Fig. 2

Fig. 2 Zoep and ntl are together required to maintain spt expression. (A–D) seven hours (60% epiboly), dorsal view, animal pole uppermost. (E and F) seven hours (60% epiboly), vegetal view. (G–I) Ten hours (bud stage), posterior view of the tail bud, dorsal is up. (A) Wild-type embryo. Spt is expressed in paraxial mesoderm progenitors involuting at the margin and the migrating prechordal mesoderm (arrow), but is excluded from the notochord progenitors (N). (B) Ntl mutant embryo; spt is expressed in paraxial and prechordal mesoderm (arrow), but is weaker in paraxial mesoderm adjacent to the notochord progenitors and the border of spt expression lacks the defined edge observed in wild-type embryos. (C) Zoep mutant embryo; spt expression is normal in cells at the margin, but is not observed in prechordal mesoderm progenitors. (D) Zoep;ntl double mutant embryo; spt is expressed at the margin but is weaker adjacent to the notochord and is not detected in prechordal mesoderm progenitors. (E and F) Vegetal view, dorsal side uppermost, of embryos in C and D, showing the distribution of spt expression in mesoderm at the margin. (G) Expression of spt in a wild-type embryo. Note the intense staining in the tail bud (arrow) and segmental plate cells either side of the nonexpressing notochord. (H) Zoep;ntl double mutant embryo; spt expression is only observed weakly in a small number of cells in the tail bud (arrow). (I) cyc;sqt double mutant embryo. Note the intense expression of spt in the tail bud.