RESUMO
During mammalian development, the Cdx1 homeobox gene exhibits an early period of expression when the embryonic body axis is established, and a later period where expression is restricted to the embryonic intestinal endoderm. Cdx1 expression is maintained throughout adulthood in the proliferative cell compartment of the continuously renewed intestinal epithelium, the crypts. In this study, we provide evidence in vitro and in vivo that Cdx1 is a direct transcriptional target of the Wnt/(beta)-catenin signaling pathway. Upon Wnt stimulation, expression of Cdx1 can be induced in mouse embryonic stem (ES) cells as well as in undifferentiated rat embryonic endoderm. Tcf4-deficient mouse embryos show abrogation of Cdx1 protein in the small intestinal epithelium, making Tcf4 the likely candidate to transduce Wnt signal in this part of gut. The promoter region of the Cdx1 gene contains several Tcf-binding motifs, and these bind Tcf/Lef1/(beta)-catenin complexes and mediate (beta)-catenin-dependent transactivation. The transcriptional regulation of the homeobox gene Cdx1 in the intestinal epithelium by Wnt/(beta)-catenin signaling underlines the importance of this signaling pathway in mammalian endoderm development.
Assuntos
Proteínas Aviárias , Proteínas do Citoesqueleto/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/genética , Proteínas Proto-Oncogênicas/metabolismo , Transdução de Sinais/fisiologia , Transativadores , Fatores de Transcrição/metabolismo , Proteínas de Peixe-Zebra , Células 3T3 , Animais , Linhagem Celular , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Endoderma , Genes Homeobox , Humanos , Mucosa Intestinal/metabolismo , Intestinos/embriologia , Fator 1 de Ligação ao Facilitador Linfoide , Camundongos , Ratos , Fatores de Transcrição TCF , Proteína 2 Semelhante ao Fator 7 de Transcrição , Fatores de Transcrição/genética , Proteínas Wnt , beta CateninaRESUMO
Requirements for intron recognition during pre-mRNA splicing in plants differ from those in vertebrates and yeast. Plant introns contain neither conserved branch points nor distinct 3' splice site-proximal polypyrimidine tracts characteristic of the yeast and vertebrate introns, respectively. However, they are strongly enriched in U residues throughout the intron, property essential for splicing. To understand the roles of different sequence elements in splicing, we are characterizing proteins involved in intron recognition in plants. In this work we show that Nicotiana plumbaginifolia, a dicotyledonous plant, contains two genes encoding different homologs of the large 50-65-kDa subunit of the polypyrimidine tract binding factor U2AF, characterized previously in animals and Schizosaccharomyces pombe. Both plant U2AF65 isoforms, referred to as NpU2AF65a and NpU2AF65b, support splicing of an adenovirus pre-mRNA in HeLa cell nuclear extracts depleted of the endogenous U2AF factor. Both proteins interact with RNA fragments containing plant introns and show affinity for poly(U) and, to a lesser extend, poly(C) and poly(G). The branch point or the 3' splice site regions do not contribute significantly to intron recognition by NpU2AF65. The existence of multiple isoforms of U2AF may be quite general in plants because two genes expressing U2AF65 have been identified in Arabidopsis, and different isoforms of the U2AF small subunit are expressed in rice.
Assuntos
Nicotiana/genética , Proteínas Nucleares , Plantas Tóxicas , Ribonucleoproteína Nuclear Pequena U2/genética , Ribonucleoproteínas/genética , Sequência de Aminoácidos , Animais , Núcleo Celular/metabolismo , Drosophila melanogaster/genética , Glutationa Transferase/genética , Células HeLa , Humanos , Substâncias Macromoleculares , Camundongos , Dados de Sequência Molecular , Splicing de RNA , Proteínas Recombinantes de Fusão/biossíntese , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Ribonucleoproteínas/química , Ribonucleoproteínas/metabolismo , Schizosaccharomyces/genética , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Fator de Processamento U2AFRESUMO
We describe here the nucleotide sequence of an anther-specific gene (sf18) from sunflower, encoding a proline- and glycine-rich polypeptide with a hydrophobic amino-terminus (signal peptide). The gene is split by a 211 bp intron and is partially related to another anther-specific gene (sf2) from sunflower with which it shares important sequence stretches in the 5' coding and upstream regions. We propose that the two gene have originated via exon shuffling, during which a copy of a DNA segment including the promoter region as well as a signal peptide coding sequence has been transferred into the upstream region of two different potential coding sequences, generating two novel genes which display the same specificity of expression and which both encode an extracellular protein. While the 5' region of the intron is highly conserved as part of the transferred region and may play a role in the selection of the 5' splice site, a common octanucleotide at the 3' end of the intron of the two genes might be involved in 3' splice site selection.
