Fig. 5

Expression of myoD in a wild-type (A) and a syu^t4 mutant embryo (B), 14-somite stage, dorsal view on flat-mounted embryo. Expression of myoD is strongly reduced in the adaxial cells, also more lateral expression in the somitic mesoderm is lower. Residual levels of myoD remain detectable in the adaxial cells, especially in the tailbud region. Double staining for twist (in situ hybridization) and Engrailed (4D9 antibody labeling) in wild-type (C) and syu^t4 mutant (D) embryo, side view on tail, 22 hpf. twist labels the early notochord in the tailbud, the hypochord and the sclerotome visible in the ventral part of the somites (all blue staining). In the syu mutant, twist staining is only slightly reduced and shifted dorsally relative to the notochord due to the abnormal shape of the somites. Engrailed positive muscle pioneers (brown staining) are absent from syu mutant embryos. Expression of col2a1 in wild-type sibling (E) and syu^t4 mutant embryo (F) at 29 hpf, side view. col2a1 labels both the medial floor plate and the hypochord. syu^t4 has no effect on medial floor plate staining. Whole-mount antibody and in situ staining for Engrailed (4D9) and fkd4, respectively, of wild-type sibling (G) and syu^t4 mutant (H) embryo at 24 hpf, dorsal view. Computer composite of two focal planes. One plane shows the nuclei of the muscle pioneers (brown). The second plane shows the cytoplasmic fkd4 staining in the ventral neural tube encompassing medial and lateral floor plate. In syu mutant embryos, muscle pioneers are absent and fkd4 expression is restricted to the medial floor plate itself. Expression of ehh (I) and twhh (J) at 15- to 17-somite stage syu^tbx392/t4 mutant embryos. The expression of both hedgehog homologs in syu mutant embryos is indistinguishable from wild-type siblings.