title: The Xenopus Brachyury promoter is activated by FGF and low concentrations of activin and suppressed by high concentrations of activin and by paired-type homeodomain proteins.
abstract: The mesoderm of Xenopus laevis arises through an inductive interaction in which signals from the vegetal hemisphere of the embryo act on overlying equatorial cells. One candidate for an endogenous mesoderm-inducing factor is activin, a member of the TGFbeta superfamily. Activin is of particular interest because it induces different mesodermal cell types in a concentration-dependent manner, suggesting that it acts as a morphogen. These concentration-dependent effects are exemplified by the response of Xbra, expression of which is induced in ectodermal tissue by low concentrations of activin but not by high concentrations. Xbra therefore offers an excellent paradigm for studying the way in which a morphogen gradient is interpreted in vertebrate embryos. In this paper we examine the trancriptional regulation of Xbra2, a pseudoallele of Xbra that shows an identical response to activin. Our results indicate that 381 bp 5' of the Xbra2 transcription start site are sufficient to confer responsiveness both to FGF and, in a concentration-dependent manner, to activin. We present evidence that the suppression of Xbra expression at high concentrations of activin is mediated by paired-type homeobox genes such as goosecoid, Mix.1, and Xotx2.
authors.affiliation: Division of Developmental Biology, National Institute for Medical Research (NIMR), The Ridgeway, London NW7 1AA, UK.
authors.forename: B V
authors.initials: BV
authors.lastname: Latinkić
authors.forename: M
authors.initials: M
authors.lastname: Umbhauer
authors.forename: K A
authors.initials: KA
authors.lastname: Neal
authors.forename: W
authors.initials: W
authors.lastname: Lerchner
authors.forename: J C
authors.initials: JC
authors.lastname: Smith
authors.forename: V
authors.initials: V
authors.lastname: Cunliffe
mesh_terms: D016475:3T3 Cells; D028341:Activins; D000595:Amino Acid Sequence; D000818:Animals; D051943:Antennapedia Homeodomain Protein; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins; D005326:Fetal Proteins; D005346:Fibroblast Growth Factors / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D051956:Goosecoid Protein; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007265:Inhibins / Q000494:pharmacology / Q000502:physiology*; D008648:Mesoderm; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D051857:Otx Transcription Factors; D010442:Peptide Chain Initiation, Translational; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins; D020825:T-Box Domain Proteins; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D014981:Xenopus; D029867:Xenopus Proteins; D000098908:Brachyury Protein
chemical_list: D028341:Activins; D051943:Antennapedia Homeodomain Protein; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D005326:Fetal Proteins; D005346:Fibroblast Growth Factors; D051956:Goosecoid Protein; D018398:Homeodomain Proteins; D007265:Inhibins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D051857:Otx Transcription Factors; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D020825:T-Box Domain Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D029867:Xenopus Proteins; D000098908:Brachyury Protein; C100368:Mix1 protein, Xenopus; C497661:Otx2 protein, Xenopus; C056478:bcd protein, Drosophila