Fig. 5

Mechanical weak muscles fibres are produced when Notch signalling is perturbed.

Transmission electronic microscopy was performed in 5 dpf pectoral fins of siblings (A) and mib^ta52b mutants (B) to analyse the ultrastructure of skeletal muscle fibres. The myofibrils with clear aligned sarcomeres are formed in the sibling embryo (A), while disintegrating myofibrils with poorly aligned sarcomeres are found in mib^ta52b mutants (B). Immunostaining performed in pectoral fins at 5 dpf using Desmin, Vinculin, phalloidin and DAPI to label the Z-discs of the sarcomeres, the zone where the skeletal muscle fibres insert distally, filamentous actin and the cell nuclei, respectively (C–P) demonstrate that Desmin (n = 10) (D) and Vinculin (n = 12) (F) are downregulated in mib^ta52b mutants when compared with their siblings (n = 10) (C, E). The same is observed in DAPT-treated embryos at 48 hpf and fixed at 5 dpf (n = 9) (H), when compared with the DMSO-treated embryos (n = 10) (G). In embryos treated with blebbistatin, Desmin (n = 9) and Vinculin (n = 12) are also downregulated (J, L) when compared with the DMSO-treated embryos (n = 12) (I, K). In blebbistatin-treated embryos, the endoskeletal disc cells present high levels of actin at the periphery and the skeletal muscle fibres are wavy with gaps between them (n = 15) (N). A down-regulation of Desmin and Vinculin is also observed in MS222-treated embryos (n = 14) (P) when compared with the control embryos (n = 13) (O).