Adult Myogenin mutants have reduced muscle with more but smaller myofibres. a Myog mutant and sib at 120 dpf from myogkg128/+ incross. Bar = 1 cm. Representative images n = 5 mutants, n = 23 sibs. b Myogkg128 or myogkg125 but not myogffh265 showed reduced standard weight compared to co-reared sibs at 120 dpf. Dots represent individuals. c Laminin immunodetection on cryosections from 120 dpf myog128/+ incross. Bar = 100 µm. Representative images, n = 3. d–f Number of muscle fibres in 0.1 mm2 of adult muscle is increased in mutants (d), whereas myofibre cross-sectional area (CSA) is decreased (e) reflecting a shift in CSA frequency distribution compared to sibs. g Fewer myonuclear profiles were present within laminin profiles in adult muscle cross-sections in mutants than in sibs, measured from 107 to 490 fibres at similar medio-lateral and dorso-ventral positions of trunk muscle of three fish per genotype. Mean ± SEM, t test. h Proportions of muscle fibres with indicated number of myonuclei within fibre cross-sectional profile. In sibs, >90% of fibres have more than one nuclear profile, compared with < 15% in mutants. Mean ± SEM, χ2 test. i NADH tetrazolium reductase stain revealed that in both mutants and sibs three fibre types are present: oxidative/slow (slow), intermediate (int) and glycolytic/fast (fast). Size of more glycolytic myofibres (yellow and green insets) is more reduced than oxidative fibres (cyan). Assay was performed on three 120 dpf adult male length-matched fish of each genotype. Representative sib (blue) or mut (red) fibres are highlighted. Mutant presents smaller slow type myofibres ectopically localised in fast domain (red inset). Representative images, n = 3. Bars = 100 μm (except for red, yellow and cyan insets = 10 μm)
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