First published online May 30, 2007
Development 134, 1201e (2007)
© The Company of Biologists Limited
Wnt off: liver on
The liver and the pancreas are specified from the foregut endoderm, but how
early foregut precursors form remains unknown. Aaron Zorn's group now report
that in Xenopus, the Wnt pathway links early gastrula-stage endoderm
patterning to organ specification. Their results, on
p. 2207, show that
while in anterior endoderm, Wnt/ß-catenin activity is repressed, inducing
liver and pancreas specification, it's upregulated in the posterior endoderm,
where foregut fate is inhibited and intestinal development occurs. Their
experimental repression of ß-catenin activity in the embryonic posterior
endoderm induced ectopic organ buds to form that express early hepatic and
pancreatic markers; increased ß-catenin activity in the foregut endoderm
repressed liver and pancreas formation. The early foregut marker,
hhex, is a target of this ß-catenin activity and is repressed
indirectly via the transcriptional repressor Vent2. Wnt signalling later
enhances liver development. Thus, turning Wnt signalling on/off at the right
moment is essential for these organs' proper formation, a finding that should
advance the differentiation of liver and pancreatic tissue from stem
cells.

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Related articles in Development:
- Repression of Wnt/ß-catenin signaling in the anterior endoderm is essential for liver and pancreas development
- Valérie A. McLin, Scott A. Rankin, and Aaron M. Zorn
Development 2007 134: 2207-2217.
[Abstract]
[Full Text]