Receptor-mediated yolk uptake is required for oskar mRNA localization and cortical anchorage of germ plasm components in the Drosophila oocyte

TheDrosophilagerm plasm is responsible for germ cell formation. Its assembly begins with localization ofoskarmRNA to the posterior pole of the oocyte. Theoskartranslation produces 2 isoforms with distinct functions: short Oskar recruits germ plasm components, whereas long Oskar remodels actin to anchor the components to the cortex. The mechanism by which long Oskar anchors them remains elusive. Here, we report that Yolkless, which facilitates uptake of nutrient yolk proteins into the oocyte, is a key cofactor for long Oskar. Loss of Yolkless or depletion of yolk proteins disrupts the microtubule alignment andoskarmRNA localization at the posterior pole of the oocyte, whereas microtubule-dependent localization ofbicoidmRNA to the anterior andgurkenmRNA to the anterior-dorsal corner remains intact. Furthermore, these mutant oocytes do not properly respond to long Oskar, causing defects in the actin remodeling and germ plasm anchoring. Thus, the yolk uptake is not merely the process for nutrient incorporation, but also crucial foroskarmRNA localization and cortical anchorage of germ plasm components in the oocyte.