Poster Sessions

Dev-42

Rieko Ajima

R. Ajima, E. Layman, K. Biris, K. Kugathasan, S. Stacker, A. Wynshaw-Boris, T. P. Yamaguchi

Wnt5a genetically interacts with Dvl2 and Vangl2/Lp to regulate the mammalian Wnt/PCP pathway

During vertebrate embryogenesis, members of the Wnt family of secreted signaling molecules regulate cell fates by activating the Wnt/beta-catenin pathway, and regulate cell movements through the Wnt/planar cell polarity (PCP) pathway. In Xenopus and zebrafish, non-canonical Wnts such as Wnt5a signal through the Wnt/PCP pathway to control specialized cell movements known as convergent-extension (CE). CE movements drive the elongation of the anterior-posterior (AP) body axis. In mammals, the function of Wnt5a and the PCP pathway are not well-understood. Mice carrying mutations in core PCP components such as Vangl2 (mutated in the Loop-tail (Lp) mouse), or combined mutations in Fz3;Fz6, and Dvl1;Dvl2, display distinctive defects in neural tube closure, AP axis extension, stereocilia polarity in the cochlea, and the outflow tract of the heart. We have previously shown that the Wnt5a mutant phenotype is distinct from PCP phenotypes since Wnt5a-/- mutants lack tails, and display skeletal, craniofacial, limb and external genitalia phenotypes but possess normal, closed, neural tubes. To further assess Wnt5a mutants for PCP phenotypes we first examined the outflow tracts of Wnt5a-/- hearts. Severe cardiovascular defects including persistent truncus arteriosus (PTA), double outlet right venticle (DORV) and subarterial ventricular septal defects (VSD) were observed. These defects are remarkably similar to the outflow tract abnormalities observed in Dvl2 and Vangl2/Lp mutants. To determine whether Wnt5a, Dvl2 and Vangl2 function in the same genetic pathway, we performed double mutant analyses. Strong synergistic interactions were observed in E13.5 embryos carrying compound mutations in Wnt5a and Dvl2 or Wnt5a and Lp including severe neural tube closure defects and enhanced skeletal defects. Wnt5a-/-;Dvl2-/- double mutants were rarely observed at this stage. Analysis of the progeny of Wnt5a;Dvl2 and Wnt5a;Lp intercrosses at earlier stages (E9.5) revealed profound defects of the neural epithelium, somites, and presomitic mesoderm (PSM) in double mutants that resulted in open neural tubes (craniorachischisis) and extreme reductions in the length of the embryonic AP axis. Marker analyses suggest that these phenotypes arise due to defects in CE movements. Taken together, our data strongly suggest that Wnt5a, Dvl2 and Vangl2 function in a common genetic PCP pathway to regulate the CE of neuroepithelium and the PSM during mammalian gastrulation, segmentation and neurulation.