Fig. 3

Gene expression and neural induction in ventralized embryos. Embryos are oriented with the animal pole to the top, except for G. (A) Schematic representation of the experiment. Noggin/Chordin COS7 cells were transplanted into ventralized blastula (4 h) from which the vegetal yolk mass had been removed. (B,C) gsc expression in normal (B) and ventralized (C) embryos at the shield stage. No gsc expression is detected in a ventralized embryo. (D) Dorsal view of normal gastrula (90%-epiboly) stained with otx2 probe and anti-Ntl antibody. The region fated to become forebrain and midbrain is positive for otx2 transcripts (dark blue), while the blastoderm margin (arrow) and the notochord (n) are positive for Ntl (light brown). (E) Lateral view of a ventralized gastrula (90%-epiboly) stained with otx2 probe and anti-Ntl antibody. The blastoderm margin is positive for Ntl (arrow), while neither Ntl staining in the notochord nor otx2 expression in the head region is detected. (F) The ventralized gastrula (90%-epiboly) stained with otx2 probe and anti-Ntl antibody. The ventralized embryo was grafted with Noggin/Chordin COS7 cells at the blastula stage. otx2 expression is induced in the anterior region around the graft (arrowheads) with a sharp posterior boundary. (G) Longitudinal section of the host shown in G along the transplanted Noggin/Chordin COS7 cells (dotted line). The posterior boundary of induced otx2 expression domain is indicated by an arrowhead. The animal pole (an) is to the left and the vegetal pole (vg) to the right. Scale bars, 100 μm.