h was shown to be active on the dorsal side of the Xenopus gastrula. As shown in Wnt11b Regulates Wnt/PCP Dependent Cilia Polarization and Morphogenesis of the GRP Next we analyzed cilia polarization, a process known to depend on Wnt/PCP. GRP explants from Wnt11b manipulated embryos were stained for cilia and cell borders using an antibody against 518303-20-3 acetylated tubulin and phalloidin. In uninjected control GRPs most cells were ciliated and cilia were localized to the posterior pole. Analysis of Wnt11b morphants and embryos 18194435 injected with DNA encoding either a dominant negative Wnt11b construct, which is specific for Wnt5/11-type ligands without affecting the canonical pathway, or wildtype Wnt11b revealed disturbed cilia polarization. Remarkably, clear differences were seen between loss-of-function scenarios and ectopic expression of Wnt11b. The ciliation rate was reduced to 50% and 66% in Wnt11b morphants and following injection of dnWnt11b DNA, respectively. Overexpression of Wnt11b did not alter the wildtype ciliation rate of about 80%, but cilia were predominantly unpolarized, i.e. arose in a central position. In addition we observed that the apical surface of GRP cells was enlarged upon Wnt11b manipulation. Average surface areas measured 193.71mm26143.00, 195.79mm2692.33 and 178.64mm2695.73 in Wnt11bMO, dnWnt11b DNA and Wnt11b DNA injected specimens, respectively, compared to 123.88mm2674.28 in control specimens, indicating an effect on GRP cell morphogenesis. Taken together, balanced levels of Wnt11b seem to be required for Wnt/PCP dependent cilia polarization and GRP morphogenesis. 2 Wnt11b in Xenopus Left-Right Development Loss of Wnt11b Disrupts Xnr1 and Coco Expression in Lateral Sensory GRP Cells GRP analyses implemented Wnt11b in the LR cascade at the level 
of flow or events downstream. They do, however, not provide an explanation as to the opposing effects of Wnt11b manipulation on Pitx2c expression, namely absence in morphants and bilateral induction upon ectopic expression. Our previous analysis of ATP4a has shown that a turbulent and attenuated ciliadriven flow is sufficient to induce the nodal-cascade in a bilateral fashion, in line with the characterization of Wnt11b DNA injected specimens presented here. In order to elucidate the opposing effect in morphants, we analyzed the lateral GRP cells which express both Xnr1 and its inhibitor Coco , and which are required for LPM Xnr1 induction. Wnt11b morphants and specimens injected with dnWnt11b showed significantly reduced expression levels of both genes. Ectopic expression of Wnt11b, in contrast, showed comparable signal strength to wildtype specimens, although domains were not aligned in parallel due to more pronounced convergent-extension phenotypes encountered in these experiments. Specificity of treatments was confirmed by co-injection of Wnt11b DNA in Wnt11b morphants, which partially restored Xnr1 expression. These differential effects on Xnr1/Coco provide an explanation for LPM Pitx2c induction in the various experiments. Wnt11b in Xenopus Left-Right Development Taken together, our data involve Wnt11b in the setup of the GRP and leftward flow. Discussion A role of Wnt signaling in LR axis development has been previously demonstrated in vertebrate model organisms including Xenopus. The sequential activity of two Wnt pathway branches is required 12176911 for cilia-driven leftward flow: canonical Wnt/b-cat signaling regulates Foxj1 expression during gastrulation in the Xenopus SM a
