In the additive model, only a trend was visible

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 XAV-939 site 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 12414725 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 9450616 required for cilia-driven leftward flow: canonical Wnt/b-cat signaling regulates Foxj1 expression during gastrulation in the Xenopus SM and in zebrafish Kupffer’s vesicle; non-canonical Wnt/PCP signaling is required for the posterior alignment of motile cilia at the frog GRP and the posterior notochord in mouse. The present work confirmed the Fz8-mediated Wnt/b-catenin dependent activation of Foxj1 expression in the SM. Wnt11b, however, contributes only marginally, if at all, to this process. Two additional canonical Wnt ligands are expressed during Xenopus gastrulation, Wnt3a and Wnt8a. Wnt3a expression starts only after the onset of Foxj1 transcription in the SM. It is therefore tempting to speculate that Wnt8a represents the main canonical activator of Foxj1 expression during gastrulation. This notion may seem contraintuitive at first glance, as Wnt8a is expressed in ventral and lateral portions of the prospective mesoderm but not in the SM itself. We have, however, previously shown that ventral and lateral portions of the mesodermal ring are competent to express Foxj1 upon activation of canonical Wnt signaling. Restriction of Foxj1 expression to the SM thus might be me