OOCYTE POLARITY DEPENDS ON REGULATION OF GURKEN BY VASA

Vasa, a DEAD box mRNA helicase similar to eIF4A, is involved in pole p lasm assembly in the Drosophila oocyte and appears to regulate transla tion of oskar and nanos mRNAs. However, several vasa alleles exhibit a wide range of early oogenesis phenotypes. Here we report a detailed a nalysis of Vasa function during early oogenesis using novel as well as previously identified hypomorphic vasa alleles, We find that vasa is required for the establishment of both anterior-posterior and dorsal-v entral polarity of the oocyte. The polarity defects of vasa mutants ap pear to be caused by a reduction in the amount of Gurken protein at st ages of oogenesis critical for the establishment of polarity. Vasa is required for translation of gurken mRNA during early oogenesis and for achieving wild-type levels of gurken mRNA expression later in oogenes is, A variety of early oogenesis phenotypes observed in vasa ovaries, which cannot be attributed to the defect in gurken expression, suggest that vasa also affects expression of other mRNAs.