Cytoplasm at the posterior pole of the early Drosophila embryo, known as polar plasm, serves as a source of information necessary for germ cell determination and for specification of the abdominal region. Likely candidates for cytoplasmic elements important in one or both of these processes are polar granules, organelles concentrated in the cortical cytoplasm of the posterior pole. Females homozygous for any one of the maternal-effect mutations, tudor, oskar, staufen, vasa, or valois give rise to embryos that lack localized polar granules, fail to form the germ cell lineage and have abdominal segment deletions. Using antibodies against a polar granule component, the vasa protein, we find that vasa synthesis or localization is affected by these mutations. In vasa mutants, synthesis of vasa protein is absent or severely restricted. In oskar and staufen mutant females, vasa synthesis appears normal, but the vasa protein is not localized. In tudor and valois mutant females, vasa is localized to the posterior pole of oocytes, but this localization is lost following egg activation. In addition to the posterior localized vasa, there is a low level of vasa distributed throughout the embryo. A function for this distributed vasa is postulated based on the observation that embryos from Bicaudal-D mothers, in which abdominal determinants are incorrectly localized to the anterior pole, do not show any ectopic vasa localization, though abdomen development at the anterior end depends on the amount of vasa protein in the embryo.
Information necessary for the formation of pole cells, precursors of the germ line, is provided maternally and localized to the posterior pole of the Drosophila egg. The maternal origin and posterior localization of polar granules suggest that they may be associated with pole cell determinants. We have generated an antibody (Mab46F11) against polar granules. In oocytes and early embryos, the Mab46F11 antigen is sharply localized to the posterior embryonic pole. In pole cells, it becomes associated with nuclear bodies within, and nuage around, the nucleus. Immunoreactivity remains associated with cells of the germ line throughout the life cycle of both males and females. This antibody recognizes a 72–74 × 10(3) Mr protein and is useful both as a pole lineage marker and in biochemical studies of polar granules.