The effect of smyd1b single or smyd1a; smyd1b double mutation on subcellular sarcomere organization in fast muscles. TEM analysis shows the sarcomere organization in fast myofibers of WT control (A, D), smyd1bsa15678 (B, E) and smyd1amb5; smyd1bsa15678 (C, F) mutant embryos at 48 hpf. Images (D, E, F) are larger images from part of A–C, respectively. The Z line and M line are indicated (D–F). Scale bars: 850 nm (A–C); 500 nm (D–F).