Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland.
Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland
Proc Natl Acad Sci U S A. 2018 Jul 3;115(27):7153-7158. doi: 10.1073/pnas.1722330115. Epub 2018 Jun 18.
Many mammalian genes are transcribed during short bursts of variable frequencies and sizes that substantially contribute to cell-to-cell variability. However, which molecular mechanisms determine bursting properties remains unclear. To probe putative mechanisms, we combined temporal analysis of transcription along the circadian cycle with multiple genomic reporter integrations, using both short-lived luciferase live microscopy and single-molecule RNA-FISH. Using the circadian promoter as our model, we observed that rhythmic transcription resulted predominantly from variations in burst frequency, while the genomic position changed the burst size. Thus, burst frequency and size independently modulated transcription. We then found that promoter histone-acetylation level covaried with burst frequency, being greatest at peak expression and lowest at trough expression, while remaining unaffected by the genomic location. In addition, specific deletions of ROR-responsive elements led to constitutively elevated histone acetylation and burst frequency. We then investigated the suggested link between histone acetylation and burst frequency by dCas9p300-targeted modulation of histone acetylation, revealing that acetylation levels influence burst frequency more than burst size. The correlation between acetylation levels at the promoter and burst frequency was also observed in endogenous circadian genes and in embryonic stem cell fate genes. Thus, our data suggest that histone acetylation-mediated control of transcription burst frequency is a common mechanism to control mammalian gene expression.
许多哺乳动物基因在短暂的、频率和大小变化的爆发中被转录，这对细胞间的变异性有很大贡献。然而，哪些分子机制决定了爆发特性尚不清楚。为了探究可能的机制，我们结合了沿昼夜节律周期的转录的时间分析和多个基因组报告基因整合，使用了短暂的荧光素酶活细胞显微镜和单分子 RNA-FISH。使用昼夜节律启动子作为我们的模型，我们观察到有节奏的转录主要是由于爆发频率的变化，而基因组位置改变了爆发大小。因此，爆发频率和大小独立地调节转录。然后，我们发现启动子组蛋白乙酰化水平与爆发频率相关，在表达高峰时最大，在表达低谷时最小，而不受基因组位置的影响。此外，ROR 反应元件的特定缺失导致组蛋白乙酰化和爆发频率的持续升高。然后，我们通过 dCas9p300 靶向组蛋白乙酰化的调节来研究组蛋白乙酰化与爆发频率之间的建议联系，结果表明乙酰化水平对爆发频率的影响大于对爆发大小的影响。在内源性昼夜节律基因和胚胎干细胞命运基因中也观察到启动子处的乙酰化水平与爆发频率之间的相关性。因此，我们的数据表明，组蛋白乙酰化介导的转录爆发频率的控制是一种控制哺乳动物基因表达的常见机制。
