Tandem repeat elements such as the diverse class of satellite repeats occupy large parts of eukaryotic chromosomes, mostly at centromeric, pericentromeric, telomeric and subtelomeric regions¹. However, some elements are located in euchromatic regions throughout the genome and have been hypothesized to regulate gene expression in cis by modulating local chromatin structure, or in trans via transcripts derived from the repeats^2,3,4. 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 quickly^5,6,7, this locus was conserved for approximately 200 million years, suggesting that it has a central function in mosquito biology. piRNA production commenced shortly after egg laying, and inactivation of the more abundant piRNA resulted in failure to degrade maternally deposited transcripts in the zygote and developmental arrest. Our results reveal a mechanism by which satellite repeats regulate global gene expression in trans via piRNA-mediated gene silencing that is essential for embryonic development.

串联重复元素，如不同类别的卫星重复，占据了真核染色体的大部分，主要位于着丝粒、着丝粒周围、端粒和亚端粒区域¹。然而，一些元素位于整个基因组的常染色质区域，并被假设通过调节局部染色质结构顺式调节基因表达，或通过重复^2,3,4的转录物调节基因表达。在这里，我们表明埃及伊蚊中的卫星重复序列通过表达两个 PIWI 相互作用的 RNA (piRNA) 来促进序列特异性基因沉默。而卫星重复序列和 piRNA 序列通常进化得非常快^5,6,7, 这个基因座保存了大约 2 亿年，表明它在蚊子生物学中具有核心功能。piRNA 的产生在产卵后不久就开始了，更丰富的 piRNA 的失活导致无法降解受精卵中母体沉积的转录物和发育停滞。我们的结果揭示了卫星重复通过 piRNA 介导的基因沉默调节反式全局基因表达的机制，这对胚胎发育至关重要。