Project description:In metazoan gonads, transposable elements (TEs) mobilization is limited by PIWI-interacting RNAs (piRNAs). These small RNAs originate from specific source loci, the piRNA clusters. piRNAs are known to silence TEs in the cells where they are produced. Endogenous retroviruses (ERVs), a subclass of TEs, pose a particular threat because they are capable of transiting from cell to cell. In this study, we reveal that piRNAs produced locally in germ cells counteract invasion by ERVs arriving from adjacent somatic cells. We reactivated the Drosophila ERVZAMin somatic gonadal cells by deleting, using CRISPR-Cas9 genome editing, its single copy in the somaticflamencopiRNA cluster, while keeping the piRNA pathway fully functional. Upon reactivation,ZAMinvaded the oocytes, resulting in transposition and severe fertility defects. We show that onceZAM-piRNAs are produced in germ cells they counter the invasion. Our study sheds new light on the mechanisms of recognition and regulation of invasive genetic elements, which is essential for the maintenance of genome integrity.
Project description:In metazoan gonads, transposable elements (TEs) mobilization is limited by PIWI-interacting RNAs (piRNAs). These small RNAs originate from specific source loci, the piRNA clusters. piRNAs are known to silence TEs in the cells where they are produced. Endogenous retroviruses (ERVs), a subclass of TEs, pose a particular threat because they are capable of transiting from cell to cell. In this study, we reveal that piRNAs produced locally in germ cells counteract invasion by ERVs arriving from adjacent somatic cells. We reactivated the Drosophila ERV ZAM in somatic gonadal cells by deleting, using CRISPR-Cas9 genome editing, its single copy in the somatic flamenco piRNA cluster, while keeping the piRNA pathway fully functional. Upon reactivation, ZAM invaded the oocytes, resulting in transposition and severe fertility defects. We show that once ZAM-piRNAs are produced in germ cells they counter the invasion. Our study sheds new light on the mechanisms of recognition and regulation of invasive genetic elements, which is essential for the maintenance of genome integrity.
Project description:In metazoan gonads, transposable elements (TEs) mobilization is limited by PIWI-interacting RNAs (piRNAs). These small RNAs originate from specific source loci, the piRNA clusters. piRNAs are known to silence TEs in the cells where they are produced. Endogenous retroviruses (ERVs), a subclass of TEs, pose a particular threat because they are capable of transiting from cell to cell. In this study, we reveal that piRNAs produced locally in germ cells counteract invasion by ERVs arriving from adjacent somatic cells. We reactivated the Drosophila ERV ZAM in somatic gonadal cells by deleting, using CRISPR-Cas9 genome editing, its single copy in the somatic flamenco piRNA cluster, while keeping the piRNA pathway fully functional. Upon reactivation, ZAM invaded the oocytes, resulting in transposition and severe fertility defects. We show that once ZAM-piRNAs are produced in germ cells they counter the invasion. Our study sheds new light on the mechanisms of recognition and regulation of invasive genetic elements, which is essential for the maintenance of genome integrity.
Project description:BACKGROUND:For species survival, the germline must faithfully transmit genetic information to the progeny. Transposable elements (TEs) constitute a significant threat to genome stability due to their mobility. In the metazoan germline, their mobilization is limited by a class of small RNAs called PIWI-interacting RNAs (piRNAs) produced by dedicated genomic loci called piRNA clusters. Although the piRNA pathway is an adaptive genomic immunity system, it remains unclear how the germline gains protection from a new transposon invasion. RESULTS:To address this question, we analyze Drosophila melanogaster lines harboring a deletion within flamenco, a major piRNA cluster specifically expressed in somatic follicular cells. This deletion leads to derepression of the retrotransposon ZAM in the somatic follicular cells and subsequent germline genome invasion. In this mutant line, we identify de novo production of sense and antisense ZAM-derived piRNAs that display a germinal molecular signature. These piRNAs originated from a new ZAM insertion into a germline dual-strand piRNA cluster and silence ZAM expression specifically in germ cells. Finally, we find that ZAM trapping in a germinal piRNA cluster is a frequent event that occurs early during the isolation of the mutant line. CONCLUSIONS:Transposons can hijack the host developmental process to propagate whenever their silencing is lost. Here, we show that the germline can protect itself by trapping invading somatic-specific TEs into germline piRNA clusters. This is the first demonstration of "auto-immunization" of a germline endangered by mobilization of a surrounding somatic TE.
Project description:Transposable elements (TEs), whose propagation can result in severe damage to the host genome, are silenced in the animal gonad by Piwi-interacting RNAs (piRNAs). piRNAs produced in the ovaries are deposited in the embryonic germline and initiate TE repression in the germline progeny. Whether the maternally transmitted piRNAs play a role in the silencing of somatic TEs is, however, unknown. Here we show that maternally transmitted piRNAs from the tirant retrotransposon in Drosophila are required for the somatic silencing of the TE and correlate with an increase in histone H3K9 trimethylation an active tirant copy. Comparison of tirant piRNAs in two Drosophila simulans natural populations.
Project description:Transposable elements (TEs), whose propagation can result in severe damage to the host genome, are silenced in the animal gonad by Piwi-interacting RNAs (piRNAs). piRNAs produced in the ovaries are deposited in the embryonic germline and initiate TE repression in the germline progeny. Whether the maternally transmitted piRNAs play a role in the silencing of somatic TEs is, however, unknown. Here we show that maternally transmitted piRNAs from the tirant retrotransposon in Drosophila are required for the somatic silencing of the TE and correlate with an increase in histone H3K9 trimethylation an active tirant copy.
Project description:Piwi-interacting RNAs (piRNAs) silence transposons in animal germ cells. piRNAs are thought to derive from long transcripts spanning transposon-rich genomic loci and to direct an autoamplification loop in which an antisense piRNA, bound to Aubergine or Piwi protein, triggers production of a sense piRNA bound to the PIWI protein Argonaute3 (Ago3). In turn, the new piRNA is envisioned to produce a second antisense piRNA. Here, we describe strong loss-of-function mutations in ago3, allowing a direct genetic test of this model. We find that Ago3 acts to amplify piRNA pools and to enforce on them an antisense bias, increasing the number of piRNAs that can act to silence transposons. We also detect a second, Ago3-independent piRNA pathway centered on Piwi. Transposons targeted by this second pathway often reside in the flamenco locus, which is expressed in somatic ovarian follicle cells, suggesting a role for piRNAs beyond the germline.