RESUMO
Members of the T-box gene family play important and diverse roles in development and disease. Here, we study the functional specificities of the Xenopus T-domain proteins Xbra and VegT, which differ in their abilities to induce gene expression in prospective ectodermal tissue. In particular, VegT induces strong expression of goosecoid whereas Xbra cannot. Our results indicate that Xbra is unable to induce goosecoid because it directly activates expression of Xom, a repressor of goosecoid that acts downstream of BMP signaling. We show that the inability of Xbra to induce goosecoid is imposed by an N-terminal domain that interacts with the C-terminal MH2 domain of Smad1, a component of the BMP signal transduction pathway. Interference with this interaction causes ectopic activation of goosecoid and anteriorization of the embryo. These findings suggest a mechanism by which individual T-domain proteins may interact with different partners to elicit a specific response.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Morfogênese , Proteínas com Domínio T/metabolismo , Transativadores/metabolismo , Proteínas de Xenopus/metabolismo , Xenopus laevis/fisiologia , Sequência de Aminoácidos , Animais , Proteínas Morfogenéticas Ósseas/metabolismo , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Ectoderma/citologia , Ectoderma/fisiologia , Proteína Goosecoid , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Conformação Proteica , Estrutura Terciária de Proteína , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Alinhamento de Sequência , Transdução de Sinais/fisiologia , Proteínas Smad , Proteína Smad1 , Proteínas com Domínio T/química , Proteínas com Domínio T/genética , Transativadores/química , Transativadores/genética , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Técnicas do Sistema de Duplo-Híbrido , Proteínas de Xenopus/genética , Xenopus laevis/embriologiaRESUMO
The Xenopus T box family member VegT is expressed maternally in the vegetal hemisphere of the embryo. Mis-expression of VegT in prospective ectodermal tissue causes ectopic activation of mesodermal and endodermal markers, and ablation of VegT transcripts prevents proper formation of the mesendoderm, with the entire embryo developing as epidermis. These observations define VegT as a key initiator of mesendodermal development in the Xenopus embryo, and in an effort to understand how it exerts its effects we have used microarray analysis to compare gene expression in control animal caps with that in ectodermal tissue expressing an activated form of VegT. This procedure allowed the identification of 99 potential VegT targets, and we went on to study the expression patterns of these genes and then to ask, for those that are expressed in mesoderm or endoderm, which are direct targets of VegT. The putative regulatory regions of the resulting 14 genes were examined for T domain binding sites, and we also asked whether their expression is down-regulated in embryos in which VegT RNA is ablated. Finally, the functions of these genes were assayed by both over-expression and by use of antisense morpholino oligonucleotides. Our results provide new insights into the function of VegT during early Xenopus development.