RESUMO
We demonstrate that the binding sites for highly conserved transcription factors vary extensively between human and mouse. We mapped the binding of four tissue-specific transcription factors (FOXA2, HNF1A, HNF4A and HNF6) to 4,000 orthologous gene pairs in hepatocytes purified from human and mouse livers. Despite the conserved function of these factors, from 41% to 89% of their binding events seem to be species specific. When the same protein binds the promoters of orthologous genes, approximately two-thirds of the binding sites do not align.
Assuntos
Sequência Conservada/genética , Regulação da Expressão Gênica , Sequências Reguladoras de Ácido Nucleico , Fatores de Transcrição/genética , Transcrição Gênica , Animais , Variação Genética , Fator 1-alfa Nuclear de Hepatócito/genética , Fator 3-beta Nuclear de Hepatócito/genética , Fator 4 Nuclear de Hepatócito/genética , Fator 6 Nuclear de Hepatócito/genética , Humanos , Camundongos , Homologia de SequênciaRESUMO
Homologous sets of transcription factors direct conserved tissue-specific gene expression, yet transcription factor-binding events diverge rapidly between closely related species. We used hepatocytes from an aneuploid mouse strain carrying human chromosome 21 to determine, on a chromosomal scale, whether interspecies differences in transcriptional regulation are primarily directed by human genetic sequence or mouse nuclear environment. Virtually all transcription factor-binding locations, landmarks of transcription initiation, and the resulting gene expression observed in human hepatocytes were recapitulated across the entire human chromosome 21 in the mouse hepatocyte nucleus. Thus, in homologous tissues, genetic sequence is largely responsible for directing transcriptional programs; interspecies differences in epigenetic machinery, cellular environment, and transcription factors themselves play secondary roles.
Assuntos
Cromossomos Humanos Par 21/genética , Regulação da Expressão Gênica , Fatores Nucleares de Hepatócito/metabolismo , Hepatócitos/metabolismo , Sequências Reguladoras de Ácido Nucleico , Transcrição Gênica , Animais , Sequência de Bases , Núcleo Celular/metabolismo , Montagem e Desmontagem da Cromatina , Imunoprecipitação da Cromatina , Cromossomos Humanos Par 21/metabolismo , Modelos Animais de Doenças , Síndrome de Down/genética , Histonas/metabolismo , Humanos , Metilação , Camundongos , Análise de Sequência com Séries de Oligonucleotídeos , Especificidade da Espécie , Sítio de Iniciação de TranscriçãoRESUMO
Maintaining quiescent cells in G0 phase is achieved in part through the multiprotein subunit complex known as DREAM, and in human cell lines the transcription factor E2F4 directs this complex to its cell cycle targets. We found that E2F4 binds a highly overlapping set of human genes among three diverse primary tissues and an asynchronous cell line, which suggests that tissue-specific binding partners and chromatin structure have minimal influence on E2F4 targeting. To investigate the conservation of these transcription factor binding events, we identified the mouse genes bound by E2f4 in seven primary mouse tissues and a cell line. E2f4 bound a set of mouse genes that was common among mouse tissues, but largely distinct from the genes bound in human. The evolutionarily conserved set of E2F4 bound genes is highly enriched for functionally relevant regulatory interactions important for maintaining cellular quiescence. In contrast, we found minimal mRNA expression perturbations in this core set of E2f4 bound genes in the liver, kidney, and testes of E2f4 null mice. Thus, the regulatory mechanisms maintaining quiescence are robust even to complete loss of conserved transcription factor binding events.
Assuntos
Fator de Transcrição E2F4/genética , Fator de Transcrição E2F4/metabolismo , Regulação da Expressão Gênica , Animais , Células Cultivadas , Sequência Conservada , Evolução Molecular , Genoma , Heterozigoto , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Modelos Biológicos , Distribuição Tecidual , Fatores de Transcrição/metabolismoRESUMO
Reactive oxygen species (ROS) such as superoxide radicals are responsible for the pathogenesis of various human diseases. ROS are generated during normal metabolic process in all of the oxygen-utilizing organisms. The copper-zinc-containing SOD (SOD1) acts as a major defense against ROS by detoxifying the superoxide anion. In model organisms, SOD1 has been shown to play a role in the aging process. However, the exact role of the SOD1 protein in the human aging process remains to be resolved. We show that SOD1 RNA interference (RNAi) induces senescence in normal human fibroblasts. This premature senescence depends on p53 induction. In contrast, in human fibroblastic cells with inactivated p53, the SOD1 RNAi is without effect. Surprisingly, in cancer cells (HeLa), the SOD1 RNAi induces cell death rather then senescence. Together, these findings support the notion that in normal human cells the SOD1 protein may play a role in the regulation of cellular lifespan by p53 and may also regulate the death signals in cancer cells.