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RNA clamping by Vasa assembles a piRNA Amplifier complex on transposon transcripts

ABSTRACT: Germline-specific Piwi-interacting RNAs (piRNAs) protect the genome against selfish genetic elements and are essential for fertility in animals. piRNAs targeting active transposons are amplified by a feed-forward loop known as the Ping-pong cycle, which links endonucleolytic slicing of target RNAs by Piwi proteins to biogenesis of new piRNAs. However, the biochemical framework for this pathway remains elusive. Here, we describe the identification of a transient Amplifier complex mediating the biogenesis of secondary piRNAs in insect cells. This complex is nucleated by the RNA helicase Vasa and contains the two Piwi proteins participating in the Ping-pong loop, the Tudor protein Qin/Kumo and antisense piRNA guides. These components assemble on the surface of Vasa's helicase domain, which functions as an RNA clamp to anchor Amplifier onto transposon transcripts. We show that ATP-dependent RNP remodelling by Vasa facilitates the transfer of 5'-sliced piRNA precursors between the Ping-pong partners, and failure to achieve this results in Drosophila female sterility.

ORGANISM(S): Bombyx mori

PROVIDER: GSE57420 | GEO | 2014/06/04

SECONDARY ACCESSION(S): PRJNA251557

REPOSITORIES: GEO

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RNA clamping by Vasa assembles a piRNA Amplifier complex on transposon transcripts

Project description:Germline-specific Piwi-interacting RNAs (piRNAs) protect the genome against selfish genetic elements and are essential for fertility in animals. piRNAs targeting active transposons are amplified by a feed-forward loop known as the Ping-pong cycle, which links endonucleolytic slicing of target RNAs by Piwi proteins to biogenesis of new piRNAs. However, the biochemical framework for this pathway remains elusive. Here, we describe the identification of a transient Amplifier complex mediating the biogenesis of secondary piRNAs in insect cells. This complex is nucleated by the RNA helicase Vasa and contains the two Piwi proteins participating in the Ping-pong loop, the Tudor protein Qin/Kumo and antisense piRNA guides. These components assemble on the surface of Vasa's helicase domain, which functions as an RNA clamp to anchor Amplifier onto transposon transcripts. We show that ATP-dependent RNP remodelling by Vasa facilitates the transfer of 5'-sliced piRNA precursors between the Ping-pong partners, and failure to achieve this results in Drosophila female sterility. Immunoprecipitated small RNA were purified from untransfected or transfected Bmn4 cells for preparation of high-throughput sequencing libraries.

2014-06-04 | E-GEOD-57420 | biostudies-arrayexpress

RNF17 blocks promiscuous activity of PIWI proteins in mouse testes [5'RACE]

Project description: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.

2014-12-17 | GSE53915 | GEO

RNF17 blocks promiscuous activity of PIWI proteins in mouse testes

2014-12-17 | GSE53919 | GEO

High throughput sequencing of Siwi and BmAGO3 associated piRNAs from Bombyx mori BmN4 cells

Project description:In germ cells, piRNAs are amplified through the Ping-Pong cycle that depends on reciprocal Slicer-mediated target RNA cleavage by two PIWI members. A germ-specific DEAD-box protein Vasa is required for the process. However, Vasa’s function is poorly understood. Here, we show that target RNAs cleaved by a Bombyx mori (silkworm) PIWI, Siwi, remain to be bound with the protein upon cleavage, but are released in the presence of Vasa in B. mori (BmVasa) and ATP. Under normal conditions, BmVasa co-purifies with Siwi, but not with second B. mori PIWI BmAgo3. However, when BmVasa loses the ATP-binding and RNA-unwinding activities, BmVasa avidly associates with Siwi and BmAgo3, which contains transposon transcripts predominantly in sense orientation, the sources of BmAgo3-piRNAs. Without BmVasa, BmAgo3 is devoid of piRNAs. Thus, BmVasa actively releases target RNAs from Siwi, upon its cleavage, to urge BmAgo3-piRNA complex formation in the Ping-Pong cycle, enabling continuous supply of piRNAs in germ cells.

2014-12-31 | GSE58221 | GEO

A critical role for nucleoporin 358 (Nup358) in transposon silencing and piRNA biogenesis in Drosophila [RNA-Seq]

Project description:Piwi-interacting RNAs (piRNAs) are a class of small non-coding RNAs that bind Piwi proteins to silence transposons and to regulate gene expression. In Drosophila germ cells, the Aubergine (Aub)-Argonaute 3 (Ago3)-dependent ping-pong cycle generates most germline piRNAs. Loading of anti-sense piRNAs amplified by this cycle enables Piwi to enter the nucleus and silence transposons. Nuclear localization is crucial for Piwi function in transposon silencing, but how this process is regulated remains unknown. It is also not known whether any of the components of the nuclear pore complex (NPC) directly function in the piRNA pathway. Here, we show that nucleoporin 358 (Nup358) and Piwi interact with each other and that a germline knockdown (GLKD) of Nup358 with short hairpin RNA prevents Piwi entry into the nucleus. The Nup358 GLKD also activated transposons, increased genomic instability, and derailed piRNA biogenesis because of a combination of decreased piRNA precursor transcription and a collapse of the ping-pong cycle. Our results point to a critical role for Nup358 in the piRNA pathway, laying the foundation for future studies to fully elucidate the mechanisms by which Nup358 contributes to piRNA biogenesis and transposon silencing.

