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XB-ART-16769
J Cell Biol March 10, 1997; 136 (5): 1123-36.

Establishment of the dorso-ventral axis in Xenopus embryos is presaged by early asymmetries in beta-catenin that are modulated by the Wnt signaling pathway.

Larabell CA , Torres M , Rowning BA , Yost C , Miller JR , Wu M , Kimelman D , Moon RT .


Abstract
Eggs of Xenopus laevis undergo a postfertilization cortical rotation that specifies the position of the dorso-ventral axis and activates a transplantable dorsal-determining activity in dorsal blastomeres by the 32-cell stage. There have heretofore been no reported dorso-ventral asymmetries in endogenous signaling proteins that may be involved in this dorsal-determining activity during early cleavage stages. We focused on beta-catenin as a candidate for an asymmetrically localized dorsal-determining factor since it is both necessary and sufficient for dorsal axis formation. We report that beta-catenin displays greater cytoplasmic accumulation on the future dorsal side of the Xenopus embryo by the two-cell stage. This asymmetry persists and increases through early cleavage stages, with beta-catenin accumulating in dorsal but not ventral nuclei by the 16- to 32-cell stages. We then investigated which potential signaling factors and pathways are capable of modulating the steady-state levels of endogenous beta-catenin. Steady-state levels and nuclear accumulation of beta-catenin increased in response to ectopic Xenopus Wnt-8 (Xwnt-8) and to the inhibition of glycogen synthase kinase-3, whereas neither Xwnt-5A, BVg1, nor noggin increased beta-catenin levels before the mid-blastula stage. As greater levels and nuclear accumulation of beta-catenin on the future dorsal side of the embryo correlate with the induction of specific dorsal genes, our data suggest that early asymmetries in beta-catenin presage and may specify dorso-ventral differences in gene expression and cell fate. Our data further support the hypothesis that these dorso-ventral differences in beta-catenin arise in response to the postfertilization activation of a signaling pathway that involves Xenopus glycogen synthase kinase-3.

PubMed ID: 9060476
PMC ID: PMC2132470
Article link: J Cell Biol
Grant support: [+]
Genes referenced: ctnnb1 epb41 gdf1 gsk3b krt12.4 myc nog prl.1 sptan1 tbx2 wnt11 wnt11b wnt5a wnt8a


Article Images: [+] show captions
References [+] :
Behrens, Functional interaction of beta-catenin with the transcription factor LEF-1. 1996, Pubmed, Xenbase


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