Connections Map Overview

Xenopus Egg Wnt/β-Catenin Pathway

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Science's STKE  15 Feb 2005:
Vol. 2005, Issue 271, pp. cm2
DOI: 10.1126/stke.2712005cm2


In embryonic development in vertebrates, β-catenin signaling promotes polarization of the embryo to establish the dorsoventral axis, and it is this process that is highlighted by the Xenopus Egg Wnt/β-Catenin Pathway. In the amphibian Xenopus, fertilization of the egg results in the establishment of a parallel array of microtubules with the plus end pointing away from the sperm entry point. Concurrent with a process of cortical rotation, in which the cortex of the egg utilizes these microtubules to rotate relative to the inner cytoplasm, there is a movement of small vesicles toward the plus end of the microtubules. Cells inheriting these vesicles are destined to give rise to dorsal and anterior structures of the embryo. Three components of the Wnt/β-catenin pathway—Dishevelled, glycogen synthase kinase 3 (GSK-3)-binding protein (GBP), and β-catenin—accumulate on the side of the egg and early embryo that receive these small vesicles. It is likely that Dishevelled and GBP are associated with the vesicles that move along the microtubules and that they promote the stabilization and dorsal accumulation of β-catenin. Although Wnts and Frizzled are present in the egg, their roles in axis specification remain unclear. Dorsal β-catenin 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, which organizes the embryonic germ layers and axes.


The Xenopus egg relies on maternally provided components to sustain early development until zygotic transcription commences at mid-blastula stage. The maternal Wnt/β-catenin pathway has been implicated as playing a key role during the first few cell divisions in establishing the future dorsal-ventral axis (Fig. 1). Although it remains unclear whether maternally provided Wnt or Frizzled homologs are required for this process, they are indeed present. Moreover, cytoplasmic components of the pathway are necessary and sufficient for axis formation, and in the case of β-catenin, glycogen synthase kinase 3 (GSK-3)–binding protein (GBP), and Dishevelled, they are expressed in a region of the early embryo appropriate to participate in axis specification. Only components of the Wnt pathway proven to be maternally expressed are shown in the pathway figure and associated Connections Map. A movie of the process of axis specification is provided in Related Resources.

Pathway Details

URL: About Connections Map

Scope: Specific

Organism: vertebrates: Amphibia: Anura: Xenopus

Tissue and Cell: embryonic structures: blastomeres

Canonical Pathway: Wnt/β-Catenin Pathway (About Connections Map)

Related Resources

Teaching Resources

R. T. Moon, β-catenin signaling and axis specification. Sci. STKE 2004, tr6 (2004). [Abstract] [Resource Details].


Fig. 1.

Pathway image captured from the dynamic graphical display of the information in the Connections Maps available 21 January 2005. For a key to the colors and symbols, and to access the underlying data, please visit the pathway (About Connections Map).

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