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Unistrand piRNA clusters are an evolutionarily conserved mechanism to suppress endogenous retroviruses across the Drosophila genus.

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van Lopik, Jasper 
Trapotsi, Maria-Anna 


The PIWI-interacting RNA (piRNA) pathway prevents endogenous genomic parasites, i.e. transposable elements, from damaging the genetic material of animal gonadal cells. Specific regions in the genome, called piRNA clusters, are thought to define each species' piRNA repertoire and therefore its capacity to recognize and silence specific transposon families. The unistrand cluster flamenco (flam) is essential in the somatic compartment of the Drosophila ovary to restrict Gypsy-family transposons from infecting the neighbouring germ cells. Disruption of flam results in transposon de-repression and sterility, yet it remains unknown whether this silencing mechanism is present more widely. Here, we systematically characterise 119 Drosophila species and identify five additional flam-like clusters separated by up to 45 million years of evolution. Small RNA-sequencing validated these as bona-fide unistrand piRNA clusters expressed in somatic cells of the ovary, where they selectively target transposons of the Gypsy family. Together, our study provides compelling evidence of a widely conserved transposon silencing mechanism that co-evolved with virus-like Gypsy-family transposons.



Humans, Animals, Female, Drosophila, Piwi-Interacting RNA, Endogenous Retroviruses, Drosophila Proteins, RNA, Small Interfering, Argonaute Proteins, DNA Transposable Elements, Drosophila melanogaster

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Nat Commun

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Nature Portfolio
Wellcome Trust (110161/Z/15/Z)
Royal Society (RSRP\R\200001)
Cancer Research UK (C14303/A17197)
Cancer Research UK (21143)
Cancer Research UK (C9545/A29580_do not transfer)
GJH is a Royal Society Wolfson Research Professor (RSRP\R\200001). This research was funded in whole, or in part, by Cancer Research UK (A21143) and the Wellcome Trust (110161/Z/15/Z).