Fig. 7. BMP inhibits pancreatic fate within the endoderm. (A) Real-time RT-PCR analysis of dorsal vegetal (VD) explants injected with TGIF2-Mo, TGIF2-Mo in combination with mTgif2 (500 pg) mRNA for the rescue, and a combination of two antisense morpholino oligonucleotides targeting both Xenopus laevis chordin (Chd-Mo) pseudoalleles (Oelgeschlager et al., 2003). The plot shows the regulation (expression ratio) of target genes in VD-injected cells versus VD-uninjected cells. The analysis was done as described in Fig. 6. (B) Eight-cell stage embryos were injected into both ventral (VV) blastomeres with xTGIF2 (1 ng) mRNA and DN-Alk3 (1 ng). All explants were collected at tailbud stage and assayed for expression of the indicated markers by RT-PCR analysis. (C) Eight-cell stage embryos were injected into both dorsal vegetal (VD) blastomeres with increasing amount of CA-Alk3 (0.5 and 1 ng). All explants were collected at tailbud stage and assayed for expression of the indicated markers by RT-PCR analysis. (D) Schematic diagrams of gastrula, neurula and tadpole stages embryos. At gastrula stage, signals from the organizer and dorsal endoderm counteract the ventralizing factor BMP, establishing the region where pancreatic fate is specified. At neurula stage, ongoing intracellular inhibition of BMP signals by TGIF2 defines the region where prospective pancreatic buds are formed (dorsal bud is boxed in black; ventral bud boxed in red). At tailbud stage, Pdx1 marks both pancreatic buds. V, ventral; D, dorsal; A, anterior; P, posterior.