Recurrent expansion and rapid evolution of the Drosophilid RNAi pathway in testis

Recurrent expansion of the RNAi effector AGO2 across ~100 Drosophila species, including lineages with ongoing AGO2 amplification, is linked to testis-biased expression.

• Why it matters: Rapidly evolving genetic conflicts require adaptable small-RNA defenses, but how broadly the Drosophila RNAi pathway expands and where it is deployed in vivo remained unclear.
• What they did: The authors analyzed >300 long-read genome assemblies across Drosophila, used transcriptome data to test testis expression bias, and applied small-RNA profiling to annotate de novo hpRNA loci in D. pseudoobscura.
• The result: They found recurrent AGO2 expansion plus extra copies of r2d2 and dicer-2 in dozens of species, with siRNAs from rampant de novo hpRNA loci in D. pseudoobscura predominantly expressed in testis.