Figure 7.

Electron micrographs of IFMs of wild-type (A–E) and ket¹⁴/+ (F–J) adult flies. (A–C and F–H) Transverse sections of muscles. (D, E, I and J) Longitudinal sections of muscles. (A and F) Arrows labeled Z indicate Z-discs. Note that one of two Z-discs in the mutant (F) does not reach the muscle bundle periphery. (B and G) Enlarged muscle bundles. Peripheral regions of bundles heterozygous for ket¹⁴ (G) are considerably disorganized. Regions enclosed by boxes are enlarged in (C and H). Arrowhead, myosin or thick filament. Arrow, actin or thin filament. The hexagonal lattice of normally packed filaments is deformed in the periphery of mutant muscle fiber bundles. (D and I) Z-disc defects and myofibril aberrations such as branching and breakage frequently found in ket¹⁴/+ IFMs are shown by arrows and arrowheads, respectively. (E and J) Myofilaments are connected to muscle cell membrane via modified terminal Z-discs (MTZ). Note that, in ket¹⁴/+ heterozygotes, modified terminal Z-discs are diminished in size and some myofilaments appear to contact to muscle cell membrane directly as shown by the arrowhead in J. Bar: (A, D, F, and I) 0.8 μm; (B and G) 0.16 μm; (E and J) 0.5 μm.