Multiple interactions between maternally-activated signalling pathways control Xenopus nodal-related genes.
We have investigated the induction of the six Xenopus nodal-related genes, Xnr1-Xnr6, by maternal determinants. The beta-catenin pathway was modelled by stimulation using Xwnt8, activin-like signalling was modelled by activin, and VegT action was studied by overexpression in animal cap explants. Combinations of factors were examined, and previously unrecognised interactions were revealed in animal caps and whole embryos. For the induction of Xnr5 and Xnr6 in whole embryos, using a beta-catenin antisense morpholino oligonucleotide or a dominant negative XTcf3, we have demonstrated an absolute permissive requirement for the beta-catenin/Tcf pathway, in addition to the requirement for VegT action. In animal caps Xnr5 and Xnr6 are induced in response to VegT overexpression, and this induction is dependent upon the concomitant activation of the beta-catenin pathway that VegT initiates in animal caps. For the induction of Xnr3, VegT interacts negatively so as to inhibit the induction otherwise observed with wnt-signalling alone. The negative effect of VegT is not the result of a general inhibition of wnt-signalling, and does not result from an inhibition of wnt-induced siamois expression. A 294 bp proximal promoter fragment of the Xnr3 gene is sufficient to mediate the negative effect of VegT. Further experiments, employing cycloheximide to examine the dependence of Xnr gene expression upon proteins translated after the mid-blastula stage, demonstrated that Xnrs 4, 5 and 6 are 'primary' Xnr genes whose expression in the late blastula is solely dependent upon factors present before the mid-blastula stage.
Rex
Maria
M
Department of Biological Sciences, University of Warwick, Coventry, UK.
Hilton
Emma
E
Old
Robert
R
D028341:Activins / Q000378:metabolism; D000818:Animals; D019070:Cell Lineage; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004707:Endoderm / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005799:Genes, Dominant; D017930:Genes, Reporter; D047908:Intracellular Signaling Peptides and Proteins; D008156:Luciferases / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism; D009035:Mothers; D055456:Nodal Signaling Ligands; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D020825:T-Box Domain Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000096:biosynthesis; D051153:Wnt Proteins; D014981:Xenopus; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
C495266:CTNNB1 protein, Xenopus; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; C105817:NODAL protein, Xenopus; D055456:Nodal Signaling Ligands; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D020825:T-Box Domain Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C103966:VegT protein, Xenopus; D051153:Wnt Proteins; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; C512832:ndr2 protein, zebrafish; C512833:nodal1 protein, Xenopus; C094620:nodal3.1 protein, Xenopus; C418882:nodal5 protein, Xenopus; C418883:nodal6 protein, Xenopus; D028341:Activins; D008156:Luciferases