Fig. 4

Heterozygous F437I and A234T mutations differentially affect myofibril assembly and stability. Each panel is representative of the myofibril population at that given stage of development, although varying levels of degeneration were observed as A234T/+ organisms aged. a Transverse and longitudinal sections from wild-type heterozygous transgenic control (pwMhc2/+) late-stage pupae. Rounded myofibril morphology with normal hexagonal packing of thick and thin filaments is observed, along with clearly demarcated M- and Z-lines in well-defined sarcomeres. b Transverse and longitudinal sections from wild-type transgenic control (pwMhc2/+) 2-h-old adults. Myofibril structure is retained. c Transverse and longitudinal sections from wild-type transgenic control (pwMhc2/+) 2-day-old adults. Myofibril structure is retained. d Transverse and longitudinal sections from heterozygous F437I/+ late-stage pupae. Myofibril morphology, hexagonal packing of thick and thin filaments, and sarcomere structure resemble a wild-type organism (panel a). e Transverse and longitudinal section from heterozygous F437I/+ 2-h-old adults. Aside from occasional missing filaments, leading to mild disruption in hexagonal packing, the sarcomere structure is normal. f Transverse and longitudinal sections from heterozygous F437I/+ 2-day-old adults. Phenotype is similar to that observed at 2 days. g Transverse and longitudinal sections from heterozygous A234T/+ late-stage pupae. Myofibril morphology is severely disrupted with some abnormalities in a hexagonal packing. Sarcomeres display Z-line irregularities with the absence of M-lines. h Transverse and longitudinal sections from heterozygous A234T/+ 2-h-old adults. Continued disruption in hexagonal packing of thick and thin filaments is observed. Z-lines are irregular, with possible sarcomere hypercontraction. i Transverse and longitudinal sections from heterozygous A234T/+ 2-day-old adults. Severe disruption in hexagonal packing of thick and thin filaments is observed, with a breakdown of myofibril boundaries. Sarcomeres contain skeins of filaments and appear to be hypercontracted. M, M-line. Z, Z-line. Scale bars, 0.5 μm