mRNA localises to the oocyte anterior by random Dynein-mediated transport and anchoring.
mRNA localises to the oocyte anterior from stage 9 of oogenesis onwards to provide a local source for Bicoid protein for embryonic patterning. Live imaging at stage 9 reveals that mRNA particles undergo rapid Dynein-dependent movements near the oocyte anterior, but with no directional bias. Furthermore, mRNA localises normally in , which abolishes the polarised microtubule organisation. FRAP and photo-conversion experiments demonstrate that the RNA is stably anchored at the anterior, independently of microtubules. Thus, mRNA is localised by random active transport and anterior anchoring. Super-resolution imaging reveals that mRNA forms 110-120 nm particles with variable RNA content, but constant size. These particles appear to be well-defined structures that package the RNA for transport and anchoring.