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Fig. 2 The blastoderm margin is the source of signals important for otx2 and gbx1 expression. (A-B') Lateral blastoderm margin transplantations into the animal pole of a wild-type host embryo. (A,B) Embryo containing cells from the blastoderm margin derived from injected wild-type embryos with a lineage tracer (brown). (A) The white arrowhead indicates a clone of non-otx2-expressing cells in the otx2 domain of a transplanted embryo. (A') Close-up of the transplanted cells. otx2 is repressed around the transplanted cells. (B) The black arrowhead indicates a clone of gbx1-expressing cells in the otx2 domain. (B') Close-up of the transplanted cells. gbx1 expression is induced around the transplanted cells. (C-J) gbx1 and otx2 expression in the absence of FGF, Nodal or Wnt signaling at 60%. (C) Control embryo stained for otx2 and Ntl protein (brown). (D) In Su5402-treated embryos, otx2 is strongly reduced and expands up to the margin at the level of the midline. (E) In MZoep embryos, otx2 expands up to the margin at the level of the midline. (F) In dkk1-injected embryos (100 pg), a posterior shift of otx2 is visible laterally (compare brackets in C and F). (G) Control embryo stained for gbx1. gbx1 is expressed dorsolaterally and absent in the margin ventrally in Su5402-treated embryos (H). (I) In MZoep embryos, gbx1 expands up to the margin. (J) dkk1-injected embryos (100 pg) do not express gbx1, showing the Wnt-dependent activation of gbx1. The black arrowheads indicate the margin. (C-J) Dorsal views, anterior upwards; (C,D,E,F) right corner, lateral views, dorsal towards the right; (G-I) right corner, animal pole views, dorsal downwards.