Fig. 4

Skeletal muscle phenotype in obscurin A RhoGEF morphant embryos at 72 hpf. Ultrastructural analysis was performed at 72 hpf on control, obscurin A (ObscMO) and obscurin A RhoGEF (ObscRhoMO) morphant embryos. In control embryos, the myofibrils are aligned in register across the sarcoplasm (A) with well defined M bands and finely “stitched” Z disks (D). In the obscurin morphant embryos (B) there is marked disturbance of myofibril organization with areas of misalignment of the M bands of adjacent myofibrils (E: ^). By comparison, the obscurin A RhoGEF morphants display myofibril organization (C) similar to control embryos but reduced myofibrillar content with more sarcoplasm devoid of myofibrils and more rounded nuclei (C, G: ^). There were also mild sarcomeric abnormalities including, infrequently, an indistinct appearance of the Z disk and absence of the M band (F: ∗) which could occur even within myofibrils demonstrating mature Z disks and M bands (F: ^). Note that in skeletal myocytes stained with DAPI, the nuclei in the obscurin A RhoGEF morphants (RhoMO) are closer together and more rounded (G) than in controls (H) consistent with reduced myofibril volume. Scale bars 2 μm (A–C), 0.5 μm (D–F) and 10 μm (G, H).