Tudor domain-containing protein involved in germ cell development, more specifically the formation of chromatoid body (during spermiogenesis), Balbiani body (during oogenesis), germ plasm (upon fertilization), and for proper miRNA expression and spliceosome maturation (PubMed:19345099, PubMed:27149095, PubMed:28263986) (By similarity). Essential for RNA-dependent helicase UPF1 localization to chromatoid body, for UPF1-UPF2 and UPF1-DDX4 interactions which are required for mRNA degradation, using the extended 3' UTR-triggered nonsense-mediated mRNA decay (NMD) pathway (PubMed:27149095). Involved in spliceosome maturation and mRNA splicing in prophase I spermatocytes through interaction with arginine N-methyltransferase PRMT5 and symmetrically arginine dimethylated SNRPB (small nuclear ribonucleoprotein-associated protein) (PubMed:28263986). Found in a mRNP complex (i.e. messenger ribonucleoproteins which correspond to mRNA with bound proteins), at least composed of TDRD1, TDRD6, TDRD7 and DDX4 (PubMed:17141210). Found in a complex, at least composed of PIWIL1, PIWIL2, DDX4 and TDRD6 (PubMed:19345099, PubMed:19584108, PubMed:19926723). Interacts with Tex19.1 and probably Tex19.2 (PubMed:28254886). Interacts with PRMT5 (PubMed:28263986). Interacts with SNRPB (when methylated); to trigger spliceosome formation (PubMed:28263986). Present in chromatoid body (CB) of spermatids, also named processing bodies (P-bodies) in somatic cells (PubMed:17141210, PubMed:19345099, PubMed:27149095). Detected in the multilobular cytoplasmic CBs (also called intermitochondrial cementin) in pachytene spermatocytes and as a single perinuclear CB in haploid round spermatids (PubMed:17141210, PubMed:19345099). Colocalizes in CB with DDX4, PIWIL1, PIWIL2, TDRD1 and TDRD7 (PubMed:17141210, PubMed:19345099). Testis specific. Expressed in primary spermatocytes at post natal (PN) day 17.5. Expressed in midpachytene stage of primary spermatocytes at PN16 and in round spermatids at PN22 (at protein level). The tudor domains recognize and bind to proteins with dimethylated arginine residues. Undergoes proteolytic cleavage near the C-terminal by an unknown protease during the transition from meiosis I to meiosis II in primary spermatocytes. Males are sterile (elongated spermatids are almost completely lacking), but viable (PubMed:19345099). Chromatoid body (CB) components mislocalize and CB architecture is distorted in round spermatids (PubMed:19345099). miRNA expression is altered (PubMed:19345099). Knockout spermatids are accompanied by distortion of chromatoid body structure, preventing UPF1-DDX4 and UPF1-UPF2 interactions, as well as disturbed association of several mRNAs with UPF1 and UPF2, and impaired long 3' UTR-triggered NMD (PubMed:27149095). Knockout diplotene spermatocytes display a reduction of PRMT5 association with SNRPB (also named SmB) and a reduction in arginine dimethylation of SNRPB, leading to an impairment in the assembly of spliceosomes (PubMed:28263986).