Institute of Immunology and Infection Research, School of Biological Sciences, The University of Edinburgh, Edinburgh EH9 3JT, UK.
Institute of Evolutionary Biology, School of Biological Sciences, The University of Edinburgh, Edinburgh EH9 3JT, UK.
Nucleic Acids Res. 2019 Apr 23;47(7):3594-3606. doi: 10.1093/nar/gkz142.
Extracellular RNA has been proposed to mediate communication between cells and organisms however relatively little is understood regarding how specific sequences are selected for export. Here, we describe a specific Argonaute protein (exWAGO) that is secreted in extracellular vesicles (EVs) released by the gastrointestinal nematode Heligmosomoides bakeri, at multiple copies per EV. Phylogenetic and gene expression analyses demonstrate exWAGO orthologues are highly conserved and abundantly expressed in related parasites but highly diverged in free-living genus Caenorhabditis. We show that the most abundant small RNAs released from the nematode parasite are not microRNAs as previously thought, but rather secondary small interfering RNAs (siRNAs) that are produced by RNA-dependent RNA Polymerases. The siRNAs that are released in EVs have distinct evolutionary properties compared to those resident in free-living or parasitic nematodes. Immunoprecipitation of exWAGO demonstrates that it specifically associates with siRNAs from transposons and newly evolved repetitive elements that are packaged in EVs and released into the host environment. Together this work demonstrates molecular and evolutionary selectivity in the small RNA sequences that are released in EVs into the host environment and identifies a novel Argonaute protein as the mediator of this.
细胞外 RNA 被提出在细胞和生物之间介导通讯，然而对于特定序列如何被选择用于输出，人们的了解相对较少。在这里，我们描述了一种特定的 Argonaute 蛋白（exWAGO），它以多个拷贝的形式分泌到由胃肠道线虫 Heligmosomoides bakeri 释放的细胞外囊泡 (EV) 中。系统发育和基因表达分析表明，exWAGO 同源物在相关寄生虫中高度保守且大量表达，但在自由生活的属 Caenorhabditis 中高度分化。我们表明，从线虫寄生虫释放的最丰富的小 RNA 不是先前认为的 microRNAs，而是由 RNA 依赖性 RNA 聚合酶产生的次级小干扰 RNA (siRNA)。在 EV 中释放的 siRNA 与那些在自由生活或寄生线虫中存在的 siRNA 具有不同的进化特性。exWAGO 的免疫沉淀表明，它与转座子和新进化的重复元件的 siRNA 特异性结合，这些 siRNA 被包装在 EV 中并释放到宿主环境中。这项工作共同证明了在 EV 释放到宿主环境中的小 RNA 序列中存在分子和进化选择性，并确定了一种新型 Argonaute 蛋白作为其介导物。
