title: Repression of organizer genes in dorsal and ventral Xenopus cells mediated by maternal XTcf3.
abstract: In the early Xenopus embryo, the dorsal axis is specified by a Wnt signal transduction pathway, involving the movement of beta-catenin into dorsal cell nuclei and its functional association with the LEF-type transcription factor XTcf3. The subsequent function of XTcf3 is uncertain. Overexpression data has suggested that it can be both an activator and repressor of downstream genes. XTcf3 mRNA is synthesized during oogenesis in Xenopus and is stored in the egg. To identify its role in dorsal axis specification, we depleted this maternal store in full-grown oocytes using antisense deoxyoligonucleotides, and fertilized them. The developmental effects of XTcf3 depletion, both on morphogenesis and the expression of marker genes, show that primarily, XTcf3 is an inhibitor, preventing both dorsal and ventral cells of the late blastula from expressing dorsal genes. We also show that simple relief from the repression is not the only factor required for dorsal gene expression. To demonstrate this, we fertilized eggs that had been depleted of both XTcf3 and the maternal transcription factor VegT. Dorsal genes normally repressed by XTcf3 are not activated in these embryos. These data show that normal dorsal gene expression in the embryo requires the transcriptional activator VegT, whilst XTcf3 prevents their inappropriate expression on the ventral side of the embryo.
authors.affiliation: Division of Developmental Biology, Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA.
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Houston
authors.forename: Matt
authors.initials: M
authors.lastname: Kofron
authors.forename: Ernesto
authors.initials: E
authors.lastname: Resnik
authors.forename: Rachel
authors.initials: R
authors.lastname: Langland
authors.forename: Olivier
authors.initials: O
authors.lastname: Destree
authors.forename: Christopher
authors.initials: C
authors.lastname: Wylie
authors.forename: Janet
authors.initials: J
authors.lastname: Heasman
mesh_terms: D000818:Animals; D060466:Axin Protein; D001755:Blastocyst / Q000502:physiology; D019521:Body Patterning / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D051956:Goosecoid Protein; D024002:HMGB Proteins / Q000235:genetics / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D055456:Nodal Signaling Ligands; D009865:Oocytes / Q000378:metabolism; D020897:Organizers, Embryonic; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D020825:T-Box Domain Proteins / Q000235:genetics / Q000502:physiology; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000378:metabolism; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins; D051176:beta Catenin
chemical_list: D060466:Axin Protein; C495266:CTNNB1 protein, Xenopus; D003598:Cytoskeletal Proteins; D051956:Goosecoid Protein; D024002:HMGB Proteins; D018398:Homeodomain Proteins; D055456:Nodal Signaling Ligands; D011506:Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C093133:SIA1 protein, Xenopus; D020825:T-Box Domain Proteins; D051820:TCF Transcription Factors; D015534:Trans-Activators; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; C103966:VegT protein, Xenopus; D029867:Xenopus Proteins; D051176:beta Catenin; C094620:nodal3.1 protein, Xenopus; C418883:nodal6 protein, Xenopus