Shutdown is a component of the Drosophila piRNA biogenesis machinery (smallRNA)

In animals, the piRNA pathway preserves the integrity of gametic genomes, guarding them against the activity of mobile genetic elements. This innate immune mechanism relies on distinct genomic loci, termed piRNA clusters, to provide a molecular definition of transposons, enabling their discrimination from genes. piRNA clusters give rise to long, single-stranded precursors which are processed into primary piRNAs through an unknown mechanism. These can engage in an adaptive amplification loop, the ping-pong cycle, to optimize the content of small RNA populations via the generation of secondary piRNAs. Many proteins have been ascribed functions in either primary biogenesis or the ping- pong cycle, though for the most part the molecular functions of proteins implicated in these pathways remain obscure. Here, we link shutdown, a gene previously shown to be required for fertility in Drosophila, to the piRNA pathway. Analysis of knockdown phenotypes in both the germ line and somatic compartments of the ovary demonstrate important roles for shutdown in both primary biogenesis and the ping-pong cycle. shutdown is a member of the FKBP family of immunophilins, with domains implicated in peptidyl-prolyl cis-trans isomerase activity and in the binding of HSP90-family chaperones. Though the relevance of these domains to piRNA biogenesis is unknown, evolutionary comparisons raise questions about the integrity of these functions in the shutdown protein. Overall design: Examination of small RNA levels from nos-GAL4 or tj-GAL4 driven UAS-dsRNA knockdowns of white, shu and piwi in ovaries of Drosophila melanogaster by deep sequencing (using Illumina GAII).