Bicaudal-C controls the spatial and temporal expression of the nanos mRNA during Drosophila oogenesis. Chiara Gamberi^1,2, Paul Lasko². 1) Institut des Recherches Cliniques de Montreal, Montreal, PQ, Canada; 2) Department of Biology, McGill University Montreal Canada.

   nanos (nos) mRNA encodes a key determinant of posterior embryonic patterning in Drosophila. Expression of Nos is temporally and spatially regulated by several proteins that interact with its mRNA and control its translation and/or its localization to the posterior of the oocyte. We found that Bicaudal-C (Bic-C) interacts directly with an element in the nos 3 UTR, negatively regulating its expression in early to mid-oogenesis through effects on its polyadenylation, stability and translation. Bic-C mutations also cause ectopic accumulation of nos mRNA in the oocyte, possibly identifying an intermediate locale for posteriorly localized mRNAs. In Bic-C mutants, or when expressing nos transgenes that are mutated for the Bic-C interaction site, ectopic Nos is produced that accumulates in large structures in the cytoplasm of the nurse cells. We further show that, unlike in the pole plasm, oskar activity is not required for Nos expression earlier in oogenesis. These results further highlight the exquisite refinement of nos post-transcriptional regulation.