RESUMO
The Iroquois genes code for homeodomain proteins that have been implicated in the neural development of Drosophila and vertebrates. We show here for the first time that Xiro-1, one of the Xenopus Iroquois genes, is expressed in the Spemann organizer from the start of gastrulation and that its overexpression induces a secondary axis as well as the ectopic expression of several organizer genes, such as chordin, goosecoid, and Xlim-1. Our results also indicate that Xiro-1 normally functions as a transcriptional repressor in the mesoderm. Overexpression of Xiro-1 or a chimeric form fused to the repressor domain of Engrailed cause similar phenotypes while overexpression of functional derivatives of Xiro-1 fused with transactivation domains (VP16 or E1A) produce the opposite effects. Finally, we show that Xiro-1 works as a repressor of bmp-4 transcription and that its effect on organizer development is dependent on BMP-4 activity. We propose that the previously observed down regulation of bmp-4 in the dorsal mesoderm during gastrulation can be explained by the repressor activity of Xiro-1 described here. Thus, Xiro-1 seems to have at least two different functions: control of neural plate and organizer development, both of which could be mediated by repression of bmp-4 transcription.
Assuntos
Proteínas Morfogenéticas Ósseas/antagonistas & inibidores , Mesoderma/fisiologia , Proteínas do Tecido Nervoso , Organizadores Embrionários/metabolismo , Fatores de Transcrição/fisiologia , Proteínas de Xenopus , Xenopus/embriologia , Animais , Proteína Morfogenética Óssea 4 , Proteínas Morfogenéticas Ósseas/metabolismo , Embrião não Mamífero/fisiologia , Proteínas Repressoras/fisiologiaRESUMO
The Snail family of genes comprise a group of transcription factors with characteristic zinc finger motifs. One of the members of this family is the Slug gene. Slug has been implicated in the development of neural crest in chick and Xenopus by antisense loss of function experiments. Here, we have generated functional derivatives of Xslug by constructing cDNAs that encode the Xslug protein fused with the transactivation domain of the virus-derived VP16 activator or with the repressor domain of the Drosophila Engrailed protein. Our results suggest that Xslug normally functions as a transcriptional repressor and that Xslug-VP16 behaves as a dominant negative of Xslug. In the present work, we confirm and extend previous results that suggest that Xslug has an important function in neural crest development, by controlling its own transcription. In addition we have uncovered a new function for Xslug. We show that Xslug is expressed in the dorsal mesendoderm at the beginning of gastrulation, where is it able to upregulate the expression of dorsal genes. On the other hand when Xslug is expressed outside of the organizer it represses the expression of ventral genes. Our results indicate that this effect on mesodermal patterning depends on BMP activity, showing that Xslug can directly control the transcription of BMP-4.
Assuntos
Proteínas Morfogenéticas Ósseas/genética , Proteínas de Drosophila , Regulação da Expressão Gênica no Desenvolvimento , Glicoproteínas , Peptídeos e Proteínas de Sinalização Intercelular , Mesoderma/fisiologia , Proteínas Repressoras/fisiologia , Fatores de Transcrição/fisiologia , Proteínas de Xenopus , Proteínas de Peixe-Zebra , Animais , Biomarcadores , Proteína Morfogenética Óssea 4 , Núcleo Celular/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Ectoderma/metabolismo , Ectoderma/fisiologia , Proteínas de Homeodomínio/genética , Mesoderma/metabolismo , Crista Neural/metabolismo , Organizadores Embrionários/metabolismo , Fator de Transcrição PAX3 , Fatores de Transcrição Box Pareados , Proteínas/genética , Proteínas Proto-Oncogênicas/genética , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Recombinantes de Fusão/fisiologia , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Fatores de Transcrição da Família Snail , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas Wnt , Xenopus laevis/embriologia , Dedos de ZincoRESUMO
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.