Widespread association of the Argonaute protein AGO2 with meiotic chromatin suggests a distinct nuclear function in mammalian male reproduction

Argonaute 2 (AGO2) is a ubiquitously expressed protein critical for regulation of mRNA translation and vital to animal development. AGO2 protein is found in both cytoplasmic and nuclear compartments, and while its cytoplasmic role is well studied, the biological relevance of nuclear AGO2 is unclear. Here, we address this problem in vivo, using developing spermatogenic cells as a model. We find that AGO2 transiently binds both chromatin and nucleus-specific mRNA transcripts of hundreds of genes required for sperm production during male meiosis in mice, and that germline conditional knockout (cKO) of Ago2 causes depletion of the encoded proteins. Correspondingly, Ago2 cKO males exhibit abnormal sperm head morphology and reduced sperm count, along with reduced postnatal viability of offspring. Together, our data reveal an unexpected nuclear role for AGO2 in enhancing expression of developmentally important genes during mammalian male reproduction. RNA-seq, eCLIP, and ChIP-seq data for AGO2 in mESCs and spermatogenic cells; eCLIP in whole testis cytoplasmic fractionArgonaute 2（AGO2）是一种广泛表达的蛋白质，对mRNA翻译调控至关重要，且对动物发育不可或缺。AGO2蛋白可定位于细胞质与细胞核两个区域，尽管其在细胞质中的功能已被广泛研究，但细胞核中AGO2的生物学意义仍不明确。本研究以发育中的生精细胞为模型，在体内探究该科学问题。我们发现，在小鼠雄性减数分裂过程中，AGO2会瞬时结合数百个精子发生必需基因的染色质及细胞核特异性mRNA转录本；生殖细胞条件性敲除（germline conditional knockout, cKO）Ago2会导致其编码蛋白的表达量显著下调。相应地，Ago2 cKO雄性小鼠表现出精子头部形态异常、精子数量减少，同时子代的出生存活率降低。综上，本研究数据揭示了AGO2此前未被发现的细胞核功能：在哺乳动物雄性生殖过程中，AGO2可增强发育关键基因的表达。本研究附带的数据集包含：小鼠胚胎干细胞（mouse embryonic stem cells, mESCs）与生精细胞中AGO2的RNA测序（RNA-seq）、增强型交联免疫沉淀测序（eCLIP）及染色质免疫沉淀测序（ChIP-seq）数据；以及全睾丸细胞质组分中的AGO2 eCLIP数据。