U1 snRNP Determines mRNA Length and Regulates Isoform Expression
U1 snRNP Determines mRNA Length and Regulates Isoform Expression
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DOI：
10.1016/j.cell.2012.05.029
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发表时间：
2012-07-06
期刊：
影响因子：
64.5
通讯作者：
Dreyfuss, Gideon
中科院分区：
文献类型：
--
作者：
Berg, Michael G.;Singh, Larry N.;Dreyfuss, Gideon
U1 snRNP (U1) 除了其剪接作用外，还可通过内含子中隐秘多腺苷酸化信号 (PAS) 处的切割和多腺苷酸化 (PCPA) 来保护前 mRNA 免于急剧过早终止。在这里，差异表达转录本的高通量测序策略 (HIDE-seq) 在不同生物体的基因组范围内绘制了 PCPA 位点图谱。令人惊讶的是，虽然 U1 耗尽终止了大约 1 kb 内的大多数新生基因转录本，但中度功能性 U1 水平降低，不足以抑制剪接，剂量依赖性地向下游转移 PCPA，并引起 mRNA 30 UTR 缩短和激活的免疫细胞和神经元细胞、干细胞和癌症的近端 3' 外显子转换特征。激活神经元的特征 mRNA 缩短可以通过 U1 减少来重现，并通过 U1 过度表达来拮抗。重要的是，我们发现神经元激活生理学固有的快速且短暂的转录上调导致相对于前体 mRNA 的 U1 短缺。其他实验表明，U1 与新生转录本的关联可以抵消共转录 PCPA，这一过程我们称之为转录，确保转录组完整性并调节 mRNA 长度。
U1 snRNP (U1), in addition to its splicing role, protects pre-mRNAs from drastic premature termination by cleavage and polyadenylation (PCPA) at cryptic polyadenylation signals (PASs) in introns. Here, a high-throughput sequencing strategy of differentially expressed transcripts (HIDE-seq) mapped PCPA sites genome wide in divergent organisms. Surprisingly, whereas U1 depletion terminated most nascent gene transcripts within similar to 1 kb, moderate functional U1 level decreases, insufficient to inhibit splicing, dose-dependently shifted PCPA downstream and elicited mRNA 30 UTR shortening and proximal 3 ' exon switching characteristic of activated immune and neuronal cells, stem cells, and cancer. Activated neurons' signature mRNA shortening could be recapitulated by U1 decrease and antagonized by U1 overexpression. Importantly, we show that rapid and transient transcriptional upregulation inherent to neuronal activation physiology creates U1 shortage relative to pre-mRNAs. Additional experiments suggest cotranscriptional PCPA counteracted by U1 association with nascent transcripts, a process we term telescripting, ensuring transcriptome integrity and regulating mRNA length.