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Dev Biol 1999 May 15;2092:282-97. doi: 10.1006/dbio.1999.9257.
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Anterior endomesoderm specification in Xenopus by Wnt/beta-catenin and TGF-beta signalling pathways.

Zorn AM , Butler K , Gurdon JB .

In Xenopus, XHex and cerberus are early marker genes of the anterior endomesoderm (AE), a subset of endoderm cells fated to form the liver and foregut and implicated in head induction. Using XHex and cerberus as markers we have examined the signals underlying AE induction. We show that the AE is specified by the early blastula in the absence of mesodermal signals but that cell-cell contact between presumptive AE cells is required. In overexpression experiments maternal Wnt/beta-catenin and TGF-beta signals (Vg1, Xnr1-2) can induce ectopic XHex and cerberus. Inhibiting these pathways with dominant interfering signalling components blocks endogenous XHex and cerberus expression. We assess the role of signals from the organiser and show that the BMP antagonists noggin and chordin are important for maintaining XHex and cerberus expression. Finally, ventral injection of XHex mRNA can induce ectopic cerberus. Our results indicate that endodermal and mesodermal patterning are closely coordinated and that the AE is likely to be specified by the combined action of dorsal Wnt/beta-catenin signals and endoderm-specific factors mediated by TGF-beta signalling. These results provide a starting point for understanding the molecular events underlying the progressive determination of endodermally derived organs, such as the liver and foregut.

PubMed ID: 10328921
Article link: Dev Biol
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: acvr2b bmp4 cer1 chrd ctnnb1 gdf1 gsc hhex mixer nodal1 nog sia1 sox17b.1 tbxt tgfb1 ventx1.2 wnt8a

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