Data from: A global change in RNA polymerase II pausing during the Drosophila midblastula transition

Massive zygotic transcription begins in many organisms during the midblastula transition when the cell cycle of the dividing egg slows down. A few genes are transcribed before this stage but how this differential activation is accomplished is still an open question. We have performed ChIP-seq experiments on tightly staged Drosophila embryos and show that
massive recruitment of RNA polymerase II (Pol II) with widespread pausing occurs de novo during the midblastula transition. However, ∼100 genes are strongly occupied by Pol II before this timepoint and most of them do not show Pol II pausing, consistent with a requirement for rapid transcription during the fast nuclear cycles. This global change in Pol II pausing correlates with distinct core promoter elements and associates a TATA-enriched promoter with the rapid early transcription. This suggests that promoters are differentially used during the zygotic genome activation, presumably because they have distinct dynamic properties.

在众多生物中，大规模合子转录（zygotic transcription）起始于中囊胚转变（midblastula transition）时期，此时分裂中的卵细胞的细胞周期会减缓。少数基因可在该阶段之前完成转录，但这种差异化激活的实现机制仍是未解之谜。我们对严格分期的果蝇（Drosophila）胚胎开展了染色质免疫共沉淀测序（ChIP-seq）实验，结果显示，在中囊胚转变时期，RNA聚合酶II（RNA polymerase II, Pol II）会被大规模招募并出现广泛的暂停现象，该过程为从头发生。然而，约100个基因在该时间点之前就已被Pol II强力结合，且其中大多数未出现Pol II暂停现象，这与快速核周期中对快速转录的需求相符。Pol II暂停现象的这一全局性变化与独特的核心启动子元件（core promoter elements）存在关联，且将富含TATA框的启动子与早期快速转录联系了起来。这表明在合子基因组激活（zygotic genome activation）过程中，不同启动子的使用模式存在差异，推测其原因在于不同启动子具有独特的动态特性。