Yang Zhaolin, Chen Kuan-Ming, Pandey Radha Raman, Homolka David, Reuter Michael, Janeiro Bruno Kotska Rodino, Sachidanandam Ravi, Fauvarque Marie-Odile, McCarthy Andrew A, Pillai Ramesh S
European Molecular Biology Laboratory, Grenoble Outstation, Univ. Grenoble Alpes-EMBL-CNRS, 71 avenue des Martyrs, 38042 France; Unit for Virus Host-Cell Interactions, Univ. Grenoble Alpes-EMBL-CNRS, 71 avenue des Martyrs, 38042 France.
Department of Oncological Sciences, Icahn School of Medicine at Sinai, One Gustave L. Levy Place, NY 10029, USA.
Mol Cell. 2016 Jan 7;61(1):138-52. doi: 10.1016/j.molcel.2015.11.009. Epub 2015 Dec 6.
PIWI-interacting RNAs (piRNAs) guide PIWI proteins to suppress transposons in the cytoplasm and nucleus of animal germ cells, but how silencing in the two compartments is coordinated is not known. Here we demonstrate that endonucleolytic slicing of a transcript by the cytosolic mouse PIWI protein MILI acts as a trigger to initiate its further 5'→3' processing into non-overlapping fragments. These fragments accumulate as new piRNAs within both cytosolic MILI and the nuclear MIWI2. We also identify Exonuclease domain-containing 1 (EXD1) as a partner of the MIWI2 piRNA biogenesis factor TDRD12. EXD1 homodimers are inactive as a nuclease but function as an RNA adaptor within a PET (PIWI-EXD1-Tdrd12) complex. Loss of Exd1 reduces sequences generated by MILI slicing, impacts biogenesis of MIWI2 piRNAs, and de-represses LINE1 retrotransposons. Thus, piRNA biogenesis triggered by PIWI slicing, and promoted by EXD1, ensures that the same guides instruct PIWI proteins in the nucleus and cytoplasm.
PIWI相互作用RNA（piRNA）引导PIWI蛋白在动物生殖细胞的细胞质和细胞核中抑制转座子，但尚不清楚这两个区室中的沉默是如何协调的。在这里，我们证明细胞质中的小鼠PIWI蛋白MILI对转录本进行内切核酸酶切割，以此作为触发因素，启动其进一步的5'→3'加工，形成不重叠的片段。这些片段作为新的piRNA在细胞质中的MILI和细胞核中的MIWI2内积累。我们还鉴定出含核酸外切酶结构域1（EXD1）是MIWI2 piRNA生物发生因子TDRD12的伙伴。EXD1同二聚体作为核酸酶无活性，但在PET（PIWI-EXD1-Tdrd12）复合物中作为RNA衔接子发挥作用。Exd1的缺失减少了由MILI切割产生的序列，影响MIWI2 piRNA的生物发生，并解除对LINE1逆转录转座子的抑制。因此，由PIWI切割引发并由EXD1促进的piRNA生物发生，确保了相同的引导序列指导细胞核和细胞质中的PIWI蛋白。
