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Mech Dev 2008 Jan 01;1251-2:58-66. doi: 10.1016/j.mod.2007.10.005.
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Expression of Siamois and Twin in the blastula Chordin/Noggin signaling center is required for brain formation in Xenopus laevis embryos.

Ishibashi H , Matsumura N , Hanafusa H , Matsumoto K , De Robertis EM , Kuroda H .

The blastula Chordin- and Noggin-expressing (BCNE) center located in the dorsal animal region of the Xenopus blastula embryo contains both prospective anterior neuroectoderm and Spemann organizer precursor cells. Here we show that, contrary to previous reports, the canonical Wnt target homeobox genes, Double knockdown of these genes using antisense morpholinos in Xenopus laevis blocked head formation, reduced the expression of the other BCNE center genes, upregulated Bmp4 expression, and nullified hyperdorsalization by lithium chloride. Moreover, gain- and loss-of-function experiments showed that Siamois and Twin expression is repressed by the vegetal transcription factor VegT. We propose that VegT expression causes maternal beta-Catenin signals to restrict Siamois and Twin expression to the BCNE region. A two-step inhibition of BMP signals by Siamois and Twin-- first by transcriptional repression of Bmp4 and then by activation of the expression of the BMP inhibitors Chordin and Noggin--in the BCNE center is required for head formation.

PubMed ID: 18036787
PMC ID: PMC2292103
Article link: Mech Dev
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: bmp4 chrd.1 ctnnb1 mix1 nodal nog otx2 sia1 sia2 vegt ventx1.2 wnt8a
Morpholinos: chrd.1 MO10 chrd.1 MO8 ctnnb1 MO1 nog MO1 sia1 MO1 sia2 MO1 vegt MO4

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