Involved in the localization of vas to the posterior pole of the oocyte. Required maternally in the germ line for efficient primordial germ cell formation. Interacts (via B30.2/SPRY domain) with vas; this interaction may be necessary for the transport of vas to the posterior pole of the oocyte. Interacts with Cul-5. May associate with the Elongin BC complex composed of Elongin-B and Elongin-C. Component of the cytoplasmic ribonucleoprotein (RNP) bodies which concentrate at the perinuclear region of the nurse cell and in punctate aggregates throughout the cytoplasm. Some cortical enrichment of these aggregates is also observed. At stage 7, accumulates in the anterior cytoplasm of the oocyte, whereas during stage 10 accumulates at the posterior pole. This posterior distribution is not maintained in later developmental stages. Expressed in ovaries, primarily in nurse cells and oocytes (at protein level). Expressed during oogenesis, in early embryos (0 to 4 hours) and in fertile adult females (at protein level). Homozygous females produce defective eggs, which desiccate and collapse soon after egg laying, or embryos, which hatch very rarely. Mutants exhibit wing morphology defects, including blistering, formation of ectopic vein material, and loss of material at the margin. Belongs to the SPSB family. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus.