An RNA-based feed-forward mechanism ensures motor switching in oskar mRNA transport

Abstract

AbstractRegulated recruitment and activity of motor proteins is essential for intracellular transport of cargoes, including ribonucleoprotein complexes (RNP). Here we show that orchestration of oskar RNP transport in the Drosophila germline relies on the interplay of two double-stranded RNA binding proteins, Staufen and the dynein adaptor Egalitarian (Egl). Following delivery of nurse cell-synthesized oskar mRNA into the oocyte by dynein, enhanced recruitment of Staufen to the RNPs results in dissociation of Egl and reduced minus end-directed transport without overtly affecting overall dynein levels on the cargo. This mechanism allows kinesin-1 to translocate the mRNA to its final destination at the posterior pole of the oocyte. Using in vitro motility assays with purified components, we find that Staufen directly antagonizes Egl-mediated activation of oskar mRNA transport by dynein. We additionally show that Egl associates with staufen mRNA in the nurse cells and mediates enrichment of the mRNA and its protein product in the ooplasm. Our observations identify a feed-forward mechanism, whereby dynein-dependent accumulation of staufen mRNA and protein in the oocyte enables motor switching during oskar mRNA transport by downregulating dynein activity.