Title : “ Vasa and translational control in the Drosophila germ line ”

The Drosophila protein Vasa (VAS) is essential maternally for posterior patterning and germ cell specification. In the developing ovary and embryo, VAS is mostly present in germline RNPs, a general term for large cytoplasmic ribonucleoprotein particles such as nuage particles and polar granules. These particles, and VAS specifically, are involved in localizing and regulating translation from asymmetrically distributed RNAs. To investigate the composition of germline RNPs, we have purified VAS-containing RNPs from chemically cross-linked embryo extracts and identified its components by mass spectrometry. The two major proteins present in the complex were Fat facets (FAF) and VAS. FAF is a deubiquitinating enzyme, and we observe an increase in VAS ubiquitination and a decrease in VAS levels in faf mutant extracts. In situ, VAS accumulation at the oocyte posterior is substantially reduced in faf mutant egg chambers, and most embryos produced by faf mutant females fail to form pole cells. We conclude that FAF interacts with VAS physically and reverses the ubiquitination of VAS, thereby protecting VAS from proteasomal degradation, stabilizing it in the Drosophila pole plasm. Other proteins and RNAs identified in these complexes will also be discussed.