01-P002 Highly dynamic and sex-specific expression of microRNAs during early ES cell differentiation

Nuage, a well conserved perinuclear organelle found in germline cells, is thought to mediate the repression of retroelements in Drosophila melanogaster by regulating the production of Piwiinteracting RNAs (piRNAs). Here, we present evidence that the nuage/piRNA pathway components can be found in cytoplasmic foci that also contain retroelement transcripts, anti-sense piRNAs and proteins involved in mRNA degradation. These mRNA degradation proteins, Decapping Proteins 1/2, Me31B and Pacman, are normally thought of as components of the Processing bodies. In spn-E and aub mutants where the production of piRNAs is compromised, piRNA pathway proteins no longer overlap the mRNA degradation proteins. Concomitantly, spn-E and aub mutant ovaries show a substantial accumulation of the full-length retroelement transcripts and prolonged stabilization of HeT-A mRNA, supporting a role of piRNAs in mediating post-transcriptional retroelement silencing. HeT-A mRNA is de-repressed in the canonical mRNA degradation mutants, indicating that these enzymes aid in removal of the full-length transcripts and/or decay intermediates.