Fig. 4

Gene expression in embryos with lateral (A–D) or vegetal (E–W) yolk removed detected by in situ hybridization and immunohistochemistry. In embryos with removed lateral yolk the expression pattern of zbmp-4 (B) and din (D) is not altered compared to the siblings (A, C). (E, F) zbmp-4 is at 70% epiboly expressed in the ventral epi- and hypoblast and dorsal prechordal plate mesoderm (E), whereas it is ubiquitously expressed in the experimental embryo (F). (G, H) din is expressed at 70% epiboly in the axial mesoderm and dorsal ectoderm (G) and absent in embryos which lack the vegetal pole (H). (I, K) At 30% epiboly nwk is expressed in the blastomeres and the YSL of the future dorsal side (I), but is absent in ventralized embryos (K). (L, M) At 90% epiboly otx-2 is expressed in the anterior-most neuroectoderm (L), but is absent in ventralized embryos (M). (N, O) anf is expressed at 90% epiboly in the anterior-most neuroectoderm (N) and is absent in the experimental cases (O). (P, Q) At tailbud stage, gsc (red, arrowheads) is expressed in the anterior prechordal plate and myoD (blue) in the paraxial mesoderm (P). Transcripts of both genes are abolished in embryos lacking the vegetal pole (Q). At the end of gastrulation sna-1 expression is found in the paraxial mesoderm and the marginal zone (R). In a ventralized embryo paraxial mesoderm expression is absent (S). (T–W) krox-20 (red) is expressed in rhombomeres 3 and 5, gata-1 (blue) marks the blood precursor cells, and Ntl (brown) stains the nuclei of the notochord and the tailbud at the five somite stage in untreated embryos (T, V). In experimental cases (U, W) krox-20 and axial Ntl expression are missing, whereas one can still find Ntl expression in the tailbud. gata-1 is expressed in a radial fashion. (A–H, L, M, and P–U) Lateral view, dorsal to the right (only in R and S is dorsal to the front); (I–K, N, O, V, and W) animal view, anterior to the left.