Fig. 5

Hh regulation of Pax7⁺ myogenic precursors occurs later than Hh induction of slow muscle fibers. Wild-type embryos were treated with cyclopamine from the 8-somite stage to the 30-somite (24 h) stage; they were then labeled for differentiated muscle fibers, slow muscle nuclei, and myogenic precursor nuclei. The numbers at the top of panel A indicate somite number. White lines frame the borders of somites: these were drawn solely with the MF20 labeling visible. (A) Merged image showing myosin (MF20, blue), slow muscle nuclei (Prox1, red), and myogenic precursor nuclei (Pax7, green). (B) A single color panel of A, showing Prox1-positive slow muscle nuclei in each somite, the number per somite is shown. All somites have an approximately wild-type number of Prox1-positive nuclei. Somites posterior to somite 18 had a loss of slow muscle fiber nuclei (data not shown, Hirsinger et al., 2004). (C) Single color panel of A, showing the Pax7-positive myogenic precursor nuclei in each somite. The number of Pax7⁺ myogenic precursors in somites 5 to 11 is similar to wild type, while posterior to somite 11, the number of Pax7⁺ myogenic precursors in each somite is increased to the level of smu^-/-; compare to Fig. 2H. Anterior to the left, dorsal up; scale bar = 50 μm.