FIG. 2.

The axin GID activates Wnt signaling and dorsalizes Xenopus embryos. (A) Accumulation of β-catenin protein. Cytoplasmic extracts from oocytes expressing β-catenin (lanes 1 to 8) and incubated in 20 mM LiCl (lane 2) or coexpressing C-terminal (lane 3), GID (lane 4), or N-terminal (lane 5) axin fragments were immunoblotted with a β-catenin antibody (30). LiCl treatment (lane 2) and the GID (lane 4 and 7) cause accumulation of cytoplasmic β-catenin. (B) Axis duplication in Xenopus tadpoles by the axin GID. Representative samples are shown at stage 40 (top right) or stage 30 (bottom right) with complete dorsal-anterior axis duplication after injection of 100 pg of axin GID mRNA into one ventral cell of a four-cell embryo. Original axis (arrow) and secondary axis (arrowhead) are indicated. UNIN, uninjected; GID, embryos injected with GID mRNA. (C) Dose-dependent axis duplication by the axin GID. GID mRNA was injected as above at the doses indicated, and axis duplication was scored in tadpoles. Presence of cement gland and eyes was scored as complete axis (solid bars); partial duplications of the trunk and/or heads lacking eyes or cement gland were scored as partial axes (open bars). FL Xaxin mRNA strongly ventralizes embryos when expressed in dorsal blastomeres (data not shown), as described for mouse axin (51).