Fig. 4

OSM is Myod dependent in zebrafish. In situ hybridisation for myog (A,C,D) or mylz2 (A), and immunodetection of MyHC (B) and Myh11 (B). Dorsal view wholemounts are oriented anterior towards the left (A, upper panels; C,D). Lateral view wholemounts are oriented anterior towards the left and dorsal towards the top (A, lower panels; B). (A) At 72 hpf, myog mRNA expression was indistinguishable from that in wild-type siblings in OSM of myf5^hu2022 mutants (red arrowheads). PHM, PFM and pharynx muscle were also unchanged (white arrowheads, green arrowheads and asterisk, respectively). Myosin mRNA (mylz2) at 120 hpf was unaltered in myf5^hu2022 mutants, suggesting OSM terminal differentiation occurs normally after reduction of Myf5 (red arrowheads). (B) OSM and smooth muscle differentiation was unaffected in myf5^hu2022 mutants (red arrowheads and white arrows, respectively). In myod^fh261 mutants, MyHC within OSM was absent, but SHM and PHM differentiated well (yellow and white arrowheads, respectively), as did oesophageal smooth muscle (white arrows). Double myf5^hu2022;myod^fh261 mutants had no striated skeletal muscle, but cardiac striated muscle (h) was readily observed, as was smooth muscle in the gastrointestinal tract and bulbus arteriosus (bu). (C,D) myog mRNA reduction in the oesophageal region of myod^fh261 mutants (C) and myod morphants (D). Asterisk indicates pharyngeal muscle. Arrowheads indicate OSM (red), SHM (yellow), pectoral fin muscle (green) and PHM (white). White arrow indicates oesophageal smooth muscle.