Widespread Expression of piRNA-like Molecules in Somatic Tissues

Piwi-interacting RNA (piRNA) are small RNA abundant in the germline across animal species. In fruit flies and mice, piRNA were implicated in maintenance of genomic integrity by transposable elements silencing. Outside of the germline, piRNA have only been found in Drosophila ovarian follicle cells. Previous studies further reported the presence of multiple piRNA-like small RNA (pilRNA) in fly heads and a small number of pilRNA in mouse tissues and human NK cells. Here, by analyzing high-throughput small RNA sequencing data in more than 130 fruit fly, mouse and rhesus macaque samples, we show widespread presence of pilRNA displaying all known characteristics of piRNA in multiple somatic tissues of these three species. In mouse pancreas and macaque epididymis, pilRNA abundance was compatible with piRNA abundance in the germline. Using in situ hybridizations, we further demonstrate pilRNA co-localization with mRNA expression of Piwi-family genes in all macaque tissues. These findings indicate that piRNA-like molecules might play important roles outside of the germline. Small RNA expression profiles were examined in five rhesus macaque tissues (testis, epididymis, prostate, seminal vesicles, cortex) and one mouse tissue (epididymis).Piwi互作RNA（Piwi-interacting RNA，简称piRNA）是一类广泛存在于各动物物种生殖系中的小型RNA。在果蝇与小鼠中，piRNA通过沉默转座因子（transposable elements）参与维持基因组完整性。在生殖系以外的组织中，piRNA仅在果蝇卵巢滤泡细胞中被发现。既往研究曾报道，果蝇头部存在多种piRNA样小RNA（piRNA-like small RNA，简称pilRNA），小鼠组织与人类自然杀伤细胞（NK cells）中也存在少量pilRNA。本研究通过分析涵盖果蝇、小鼠与恒河猴（rhesus macaque）的130余例样本的高通量小RNA测序（high-throughput small RNA sequencing）数据，证实这三个物种类别的多种体细胞组织中广泛存在具备piRNA所有已知特征的pilRNA。在小鼠胰腺与恒河猴附睾中，pilRNA的丰度可与生殖系中的piRNA丰度相匹敌。借助原位杂交（in situ hybridizations）技术，本研究进一步证明，在恒河猴所有受试组织中，pilRNA均与Piwi家族基因的mRNA表达共定位。上述研究结果表明，piRNA样分子可能在生殖系之外发挥重要生物学功能。本研究对5种恒河猴组织（睾丸、附睾、前列腺、精囊、皮层）以及1种小鼠组织（附睾）的小RNA表达谱进行了检测分析。