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. 2001 Jun 15;15(12):1563–1576. doi: 10.1101/gad.195801

Figure 5.

Figure 5

Ubo is essential for the Hh-mediated specification of slow fibers and genetically acts downstream from shh and gli2. (A, C, E, G) Myotomes of wild-type embryos injected with shh / dnPKA mRNA, showing ectopic mAb S58 immunoreactivity (A, green), supernumerary Engrailed (Eng)-expressing muscle pioneers (MPs) (C, red), ectopic Prox1 (E, green), and loss of fast MyHC (G, green; residual expression is indicated by the arrow). The mononucleate nature of the ectopic MPs shown in C is indicated (arrows). Note the flattened, elongated nuclei of these ectopic fibres. (B,D,F, H) Myotomal segments of similarly injected and stained ubo embryos. (B) The levels of ectopic slow MyHC expression are strikingly low. (D) Ectopic Eng is induced to an extent similar to that in wild-type embryos, but the levels are comparatively low. Prox1 expression cannot be induced under such conditions in the mutant embryos (F), and they also exhibit high levels of fast MyHC expression (H). The multinucleate nature of the fibers are indicated (arrows in D and H). Note the rounded shape of the nuclei of these fibers. Embryos shown in panels E and F were coinjected with mRNA-encoding nuclear-localized β-galactosidase as a tracer (red) to control for the distribution of injected RNAs; those in panels G and H were counterstained with propidium iodide (red) to reveal the nuclei, whereas those in C and D were coinjected with the α-actin-GFP plasmid to individually label the muscle fibers (green). (I) The pattern of slow fibers in a shh (syu) mutant embryo. Note that the numbers of fibers are reduced, and there are no MP cells (compare with wild-type embryo in Fig. 3A). The pattern of slow MyHC expression in these fibers, however, appears normal and the muscles are mononucleate (arrow in inset). (J) Similar image of an syu;ubo double mutant embryo, showing the pattern of slow fibers which is similar to ubo single mutants and even more dramatically affected (compare with Fig. 3B). Note that the few slow MyHC-associated fibers seen in these situations, like in ubo mutants, are multinucleated (arrows in inset). (K) The myotomal segments of an yot;ubo double mutant embryo, showing complete absence of slow MyHC expression, a phenotype indistinguishable from yot single mutants.