A satellite repeat-derived piRNA controls embryonic development of Aedes

Tandem repeat elements such as the diverse class of satellite repeats occupy large parts of eukaryotic chromosomes, mostly at (peri)centromeric and (sub)telomeric regions(1). Some elements, however, are located in euchromatic regions throughout the genome and were hypothesized to regulate gene expression in cis by modulating local chromatin structure, or in trans via repeat-derived transcripts(2–4). Here we show that a satellite repeat in the mosquito Aedes aegypti promotes sequence-specific gene silencing via the expression of two PIWI-interacting RNAs (piRNAs). Whereas satellite repeats and piRNA sequences generally evolve extremely fast(5–7), this locus was conserved for approximately 200 million years, suggesting a central function in mosquito biology. piRNA production commenced shortly after egg-laying, and inactivation of the more abundant of the piRNAs resulted in failure to degrade maternally provided transcripts and developmental arrest. Our results reveal a novel mechanism by which satellite repeats regulate global gene expression in trans via piRNA-mediated gene silencing that is essential for embryonic development.