The translational repressor Cup is required for germ plasm assembly and germ cell development in Drosophila.

RNA localization is a cellular mechanism used to localize proteins to sub-cellular domains and to control protein synthesis regionally. In oocytes, RNA localization has profound implications for development, generating asymmetric protein distributions that promote morphological and functional cell polarization and establish regional fates in the future embryo. One such fate is that of the germ cell lineage. In Drosophila, germ cell formation depends on maternal inherited factors localized in the posterior pole region of oocytes and early embryos, named germ plasm. Oskar (Osk), a key determinant of germ plasm assembly, is both necessary and sufficient for germ-line formation and posterior patterning The localization of oskar (osk) mRNA starts during oogenesis and it is mediated by trans-acting factors several of which have been shown to have roles in post-transcriptional regulation of RNA, such as splicing, translational control and degradation. However, most of the molecular mechanisms underlying osk mRNA localization are still unclear (Zhou Y. and King ML, 2004). During the course of my study, I have demonstrated that Cup, a translational regulator of specific mRNAs, localizes to both nuage, a germ-line perinuclear organelle assembled during early oogenesis, and germ plasm. Moreover, Cup protein interacts with Osk and Vasa (Vas) to assure anchoring, stabilization and/or maintenance of germ plasm particles to the posterior pole of oocytes and early embryos. According to these results, homozygous cup mutant embryos display a reduced number of germ cells, respect to the heterozygous cup mutants. The latest embryos exhibit in turn less germ cells than wild type. Finally, cup and osk interact genetically, since reducing cup copy number further decreases the total number of germ cells observed in heterozygous osk mutant embryos. In this thesis, I shed light on a novel role of Cup during germ plasm assembly and germ cell development in Drosophila.