Expression of prdm1 in the nervous system of BMP mutant zebrafish embryos. BMP mutants are visualized from the ventral side, where the reduction or expansion of the neural crest/RB sensory neuron domain is observed. Ventral (A–H) views of 12 hpf wildtype and BMP mutant embryos. swr (Bmp2b) mutant embryos (B, F) show an absence of prdm1 mRNA at the lateral border of the neural plate (compare to wildtype in A, E). The domain of expression of prdm1 is expanded in sbn (Smad5) embryos at 12 hpf (Low (C) and high (G) magnification; ventral views, compare to ventral view in wildtype in E), consistent with an increase of the neural crest/RB sensory neuron domain. Low (D) and high (H) magnification views of 12 hpf snh (Bmp7) showing a reduction in expression in the neural crest/RB sensory neuron domain of these embryos (arrows in D, H; compare to wildtype in A, E). Dorsal view of wildtype embryo in (I) as compared to dorsal views of swr (J), sbn (K), and snh (L) show that the adaxial expression (arrow in J) remains. Below, images are schematic representations of the neural crest domain in each of the mutant embryos as compared to wildtype. Since the BMP mutants are ventralized and the neural plate domain is expanded, the neural plate border form on the ventral side in sbn and snh and is completely absent in swr. Abbreviations: wt, wildtype; swr, swirl; sbn, somitabun; snh, snailhouse; A, adaxial cells. For (A–D), scale bar is shown in A and is 50 μm; for (E–L), scale bar is in E and is 50 μm.