School of Biosciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom.
Genetics. 2011 Sep;189(1):97-107. doi: 10.1534/genetics.111.131383. Epub 2011 Jul 29.
Regulation of alternative mRNA processing by ELAV (embryonic lethal abnormal visual system)/Hu proteins is mediated by binding to AU-rich elements of low complexity. Since such sequences diverge very rapidly during evolution, it has not been clear if ELAV regulation is maintained over extended phylogenetic distances. The transcription factor Erect wing (Ewg) is a major target of ELAV in Drosophila melanogaster and coordinates metabolic gene expression with regulation of synaptic plasticity. Here, we demonstrate evolutionary conservation of ELAV regulation of ewg despite massive degeneration of its binding site and of associated elements in the regulated intronic 3'-end processing site in distantly related Drosophila virilis. In this species, the RNA-binding part of ELAV protein is identical to D. melanogaster. ELAV expression as well as expression and regulation of ewg are also conserved. Using in vitro binding assays and in vivo transgene analysis, we demonstrate, however, that the ELAV-binding site of D. virilis is fully functional in regulating alternative splicing of ewg intron 6 in D. melanogaster. Known features of the ELAV-binding site, such as the requirement of multiple poly(U) motifs spread over an extended binding site of ∼150 nt and a higher affinity to the 3' part of the binding site, are conserved. We further show that the 135-bp ELAV-binding site from D. melanogaster is sufficient for ELAV recruitment in vivo. Hence, our data suggest that ELAV/Hu protein-regulated alternative RNA processing is more conserved than anticipated from the alignment of degenerate low-complexity sequences.
ELAV（胚胎致死异常视觉系统）/Hu 蛋白通过结合低复杂性的 AU 丰富元件来调节替代 mRNA 加工。由于这些序列在进化过程中迅速分化，因此尚不清楚 ELAV 调节是否在广泛的系统发育距离内得到维持。转录因子 Erect wing（Ew）是果蝇中 ELAV 的主要靶标，它协调代谢基因表达与突触可塑性调节。在这里，我们证明了尽管在远缘果蝇 D. virilis 中，其结合位点及其调节的内含子 3'-末端加工位点的相关元件发生了巨大退化，但 Ew 的 ELAV 调节仍然具有进化保守性。在这个物种中，ELAV 蛋白的 RNA 结合部分与 D. melanogaster 相同。ELAV 的表达以及 Ew 的表达和调节也是保守的。然而，通过体外结合测定和体内转基因分析，我们证明 D. virilis 的 ELAV 结合位点在调节 D. melanogaster 中 Ew 内含子 6 的选择性剪接方面是完全功能性的。ELAV 结合位点的已知特征，例如需要多个散布在约 150 个核苷酸的扩展结合位点上的多聚（U）基序，以及与结合位点 3' 部分的更高亲和力，都是保守的。我们进一步表明，来自 D. melanogaster 的 135bp ELAV 结合位点足以在体内招募 ELAV。因此，我们的数据表明，ELAV/Hu 蛋白调节的替代 RNA 加工比从退化的低复杂度序列的比对所预期的更保守。
