Fig. 6

Hedgehog signalling sustains residual fusion and mymk expression. a ISH for myomaker (mymk) at 20 hpf revealed that residual expression in myog mutant is enriched in the medial region of the somite close to notochord (arrows in transverse sections from indicated axial level, dorsal to top). Note lack of expression in mononucleate slow pioneer fibres (arrowheads, upper panel). Representative images n = 6 mutants, n = 14 wt sibs (mymk) b ISH (lateral view, dorsal to top) and qPCR analysis showing that cyclopamine (CyA) treatment of myog^kg125 embryos almost abolished mymk mRNA compared to ethanol (EtOH) vehicle control. CyA effectiveness is shown by the absence of unstained slow muscle pioneer cells (arrowhead). Mean fold change ± SEM from three independent experiments on embryos from separate lays of myog^kg125 (circles) and myog^kg128 (squares and triangles) analysed on separate days, paired t test statistic. Representative images n = 4 EtOH, n = 6 CyA. c Optical confocal sections of the medial region of somites 17 of β-actin:EGFP;myog^kg128/+ incross treated with vehicle or CyA. Transverse-section panels show medial position (yellow lines) of respective longitudinal section for each condition. CyA abolished residual fusion in the medial myotome of mutant embryos (arrowheads) but did not detectably affect fusion in sibs. Note that the residual multinucleate fibres in myog^kg125 mutant appear larger than adjacent mononucleate fibres in EtOH but are lacking in CyA. nt: neural tube, nc: notochord. Representative images n = 5 mutants, n = 3 sibs (EtOH); n = 4 mutants, n = 6 sibs (CyA). Bars = 50 μm