β-Catenin has a highly conserved function in axial patterning in metazoan embryos. In species as diverse as frogs and sea urchins,β-catenin localises to nuclei at one pole of cleavage-stage embryos,where it activates the transcription factors required for axis specification. On p. 2947, Weitzel and colleagues investigate how, in sea urchins, β-catenin localisation at the vegetal pole is achieved. In vivo measurements of the half-life of GFP-tagged β-catenin reveal a marked gradient of β-catenin stability along the animal-vegetal axis during early cleavage. This gradient depends on glycogen synthase kinase-3-β (GSK3β), which by phosphorylatingβ-catenin marks it for degradation. GSK3β activity, in turn, is inhibited by dishevelled (Dsh), which is activated in vegetal cells. The researchers also identify regions of Dsh that are required for its vegetal targeting, thus shedding light on the molecular mechanisms of early axial patterning in the sea urchin and potentially elsewhere.

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