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Proc Natl Acad Sci U S A 2010 Sep 14;10737:16160-5. doi: 10.1073/pnas.1007725107.
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Wnt/beta-catenin signaling is involved in the induction and maintenance of primitive hematopoiesis in the vertebrate embryo.

Tran HT , Sekkali B , Van Imschoot G , Janssens S , Vleminckx K .

The formation of primitive (embryonic) blood in vertebrates is mediated by spatio-temporally restricted signaling between different tissue layers. In Xenopus, in which primitive blood originates in the ventral blood island, this involves the secretion of bone morphogenetic protein (BMP) ligands by the ectoderm that signal to the underlying mesoderm during gastrulation. Using novel transgenic reporter lines, we report that the canonical Wnt/β-catenin pathway is also activated in the blood islands in Xenopus. Furthermore, Wnt-reporter activity was also detected in the blood islands of the mouse yolk sac. By using morpholino-mediated depletion in Xenopus, we identified Wnt4 as the ligand that is expressed in the mesoderm of the ventral blood island and is essential for the expression of hematopoietic and erythroid marker genes. Injection of an inducible Wnt-interfering construct further showed that, during gastrulation, Wnt/β-catenin signaling is required both in the mesoderm and in the overlying ectoderm for the formation of the ventral blood island. Using recombination assays with embryonic explants, we document that ectodermal BMP4 expression is dependent on Wnt4 signals from the mesoderm. Our results thus reveal a unique role for Wnt4-mediated canonical signaling in the formation and maintenance of the ventral blood island in Xenopus.

PubMed ID: 20805504
PMC ID: PMC2941280
Article link: Proc Natl Acad Sci U S A

Species referenced: Xenopus laevis
Genes referenced: bmp4 cd4 cer1 chrd ctnnb1 dkk1 eef1a1 fli1 fzd2 fzd3 fzd5 fzd7 gal.2 gsc hba3 hhex lmo2 msx1 nodal nodal1 nodal3.1 nodal3.2 pc.1 psmd6 rspo3 tal1 wnt1 wnt2b wnt3a wnt4 wnt6 wnt7b wnt8b wnt9b
Morpholinos: wnt4 MO1

Article Images: [+] show captions
References [+] :
Bauer, The cleavage stage origin of Spemann's Organizer: analysis of the movements of blastomere clones before and during gastrulation in Xenopus. 1994, Pubmed, Xenbase