Wnt signaling and β-catenin dependent gene expression plays a critical role during the formation of different body regions in the early embryo. Experimentally modified embryos that do not express this protein will fail to develop mesoderm and initiate gastrulation.
Early embryos endomesoderm specification also involves the activation of the β-catenin dependent transcripional activity by the first morphogenetic movements of embryogenesis, though mechanotransduction processes. This feature being shared by vertebrate and arthropod bilateria, and by cnidaria, it was proposed to have been evolutionary inherited from its possible involvement in the endomesoderm specification of first metazoa.
During the blastula and gastrula stages, Wnt as well as BMP and FGF pathways will induce the antero-posterior axis formation, regulate the precise placement of the primitive streak (gastrulation and mesoderm formation) as well as the process of neurulation (central nervous system development).
In Xenopus oocytes, β-catenin is initially equally localized to all regions of the egg, but it is targeted for ubiquitination and degradation by the β-catenin destruction complex. Fertilization of the egg causes a rotation of the outer cortical layers, moving clusters of the Frizzled and Dsh proteins closer to the equatorial region. β-catenin will be enriched locally under the influence of Wnt signaling pathway in the cells that inherit this portion of the cytoplasm. It will eventually translocate to the nucleus to bind TCF3 in order to activate several genes that induce dorsal cell characteristics. This signaling results in a region of cells known as the grey crescent, which is a classical organizer of embryonic development. If this region is surgically removed from the embryo, gastrulation does not occur at all. β-Catenin also plays a crucial role in the induction of the blastopore lip, which in turn initiates gastrulation. Inhibition of GSK-3 translation by injection of antisense mRNA may cause a second blastopore and a superfluous body axis to form. A similar effect can result from the overexpression of β-catenin.