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Fig. 4 High levels of Bmp signaling are important for ventral mesoderm patterning during gastrulation but not afterward. Embryos were heatshocked in an air incubator at 3 hpf for 1 hour, or heatshocked continuously from bud stage, sorted for GFP fluorescence and fixed at the 12-somite stage. Expression of flk-1 (A-C), gata1 (D-F) or pax2.1 (G-I) was then examined by in-situ hybridization. Non-transgenic embryos heatshocked under either protocol were identical, so only a single example is shown for the –GFP samples (C,F,I). Expression of all three markers was reduced in transgenic embryos (A,D,G) compared with wild-type siblings (C,F,I) after 3 hpf heatshocks. Gene expression was unaltered following post-gastrula heatshocks (B,E,H). Arrows in A-C denote flk-1-expressing cells. Arrowheads in G-I denote pax2.1 expression in the otic placode, while brackets indicate pax2.1 expression in the pronephric ducts and tubules. Views in A-C and G-I are dorsal, with anterior to the top. (D-F) Posterior views of embryos.