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Development 2011 Aug 01;13815:3297-306. doi: 10.1242/dev.058792.
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Wnt6 activates endoderm in the sea urchin gene regulatory network.

Croce J , Range R , Wu SY , Miranda E , Lhomond G , Peng JC , Lepage T , McClay DR .

In the sea urchin, entry of β-catenin into the nuclei of the vegetal cells at 4th and 5th cleavages is necessary for activation of the endomesoderm gene regulatory network. Beyond that, little is known about how the embryo uses maternal information to initiate specification. Here, experiments establish that of the three maternal Wnts in the egg, Wnt6 is necessary for activation of endodermal genes in the endomesoderm GRN. A small region of the vegetal cortex is shown to be necessary for activation of the endomesoderm GRN. If that cortical region of the egg is removed, addition of Wnt6 rescues endoderm. At a molecular level, the vegetal cortex region contains a localized concentration of Dishevelled (Dsh) protein, a transducer of the canonical Wnt pathway; however, Wnt6 mRNA is not similarly localized. Ectopic activation of the Wnt pathway, through the expression of an activated form of β-catenin, of a dominant-negative variant of GSK-3β or of Dsh itself, rescues endomesoderm specification in eggs depleted of the vegetal cortex. Knockdown experiments in whole embryos show that absence of Wnt6 produces embryos that lack endoderm, but those embryos continue to express a number of mesoderm markers. Thus, maternal Wnt6 plus a localized vegetal cortical molecule, possibly Dsh, is necessary for endoderm specification; this has been verified in two species of sea urchin. The data also show that Wnt6 is only one of what are likely to be multiple components that are necessary for activation of the entire endomesoderm gene regulatory network.

PubMed ID: 21750039
PMC ID: PMC3133919
Article link: Development
Grant support: [+]

Genes referenced: gsk3a LOC100887844 LOC575170 LOC584189 LOC594353 wnt6
Morpholinos: wnt16 MO2 wnt16 MO3 wnt6 MO3 wnt6 MO4 wnt7b MO2 wnt8a MO7 wnt8a MO8

References [+] :
Cha, Wnt11/5a complex formation caused by tyrosine sulfation increases canonical signaling activity. 2009, Pubmed