2018-05-14 | GSE103564 | GEO

A critical role for nucleoporin 358 (Nup358) in transposon silencing and piRNA biogenesis in Drosophila [GRO-seq]

2018-05-14 | GSE114137 | GEO

A critical role for nucleoporin 358 (Nup358) in transposon silencing and piRNA biogenesis in Drosophila [ncRNA-seq]

2018-05-14 | GSE114136 | GEO

Shutdown is a component of the Drosophila piRNA biogenesis machinery (smallRNA)

Project description:In animals, the piRNA pathway preserves the integrity of gametic genomes, guarding them against the activity of mobile genetic elements. This innate immune mechanism relies on distinct genomic loci, termed piRNA clusters, to provide a molecular definition of transposons, enabling their discrimination from genes. piRNA clusters give rise to long, single-stranded precursors which are processed into primary piRNAs through an unknown mechanism. These can engage in an adaptive amplification loop, the ping-pong cycle, to optimize the content of small RNA populations via the generation of secondary piRNAs. Many proteins have been ascribed functions in either primary biogenesis or the ping- pong cycle, though for the most part the molecular functions of proteins implicated in these pathways remain obscure. Here, we link shutdown, a gene previously shown to be required for fertility in Drosophila, to the piRNA pathway. Analysis of knockdown phenotypes in both the germ line and somatic compartments of the ovary demonstrate important roles for shutdown in both primary biogenesis and the ping-pong cycle. shutdown is a member of the FKBP family of immunophilins, with domains implicated in peptidyl-prolyl cis-trans isomerase activity and in the binding of HSP90-family chaperones. Though the relevance of these domains to piRNA biogenesis is unknown, evolutionary comparisons raise questions about the integrity of these functions in the shutdown protein. Examination of small RNA levels from nos-GAL4 or tj-GAL4 driven UAS-dsRNA knockdowns of white, shu and piwi in ovaries of Drosophila melanogaster by deep sequencing (using Illumina GAII).

2012-06-30 | E-GEOD-38089 | biostudies-arrayexpress

piRNA-mediated transgenerational inheritance of an acquired trait

Project description:The maintenance of genome integrity is an essential trait to the successful transmission of genetic information. In animal germ cells, piRNAs guide PIWI proteins to silence transposable elements (TEs) in order to maintain genome integrity. In insects, most of TE silencing in the germline is achieved by secondary piRNAs that are produced by a feed-forward loop (the ping-pong cycle), which requires the piRNA-directed cleavages of two types of RNAs: mRNAs of functional euchromatic TEs and heterochromatic transcripts that contain defective TE sequences. The first cleavage which initiates such amplification loop remains poorly understood. Taking advantage of the existence of strains that are devoid of functional copies of the LINE-like I-element, we report that in such Drosophila ovaries, the initiation of a ping-pong cycle is achieved only by secondary I-element piRNAs that are produced in the ovary and deposited in the embryonic germline. This unusual secondary piRNA biogenesis, detected in the absence of functional I-element copies, results from the processing of sense and antisense transcripts of several different defective I-elements. Once acquired, for instance after ancestor aging, this capacity to produce heterochromatic-only secondary piRNAs is partially transmitted through generations via maternal piRNAs. Furthermore, such piRNAs acting as ping-pong initiators in a chromatin-independent manner confer to the progeny a high capacity to repress the I-element mobility. Our study explains at the molecular level the basis for epigenetic memory of maternal immunity that protects females from hybrid dysgenesis caused by transposition of paternally inherited functional I-elements. Comparison of Drosophila small RNA populations in ovaries and/or eggs from 3-day-old or 25-day-old females.

2012-04-13 | E-GEOD-34506 | biostudies-arrayexpress

Binding of guide piRNA triggers methylation of the unstructured N-terminal region of Aub leading to assembly of the piRNA amplification complex

Project description:In Drosophila, Piwi proteins use guide piRNAs to repress selfish genomic elements, protecting the genomic integrity of gametes and ensuring the fertility of animal species. Efficient transposon repression depends on amplification of piRNA guides in the ping-pong cycle, which in Drosophila entails tight cooperation between two Piwi proteins, Aub and Ago3. Here we show that post-translational modification, symmetric dimethylarginine (sDMA), of Aub is essential for piRNA biogenesis, transposon silencing and fertility. Methylation is triggered by loading of a piRNA guide into Aub, which exposes its unstructured N-terminal region to the PRMT5 methylosome complex. Thus, sDMA modification is a signal that Aub is loaded with piRNA guide. Amplification of piRNA in the ping-pong cycle requires assembly of a tertiary complex scaffolded by Krimper, which simultaneously binds the N-terminal regions of Aub and Ago3. To promote generation of new piRNA, Krimp uses its two Tudor domains to bind Aub and Ago3 in opposite modification and piRNA-loading states. Our results reveal essential functions of post-translational modifications in unstructured regions of Piwi proteins and of Tudor domains capable of discriminating between modification states in piRNA biogenesis and silencing.

2020-06-25 | GSE153156 | GEO

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