The role of Tudor-SN in spermatogenesis and the Piwi-piRNA pathway. Hsueh-Yen Ku, Vamsi Gangaraju, Haifan Lin. Stem Cell Center and Department of Cell Biology, Yale University School of Medicine, New Haven, CT.

   PIWI proteins associate with piRNAs and function in epigenetic programming, post-transcriptional regulation, and transposon silencing to protect germline development. Based on the size exclusion chromatography and mass-spectrometry (MS) analysis of Drosophila embryos, we identified Tudor-SN (Tudor staphylococcal nuclease, TSN), an evolutionarily conserved protein, as a PIWI-interacting protein. Tudor-SN contains five staphylococcal nuclease-like domains (SN1-SN5) and a methyl lysine/arginine recognizing Tudor (Tud) domain. Tudor-SN has been shown to participate in a variety of RNA regulations, such as RNA-induced silencing complex (RISC), cleavage of hyper-edited miRNAs, and mRNA splicing. Here we show that Tudor-SN interacts with PIWI in vivo, and they are colocalized in the primordial germ cells (PGCs) in early embryos. Tudor-SN is ubiquitously expressed and is enriched in the cytoplasm of both germline and somatic cells in ovaries and testes. In tudor-sn mutant testes, spermatocytes are overexpanded, creating an enlarged tumour-like phenotype. In addition, mature sperms are present in the apical region of the mutant testis. Further genetic analysis demonstrated piwi mutant rescues tudor-sn mutant phenotype in a dosage-dependent manner. Our results suggest that Piwi and Tudor-SN antagonize each other to ensure proper spermatogenesis in Drosophila. We are currently working on the deep sequencing of tudor-sn mutant testes to examine the role of Tudor-SN in the piRNA pathway and mRNA regulations.