Fig. 5.

Ultrastructure of myofibrils expressing two IBM3 E701K Mhc genes and one wild-type Mhc gene show enhanced myofibrillar degeneration and Z-line streaming. Transmission electron micrographs of longitudinal and transverse sections through IFM myofibrils from 4-week-old adult flies. PwMhc2/PwMhc2/+ transgenic control myofibrils (top row) contain well-organized sarcomeres (A), with a double-hexagonal lattice of thick and thin filaments (A′). Myofibrils from (B) E701K-3/E701K-3/+ and (C) E701K-5/E701K-5/+ IFMs show severely disordered sarcomeres with non-linear Z-lines (arrowheads) and Z-line streaming. Although some normally structured sarcomeres are present, the overall phenotype is dramatically worsened compared with mutant heterozygotes (Fig. 2). In transverse sections (B′,C′) myofibrillar disorder and mislocalization of Z-line material is evident (arrows). Scale bars: 2 µm (longitudinal sections); 1 µm (transverse sections).