Myogenin is required for normal larval muscle growth. a, b ISH for mylpfa mRNA showing similar level of expression of fast myosin but reduced extent of somitic muscle in mutants (a, red brackets) at 1 and 2 dpf. Myotome height (b) is significantly reduced in myogkg128 mutants at 1 and 2 dpf. Representative images n = 9 + 18 mutants, n = 35 + 63 sibs. c Larval length is unaffected in mutant at 2 dpf, showing that muscle reduction is not due to overall reduced size of mutant larvae. d Schematic of myotome volume measurement. β-actin:EGFP;myogkg128/+ fish were incrossed and progeny imaged by confocal microscopy. Lateral and three equi-spaced transverse images of somite 17 were collected from each larva at each stage (dashed lines). Transverse area (red outline) multiplied by somite length (cyan dashed line) yielded myotome volume for each fish at each stage. e Optical transverse-sections of β-actin:EGFP;myogkg128 mutants show reduced myotome area at 2, 3 and 5 dpf compared to sibs (dashed red lines). Boxes are shown magnified beneath highlighting smaller fibre cross-sections in mutants (dashed white lines). Representative images n = 6 mutants, n = 14 sibs (2 dpf); n = 5 mutants, n = 18 sibs (3 dpf); n = 9 mutants, n = 13 sibs (5 dpf). f Myotome volume reduction in myogkg128 mutants at 2, 3 and 5 dpf. g–i. Myotome length (g), number of fast fibres per cross section (h) and fibre volume (i) at 2 dpf compared by t tests. Bars = 50 μm. nt: neural tube, nc: notochord
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