Cup is a nucleocytoplasmic shuttling protein that interacts with the eukaryotic translation initiation factor 4E to modulate Drosophila ovary development.

In Drosophila, the product of the fs (2)cup gene (Cup) is known to be crucial for diverse aspects of female germ-line development. Its functions at the molecular level, however, have remained mainly unexplored. Cup was found to directly associate with eukaryotic translation initiation factor 4E (eIF4E). In this report, we show that Cup is a nucleocytoplasmic shuttling protein and that the interaction with eIF4E promotes retention of the Cup protein in the cytoplasm. Cup is required for the correct accumulation and localization of eIF4E within the posterior cytoplasm of developing oocytes. We furthermore show that cup and eIF4E interact genetically, because a reduction in the level of eIF4E activity deteriorates the development and growth of ovaries bearing homozygous cup mutant alleles. Our results reveal a crucial role for the Cup-eIF4E complex in ovary-specific developmental programs.