mRNA localization and ER-based protein sorting mechanisms dictate the use of transitional endoplasmic reticulum-golgi units involved in gurken transport in Drosophila oocytes.
The anteroposterior and dorsoventral axes of the future embryo are specified within Drosophila oocytes by localizing gurken mRNA, which targets the secreted Gurken transforming growth factor-alpha synthesis and transport to the same site. A key question is whether gurken mRNA is targeted to a specialized exocytic pathway to achieve the polar deposition of the protein. Here, we show, by (immuno)electron microscopy that the exocytic pathway in stage 9-10 Drosophila oocytes comprises a thousand evenly distributed transitional endoplasmic reticulum (tER)-Golgi units. Using Drosophila mutants, we show that it is the localization of gurken mRNA coupled to efficient sorting of Gurken out of the ER that determines which of the numerous equivalent tER-Golgi units are used for the protein transport and processing. The choice of tER-Golgi units by mRNA localization makes them independent of each other and represents a nonconventional way, by which the oocyte implements polarized deposition of transmembrane/secreted proteins. We propose that this pretranslational mechanism could be a general way for targeted secretion in polarized cells, such as neurons.
Herpers
Bram
B
The Cell Microscopy Centre, Department of Cell Biology, University Medical Centre Utrecht, 3584CX Utrecht, The Netherlands.
Rabouille
Catherine
C
D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004058:Diffusion; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D004530:Egg Yolk; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005089:Exocytosis; D006056:Golgi Apparatus / Q000378:metabolism*; D017403:In Situ Hybridization; D008854:Microscopy, Electron; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism*; D021381:Protein Transport; D034443:RNA Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D016211:Transforming Growth Factor alpha / Q000235:genetics / Q000378:metabolism*
D029721:Drosophila Proteins; D012333:RNA, Messenger; D016211:Transforming Growth Factor alpha; C083730:grk protein, Drosophila