Assuntos
Éxons/genética , Rearranjo Gênico , Genes de Plantas/genética , Helianthus/genética , Sinais Direcionadores de Proteínas/genética , Sequência de Aminoácidos , Sequência de Bases , Sequência Conservada , Biblioteca Genômica , Íntrons/genética , Modelos Genéticos , Dados de Sequência Molecular , Proteínas de Plantas/genética , Sequências Reguladoras de Ácido Nucleico/genética , Mapeamento por Restrição , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , Distribuição TecidualRESUMO
We have isolated, via differential hybridization screening of a floral cDNA library from sunflower, a cDNA clone that hybridizes to a 1100 nucleotide-long mRNA found exclusively in mature pollen grains. The cDNA encodes a 219 amino acid-long polypeptide containing two potential zinc fingers alternating with two basic domains. A similar organization is found in the erythroid-specific transcription factor Eryf1 from chicken and its murine homolog GF-1. The C-terminus of the protein contains a sixfold repeat of the pentapeptide sequence (S,T,A)(E,D)TQN. These features suggest that the SF3 protein is a transcription factor required for the expression of late pollen genes. The SF3 gene is a member of a multicopy gene family. A genomic copy of the gene has been isolated and sequenced; it is split by four short, AT-rich introns.
Assuntos
Helianthus/genética , Proteínas de Plantas/genética , Fatores de Transcrição/genética , Dedos de Zinco/genética , Sequência de Aminoácidos , Sequência de Bases , Evolução Biológica , Clonagem Molecular , Proteínas de Ligação a DNA/genética , Fatores de Ligação de DNA Eritroide Específicos , Íntrons/genética , Dados de Sequência Molecular , Família Multigênica/genética , Pólen , Sequências Repetitivas de Ácido Nucleico/genética , Homologia de Sequência de Aminoácidos , Distribuição Tecidual , Transcrição GênicaRESUMO
We have isolated and sequenced an anther-specific gene from sunflower which encodes an 800-nucleotide transcript detectable in the peripheral anther cells. It contains an intron of 2615 bp, which separates the first exon (77 bp) coding for a putative signal peptide of 21 amino acids, from the second exon (563 bp) coding for a 100 amino acid polypeptide. The 5' and 3' untranslated regions comprise respectively 13 and 264 bp. The SF2 gene is present in the sunflower genome in several copies, all or most of which contain a closely related intron.
Assuntos
Helianthus/química , Íntrons , Proteínas de Plantas/genética , Sinais Direcionadores de Proteínas/genética , Sequência de Aminoácidos , Bacteriófagos/genética , Sequência de Bases , Southern Blotting , Núcleo Celular/química , DNA/genética , Escherichia coli/genética , Genes Bacterianos , Genes Virais , Dados de Sequência Molecular , Plasmídeos , Mapeamento por Restrição , Transcrição GênicaAssuntos
Helianthus/genética , Proteínas de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , DNA , Helianthus/anatomia & histologia , Dados de Sequência Molecular , Especificidade de Órgãos , Peptídeos/genética , Sinais Direcionadores de Proteínas/genética , RNA Mensageiro , Alinhamento de SequênciaRESUMO
The wheat mitochondrial (mt) cox3 has been localized and sequenced. The gene exists as a single copy in the wheat mt master chromosome and is transcribed into a single 1.2 kb RNA, whose extremities have been mapped. Comparison of the wheat and Oenothera cox3 sequences gives ambiguous indications concerning the amino acid coded by the codon CGG. Upstream and downstream of the wheat cox3 gene, two short sequences of 43 bp and 69 bp respectively are present, which are almost identical to sequences present in the flanking regions of other plant mitochondrial genes. These common sequences seem to have played a role in the rearrangements which caused sequence divergence of the plant mt genomes during evolution. Furthermore, mapping of wheat and maize cox3 and cob transcripts suggests that some of these common sequences can play a role in the regulation of transcription or processing.
