Fig. 4

Defective sarcomere organisation in smyhc1^kg179/kg179 mutants. Sibling zebrafish from smyhc1^kg179/+ in-crosses mounted dorsal up, anterior to left, shown in wholemount (A, upper panel) or maximal intentisity projection confocal stacks. A) Slow MyHC immunofluorescent detection with antibody S58 at 3 dpf shows signal in superficial slow fibres (SSFs) of heterozygote sibling (n ​= ​8/8 sibs) but its absence in mutant (asterisks), despite the presence in mutant of signal in cranial, cardiac (arrows), and specific somite-derived muscle (arrowheads; n ​= ​6/6). White boxes are shown enlarged beneath to highlight S58 signal in thin nascent SSFs at dorsal and ventral somitic extremes and muscle pioneers at the horizontal myoseptum in mutant (arrowheads). B) Immunodetection of slow MyHC with antibody F59 and α-actinin to mark Z-disks and phalloidin staining to reveal filamentous actin in somite 17/18 region at 24 hpf. Note the absence of organised Z-lines and thin filament arrays in the mutant but the persistence of signal at the verticle myoseptum (filled arrowheads). Boxed areas magnified beneath show repeated F-actin structures in mutant (open arrowheads) that appear to lack α-actinin. C) Immunodetection of slow MyHC with antibody S58 and all sarcomeric MyHC with A4.1025 reveals lack MyHC in mutant slow fibres but presence in underlying fast fibres in somite 16–19 region at 3 dpf. Note the poor binding of A4.1025 to fast fibres in the wild type, presumably due to adsorption to slow fibres. Abbreviations: ahm – anterior hypaxial muscle, sca - supracranialis anterior, scp - supracranialis posterior. Bars ​= ​100 ​μm.