Fig. 1. Dominant-negative Xtcf3 (dn-Xtcf3) blocks endogenous dorsal axis in a stage-dependent manner. (A-C) Ventralized phenotypes caused by dn-Xcf3. (A) Group I phenotype: embryos lack all dorsal-anterior structures and fail to undergo convergent extension. (B) Group II phenotype: embryos lack head structures, but maintain trunk and tail or tail alone. (C) Group III phenotype: embryos develop dorsal and anterior structures and are either normal or have small eyes and slightly reduced heads. (D) Percentage of group I, II, III embryos caused by dn-Xtcf3 mRNA injection at the four-cell stage (4cs/d2; 500 pg for each dorsal blastomere), the eight-cell stage (8cs/d4; 250 pg for each dorsal blastomere), and 16-cell stage (16cs/d4; 250 pg for each dorsal-midline blastomere). (E) Luciferase assays for embryos injected dorsally with Lef-luciferase reporter (Lef-fos) alone (Hsu et al., 1998) or with dn-Xtcf3 at the four- or the 16-cell stage. (F) Phenotypes in embryos [as in (D)] injected with ßTGR (500 pg into each dorsal blastomere at the four-cell stage). Injected embryos were cultured in normal medium (untreated) or in medium containing dexamethasone (dex) from various stages (four-cell to 128-cell) until the gastrula stage. This experiment was repeated three times (with >50 embryos per group) with similar results.