Pervasive RNA localization in Drosophila ovaries. Helena Jambor, Pavel Mejstrik, Stephan Saalfeld, Pavel Tomancak. Max Planck Institute of Molecular Cell Biology and Genetics.

   Eukaryotic cells use RNA localization coupled with translational control to restrict protein activity. Localized transcripts are found in most species, but their biological role is best understood in the Drosophila ovary, where local mRNAs in the oocyte determine the embryonic body axes. Furthermore, a high number of mRNAs were shown to be asymmetrically distributed in the embryo.
   To decipher the importance of prevalent mRNA localization, we started by probing mRNA distributions globally during Drosophila oogenesis. We combined quantitative methods to probe mRNA expression with fluorescent in situ hybridization (FISH) and developed a method for high-throughput egg-chamber isolation, FISH and screening. The collected 3D-datasets are deposited into a public database along with a systematic annotation of the mRNA localization to enable analysis of the data. We analyzed the distribution of over 4000 mRNAs in the ovary, of which 70 percent are expressed and 1000 show a restricted expression domain.
   Among the candidates, we find many mRNAs that co-localize with the maternal determinants at the anterior an posterior pole and are now investigating whether their localization requires the known mRNA localization machinery. Importantly, we also observe instances of mRNAs that localize to equivalent subcellular sites in two ovarian cell types, supporting the current view that the RNA localization machinery and localization signals are re-used in different cell types. In addition, we discovered novel sites of subcellular mRNA enrichment, particularly in the nurse cell portion of the syncytial egg-chamber. Ongoing research is focused on determining whether localized mRNAs result in asymmetric protein distributions and discovering over-represented motifs responsible for the post-transcriptional regulation of co-clustered mRNAs.