RESUMO
In Xenopus development, during meiosis and cleavage, the extent of polyadenylation plays a central role in regulating the expression of transcripts and this is mediated by cis regulatory cytoplasmic polyadenylation elements (CPE) in the 3'-UTRs. We have identified a palindromic CPE in the mRNA of Xenopus Id3 which is conserved in the Id genes from other vertebrates. It promotes cytoplasmic polyadenylation and is negatively regulated by sequences further upstream in the 3'-UTR. This palindromic CPE promotes polyadenylation in both the epithelial and sensorial layers of the dorsal ectoderm in early embryos, but association with the upstream negative element blocks this effect in the epithelial layer. The asymmetric polyadenylation may be important for establishing a prepattern of transcriptional regulators.
Assuntos
Citoplasma/genética , Proteínas de Neoplasias , Sequências Reguladoras de Ácido Nucleico , Proteínas Repressoras , Fatores de Transcrição/genética , Xenopus/embriologia , Regiões 3' não Traduzidas , Sequência de Aminoácidos , Animais , Sequência de Bases , Blastocisto/fisiologia , Proteínas de Ligação a DNA/genética , Embrião não Mamífero/citologia , Embrião não Mamífero/fisiologia , Feminino , Gástrula/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Hibridização In Situ , Proteína 2 Inibidora de Diferenciação , Proteínas Inibidoras de Diferenciação , Dados de Sequência Molecular , Oócitos/fisiologia , RNA Mensageiro/metabolismo , Fatores de Transcrição/metabolismoRESUMO
The MEF-2 proteins are a family of transcriptional activators that have been detected in a wide variety of cell types. In skeletal muscle cells, MEF-2 proteins interact with members of the MyoD family of transcriptional activators to synergistically activate gene expression. Similar interactions with tissue or lineage-specific cofactors may also underlie MEF-2 function in other cell types. In order to screen for such cofactors, we have used a transcriptionally inactive mutant of Xenopus MEF2D in a yeast two-hybrid screen. This approach has identified a novel protein expressed in the early embryo that binds to XMEF2D and XMEF2A. The MEF-2 interacting transcription repressor (MITR) protein binds to the N-terminal MADS/MEF-2 region of the MEF-2 proteins but does not bind to the related Xenopus MADS protein serum response factor. In the early embryo, MITR expression commences at the neurula stage within the mature somites and is subsequently restricted to the myotomal muscle. In functional assays, MITR negatively regulates MEF-2-dependent transcription and we show that this repression is mediated by direct binding of MITR to the histone deacetylase HDAC1. Thus, we propose that MITR acts as a co-repressor, recruiting a specific deacetylase to downregulate MEF-2 activity.