Figure 9. The open conformation of Dvl disrupts CE by activating Jun N-terminal kinase (JNK).
(A) Western blot of phosphorylated JNK in ventral mesoderm cells overexpressing wild-type XDsh or its mutants. At equivalent protein level, Xdd1 and XDsh-CΔ8 more potently induce JNK phosphorylation than wild-type XDsh. (B) Xenopus 4-cell stage embryos were dorsally coinjected with equal quantities of wild-type XDsh mRNA or XDsh-CΔ8 mRNA (500 pg) and the AP1-luciferase reporter DNA (200 pg); luciferase activity was assayed at the late gastrula stage. Inset shows a representative Western blot using anti-myc antibody to control XDsh and XDsh-CΔ8 protein levels. Values are the mean and SD from three independent experiments (XDsh vs XDsh-CΔ8, p < 0.05). (C–H) The dominant negative JNK mutant (dnJNK) rescues activin-induced explant elongation blocked by overexpression of XDsh-CΔ8 or Xdd1. (C) Uninjected explants treated with activin show extensive elongation. (D) XDsh-injected explants treated with activin show moderate inhibition of explant elongation. (E) Injection of XDsh-CΔ8 strongly inhibits explant elongation. (F) Injection of Xdd1 similarly inhibits explant elongation as injection of XDsh-CΔ8. (G, H) dnJNK rescues explant elongation inhibited by XDsh-CΔ8 or Xdd1. (I) dnJNK also recues CE defects produced by overexpression of XDsh-CΔ8 or Xdd1 in whole embryos. Phenotypes are severe (green), mild (red), and normal (blue). Numbers on the top indicate total embryos scored from three independent experiments.