PIWI-interacting RNAs (piRNAs) and their associated PIWI clade Argonaute proteins constitute the core of the piRNA pathway. In gonadal cells, this conserved pathway is crucial for genome defense, and its main function is to silence transposable elements. This is achieved through posttranscriptional and transcriptional gene silencing. Precursors that give rise to piRNAs require specialized transcription and transport machineries because piRNA biogenesis is a cytoplasmic process. The ping-pong cycle, a posttranscriptional silencing mechanism, combines the cleavage-dependent silencing of transposon RNAs with piRNA production. PIWI proteins also function in the nucleus, where they scan for nascent target transcripts with sequence complementarity, instructing transcriptional silencing and deposition of repressive chromatin marks at transposon loci. Although studies have revealed numerous factors that participate in each branch of the piRNA pathway, the precise molecular roles of these factors often remain unclear. In this review, we summarize our current understanding of the mechanisms involved in piRNA biogenesis and function.

中文翻译：

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piRNA指导的基因组防御：从生物发生到沉默。

PIWI相互作用RNA（piRNA）及其相关的PIWI进化枝Argonaute蛋白构成piRNA途径的核心。在性腺细胞中，该保守途径对于基因组防御至关重要，其主要功能是沉默转座因子。这是通过转录后和转录基因沉默来实现的。产生piRNA的前体需要专门的转录和转运机制，因为piRNA的生物发生是细胞质过程。乒乓循环是转录后的沉默机制，将转座子RNA的裂解依赖性沉默与piRNA产生结合在一起。PIWI蛋白还在细胞核中起作用，在那里它们扫描具有序列互补性的新生靶标转录物，指示转录沉默和抑制性染色质标记在转座子基因座处的沉积。尽管研究已经揭示了参与piRNA途径每个分支的众多因素，但是这些因素的确切分子作用通常仍然不清楚。在这篇综述中，我们总结了对piRNA生物发生和功能所涉及机制的当前理解。