RNF17 blocks promiscuous activity of PIWI proteins in mouse testes

Abstract

PIWI proteins and their associated piRNAs protect germ cells from the activity of mobile genetic elements. Two classes of piRNAs-primary and secondary-are defined by their mechanisms of biogenesis. Primary piRNAs are processed directly from transcripts of piRNA cluster loci, whereas secondary piRNAs are generated in an adaptive amplification loop, termed the ping-pong cycle. In mammals, piRNA populations are dynamic, shifting as male germ cells develop. Embryonic piRNAs consist of both primary and secondary species and are mainly directed toward transposons. In meiotic cells, the piRNA population is transposon-poor and largely restricted to primary piRNAs derived from pachytene piRNA clusters. The transition from the embryonic to the adult piRNA pathway is not well understood. Here we show that RNF17 shapes adult meiotic piRNA content by suppressing the production of secondary piRNAs. In the absence of RNF17, ping-pong occurs inappropriately in meiotic cells. Ping-pong initiates piRNA responses against not only transposons but also protein-coding genes and long noncoding RNAs, including genes essential for germ cell development. Thus, the sterility of Rnf17 mutants may be a manifestation of a small RNA-based autoimmune reaction.

Germ granule-mediated RNA regulation in male germ cells

“…However, it has later been demonstrated that young, potentially active elements are enriched in pachytene piRNA clusters. These elements show a bias in orientation to enable the production of antisense piRNAs that play a role in suppressing transposons during meiosis , Hirano et al 2014, Wasik et al 2015. In addition to the transposon silencing, pachytene piRNAs have been shown to be involved in the degradation of mRNAs and lncRNAs in late meiotic and haploid cells , Goh et al 2015, Gou et al 2015, Watanabe et al 2015, Zhang et al 2015.…”

“…Therefore, the ping-pong cycle seems to be rather inactive in these cells and pachytene piRNAs are produced mainly by the primary processing pathway. In fact, a Tudor protein RNF17 has been shown to repress secondary piRNA amplification in adult gonads, and the deletion of RNF17 in mice unleashed ping-pong during meiosis and caused aberrant production of piRNAs and degradation of genic transcripts (Wasik et al 2015). Pachytene piRNAs were originally reported to be depleted from transposon sequences (Girard et al 2006).…”

“…Although MILI and MIWI have been shown to be capable of engaging in the ping-pong cycle in meiotic www.reproduction-online.org cells (Wasik et al 2015), the general analysis of pachytene piRNAs in adult testes do not show strong ping-pong signatures (Beyret et al 2012). Therefore, the ping-pong cycle seems to be rather inactive in these cells and pachytene piRNAs are produced mainly by the primary processing pathway.…”

Extensive nuclear gyration and pervasive non-genic transcription during primordial germ cell development in zebrafish

“…Ping-pong signal was determined by calculating the base pair distance between the 5' of piRNAs overlapping in opposite strands (Brennecke et al, 2007). The Z-score was calculated as in Wasik et al (Wasik et al, 2015), and is defined as Z = (P10-M)/SD, where P10 is the number of reads pairs with 10 bp overlap, and M and S are the mean and standard deviation, respectively, of the number of read pairs at with 1-9 and 11-30 overlap. Sense / Antisense bias was determined by calculating the ratio of reads mapping in the same or the opposite strand for each annotated transposable elements (DNA or RNA in repeatmasker).…”

An Evolutionarily Conserved piRNA-producing Locus Required for Male Mouse Fertility

“…Loss of proteins required to make pachytene piRNAs, including the pachytene piRNA-binding protein, MIWI (PIWIL1), invariably arrests spermatogenesis without producing sperm, rendering males sterile (Deng and Lin, 2002;Reuter et al, 2011;Zheng and Wang, 2012;Li et al, 2013;Castañeda et al, 2014;Wasik et al, 2015). Yet loss of the chromosome 17 pachytene piRNA-producing locus, 17-qA3.3-27363(−),26735(+) (henceforth, pi17), has no detectable phenotype or impact on male fertility (Homolka et al, 2015), even though pi17 produces ~16% of all pachytene piRNAs in pachytene spermatocytes.…”