Functions of the Tudor-domain containing protein TDRD6 in male germ cells

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Tudor domains bind methylated arginine in proteins and may bind nucleic acids. In germ cells, the molecular and cellular roles of several tudor domain bearing proteins are little understood, yet some reports indicate central and essential functions. TDRD6 is specifically expressed starting in late pachytene in spermatocytes. Initially distributed throughout the cell it concentrates during meiosis in some dispersed granule-like chromatoid bodies (CB; type I), then in spermatids it concentrates in the one perinuclear CB (type II). In the 1st funding period we identified and characterized two hitherto unknown major functions for TDRD6, both relating to large protein-RNA complexes: roles (i) in nonsense-mediated mRNA decay (NMD) and (ii) in spliceosome assembly. Our studies on TDRD6 in spermatid NMD were recently published (Fanourgakis et al., 2016), the data on the role of TDRD6 in spermatocyte splicing are submitted (Akpinar et al., 2016). Very recent data also suggest an additional nuclear localisation of TDRD6. Based on the data generated during the 1st funding period our hypothesis is that TDRD6 acts in assembling diverse RNA-related protein complexes and intracellular bodies that harbor arginine-methylated proteins. In addition, TDRD6 controls arginine methylation itself by regulating the methyl transferase PRMT5. Therefore, TDRD6 appears as a central regulator of processes in spermatogenesis, which depend on symmetric dimethylation of arginine of proteins.In the requested 2nd funding period, we plan to determine fundamental properties of TDRD6 underlying its role in protein complex assembly and its relationship to PRMT5.Our specific aims for the next funding period therefore are:(1) To understand the regulation of TDRD6 (2) To understand how TDRD6 controls PRMT5(3) To decipher the role of TDRD6 in the nucleusWe have developed a plethora of tools and methods to address these questions including TDRD6 deficiency mice, mice carrying a fully functional TDRD6-LAP transgene, mice allowing sorting of specific spermatocyte/spermatid populations, as well as RIP, chromatoid body proteomics and transcriptomics. We expect to obtain important insights into TDRD6 and PRMT5, which will in mid-term allow us to further study in detail the activities of TDRD6 complexes in NMD and splicing as well as to identify potential further roles of TDRD6.