Muscle degeneration in sof mutants results from detachment of
myofibres from the vertical myoseptum. Lateral views of wild-type muscle
(A,C,E) show fibres spanning the somite between adjacent myosepta, whereas in
sof mutants (B,D,F), lesions rapidly develop. (A,B)
Whole-mount immunohistochemistry using an antibody against slow myosin
demonstrates that, although slow fibres develop normally in sof
embryos, by 30 hpf fibres have already detached from the myoseptum.
(C-F) DIC images of axial muscle. By 72 hpf, the sof embryo
appears severely damaged, with numerous detached fibres scarring the myotome.
A magnified view of a single detached fibre (F) shows the characteristic
invaginated membrane (arrows) and retraction groove (arrowhead). (G)
Retraction of a single fibre (arrowhead), from left of frame to right, in a 72
hpf sof embryo. Still images taken from Movie 1 in the supplementary
material, with elapsed time indicated in seconds.