Functional implications of the emergence of alternative splicing in hnRNP A/B transcripts
Functional implications of the emergence of alternative splicing in hnRNP A/B transcripts
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DOI：
10.1261/rna.2142810
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发表时间：
2010-09-01
期刊：
影响因子：
4.5
通讯作者：
Smith, Ross
中科院分区：
文献类型：
--
作者：
Han, Siew Ping;Kassahn, Karin S.;Smith, Ross
异质核核糖核蛋白（hnRNP）A/B是RNA结合蛋白家族，其参与核酸代谢的各个方面，包括mRNA运输、端粒维持和剪接。它们既是选择性剪接的调节者又是靶点，其转录物的选择性剪接模式在不同物种的旁系同源物和直系同源物之间存在差异。令人惊讶的是，这种剪接变异的程度及其对转录后调控的影响在很大程度上仍未被探索。在这里，我们进行了详细的分析hnRNP A/B序列和表达模式在六种脊椎动物。通过引入新的剪接位点、改变现有剪接位点的强度以及积累辅助剪接调控基序，出现了替代外显子。观察到的异构体表达模式可以归因于顺式元件的频率和强度。我们发现了哺乳动物中剪接变异增加的趋势，并在人类和鸡中鉴定了新的选择性剪接异构体。下拉和翻译分析表明，包含替代外显子改变了hnRNP A/B蛋白对其同源核酸的亲和力和修饰的蛋白表达水平。由于hnRNP A/B调节mRNA加工中的几个关键步骤，在多个细胞环境和物种中涉及不同的hnRNP同种型意味着这些系统的转录输出的伴随差异。我们的结论是，hnRNP A/B的选择性剪接的出现，促进了他们的角色的多样化，在选择性剪接的调节，从而增加了一个意想不到的层在脊椎动物中的转录调控复杂性。
The heterogeneous nuclear ribonucleoproteins (hnRNPs) A/B are a family of RNA-binding proteins that participate in various aspects of nucleic acid metabolism, including mRNA trafficking, telomere maintenance, and splicing. They are both regulators and targets of alternative splicing, and the patterns of alternative splicing of their transcripts have diverged between paralogs and between orthologs in different species. Surprisingly, the extent of this splicing variation and its implications for post-transcriptional regulation have remained largely unexplored. Here, we conducted a detailed analysis of hnRNP A/B sequences and expression patterns across six vertebrates. Alternative exons emerged via the introduction of new splice sites, changes in the strengths of existing splice sites, and the accumulation of auxiliary splicing regulatory motifs. Observed isoform expression patterns could be attributed to the frequency and strength of cis-elements. We found a trend toward increased splicing variation in mammals and identified novel alternatively spliced isoforms in human and chicken. Pulldown and translational assays demonstrated that the inclusion of alternative exons altered the affinity of hnRNP A/B proteins for their cognate nucleic acids and modified protein expression levels. As the hnRNPs A/B regulate several key steps in mRNA processing, the involvement of diverse hnRNP isoforms in multiple cellular contexts and species implies concomitant differences in the transcriptional output of these systems. We conclude that the emergence of alternative splicing in the hnRNPs A/B has contributed to the diversification of their roles in the regulation of alternative splicing and has thus added an unexpected layer of regulatory complexity to transcription in vertebrates.