Fig. 3. xTGIF2 behaves as a modifier of the endoderm. (A) Xenopus eight-cell stage embryos were injected into both ventral (VV) or dorsal vegetal (VD) blastomeres with xTGIF2 (1 ng) mRNA. Vegetal explants were dissected at early gastrula stage (stage 10). Uninjected VV or VD pole halves were used as control for their regional differences in the expression of endodermal markers. All explants were collected at tailbud stage and assayed for expression of the indicated markers by RT-PCR analysis. (B) Animal caps injected with VegT (60 pg) mRNA and/or xTGIF2 mRNA, as indicated. The explants were cultured until stage 30 (tailbud) and analyzed for expression of the indicated markers. (C) Eight-cell stage embryos were injected into ventral vegetal (VV) blastomeres with xTGIF2 (1 ng) mRNA. Uninjected VV or VD pole halves were used as control. All explants assayed at tailbud stage for expression of the indicated mesodermal markers by RT-PCR analysis. (D-E'') Lineage-tracing analysis of endodermal cells injected with xTGIF2 mRNA. (D) Ventral vegetal explants isolated from uninjected or xTGIF2+lacZ-co-injected embryos were stained for β-gal and assayed for Pdx1 expression by in situ hybridization at tailbud stage. The β-gal staining (blue) and ectopic Pdx1 (red) expression co-localize in endodermal explants (see arrowheads). (E) Whole-mount in situ hybridization analysis of Pdx1 expression in xTGIF2+lacZ-co-injected embryos. White dashed outline demarcates the region of the embryo magnified in E'. Arrowheads indicate purple cells stained for β-gal (blue) and positive for Pdx1 (red). (E'') Transverse section through the stained endodermal region shown in E'.