Localization of gurken RNA in Drosophila oogenesis requires elements in the 5 ' and 3 ' regions of the transcript

During Drosophila oogenesis, signaling between the germline and the soma le ads to the establishment of polarity in the egg and embryo. This process in volves the interaction of gurken (grk), a TGF alpha-like protein, with torp edo (fog), the Drosophila EGF receptor (Egfr). In early stage egg chambers, grk RNA is present predominantly along the posterior cortex of the oocyte, and in mid stage egg chambers, the grk transcript becomes tightly localize d to the future dorsal anterior corner of the oocyte. This localization of grk RNA restricts the distribution of Gurken protein and is critical in def ining both the anterior-posterior and dorsal-ventral axes of the egg. We ha ve determined the genomic sequence of the grk gene. By testing the requirem ent of various fragments of grk RNA in the localization process, we find lo calization signals present in both the 5' and 3' regions of the gene. Seque nces in the 5' noncoding region allow for accumulation of the transcript wi thin the oocyte in early stage egg chambers, while signals in the coding re gion and the 3'UTR are necessary for localization in mid to late stage egg chambers. Active translation is not required for localization of the grk RN A. The mechanism of gurken RNA localization, therefore, differs from that o f other localized RNAs studied to date. (C) 2000 Academic Press.