RESUMO
Proteins are manufactured by ribosomes-macromolecular complexes of protein and RNA molecules that are assembled within major nuclear compartments called nucleoli1,2. Existing models suggest that RNA polymerases I and III (Pol I and Pol III) are the only enzymes that directly mediate the expression of the ribosomal RNA (rRNA) components of ribosomes. Here we show, however, that RNA polymerase II (Pol II) inside human nucleoli operates near genes encoding rRNAs to drive their expression. Pol II, assisted by the neurodegeneration-associated enzyme senataxin, generates a shield comprising triplex nucleic acid structures known as R-loops at intergenic spacers flanking nucleolar rRNA genes. The shield prevents Pol I from producing sense intergenic noncoding RNAs (sincRNAs) that can disrupt nucleolar organization and rRNA expression. These disruptive sincRNAs can be unleashed by Pol II inhibition, senataxin loss, Ewing sarcoma or locus-associated R-loop repression through an experimental system involving the proteins RNaseH1, eGFP and dCas9 (which we refer to as 'red laser'). We reveal a nucleolar Pol-II-dependent mechanism that drives ribosome biogenesis, identify disease-associated disruption of nucleoli by noncoding RNAs, and establish locus-targeted R-loop modulation. Our findings revise theories of labour division between the major RNA polymerases, and identify nucleolar Pol II as a major factor in protein synthesis and nuclear organization, with potential implications for health and disease.
Assuntos
Nucléolo Celular/enzimologia , Nucléolo Celular/genética , DNA Ribossômico/genética , RNA Polimerase II/metabolismo , RNA não Traduzido/biossíntese , RNA não Traduzido/genética , Ribossomos/metabolismo , Proteína 9 Associada à CRISPR/genética , Proteína 9 Associada à CRISPR/metabolismo , Linhagem Celular Tumoral , Nucléolo Celular/fisiologia , DNA Helicases/metabolismo , DNA Intergênico/genética , Humanos , Enzimas Multifuncionais/metabolismo , Biossíntese de Proteínas , Estruturas R-Loop , RNA Helicases/metabolismo , RNA Polimerase I/antagonistas & inibidores , RNA Polimerase I/metabolismo , Ribonuclease H/metabolismo , Ribossomos/química , Ribossomos/genética , Sarcoma de Ewing/genética , Sarcoma de Ewing/patologiaRESUMO
Genome expression and stability are dependent on biological processes that control repetitive DNA sequences and nuclear compartmentalization. The phase separation of macromolecules has recently emerged as a major player in the control of biological pathways. Here, we summarize recent studies that collectively reveal intersections between phase separation, repetitive DNA elements, and nuclear compartments. These intersections modulate fundamental processes, including gene expression, DNA repair, and cellular lifespan, in the context of health and diseases such as cancer and neurodegeneration.
Assuntos
Regulação da Expressão Gênica/genética , Genoma/genética , Neoplasias/genética , Doenças Neurodegenerativas/genética , Sequências Repetitivas de Ácido Nucleico/genética , Envelhecimento/genética , Compartimento Celular/genética , Reparo do DNA/genética , Loci Gênicos/genética , HumanosRESUMO
Calorie restriction (CR) is a broadly effective environmental intervention that extends life by operating through numerous biological processes. Here, we discuss how non-coding RNA (ncRNA) molecules act as mediators and targets of lifespan-extending CR. We also highlight how these RNA molecules connect CR to its effects on genome stability, cell metabolism, programmed cell death, senescence, cancer, and neurodegeneration. We anticipate that an advanced understanding of the connections between CR and non-coding RNA will provide unique insights into aging mechanisms while pointing to novel approaches aimed at modulating aging and age-related diseases.