The translational repressor Cup is required for germ cell development in Drosophila

In Drosophila, germ cell formation depends on inherited maternal factors localized in the posterior pole region of oocytes and early embryos, known as germ plasm. Here, we report that heterozygous cup mutant ovaries and embryos have reduced levels of Staufen (Stau), Oskar (Osk) and Vasa (Vas) proteins at the posterior pole. Moreover, we demonstrate that Cup interacts with Osk and Vas to ensure anchoring and/or maintenance of germ plasm particles at the posterior pole of oocytes and early embryos. Homozygous cup mutant embryos have a reduced number of germ cells, compared to heterozygous cup mutants, which, in turn, have fewer germ cells than wild-type embryos. In addition, we show that cup and osk interact genetically, because reducing cup copy number further decreases the total number of germ cells observed in heterozygous osk mutant embryos. Finally, we detected cup mRNA and protein within both early and late embryonic germ cells, suggesting a novel role of Cup during germ cell development in Drosophila.