| Tudor domains are found in many organisms and have been implicated in protein-protein interactions in which methylated protein substrates bind to these domains. Here, we present evidence for the involvement of specific Tudor domains in germline development. Drosophila Tudor, the founder of the Tudor domain family, contains 11 Tudor domains and is a component of polar granules and nuage, electron-dense organelles characteristic of the germline in many organisms, including mammals. In this study, we investigated whether the 11 Tudor domains fulfill specific functions for polar granule assembly, germ cell formation and abdomen formation. We find that even a small number of non-overlapping Tudor domains or a substantial reduction in overall Tudor protein is sufficient for abdomen development. In stark contrast, we find a requirement for specific Tudor domains in germ cell formation, Tudor localization and polar granule architecture. Tudor domains consist of four β-strands that fold into a barrel-like structure. Structural analysis and sequence alignment of an individual Drosophila Tudor domain confirms the presence of an aromatic cage, which is crucial for recognition and binding to methylated targets. Recent studies show that Aubergine (Aub), a germline-specific Argonaute protein, contains symmetric dimethl-arginines (sDMAs), and that Aub associates with Tudor through its sDMA modification. To test if individual Tudor domains play specific roles in germ cell formation and in Aub association, we mutated aromatic residues in individual Tudor domains. Aub localization and stability are affected when the aromatic cage in Tudor domain 8 or 10 is mutated but only D10 affects germ cell formation, suggesting that Aub localization is not sufficient for germ cell formation. |
