zucchini and squash encode two novel components required for RNAi processes in the Drosophila germline

Attilio Pane, Kristina Wehr, Trudi Schupbach. Dept. of Molecular Biology, Princeton University, Princeton, NJ.

RNAi is a widespread mechanism by which organisms regulate gene expression and defend their genomes against viruses and transposable elements. Here we report the identification of Drosophila zucchini (zuc) and squash (squ), two members of the “spindle” class genes which function as novel factors in germline RNAi processes. zuc and squ mutant females are sterile and produce eggs with a range of dorsal-ventral defects due to the down-regulation of Gurken during oogenesis. We show that Zuc and Squ localize to the perinuclear nuage and interact with Aubergine, a protein belonging to the PIWI class of Argonaute proteins. These observations point to a function for Zuc and Squ in RNAi processes. In support of this conclusion, we find that Oskar protein is ectopically expressed in early oocytes, where it is normally silenced by RNAi mechanisms. Furthermore, mutations in zuc and squ induce the upregulation of Het-A and Tart, two telomere-specific transposable elements, and the expression of Stellate protein in the Drosophila germline. Our results demonstrate that zuc and squ are required for RNAi mediated silencing of transposable elements and tandem repeats in the germline and have profound effects on axis formation during oogenesis.

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