Endogenous siRNAs from naturally formed dsRNAs regulate transcripts in mouse oocytes
Endogenous siRNAs from naturally formed dsRNAs regulate transcripts in mouse oocytes
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DOI：
10.1038/nature06908
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发表时间：
2008-05-22
期刊：
影响因子：
64.8
通讯作者：
Sasaki, Hiroyuki
中科院分区：
文献类型：
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作者：
Watanabe, Toshiaki;Totoki, Yasushi;Sasaki, Hiroyuki
RNA干扰（RNAi）是双链RNA（dsRNA）以序列依赖性方式抑制特定转录物的机制。dsRNA通过Dicer加工成21 - 24个核苷酸的小干扰RNA（siRNA），然后掺入argonaute（Ago）蛋白中（1 - 4）。仅在具有RNA依赖性RNA聚合酶（RdRP）的生物体中观察到内源性siRNA的基因调节（5 - 10）。在哺乳动物中，没有发现RdRP活性，内源性siRNA的生物起源和功能在很大程度上仍然未知。在这里，我们表明，使用小鼠卵母细胞，内源性siRNA是来自天然存在的dsRNA，并在基因表达的调控中发挥作用。通过深度测序，我们在生长的卵母细胞中鉴定了大量与25 - 27个核苷酸的Piwi相互作用RNA（piRNA）相似的和与对应于信使RNA或反转录转座子的21个核苷酸的siRNA相似的两者。piRNA与Mili结合并在逆转录转座子的调节中起作用。siRNA专门定位于反转录转座子或产生能够形成dsRNA结构的转录物的其他基因组区域。反向重复结构、双向转录和来自不同基因座的反义转录物是dsRNA的来源。一些siRNA的前体转录物来源于表达的假基因，这表明假基因的作用之一是通过RNAi调节起始源mRNA的水平。Dicer或Ago2的缺失导致siRNA水平降低和与siRNA互补的逆转录转座子和蛋白质编码转录物水平增加。因此，RNAi途径调节小鼠卵母细胞中的蛋白质编码转录物和反转录转座子。我们的研究结果揭示了内源性siRNA在哺乳动物卵母细胞中的作用，并表明缺乏RdRP活性的生物体可以从天然存在的dsRNA产生功能性内源性siRNA。
RNA interference (RNAi) is a mechanism by which doublestranded RNAs (dsRNAs) suppress specific transcripts in a sequence-dependent manner. dsRNAs are processed by Dicer to 21-24-nucleotide small interfering RNAs (siRNAs) and then incorporated into the argonaute (Ago) proteins(1-4). Gene regulation by endogenous siRNAs has been observed only in organisms possessing RNA- dependent RNA polymerase (RdRP)(5-10). In mammals, where no RdRP activity has been found, biogenesis and function of endogenous siRNAs remain largely unknown. Here we show, using mouse oocytes, that endogenous siRNAs are derived from naturally occurring dsRNAs and have roles in the regulation of gene expression. By means of deep sequencing, we identify a large number of both similar to 25-27-nucleotide Piwi-interacting RNAs (piRNAs) and similar to 21-nucleotide siRNAs corresponding to messenger RNAs or retrotransposons in growing oocytes. piRNAs are bound to Mili and have a role in the regulation of retrotransposons. siRNAs are exclusively mapped to retrotransposons or other genomic regions that produce transcripts capable of forming dsRNA structures. Inverted repeat structures, bidirectional transcription and antisense transcripts from various loci are sources of the dsRNAs. Some precursor transcripts of siRNAs are derived from expressed pseudogenes, indicating that one role of pseudogenes is to adjust the level of the founding source mRNA through RNAi. Loss of Dicer or Ago2 results in decreased levels of siRNAs and increased levels of retrotransposon and protein-coding transcripts complementary to the siRNAs. Thus, the RNAi pathway regulates both protein-coding transcripts and retrotransposons in mouse oocytes. Our results reveal a role for endogenous siRNAs in mammalian oocytes and show that organisms lacking RdRP activity can produce functional endogenous siRNAs from naturally occurring dsRNAs.