Visualization of RNP dynamics and composition in Drosophila

Localized transcripts direct asymmetric cellular processes in a wide range of biological contexts. A particularly well-studied model system has been the Drosophila oocyte, in which proper localization of mRNAs is required for successful embryo development. The germ plasm, a specialized cytoplasm enriched in ribonucleoprotein (RNP) particles, must accumulate at the posterior of the egg in order for primordial germ cells to properly segregate during embryo development.;An unanswered question has been how germ plasm RNPs maintain their localization in the oocyte: days or even weeks can pass between egg maturation and fertilization. While actin-based anchoring mechanisms have been previously implicated, we have discovered through high-resolution live imaging that, surprisingly, there is continued trafficking of germ plasm RNPs at the posterior of the oocyte. Further, this motility is required for long-term retention. Thus, we propose that anchoring may actually be a dynamic state in which motility provides robustness over long periods of developmental time (or in the face of environmental perturbations).;A second question has been how germ plasm RNPs are organized: are a number of RNA species organized into higher-order complexes or are distinct RNA species packaged into distinct granules? We have adapted a single molecule fluorescent in situ hybridization (smFISH) approach to address this question through the visualization of individual RNPs. We identified at least two "particle groups" containing distinct, non-overlapping sets of RNA species and proteins. We propose that these groupings reflect when the activity of contained transcripts is required (e.g. in the oocyte versus in the embryo).