The interplay between the Argonaute proteins Piwi and Aub within Drosophila germarium is critical for oogenesis, piRNA biogenesis and TE silencing

Transposable elements (TEs) have invaded most genomes and constitute up to 50%of the human genome. Machinery based on small non-coding piRNAs has evolved toinhibit their expression at the transcriptional and post-transcriptional levels.Surprisingly, this machinery is weakened during specific windows of time in mice,flies or plants, allowing the expression of TEs in germline cells. The function of thisde-repression remains unknown. In Drosophila, we have previously shown that thisdevelopmental window is characterized by a reduction of Piwi expression in dividinggerm cells. Here, we show that the unique knock-down of Aub in these cells leads tofemale sterility. It correlates with defects in piRNA amplification, an increased Piwiexpression and an increased silencing of transcriptionally silenced TEs. Thesedefects are similar to those observed when Aub is depleted in the whole germlinewhich underlies the crucial role of this developmental window for both oogenesis andTE silencing. We further show that, with age, some fertility is recovered which isconcomitant to a decrease of Piwi and TE silencing. These data pinpoint the Pilp as atremendously important step for female fertility and genome stability. They furthershow that such a restricted developmental niche of germ cells may senseenvironmental changes, such as ageing, to protect the germline all along the life.