Microprocessor recruitment to elongating RNA Polymerase II is required for differential expression of microRNAs

The cellular abundance of mature microRNAs (miRNAs) is dictated by the efficiency of nuclear processing of primary miRNA transcripts (pri-miRNAs) into pre-miRNA intermediates. The Microprocessor complex of Drosha and DGCR8 carries this out, but it has been unclear what controls Microprocessor's differential processing of various pri-miRNAs. Here, we show that Drosophila DGCR8 (Pasha) directly associates with the C terminal domain of the RNA polymerase II elongation complex when it is phosphorylated by the Cdk9 kinase (pTEFb). When association is blocked by loss of Cdk9 activity, a global change in pri-miRNA processing is detected. Processing of pri-miRNAs with a UGU sequence motif in their apical junction domain increases, while processing of pri-miRNAs lacking this motif decreases. Therefore, phosphorylation of RNA polymerase II recruits Microprocessor for co-transcriptional processing of non-UGU pri-miRNAs that would otherwise be poorly processed. In contrast, UGU-positive pri-miRNAs are robustly processed by Microprocessor independent of RNA polymerase association. There are 2 samples, one control and one experimental

成熟微RNA（miRNAs）的细胞丰度，由初级miRNA转录本（pri-miRNAs）经细胞核加工为前miRNA中间产物的效率所决定。由Drosha与DGCR8组成的微处理器复合物（Microprocessor complex）负责完成这一加工过程，但此前一直不清楚是什么因素调控该复合物对不同pri-miRNAs的差异化加工。本研究显示，果蝇DGCR8（Pasha）可直接结合经Cdk9激酶（pTEFb）磷酸化的RNA聚合酶II延伸复合物的羧基末端结构域。当Cdk9活性缺失阻断这一结合时，全局pri-miRNA的加工模式发生显著改变：带有UGU序列基序的顶端连接结构域的pri-miRNAs加工效率提升，而缺乏该基序的pri-miRNAs加工效率则下降。由此可见，RNA聚合酶II的磷酸化可招募微处理器复合物，对非UGU型pri-miRNAs进行共转录加工——这类pri-miRNAs若缺乏该招募过程则难以被有效加工。与之相反，带有UGU基序的pri-miRNAs可被微处理器复合物高效加工，且不依赖于RNA聚合酶的结合。本数据集包含2个样本：1个对照组与1个实验组。