RESUMO
The ectoderm of the pre-gastrula Xenopus embryo has previously been shown to be at least partially patterned along the dorsal-ventral axis. The early expression of the anti-neural homeodomain gene Dlx3 is localized to the ventral ectoderm by a mechanism that occurs prior to gastrulation and is independent of the Spemann organizer. The repression of Dlx3 is mediated by signaling though beta-catenin, but is probably not dependent on the induction of the Xnr3 or chordin genes by beta-catenin. We propose a model in which this early regulation of Dlx3 accounts for the pro-neural bias of dorsal ectoderm.
Assuntos
Proteínas do Citoesqueleto/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/genética , Transdução de Sinais , Transativadores , Fatores de Transcrição/genética , Proteínas de Xenopus , Xenopus laevis/embriologia , Animais , Proteínas do Citoesqueleto/genética , Ectoderma , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Proteínas de Homeodomínio/fisiologia , Cloreto de Lítio/farmacologia , Fator de Crescimento Transformador beta/genética , Xenopus laevis/genética , beta CateninaRESUMO
Patterning of the embryonic ectoderm is dependent upon the action of negative (antineural) and positive (neurogenic) transcriptional regulators. Msx1 and Dlx3 are two antineural genes for which the anterior epidermal-neural boundaries of expression differ, probably due to differential sensitivity to BMP signaling in the ectoderm. In the extreme anterior neural plate, Dlx3 is strongly expressed while Msx1 is silent. While both of these factors prevent the activation of genes specific to the nascent central nervous system, Msx1 inhibits anterior markers, including Otx2 and cement gland-specific genes. Dlx3 has little, if any, effect on these anterior neural plate genes, instead providing a permissive environment for their expression while repressing more panneural markers, including prepattern genes belonging to the Zic family and BF-1. These properties define a molecular mechanism for translating the organizer-dependent morphogenic gradient of BMP activity into spatially restricted gene expression in the prospective anterior neural plate.
Assuntos
Padronização Corporal , Sistema Nervoso Central/embriologia , Proteínas de Homeodomínio/metabolismo , Fatores de Transcrição/metabolismo , Proteínas de Xenopus , Animais , Proteínas Morfogenéticas Ósseas , Ectoderma , Indução Embrionária , Gástrula , Regulação da Expressão Gênica no Desenvolvimento , Teste de Complementação Genética , Proteínas de Homeodomínio/isolamento & purificação , Fator de Transcrição MSX1 , Modelos Biológicos , Distribuição Tecidual , Fatores de Transcrição/isolamento & purificação , Xenopus laevisRESUMO
PCR-based methods and mobility shift competition assays were used to determine the basic biochemical features of the homeodomain transcription factor Distal-less 3 (Dlx3), including an optimal DNA binding site, the binding constant and dissociation rates of this protein. Expression of Dlx3 protein in either HeLa cells or Xenopus embryos resulted in strong activation of a model target gene construct containing three tandem copies of the Dlx3 binding site upstream from the TATA element. In addition, deletion analysis revealed that transcriptional activation by Dlx3 depends on two subdomains located on either side of the homeobox: removal of either subdomain resulted in complete loss of Dlx3 function. These observations provide new insight regarding the function of Dlx3 in vertebrate development and tissue differentiation and also suggest a mechanism for the dominant inheritance pattern of a hereditary disease resulting from mutation of the DLX3 gene in human.
