RESUMO
Both position-effect variegation (PEV) in Drosophila and telomeric position-effect in yeast (TPE) result from the mosaic inactivation of genes relocated next to a block of centromeric heterochromatin or next to telomeres. In many aspects, these phenomena are analogous to other epigenetic silencing mechanisms, such as the control of homeotic gene clusters, X-chromosome inactivation and imprinting in mammals, and mating-type control in yeast. Dominant mutations that suppress or enhance PEV are thought to encode either chromatin proteins or factors that directly affect chromatin structure. We have identified an insertional mutation in Drosophila that enhances PEV and reduces transcription of the gene in the eye-antenna imaginal disc. The gene corresponds to that encoding the transcriptional regulator RPD3 in yeast, and to a human histone deacetylase. In yeast, RRD3-deletion strains show enhanced TPE, suggesting a conserved role of the histone deacetylase RPD3 in counteracting genomic silencing. This function of RPD3, which is in contrast to the general correlation between histone acetylation and increased transcription, might be due to a specialized chromatin structure at silenced loci.
Assuntos
Proteínas Fúngicas/metabolismo , Regulação Fúngica da Expressão Gênica , Regulação da Expressão Gênica , Genes de Insetos , Histona Desacetilases/metabolismo , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Animais , Clonagem Molecular , Elementos de DNA Transponíveis , Proteínas de Drosophila , Drosophila melanogaster , Proteínas Fúngicas/química , Proteínas Fúngicas/genética , Histona Desacetilase 1 , Histona Desacetilases/química , Histona Desacetilases/genética , Humanos , Dados de Sequência Molecular , Mutagênese Insercional , Proteínas Repressoras , Saccharomyces cerevisiae , Proteínas de Saccharomyces cerevisiae , Telômero/fisiologia , Fatores de Transcrição/química , Fatores de Transcrição/genéticaRESUMO
A dominant insertional P-element mutation enhances position-effect variegation in Drosophila melanogaster. The mutation is homozygous, viable, and fertile and maps at 64E on the third chromosome. The corresponding gene was cloned by transposon tagging. Insertion of the transposon upstream of the open reading frame correlates with a strong reduction of transcript level. A transgene was constructed with the cDNA and found to have the effect opposite from that of the mutation, namely, to suppress variegation. Sequencing of the cDNA reveals a large open reading frame encoding a putative ubiquitin-specific protease (Ubp). Ubiquitin marks various proteins, frequently for proteasome-dependent degradation. Ubps can cleave the ubiquitin part from these proteins. We discuss the link established here between a deubiquitinating enzyme and epigenetic silencing processes.
Assuntos
Mapeamento Cromossômico , Drosophila melanogaster/enzimologia , Drosophila melanogaster/genética , Endopeptidases/genética , Endopeptidases/metabolismo , Transcrição Gênica , Sequência de Aminoácidos , Animais , Animais Geneticamente Modificados , Sequência de Bases , Cruzamentos Genéticos , Embrião não Mamífero , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Regulação Enzimológica da Expressão Gênica , Genes Homeobox , Genes de Insetos , Homozigoto , Masculino , Dados de Sequência Molecular , Mutagênese Insercional , Fases de Leitura Aberta , Pigmentação , Recombinação Genética , Mapeamento por Restrição , Homologia de Sequência de AminoácidosRESUMO
A procedure is described to isolate DNA probes from the bovine genome that are enriched in sites for the so-called rare cutter restriction endonucleases. A collection of SacII (CvCGCGG)-Hin-dIII fragments from bovine sperm was established in the plasmid Bluescript. 180 clones were picked at random and analysed for the presence of inserts with sites for the following rare cutters: EagI, BsshII, NarI, MluI, NruI, NaeI: 70% of the clones contained at least 1 site and 5% contained four different such sites. 22.8% had multiple sites for one or more of the rare cutters tested. Sequence analysis for 16 clones confirmed the cloning of DNA with a G+C content and a proportion of CpG vs GpCs indicative of CpG islands.
Assuntos
Bovinos/genética , Sondas de DNA/isolamento & purificação , Fosfatos de Dinucleosídeos/genética , Biblioteca Gênica , Animais , Clonagem Molecular , Citosina/análise , Desoxirribonucleases de Sítio Específico do Tipo II , Eletroforese em Gel de Ágar/veterinária , Escherichia coli/genética , Guanina/análise , Masculino , Análise de Sequência , Transformação GenéticaRESUMO
LA hipocalcemia produce manifestaciones clínicas bien definidas, que abarcan una amplia gama desde parestesias periorales transitorias hasta tetania franca, convulsiones, arritmias y muerte. Son múltiples las causas de hipocalcemia y el tratamiento definitivo varia con la anomalia subyacente. En este artículo se analiza el enfoque diagnóstico de la hipocalcemia y con la base en las alteraciones fisiopatológicas responsables de la misma se establecen las medidas terapéuticas tanto para los casos agudos como para el tratamiento a largo plazo de estos pacientes.
Assuntos
Humanos , Hipocalcemia/diagnóstico , Hipocalcemia/etiologia , Hipocalcemia/fisiopatologia , Hipocalcemia/terapiaRESUMO
The effects of intravenous glucose, insulin and glucagon admininistration on the hepatic glycogen synthase and glycogen phosphorylase systems were assessed in the anesthetized rhesus monkey. Results were correlated with measurements of hepatic cyclic AMP (cAMP) concentrations and plasma glucose, insulin, and glucagon concentrations. Both glucose and insulin administration promoted significant inactivation of phosphorylase by 1 min, which was followed by more gradual activation of synthase. Neither glucose nor insulin caused significant changes in hepatic cAMP. Marked hyperglucagonemia resulting from insulin-induced hypoglycemia did not cause increases IN in hepatic cAMP, suggesting that the elevated insulin levels possibly inhibited glucagon action on the hepatic adenylate cyclase-cAMP system. Glucagon administration caused large increases in hepatic cAMP and activation of phosphorylase within 1 min, followed by more gradual inactivation of synthase when it had been previously activated by glucose. Concomitant glucose infusion, with resulting increased plasma insulin concentrations, markedly diminished the duration of hepatic cAMP elevations following glucagon adminstration, again suggesting an insulin inhibition of glucagon action on the hepatic adenylate-cAMP system.
