β-catenin Signaling and Axis Specification

Randall T. Moon*

Howard Hughes Medical Institute and Department of Pharmacology, University of Washington School of Medicine, Seattle, WA 98195 USA

*Contact information. E-mail, rtmoon{at}

Animation. β-catenin (β-CAT) signaling during axis specification in vertebrates based on analysis of embryos of the amphibian Xenopus. Prior to fertilization components of the Wnt/β-catenin pathway, Dishevelled (Dsh) and β-CAT, are uniformly distributed and β-CAT is degraded by a ubiquitin (U)-proteasome process following phosphorylation by glycogen synthase kinase 3 (GSK-3). Sperm entry causes a calcium wave and then the microtubules become oriented with the plus ends pointing away from the sperm entry point. Dsh accumulates in the side opposite sperm entry, which will become the anterior and dorsal structures, possibly by association with vesicles that move along the oriented microtubules. The accumulation of Dsh promotes the stabilization and dorsal accumulation of β-CAT, which then activates direct target genes, including the homeobox genes siamois and twinned. Activation of these genes on the prospective dorsal side is necessary and sufficient for formation of the gastrula organizer (Spemann Organizer), which organizes the embryonic germ layers and axes.

Animation by: Cameron Slayden

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R. T. Moon, Xenopus Egg Wnt/β-catenin Pathway. Sci. STKE (Connections Map, as seen August 2003),;CMP_6031.


Citation: R. T. Moon, β-catenin signaling and axis specification. Sci. STKE (Supplement to Connections Maps, August 2003),;CMP_6031/DC1.