Nuclearization of β-catenin in ectodermal precursors confers organizer-like ability to induce endomesoderm and pattern a pluteus larvaReport as inadecuate

Nuclearization of β-catenin in ectodermal precursors confers organizer-like ability to induce endomesoderm and pattern a pluteus larva - Download this document for free, or read online. Document in PDF available to download.


, 4:31

First Online: 04 November 2013Received: 08 August 2013Accepted: 26 September 2013


BackgroundIn many bilaterians, asymmetric activation of canonical Wnt cWnt signaling at the posterior pole is critical for anterior-posterior AP body axis formation. In 16-cell stage sea urchins, nuclearization of β-catenin in micromeres activates a gene regulatory network that defines body axes and induces endomesoderm. Transplanting micromeres to the animal pole of a host embryo induces ectopic endomesoderm in the mesomeres ectoderm precursors whereas inhibiting cWnt signaling blocks their endomesoderm-inducing activity and the micromeres become ectoderm-like. We have tested whether ectopic activation of cWnt signaling in mesomeres is sufficient to impart the cells with organizer-like abilities, allowing them to pattern normal embryonic body axes when recombined with a field of mesomeres.

ResultsFertilized eggs were microinjected with constitutively active Xenopus β-catenin actβ-cat mRNA and allowed to develop until the 16-cell stage. Two mesomeres from injected embryos were then recombined with isolated animal halves AH from uninjected 16-cell stage embryos. Control chimeras produced animalized phenotypes hollow balls of ectoderm and rarely formed skeletogenic mesoderm SM-derived spicules, endoderm or pigment cells, a type of non-skeletogenic mesoderm NSM. In contrast, over half of the 0.5 pg-pL actβ-cat mesomere-AH chimeras formed a partial or complete gut exhibiting AP polarity, contained mesenchyme-like cells similar to SM, and produced pigment cells. At three days, chimeras formed plutei with normal embryonic body axes. When fates of the actβ-cat mRNA-injected mesomeres were tracked, we found that injected mesomeres formed mesenchyme-like and pigment cells, but endoderm was induced. Higher concentrations of actβ-cat mRNA were less likely to induce endoderm or pigment cells, but had similar mesenchyme-like cell production to 0.5 pg-pL actβ-cat mesomere-AH chimeras.

ConclusionsOur results show that nuclear β-catenin is sufficient to endow naïve cells with the ability to act as an organizing center and that β-catenin has both cell-autonomous and non-autonomous effects on cell fate specification in a concentration-dependent manner. These results are consistent with the hypothesis that a shift in the site of early cWnt signaling in cleaving embryos could have modified polarity of the main body axes during metazoan evolution.

Keywordsβ-catenin Organizing center Sea urchin Lytechinus variegatus Animal-vegetal axis Development Wnt signaling Anterior-posterior polarity Endomesoderm AbbreviationsActβ-catActivated β-catenin

AHAnimal half

ANEAnterior neuroectoderm



cWntCanonical Wnt


GSK-3βGlycogen synthase kinase-3β

hpfHours post fertilization

NSMNon-skeletogenic mesoderm

PNEPosterior neuroectoderm

RDXRhodamine dextran

SMSkeletogenic mesoderm.

Electronic supplementary materialThe online version of this article doi:10.1186-2041-9139-4-31 contains supplementary material, which is available to authorized users.

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Author: Christine A Byrum - Athula H Wikramanayake


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