Symmetry breaking in amphibian eggs depends on microtubule-driven cortical rotation. Rotation leads to the asymmetric enrichment of nuclear localised β-catenin and the subsequent formation of a dorsal ‘organiser’. The role, if any, of Wnt ligands upstream of cortical rotation is unclear. Now, Douglas Houston and colleagues find that maternal Wnt11b is a permissive factor for dorsoventral patterning and for gastrulation. Using CRISPR/Cas9, they create and analyse F2 mutant Xenopus laevis females, and recover maternally mutant eggs to specifically test the contribution of maternal wnt11b. They discover that gastrulation is delayed in all embryos lacking maternal wnt11b although, in some cases, axial tissues do form. The delay in gastrulation correlates with reduced expression of mesoderm and endoderm genes. They observe that zygotes lacking maternal wnt11b have disorganised vegetal cortical microtubules and more variable plus-end growth dynamics, resulting in less robust cortical rotation. In addition, the authors uncover a zygotic role for wnt11b in left-right symmetry. Together, these data demonstrate roles for wnt11b in setting up cortical rotation via microtubule organisation, which is required for dorsoventral axis specification, and for promoting gastrulation.
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