Fig. 7

GA and forskolin inhibit formation of eng-2-expressing muscle pioneer cells. (A and D) Control. (B and E) GA treatment beginning at 50% epiboly. (C and F) Forskolin treatment beginning at 50% epiboly. (A–C) Whole 18-h-old embryos. (D–F) Two anterior somites at comparable positions within the trunk of these embryos. In situ hybridization for the detection of eng-2 mRNA was carried out as described under Materials and Methods. All embryos are lateral views with anterior to the left and dorsal to the top. Muscle pioneers, which can be distinguished from other striated muscle cells by high levels of eng-2 expression, normally develop at the D–V midline of the myotome at the future location of the horizontal myoseptum (arrows in A and D) but are absent from this location in GA-treated and forskolin-treated embryos (arrows in E and F). However, activation of eng-2 expression in cells of the midbrain/hindbrain boundary is unaffected by GA or forskolin treatment (asterisks in A–C). Scale bar in A–C, 100 μm. Scale bar in D–F, 20 μm.