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Fig. 6 FGF-8 acts upstream of BMP2 and BMP4. (A-D) Expression of BMP2 and BMP4 at gastrula stage (60% epiboly) in wild type (A,C) and in embryos injected with FGF-8 RNA (B,D) showing that BMP labeling is absent from the ventral domain of the injected embryos. (A,B) BMP2 expression in wild type (A) and in FGF-8- injected embryos in B. (C,D) BMP4 expression in wild-type (C) and in FGF-8-injected embryos (D). (E,F) Expression at early gastrulation stage of FGF-8 in an embryo injected with BMP2 RNA (F) and its corresponding sibling (E). FGF8 expression is not affected by BMP2. (A-D) Lateral view; (E,F) animal pole view. dm, dorsal mesendoderm; pa, animal pole; ysl, yolk syncytial layer; WT, wild type; D, dorsal; V, ventral. Arrowheads in A-D show the position of the margin. Arrows in E-F indicate the limits of FGF8 gradient of expression.