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Retrovirus insertions in host transcripts trigger de novo piRNA immunity.

Baptiste Rafanel1,2, Liudmila Protsenko1,2, Dominik Handler1

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Drosophila melanogaster developed PIWI-interacting RNA (piRNA) immunity against the Tirant retrovirus through two novel piRNA biogenesis pathways. These adaptive mechanisms enable rapid genome defense against transposable elements.

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Area of Science:

  • Genetics
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Host defense mechanisms against transposable elements are not fully understood.
  • The PIWI-interacting RNA (piRNA) pathway is crucial for transposon control in many organisms.

Purpose of the Study:

  • To investigate how Drosophila melanogaster acquired piRNA-mediated immunity against the endogenous retrovirus Tirant.
  • To elucidate the mechanisms of de novo piRNA biogenesis in response to new transposon invasion.

Main Methods:

  • Genetics
  • Small RNA sequencing
  • Population genomics
  • Analysis of transposon insertions and piRNA production

Main Results:

  • Identified two distinct pathways for de novo piRNA biogenesis against Tirant.
  • The primary pathway involves insertions into the flamenco locus, a known transposon control center.
  • A second, potent pathway arises from Tirant insertions within host gene 3' UTRs, requiring transcription but not specific gene identity.

Conclusions:

  • Host gene transcription can inadvertently initiate piRNA production when transposons insert into exons.
  • This flexible mechanism allows for rapid, adaptive genome defense against newly invading transposable elements.
  • Findings challenge existing models of piRNA precursor specification, highlighting a novel host defense strategy.