Localized RNAs are enriched in cytoskeletal extracts of Drosophila oocytes

Maternal mRNAs localized within the Drosophila oocyte encode positional information which specifies the pattern of the early embryo. With the goal of identifying molecules involved in RNA localization, we have developed a subcellular fractionation procedure which enriches for localized RNAs. Most RNAs and cellular proteins are solubilized by this method and are recovered in the supernatant fraction. However, five localized RNAs we examined are recovered in the detergent-insoluble pellet, despite temporal and spatial differences in their patterns of expression. These RNAs appear to be associated with a large, detergent-insoluble component of the oocyte. This association is specific for the oocyte proper, as localized RNAs in nurse cells and early embryos do not show this behavior. The fractionation behavior of these RNAs appears directly related to their localization in the oocyte, since fractionation and localization exhibit the same cytoskeletal and genetic requirements. The cortical cytoskeleton of the oocyte is a likely candidate for the localization substratum.