Fig. 5. Cooperation between oep and fgf is required before the onset of gastrulation for the maintenance of dorsal mesoderm. (A-D) Flat mounts of embryos taken from the progeny of Zoep;ace double-heterozygous parents (the genotype, which is inferred from the phenotype and statistical analysis, is indicated top right). (A-B) Embryos at 90% epiboly, ntl staining occurs at the notochord and presumptive mesoderm at the margin of the blastoderm and hgg1 staining at the presumptive hatching gland (red), myoD staining labels adaxial cells, and her5 staining the presumptive midbrain-hindbrain boundary (blue). (C-D) Embryos injected with caged dextran-fluorescein at the one-cell stage, laser irradiated at the shield stage at the level of the embryonic shield, fixed and stained at the end of gastrulation for ntl and hgg1 (blue) and fluorescein (brown). Arrow points to the anterior limit of migration of the labelled cells in D. (E-H) Flat mounts of embryos taken from the progeny of oep heterozygous parents (the genotype, inferred from the phenotype and statistical analysis, is indicated top right), treated with 10 µM SU5402 for various periods of time (as shown), fixed at 90% epiboly and stained for ntl (blue) and hgg1 (red). Wild-type embryos appear to be unaffected by SU5402 treatment.