The roles of three signaling pathways in the formation and function of the Spemann Organizer.
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.
Xanthos
Jennifer B
JB
Division of Developmental Biology, Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, Ohio 45229-3039, USA.
Kofron
Matthew
M
Tao
Qinghua
Q
Schaible
Kyle
K
Wylie
Christopher
C
Heasman
Janet
J
D000818:Animals; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D009865:Oocytes; D020897:Organizers, Embryonic / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000037:antagonists & inhibitors; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051785:Smad Proteins; D051899:Smad2 Protein; D020825:T-Box Domain Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D051153:Wnt Proteins; D014981:Xenopus; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D000099176:Noggin Protein
D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D010770:Phosphotransferases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051785:Smad Proteins; D051899:Smad2 Protein; D020825:T-Box Domain Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D000099176:Noggin Protein; C495266:CTNNB1 protein, Xenopus; C497402:MXD1 protein, Xenopus; C497785:Smad2 protein, Xenopus; C103966:VegT protein, Xenopus; C525822:bmp7.1 protein, Xenopus; C525826:bmp7a protein, zebrafish