PIWI-interacting RNAs (piRNAs) are germ cell-specific small non-coding RNAs that are essential for silencing transposable elements. Substantial efforts in the past decade have led to an understanding of how piRNAs are made. Primary piRNA biogenesis is initiated with transcription of piRNA precursors, followed by cleavage into piRNA intermediates, and finally, maturation by 3′ end trimming and 2′-O-methylation. Secondary piRNA biogenesis occurs through an amplification loop (ping pong pathway); the piRNA pools generated through primary processing guide MILI protein to cleave the target RNA for piRNA generation in a feed-forward loop that accelerates production of the piRNAs. Papi/Tdrkh has been implicated in processing the 3′ ends of piRNAs1,2, however, Papi/Tdrkh lacks a recognized domain for nuclease activity. Recently, two independent studies identified the proteins that function as piRNA 3′ end trimmers in silkworms-the poly(A) specific ribonuclease PARN-1 and the PARN-like ortholog PNLDC13,4.

中文翻译：

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PNLDC1在小鼠piRNA 3'末端修剪和雄性育性中的重要作用

PIWI相互作用RNA（piRNA）是生殖细胞特异性的小型非编码RNA，对于沉默转座因子至关重要。在过去的十年中，大量的努力导致人们对piRNA的产生方式有了了解。最初的piRNA生物发生始于piRNA前体的转录，然后裂解为piRNA中间体，最后通过3'末端修饰和2'-O-甲基化使其成熟。二次piRNA生物发生是通过扩增环（乒乓路径）发生的。通过一级加工产生的piRNA池可引导MILI蛋白在前馈环中切割靶RNA，以生成piRNA，从而加速piRNA的产生。Papi / Tdrkh与pi​​RNAs1,2的3'末端有关，但是，Papi / Tdrkh缺乏公认的核酸酶活性结构域。最近，