Opposing roles for Egalitarian and Staufen in transport, anchoring and localization of oskar mRNA in the Drosophila oocyte

• Published in: PLoS genetics Vol. 17; no. 4; p. e1009500
• Main Authors: Mohr, Sabine, Kenny, Andrew, Lam, Simon T. Y., Morgan, Miles B., Smibert, Craig A., Lipshitz, Howard D., Macdonald, Paul M.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 02.04.2021; Public Library of Science (PLoS)
• Subjects: Animals; Binding sites; Biology and Life Sciences; Drosophila; Drosophila melanogaster - genetics; Drosophila melanogaster - growth & development; Drosophila Proteins - genetics; Drosophila Proteins - ultrastructure; Egalitarianism; Embryos; Genetic aspects; Insects; Inverted Repeat Sequences - genetics; Localization; Messenger RNA; Mutation; Mutation - genetics; Non-coding RNA; Nurse cells; Oocytes; Oocytes - growth & development; Oogenesis; Phylogenetics; Physiological aspects; Proteins; Research and Analysis Methods; RNA transport; RNA-Binding Proteins - genetics; RNA-Binding Proteins - ultrastructure; Transcription; United States
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1009500

Localization of oskar mRNA includes two distinct phases: transport from nurse cells to the oocyte, a process typically accompanied by cortical anchoring in the oocyte, followed by posterior localization within the oocyte. Signals within the oskar 3’ UTR directing transport are individually weak, a feature previously hypothesized to facilitate exchange between the different localization machineries. We show that alteration of the SL2a stem-loop structure containing the oskar transport and anchoring signal (TAS) removes an inhibitory effect such that in vitro binding by the RNA transport factor, Egalitarian, is elevated as is in vivo transport from the nurse cells into the oocyte. Cortical anchoring within the oocyte is also enhanced, interfering with posterior localization. We also show that mutation of Staufen recognized structures (SRSs), predicted binding sites for Staufen, disrupts posterior localization of oskar mRNA just as in staufen mutants. Two SRSs in SL2a, one overlapping the Egalitarian binding site, are inferred to mediate Staufen-dependent inhibition of TAS anchoring activity, thereby promoting posterior localization. The other three SRSs in the oskar 3’ UTR are also required for posterior localization, including two located distant from any known transport signal. Staufen, thus, plays multiple roles in localization of oskar mRNA.