RESUMO
The epigenetic activator Mixed lineage leukemia 1 (MLL1) is paramount for embryonic development and hematopoiesis. Here, we demonstrate that the long, noncoding RNA (lncRNA) Mistral (Mira) activates transcription of the homeotic genes Hoxa6 and Hoxa7 in mouse embryonic stem cells (mESC) by recruiting MLL1 to chromatin. The Mira gene is located in the spacer DNA region (SDR) separating Hoxa6 and Hoxa7, transcriptionally silent in mESCs, and activated by retinoic acid. Mira-mediated recruitment of MLL1 to the Mira gene triggers dynamic changes in chromosome conformation, culminating in activation of Hoxa6 and Hoxa7 transcription. Hoxa6 and Hoxa7 activate the expression of genes involved in germ layer specification during mESC differentiation in a cooperative and redundant fashion. Our results connect the lncRNA Mira with the recruitment of MLL1 to target genes and implicate lncRNAs in epigenetic activation of gene expression during vertebrate cell-fate determination.
Assuntos
Diferenciação Celular/genética , Cromatina/metabolismo , Células-Tronco Embrionárias/metabolismo , Proteínas de Homeodomínio/metabolismo , Proteína de Leucina Linfoide-Mieloide/metabolismo , Proteínas de Neoplasias/metabolismo , RNA não Traduzido/fisiologia , Animais , Células-Tronco Embrionárias/citologia , Histona-Lisina N-Metiltransferase , Proteínas de Homeodomínio/genética , Camundongos , Proteínas de Neoplasias/genética , Ativação Transcricional/genéticaRESUMO
HOXA Transcript Antisense RNA, Myeloid-Specific 1 (HOTAIRM1) is a conserved long non-coding RNA (lncRNA) involved in myeloid and neural differentiation that is deregulated in acute myeloid leukemia and other cancers. Previous studies focused on the nuclear unspliced HOTAIRM1 transcript, however cytoplasmic splice variants exist whose roles have remained unknown. Here, we report novel functions of HOTAIRM1 in the kidney. HOTAIRM1 transcripts are induced during renal lineage differentiation of embryonic stem cells and required for expression of specific renal differentiation genes. We show that the major HOTAIRM1 transcript in differentiated cells is the spliced cytoplasmic HM1-3 isoform and that HM1-3 is downregulated in >90% of clear cell renal cell carcinomas (ccRCCs). Knockdown of HM1-3 in renal cells deregulates hypoxia-responsive and angiogenic genes, including ANGPTL4. Furthermore, HOTAIRM1 transcripts are downregulated by hypoxia-mimetic stress and knockdown of the cytoplasmic HM1-3 isoform in normoxic cells post-transcriptionally induces Hypoxia-Inducible Factor 1α (HIF1α) protein, a key activator of ANGPTL4. Our results demonstrate the pervasive downregulation of the specific HOTAIRM1 cytoplasmic isoform HM1-3 in ccRCC and suggest possible roles of HOTAIRM1 in kidney differentiation and suppression of HIF1-dependent angiogenic pathways.
Assuntos
Proteína 4 Semelhante a Angiopoietina/genética , Carcinoma de Células Renais/genética , Subunidade alfa do Fator 1 Induzível por Hipóxia/genética , MicroRNAs/genética , Apoptose/genética , Carcinoma de Células Renais/patologia , Diferenciação Celular/genética , Linhagem Celular Tumoral , Linhagem da Célula/genética , Proliferação de Células/genética , Regulação Neoplásica da Expressão Gênica/genética , Humanos , Rim/crescimento & desenvolvimento , Rim/patologia , Isoformas de Proteínas/genética , Transdução de Sinais/genética , Hipóxia Tumoral/genéticaRESUMO
Organogenesis involves cell proliferation followed by complex determination and differentiation events that are intricately controlled in time and space. The instructions for these different steps are, to a large degree, implicit in the gene expression profiles of the cells that partake in organogenesis. Combining fluorescence-activated cell sorting and SAGE, we analyzed genomic expression patterns in the developing eye of Drosophila melanogaster. Genomic activity changes as cells pass from an uncommitted proliferating progenitor state through determination and differentiation steps toward a specialized cell fate. Analysis of the upstream sequences of genes specifically expressed during the proliferation phase of eye development implicates the transcription factor DREF and its inhibitor dMLF in the control of cell growth in this organ.
Assuntos
Proteínas de Drosophila/genética , Olho/embriologia , Regulação da Expressão Gênica no Desenvolvimento , Fatores de Transcrição/genética , Animais , Drosophila melanogaster/embriologia , Drosophila melanogaster/genética , Olho/citologia , Perfilação da Expressão Gênica , Organogênese/genéticaRESUMO
Long non-coding RNAs (lncRNAs) are a class of RNA molecules that are changing how researchers view eukaryotic gene regulation. Once considered to be non-functional products of low-level aberrant transcription from non-coding regions of the genome, lncRNAs are now viewed as important epigenetic regulators and several lncRNAs have now been demonstrated to be critical players in the development and/or maintenance of cancer. Similarly, the emerging variety of interactions between lncRNAs and MYC, a well-known oncogenic transcription factor linked to most types of cancer, have caught the attention of many biomedical researchers. Investigations exploring the dynamic interactions between lncRNAs and MYC, referred to as the lncRNA-MYC network, have proven to be especially complex. Genome-wide studies have shown that MYC transcriptionally regulates many lncRNA genes. Conversely, recent reports identified lncRNAs that regulate MYC expression both at the transcriptional and post-transcriptional levels. These findings are of particular interest because they suggest roles of lncRNAs as regulators of MYC oncogenic functions and the possibility that targeting lncRNAs could represent a novel avenue to cancer treatment. Here, we briefly review the current understanding of how lncRNAs regulate chromatin structure and gene transcription, and then focus on the new developments in the emerging field exploring the lncRNA-MYC network in cancer.
RESUMO
DNA methylation is fundamental for the stability and activity of genomes. Drosophila melanogaster and vertebrates establish a global DNA methylation pattern of their genome during early embryogenesis. Large-scale analyses of DNA methylation patterns have uncovered revealed that DNA methylation patterns are dynamic rather than static and change in a gene-specific fashion during development and in diseased cells. However, the factors and mechanisms involved in dynamic, postembryonic DNA methylation remain unclear. Methylation of lysine 9 in histone H3 (H3-K9) by members of the Su(var)3-9 family of histone methyltransferases (HMTs) triggers embryonic DNA methylation in Arthropods and Chordates. Here, we demonstrate that Drosophila SETDB1 (dSETDB1) can mediate DNA methylation and silencing of genes and retrotransposons. We found that dSETDB1 tri-methylates H3-K9 and binds methylated CpA motifs. Tri-methylation of H3-K9 by dSETDB1 mediates recruitment of DNA methyltransferase 2 (Dnmt2) and Su(var)205, the Drosophila ortholog of mammalian "Heterochromatin Protein 1", to target genes for dSETDB1. By enlisting Dnmt2 and Su(var)205, dSETDB1 triggers DNA methylation and silencing of genes and retrotransposons in Drosophila cells. DSETDB1 is involved in postembryonic DNA methylation and silencing of Rt1b{} retrotransposons and the tumor suppressor gene retinoblastoma family protein 1 (Rb) in imaginal discs. Collectively, our findings implicate dSETDB1 in postembryonic DNA methylation, provide a model for silencing of the tumor suppressor Rb, and uncover a role for cell type-specific DNA methylation in Drosophila development.