RESUMO
Ligand-bound nuclear receptors (NRs) recruit cofactors such as members of the p160 family and CREB-binding protein (CBP) to activate transcription. We have cloned the Xenopus homologue of the human transcription intermediary factor 2 (TIF2), a member of the p160 family of cofactors. Xenopus TIF2 (XTIF2) mRNA is expressed homogeneously during late blastula-early gastrula stages and later becomes highly expressed in the notochord. To study the function of XTIF2 during development, we have used two dominant negative constructs, one encompassing the NR-binding domain and the other the CBP interacting region of XTIF2. Overexpression of the XTIF2 dominant negative mRNAs causes ectopic expression of Xenopus Brachyury (Xbra) and MyoD in all tissue layers. Moreover, ectopic expression of the dominant negative construct that contains the CBP-binding region produces strong phenotypes at hatching stage such as loss of head structures, shortened trunks and open blastopores, which can be rescued by XTIF2 coexpression. These observed defects are due, at least in part, to repression of dorsal mesoderm and endoderm genes. Our data suggest the existence of a NR pathway that requires XTIF2 and CBP to repress Xbra and XMyoD.
Assuntos
Proteínas Fetais , Regulação da Expressão Gênica no Desenvolvimento , Proteína MyoD/genética , Proteínas Nucleares/metabolismo , Receptores Citoplasmáticos e Nucleares/metabolismo , Proteínas com Domínio T/genética , Transativadores/metabolismo , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Animais , Sequência de Bases , Biomarcadores , Proteína de Ligação a CREB , Clonagem Molecular , DNA Complementar , Expressão Gênica , Humanos , Mesoderma , Camundongos , Dados de Sequência Molecular , Proteínas Nucleares/genética , Proteínas Nucleares/fisiologia , Coativador 2 de Receptor Nuclear , Homologia de Sequência de Aminoácidos , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologia , Xenopus/embriologiaRESUMO
The forkhead type Brain Factor 2 from mouse and chicken help pattern the forebrain, optic vesicle and kidney. We have isolated a Xenopus homolog (Xbf2) and found that during gastrulation it is expressed in the dorsolateral mesoderm, where it helps specify this territory by downregulating BMP-4 and its downstream genes. Indeed, Xbf2 overexpression caused partial axis duplication. Interference with BMP-4 signaling also occurs in isolated animal caps, since Xbf2 induces neural tissue. Within the neurula forebrain, Xbf2 and the related Xbf1 gene are expressed in the contiguous diencephalic and telencephalic territories, respectively, and each gene represses the other. Finally, Xbf2 seems to participate in the control of neural crest migration. Our data suggest that XBF2 interferes with BMP-4 signaling, both in mesoderm and ectoderm.
Assuntos
Proteínas de Ligação a DNA/fisiologia , Mesoderma/fisiologia , Proteínas do Tecido Nervoso/fisiologia , Crista Neural/fisiologia , Prosencéfalo/embriologia , Proteínas de Xenopus , Xenopus/embriologia , Xenopus/metabolismo , Sequência de Aminoácidos , Animais , Clonagem Molecular , Proteínas de Ligação a DNA/metabolismo , Indução Embrionária , Fatores de Transcrição Forkhead , Galactosídeos/metabolismo , Expressão Gênica , Hibridização In Situ , Indóis/metabolismo , Dados de Sequência Molecular , Fatores de Tempo , Proteína 1 Relacionada a TwistRESUMO
The Drosophila homeoproteins Ara and Caup are members of a combination of factors (prepattern) that control the highly localized expression of the proneural genes achaete and scute. We have identified two Xenopus homologs of ara and caup, Xiro1 and Xiro2. Similarly to their Drosophila counterparts, they control the expression of proneural genes and, probably as a consequence, the size of the neural plate. Moreover, Xiro1 and Xiro2 are themselves controlled by noggin and retinoic acid and, similarly to ara and caup, they are overexpressed by expression in Xenopus embryos of the Drosophila cubitus interruptus gene. These and other findings suggest the conservation of at least part of the genetic cascade that regulates proneural genes, and the existence in vertebrates of a prepattern of factors important to control the differentiation of the neural plate.