Fig. 3

Fig. 3 smad1 expression A–C: and regulation of smad1D–J: and smad5K,L: expression during gastrulation. A: smad1 at 80% epiboly, lateral view, dorsal right. smad1 is expressed on the ventral side of the embryo. B, C: smad1 at tailbud stage, lateral view (B) and animal view (C), dorsal right. smad1 is expressed on the ventral side of the embryo, with highest mRNA levels in lateral regions, which give rise to the epidermis and neural crest (indicated by arrows in B and C). In addition, smad1 is expressed in the notochord anlage in the dorsal midline (indicated by arrowhead in C). D–J: Ventral smad1 expression is positively regulated by Bmp2b, but not by Bmp4. D–I: smad1, 80% epiboly, animal view, dorsal right. D: Wild-type control. E: bmp2b mutant swr^ta72, lacking smad1 transcripts. F: smad5 mutant sbn^dtc24, with strongly reduced smad1 mRNA levels. G: Chordino mutant din^tt250, with a dorsally expanded smad1 expression domain. H: Wild type after injection of bmp2b mRNA (2.5 pg/embryo), with a dorsally expanded smad1 expression domain and elevated smad1 mRNA levels. I: Wild type after injection of bmp4 mRNA (0.5 pg/embryo), displaying unaltered smad1 expression. J: Reverse transcriptase–polymerase chain reaction analysis for transcripts of smad1, evel (Joly et al., 1993) and ef1α (Nordness et al., 1994) in total zebrafish embryos at 80% epiboly stage after injection of 2.5 pg/embryo bmp2b mRNA or 0.5 pg/embryo bmp4 mRNA at the one-cell stage, in comparison to uninjected control embryos. Both bmp2b- and bmp4-injected embryos show a significant increase of eve1 mRNA levels, whereas an increase of smad1 mRNA levels is only seen in bmp2b-, but not in bmp4-injected embryos. bmp2b- and bmp4-injected sibling embryos of (H–J) were raised to day 1 and showed ventralized phenotypes of comparable strengths and with similar frequencies (see Table 1). K, L: smad5 is expressed independently of bmp2b. Ninety percent epiboly, lateral view, dorsal right. K: Wild type. L: swr mutant, displaying unaltered smad5 mRNA levels. The weaker signal on the ventral side of the wild-type embryo (K) is because of fewer cells in this region compared to the swr mutant (L).