The evolutionarily conserved piRNA-producing locus pi6 is required for male mouse fertility

Abstract

Pachytene piRNAs, which comprise >80% of small RNAs in the adult mouse testis, have been proposed to bind and regulate target RNAs like miRNAs, cleave targets like siRNAs, or lack biological function altogether. Although piRNA pathway protein mutants are male sterile, no biological function has been identified for any mammalian piRNA-producing locus. Here, we report that males lacking piRNAs from a conserved mouse pachytene piRNA locus on chromosome 6 ( pi6 ) produce sperm with defects in capacitation and egg fertilization. Moreover, heterozygous embryos sired by pi6 −/− fathers show reduced viability in utero. Molecular analyses suggest that pi6 piRNAs repress gene expression by cleaving mRNAs encoding proteins required for sperm function, pi6 also participates in a network of piRNA-piRNA precursor interactions that initiate piRNA production from a second piRNA locus on chromosome 10 as well as pi6 itself. Our data establish a direct role for pachytene piRNAs in spermiogenesis and embryo viability.

Sperm acrosome overgrowth and infertility in mice lacking chromosome 18 pachytene piRNA

“…Using a luciferase assay system, we investigated the ability of the aforementioned annotated Chr18 piRNAs to target cognate sequences of the 3'-UTR of Golga2. In agreement with a recent report 54 , we found that more than one Chr18 piRNA can target the same cleavage site with a mismatch tolerance between n16 to 31 (Fig. 6b, bottom).…”

“…Although post-transcriptional repression of mRNA targets by miRNAs is well documented 60 , a potential role for pachytene piRNAs in targeting specific RNAs for degradation also has been reported 16,17,54 . Chr18 piRNAs can bind with complementarity to Golga2 transcripts by pairing to nt 2-15 of the piRNA seed and cleaving the target 3'-UTR 18 which would lead to degradation of the transcript.…”

piRNA-mediated gene regulation and adaptation to sex-specific transposon expression inD. melanogastermale germline

“…The function of pachytene piRNAs is under active debate as no obvious targets can be easily discerned by analysis of their sequences (Aravin et al, 2006;Girard et al, 2006). Recently, knockout of one pachytene piRNA cluster led to unexpected conclusion that a small fraction of piRNAs promote biogenesis from other piRNA clusters and regulate the expression of a few host genes, while the vast majority do not target any transcripts (Wu et al, 2020). Thus, mammalian pachytene piRNAs can be considered a selfish system that occasionally involves in regulation of the host gene expression.…”

Diverse Defenses: A Perspective Comparing Dipteran Piwi-piRNA Pathways

“…Nevertheless, there is still progress to further dissect Piwi pathways in Drosophilid spermatogonia such as possible nuclear to cytoplasmic shuttling of PIWI during spermatogonia mitosis [ 85 ]. Overall though, there are much fewer studies discussing piRNA biogenesis in the Drosophila male germline [ 86 , 87 , 88 , 89 , 90 ] compared to the female germline, which we predict may also be the trend in mosquitoes if spermatogenesis development patterns are similar.…”