Mutations affecting piRNA system components alter snRNA levels in Drosophila ovaries. Alina P Korbut, Sergey Lavrov, Vladimir Gvozdev. Institute of Molecular Genetics, Moscow, Russian Federation.

   It is well known that piRNAs silence transposons and other types of repeats in the animal germline. Several proteins play crucial roles in the process of piRNA-mediated silencing, e.g., Argonaute proteins of Piwi subfamily, RNA helicases, and others. Piwi is one of the central proteins of the namesake pathway (piRNA for Piwi-interacting RNA). Importance of Spn-E and armitage RNA helicases is also well-established, although details concerning particular functions of those proteins in the pathway remain unclear. In order to identify new targets of piRNA system components we performed microarray-based expression profiling of Drosophila mutant ovaries where one of the listed proteins was absent due to a mitation. We didn't observe significant alterations in abundance of the majority of unique transcripts in all three mutations, but the levels of all core histone transcripts increased in PiwiNT mutant ovaries. Quantities of snRNAs tested on the microarrays, namely U2, U5, U6 also increased significantly. Those effects were confirmed by real-time PCR and Nothern blotting. The amount of U7 snRNA increase as well in case of PiwiNT mutation, according to qPCR data. We assume that observed impact on histone RNAs may be indirect, via changes of U7 snRNA level, since this type of snRNA is essential for histone mRNA maturation.