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Fig. 6 Mef2 controls a transcriptional module involved in thick filament assembly. Confocal immunofluorescence of sarcomeric components in a 24-hpf midbody somite of control or mef2d/c MO-injected zebrafish embryos in fast (A, medial) or slow (A, superficial, B-F) fibres; lateral view slice and insets of stack, anterior to left, dorsal to top. (A) MyHC is absent from fast fibres (asterisk) and concentrated at fibre ends in slow fibres (arrowhead) in morphants, whereas actin is diffusely dispersed in cytoplasm of both fibre types (arrows). Blue dashes indicate somite borders. (B-D) z-line components α-actinin and titin and thin filament protein α-tropomyosin are concentrated in cytoplasmic puncta (arrowheads) and at fibre termini (arrows) after Mef2 knockdown. (E,F) M-line component MyBP-C is absent from residual myofibrils in morphants with regular sarcomere z-line spacing (arrowheads). Scale bars: 20 μm.