nodes corresponding to troponin complexes (pink arrow heads, blue inset). A slice of the same location but 7 nm above from the rest of the slice is shown inset. Scale bar, 100 nm.

(D) Larger view of insets described in (A)–(C), with cartoon depictions of densities. Scale bar, 20 nm.

See also Figure S1.