Transposons are parasitic genetic elements that are present in all eukaryotic genomes sequenced to date. Uncontrolled expression of transposons threats the genome integrity, therefore the expression of transposons is tightly suppressed by host defence mechanisms. piRNA-guided gene silencing plays a central role in silencing transposons in animal gonads. Unlike micro-RNAs and siRNAs, piRNAs are made from single-stranded RNA by a Dicer-independent mechanism. piRNA biogenesis is highly selective for transposon anti-sense RNA, yet is thought to have a flexibility and adaptivity in order to deal with newly invaded transposon sequences. No sequence motifs or secondary structures in RNA have been shown to guide the production of piRNAs.
In the present work, we report that the RNA helicase fs(1)Yb selects substrate RNAs for piRNA production in Drosophila ovaries. Upon depletion of fs(1)Yb, piRNAs derived from the genomic locus called flamenco, which produces around a half of transposon anti-sense piRNAs, are severely reduced while other genomic loci including mRNAs start to produce more piRNAs compared to wild type cells. We will discuss about our model of how fs(1)Yb selects flamenco RNA against other cellular RNAs.