Male germ cells express abundant endogenous siRNAs

Abstract

In mammals, endogenous siRNAs (endo-siRNAs) have only been reported in murine oocytes and embryonic stem cells. Here, we show that murine spermatogenic cells express numerous endo-siRNAs, which are likely to be derived from naturally occurring doublestranded RNA (dsRNA) precursors. The biogenesis of these testicular endo-siRNAs is DROSHA independent, but DICER dependent. These male germ cell endo-siRNAs can potentially target hundreds of transcripts or thousands of DNA regions in the genome. Overall, our work has unveiled another hidden layer of regulation imposed by small noncoding RNAs during male germ cell development.RNA interference | spermatogenesis | testis | interferon response R NA interference (RNAi) is a highly conserved gene silencing mechanism by which double-stranded RNAs (dsRNAs) are processed into single-stranded RNAs (ssRNAs) followed by loading onto effector complexes to modulate gene expression (1, 2). Small interfering RNAs (siRNAs) represent one of several distinct classes of small noncoding RNAs identified so far. Previously, siRNAs mainly referred to small ssRNAs processed in the host cells from exogenous dsRNAs (e.g., hairpin dsRNAs, synthetic short dsRNAs, etc.), and these artificial siRNAs have been widely used to suppress target gene expression both in vitro and in vivo (3-5). Endogenous siRNAs (endo-siRNAs) were initially identified in yeasts, plants, and Caenorhabditis elegans (6-9), and biogenesis of endo-siRNAs in these organisms depends on the activity of RNAdependent RNA polymerase (RdRP), which catalyzes the replication of RNA from an RNA template (8-11). Double-stranded RNAs (dsRNAs) produced by RdRP are then cleaved by the RNase III DICER to generate single-stranded mature endo-siRNAs. By associating with Argonaute (AGO) proteins, siRNAs negatively regulate the expression of targeting genes at posttranscriptional levels by inducing mRNA degradation and/or translational suppression (10-12). Alternatively, these endo-siRNAs can function as guidance molecules to direct associated protein factors to target specific genomic regions by DNA cytosine methylation or promoting the formation of heterochromatin (13,14).Although RdRP has not been found in flies or mice, certain cell types of these two species appear to be able to generate endosiRNAs by processing the naturally occurring dsRNAs (15-23). These dsRNA precursors include hairpin-dsRNAs, trans-natural antisense transcript-derived dsRNAs (trans-nat-dsRNAs), and cisnatural antisense transcript-derived dsRNAs (cis-nat-dsRNAs)

Double-stranded RNA made in C. elegans neurons can enter the germline and cause transgenerational gene silencing

“…Consistent with this possibility, small RNAs have been found in circulation in mammals (35); dsRNAs have been detected in mammalian germ cells (36)(37)(38); and injection of RNAs into the early mouse embryo can trigger epigenetic silencing (39). However, even if RNAs from somatic cells are transported to the germline in mammals, they may not always initiate transgenerational inherited effects because they have to escape mechanisms that reprogram epigenetic information in each generation (40).…”

MicroRNAs and HIV-1: Complex Interactions

“…Mammalian piRNAs number between an estimated 50,000 and 200,000 distinct entities (7); the human genome encodes ϳ2000 miRNAs (miRBase). Currently, the number of endogenous siRNAs in mammalian cells remains incompletely understood and is still poorly characterized (8). RNases that participate in the generation of these small ncRNAs include: Drosha (miRNA), Dicer (siRNA and miRNA), and Argonaute (piRNA) (Fig.…”

Petits ARN non codants et spermatogenèse

“…De multiples prédictions bio-informatiques suggèrent que les miARN modulent l'expression de près de 60 % des gènes de mammifères (pour revue voir [4] [8,9]. Jusqu'à présent, le nombre de miARN identifiés dans le testicule est évalué à 141.…”

“…Cette nouvelle classe de petits ARN non codants a été décrite dans les ovocytes [12], les cellules souches embryonnaires [13] et récemment dans les cellules germinales mâles [9]. Les données détaillant le rôle et l'importance de ces endo-siARN dans la régulation de la spermatogenèse sont toujours parcellaires, même si une étude récente a montré l'expression d'au moins 73 endo-siARN dans le testicule de souris, dont certains sont capables d'induire la dégradation d'ARNm cibles in vitro [9]. piARN : gardiens de l'intégrité génétique de la lignée germinale mâle Environ 30 à 40 % du génome des mammifères sont composés d'éléments transposables [14].…”