Fig. 2. Ventral overexpression of HI-Xmsx-1 induces an ectopic head. (A) Schematic drawing of the different forms of Xmsx-1. (Top) Wild-type Xmsx-1 protein. Activating forms of Xmsx-1, HI-Xmsx-1 (middle), and TI-Xmsx-1 (bottom), were constructed by fusing the 81 amino acids of the VP16 activation domain (black box, VP16 AD) with the full-length and C-terminal 137 amino acid region of Xmsx-1 protein, respectively. The amino acid numbers of several junction sites are shown above each drawing. The homeodomain is indicated by the gray box (HD). (B-D) Phenotypes of mRNA-injected embryos. (E,F) Staining with the notochord- and otic vesicle-specific antibody, MZ15. Four-cell stage Xenopus embryos were ventrally injected with 500 pg of TI-Xmsx-1 (B,E) or HI-Xmsx-1 (C,F) mRNA alone or coinjected with 500 pg of HI-Xmsx-1 and 1 ng of wild-type Xmsx-1 mRNA (D). HI-Xmsx-1-injected embryos formed a secondary axis with an ectopic head containing eye(s), cement gland and short notochord in the ventral side. The ectopic head region is magnified in the right side of C. The ectopic head phenotype was rescued by wild-type Xmsx-1. cg, cement gland; ey, eye; 2°, secondary axis.
