Distinct functions for the Drosophila piRNA pathway in genome maintenance and telomere protection

Drosophila aub, armi, rhi and ago3 mutations reduce total anti-sense piRNA levels and disrupt transposon silencing. All four mutations lead to maternal-effect embryonic lethality, which we show is linked to fragmentation of the zygotic genome. However, mutations in aub and armi also lead to telomere fusions, disrupt assembly of the telomere protection complex, and reduce expression of 19 to 22nt sense strand RNAs from a fourth chromosome cluster that encodes telomere-specific piRNAs. We therefore propose that abundant anti-sense piRNAs suppress transposon expression and maintain genome integrity, and that a sense strand piRNA sub-polulation directs assembly of the telomere protection complex.