Fig. 3. Dishevelled-dependent canonical WNT signals govern embryo patterning. (A) Dishevelled is required to maintain segment polarity in Drosophila. A WNT signal (blue) is produced in the posterior of each segment and is received by Frizzled receptors on the anterior-most cell of the neighboring segment. This canonical WNT signal is transduced by Dishevelled. (B) A wild-type Drosophila embryo (top) and an embryo with disrupted canonical Wingless/WNT signaling (bottom). Images courtesy of K. Wharton (University of Texas, Southwestern Medical School). (C) Canonical WNT signals govern both dorsoventral patterning of the mesoderm (orange denotes dorsal; red, ventral) and anteroposterior patterning of the neuroectoderm (light blue denotes anterior; dark blue, posterior). (D) A normal Xenopus embryo (top) and an embryo with a duplicated axis resulting from ectopic ventral activation of canonical WNT signaling (bottom).