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PLoS Biol 2012 Jan 01;103:e1001286. doi: 10.1371/journal.pbio.1001286.
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Maternal xNorrin, a canonical Wnt signaling agonist and TGF-β antagonist, controls early neuroectoderm specification in Xenopus.

Xu S , Cheng F , Liang J , Wu W , Zhang J .

Dorsal-ventral specification in the amphibian embryo is controlled by β-catenin, whose activation in all dorsal cells is dependent on maternal Wnt11. However, it remains unknown whether other maternally secreted factors contribute to β-catenin activation in the dorsal ectoderm. Here, we show that maternal Xenopus Norrin (xNorrin) promotes anterior neural tissue formation in ventralized embryos. Conversely, when xNorrin function is inhibited, early canonical Wnt signaling in the dorsal ectoderm and the early expression of the zygotic neural inducers Chordin, Noggin, and Xnr3 are severely suppressed, causing the loss of anterior structures. In addition, xNorrin potently inhibits BMP- and Nodal/Activin-related functions through direct binding to the ligands. Moreover, a subset of Norrin mutants identified in humans with Norrie disease retain Wnt activation but show defective inhibition of Nodal/Activin-related signaling in mesoderm induction, suggesting that this disinhibition causes Norrie disease. Thus, xNorrin is an unusual molecule that acts on two major signaling pathways, Wnt and TGF-β, in opposite ways and is essential for early neuroectoderm specification.

PubMed ID: 22448144
PMC ID: PMC3308935
Article link: PLoS Biol

Species referenced: Xenopus
Genes referenced: actl6a ag1 babam2 bmp4 chrd ctnnb1 dkk1 egr2 foxg1 gal.2 gsc hoxb9 hoxc9-like lrp1 lrp5 lrp6 mrc1 myc ncam1 ndp nodal nodal1 nodal3.1 nodal3.2 nog odc1 otx2 pax6 sia1 smad1 sox2 sox3 tbxt wnt11 wnt8a
GO keywords: ectoderm development [+]
Antibodies: Myc Ab5 Notochord Ab2
Morpholinos: ndp MO1 ndp MO2

Disease Ontology terms: Norrie disease

Article Images: [+] show captions
References [+] :
Agius, Endodermal Nodal-related signals and mesoderm induction in Xenopus. 2000, Pubmed, Xenbase