title: A screen for targets of the Xenopus T-box gene Xbra.
abstract: Brachyury (T), a member of the T-box gene family, is essential for the formation of posterior mesoderm and notochord in vertebrate development. Expression of the Xenopus homologue of Brachyury, Xbra, causes ectopic ventral and lateral mesoderm formation in animal cap explants and co-expression of Xbra with Pintallavis, a forkhead/HNF3beta-related transcription factor, induces notochord. Although eFGF and the Bix genes are thought to be direct targets of Xbra, no other target genes have been identified. Here, we describe the use of hormone-inducible versions of Xbra and Pintallavis to construct cDNA libraries enriched for targets of these transcription factors. Five putative targets were isolated: Xwnt11, the homeobox gene Bix1, the zinc-finger transcription factor Xegr-1, a putative homologue of the antiproliferative gene BTG1 called Xbtg1, and BIG3/1A11, a gene of unknown function. Expression of Xegr-1 and Xbtg1 is controlled by Pintallavis alone as well as by a combination of Xbra and Pintallavis. Overexpression of Xbtg1 perturbed gastrulation and caused defects in posterior tissues and in notochord and muscle formation, a phenotype reminiscent of that observed with a dominant-negative version of Pintallavis called Pintallavis-En(R). The Brachyury-inducible genes we have isolated shed light on the mechanism of Brachyury function during mesoderm formation. Specification of mesodermal cells is regulated by targets including Bix1-4 and eFGF, while gastrulation movements and perhaps cell division are regulated by Xwnt11 and Xbtg1.
authors.affiliation: Division of Developmental Biology, National Institute for Medical Research, London, UK.
authors.forename: Y
authors.initials: Y
authors.lastname: Saka
authors.forename: M
authors.initials: M
authors.lastname: Tada
authors.forename: J C
authors.initials: JC
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics; D003907:Dexamethasone / Q000378:metabolism / Q000494:pharmacology; D051766:Early Growth Response Protein 1; D051858:Forkhead Transcription Factors; D005775:Gastrula; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D016147:Genes, Tumor Suppressor; D006023:Glycoproteins / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D017874:Immediate-Early Proteins; D008648:Mesoderm; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051153:Wnt Proteins; D014981:Xenopus / Q000196:embryology / Q000235:genetics; D029867:Xenopus Proteins
chemical_list: C115868:Bix1 protein, Xenopus; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C486111:EGR1 protein, Xenopus; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D051858:Forkhead Transcription Factors; C000598904:FoxA4 protein, Xenopus; D006023:Glycoproteins; D018398:Homeodomain Proteins; D017874:Immediate-Early Proteins; D009363:Neoplasm Proteins; C080209:Not protein, Xenopus; D011993:Recombinant Fusion Proteins; D020825:T-Box Domain Proteins; C116765:TBXT protein, Xenopus; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D029867:Xenopus Proteins; C512785:wnt11b protein, Xenopus; C074086:BTG1 protein, human; D003907:Dexamethasone