title: The beta-catenin/VegT-regulated early zygotic gene Xnr5 is a direct target of SOX3 regulation.
abstract: In Xenopus laevis, beta-catenin-mediated dorsal axis formation can be suppressed by overexpression of the HMG-box transcription factor XSOX3. Mutational analysis indicates that this effect is due not to the binding of XSOX3 to beta-catenin nor to its competition with beta-catenin-regulated TCF-type transcription factors for specific DNA binding sites, but rather to SOX3 binding to sites within the promoter of the early VegT- and beta-catenin-regulated dorsal-mesoderm-inducing gene Xnr5. Although B1-type SOX proteins, such as XSOX3, are commonly thought to act as transcriptional activators, XSOX3 acts as a transcriptional repressor of Xnr5 in both the intact embryo and animal caps injected with VegT RNA. Expression of a chimeric polypeptide composed of XSOX3 and a VP16 transcriptional activation domain or morpholino-induced decrease in endogenous XSOX3 polypeptide levels lead to an increase in Xnr5 expression, as does injection of an anti-XSOX3 antibody that inhibits XSOX3 DNA binding. These observations indicate that maternal XSOX3 acts in a novel manner to restrict Xnr5 expression to the vegetal hemisphere.
authors.affiliation: Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA.
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Tamara
authors.initials: T
authors.lastname: Basta
authors.forename: Eric D
authors.initials: ED
authors.lastname: Jensen
authors.forename: M W
authors.initials: MW
authors.lastname: Klymkowsky
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000378:metabolism; D001483:Base Sequence; D019521:Body Patterning / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D006367:HeLa Cells; D006609:High Mobility Group Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055456:Nodal Signaling Ligands; D009687:Nuclear Proteins / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D055748:SOXB1 Transcription Factors; D020825:T-Box Domain Proteins / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000196:embryology* / Q000502:physiology; D051176:beta Catenin
chemical_list: D000906:Antibodies; C495266:CTNNB1 protein, Xenopus; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D018398:Homeodomain Proteins; D055456:Nodal Signaling Ligands; D009687:Nuclear Proteins; D016376:Oligonucleotides, Antisense; D011506:Proteins; C093133:SIA1 protein, Xenopus; C527785:SOX3 protein, human; D055748:SOXB1 Transcription Factors; C527788:Sox3 protein, Xenopus; D020825:T-Box Domain Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C103966:VegT protein, Xenopus; D029867:Xenopus Proteins; D051176:beta Catenin; C418882:nodal5 protein, Xenopus