BTBD18 licenses piRNA-generating loci to support mouse germ cell development

PIWI-interacting RNAs (piRNAs) are small non-coding RNAs essential for animal germ cell development. Despite intense investigation of post-transcriptional processing, piRNA biogenesis at the chromatin level remains enigmatic. Here we document that BTBD18 is a pachytene nuclear protein in mouse testes that occupies intergenic pachytene piRNA-producing loci with remarkable genome-wide specificity. Deficiency of Btbd18 in mice results in disrupted piRNA biogenesis and male sterility. Transcriptome profiling, chromatin accessibility and RNA polymerase II occupancy demonstrate that BTBD18 facilitates expression of pachytene piRNA precursors by promoting transcription elongation. Therefore, we conclude that BTBD18 functionally licenses genomic sources of piRNAs for transcription activation in mice, and propose that piRNA precursor biogenesis is regulated by transcriptional elongation. RNA-seq, small RNA-seq, ChIP-seq, and ATAC-seq were performed using mouse testes or purified testicular cells with indicated genotypes.PIWI互作RNA（PIWI-interacting RNAs，简称piRNAs）是一类小型非编码RNA，对动物生殖细胞发育至关重要。尽管学界已对其转录后加工机制开展了大量深入研究，但染色质层面的piRNA生物生成过程仍未被完全阐明。本研究证实，BTBD18是小鼠睾丸中的粗线期核蛋白，能以极高的全基因组特异性结合基因间隔区的粗线期piRNA生成位点。Btbd18功能缺失的小鼠会出现piRNA生物生成紊乱，并导致雄性不育。转录组分析、染色质可及性检测、RNA聚合酶II结合富集实验结果显示，BTBD18通过促进转录延伸，增强粗线期piRNA前体的表达。因此，本研究认为BTBD18可功能性地赋予小鼠基因组piRNA生成位点转录激活的能力，并提出piRNA前体的生物生成过程受转录延伸机制调控。本研究采用携带指定基因型的小鼠睾丸或纯化的睾丸细胞，开展了RNA测序（RNA-seq）、小RNA测序（small RNA-seq）、染色质免疫沉淀测序（ChIP-seq）及转座酶可及性测序（ATAC-seq）实验。