VASA (VAS), a key protein in establishing the specialized translational activity of the Drosophila pole plasm, accumulates at the posterior pole of the developing oocyte. We identified a gene, gustavus (gus), that encodes a protein that interacts with VAS. A gus mutation blocks posterior localization of VAS, as does deletion of a segment of VAS containing the GUS binding site. Like VAS, GUS is present in cytoplasmic ribonucleoprotein particles. Heterozygotes for gus or a deletion including gus produce embryos with fewer pole cells and posterior patterning defects. Therefore, GUS is essential for the posterior localization of VAS. However, gus is not required for the posterior localization of oskar (osk). Apparent gus orthologs are present in mammalian genomes.

Bicaudal-C (Bic-C) is required during Drosophila melanogaster oogenesis for several processes, including anterior-posterior patterning. The gene encodes a protein with five copies of the KH domain, a motif found in a number of RNA-binding proteins. Using antibodies raised against the BIC-C protein, we show that multiple isoforms of the protein exist in ovaries and that the protein, like the RNA, accumulates in the developing oocyte early in oogenesis. BIC-C protein expressed in mammalian cells can bind RNA in vitro, and a point mutation in one of the KH domains that causes a strong Bic-C phenotype weakens this binding. In addition, oskar translation commences prior to posterior localization of oskar RNA in Bic-C ؊ oocytes, indicating that Bic-C may regulate oskar translation during oogenesis.Anterior-posterior polarity in Drosophila melanogaster is established during oogenesis through the asymmetric localization of many RNAs and proteins in the egg (17, 45). Localized molecules include the oskar (osk) and nanos (nos) RNAs, which are localized at the posterior of the developing oocyte during midoogenesis and are required to specify posterior pattern information (11,22,48,49). Eggs with osk or nos RNA mislocalized at the anterior produce bicaudal embryos whose posterior structures are duplicated at their anterior ends (12,14). In addition to asymmetric RNA distribution, the localization of many maternally expressed proteins occurs through translational regulation of their RNAs (30). For example, translation of osk is repressed until posterior localization of its RNA at stage 9 of oogenesis. This translational repression is mediated in part by Bruno, a protein which interacts with specific sequences (termed BREs, for Bruno response elements) in the osk 3Ј untranslated region (UTR). In oocytes produced by females with a transgene lacking BREs (osk-BRE Ϫ

The Drosophila kep1 gene encodes an RNA binding protein related to the murine QUAKING apoptotic inducer. We have previously shown that kep1 can induce apoptosis when transfected into different cell lines. To better define the role of Kep1 in apoptosis, we generated kep1 null flies. These flies were viable, but females displayed reduced fertility, with approximately half of the eggs laid from kep1؊ homozygotes failing to hatch. In addition, loss of kep1 suppressed GMR-rpr-mediated apoptosis in the Drosophila eye, and kep1 mutant flies had increased susceptibility to Escherichia coli infection. We found that Kep1 bound dredd RNA in vitro, and that extracts prepared from kep1 mutant ovaries had markedly reduced proteolytic cleavage activity toward the caspase-8 target substrate IETD-7-amino-4-trifluoromethyl coumarin. We observed increased levels of the ␤ isoform of dredd mRNA in kep1 mutants as compared with wild-type. Taken together, our results suggest that Kep1 regulates apoptosis by influencing the processing of dredd RNA.

The Drosophila gene vasa is required for pole plasm assembly and function, and also for completion of oogenesis. To investigate the role of vasa in oocyte development, we generated a new null mutation of vasa, which deletes the entire coding region. Analysis of vasa-null ovaries revealed that the gene is involved in the growth of germline cysts. In vasa-null ovaries, germaria are atrophied, and contain far fewer developing cysts than do wild-type germaria; a phenotype similar to, but less severe than, that of a null nanos allele. The null mutant also revealed roles for vasa in oocyte differentiation, anterior-posterior egg chamber patterning, and dorsal-ventral follicle patterning, in addition to its better-characterized functions in posterior embryonic patterning and pole cell specification. The anterior-posterior and dorsal-ventral patterning phenotypes resemble those observed in gurken mutants. vasa-null oocytes fail to efficiently accumulate many localized RNAs, such as Bicaudal-D, orb, oskar, and nanos, but still accumulate gurken RNA. However, GRK accumulation in the oocyte is severely reduced in the absence of vasa function, suggesting a function for VASA in activating gurken translation in wild-type ovaries.

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