
Development September 1, 2002; 129 (17): 4027-43.

The roles of three signaling pathways in the formation and function of the Spemann Organizer.

Xanthos JB , Kofron M , Tao Q , Schaible K , Wylie C , Heasman J .

Since the three main pathways (the Wnt, VegT and BMP pathways) involved in organizer and axis formation in the Xenopus embryo are now characterized, the challenge is to understand their interactions. Here three comparisons were made. Firstly, we made a systematic comparison of the expression of zygotic genes in sibling wild-type, VegT-depleted (VegT(-)), beta-catenin-depleted (beta-catenin(-)) and double depleted (VegT(-)/beta-catenin(-)) embryos and placed early zygotic genes into specific groups. In the first group some organizer genes, including chordin, noggin and cerberus, required the activity of both the Wnt pathway and the VegT pathway to be expressed. A second group including Xnr1, 2, 4 and Xlim1 were initiated by the VegT pathway but their dorsoventral pattern and amount of their expression was regulated by the Wnt pathway. Secondly, we compared the roles of the Wnt and VegT pathways in producing dorsal signals. Explant co-culture experiments showed that the Wnt pathway did not cause the release of a dorsal signal from the vegetal mass independent from the VegT pathway. Finally we compared the extent to which inhibiting Smad 1 phosphorylation in one area of VegT(-), or beta-catenin(-) embryos would rescue organizer and axis formation. We found that BMP inhibition with cm-BMP7 mRNA had no rescuing effects on VegT(-) embryos, while cm-BMP7 and noggin mRNA caused a complete rescue of the trunk, but not of the anterior pattern in beta-catenin(-) embryos.

PubMed ID: 12163406
Article link: Development
Grant support: [+]
Genes referenced: bmp7.1 bmp7.2 cer1 chrd.1 ctnnb1 gal.2 gsc lhx1 myod1 nodal nodal1 nodal2 nodal3.1 nodal3.2 nog odc1 smad1 smad2 tbx2 vegt wnt3 wnt8a
Morpholinos: ctnnb1 MO1

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