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Scaffold proteins play crucial roles in subcellular organization and function. In many organisms, proteins with multiple Tudor domains are required for the assembly of membraneless RNA–protein organelles (germ granules) in germ cells. Tudor domains are protein–protein interaction modules which bind to methylated polypeptides.DrosophilaTudor protein contains 11 Tudor domains, which is the highest number known in a single protein. The role of each of these domains in germ cell formation has not been systematically tested, and it is not clear if some domains are functionally redundant. Using CRISPR methodology, we generated mutations in several uncharacterized Tudor domains and showed that they all caused defects in germ cell formation. Mutations in individual domains affected Tudor protein differently, causing reduction in protein levels and defects in subcellular localization and in the assembly of germ granules. Our data suggest that multiple domains of Tudor protein are all needed for efficient germ cell formation, highlighting the rational for keeping many Tudor domains in protein scaffolds of biomolecular condensates inDrosophilaand other organisms. 

Abstract Scaffold proteins play crucial roles in subcellular organization and function. In many organisms, proteins with multiple Tudor domains are required for the assembly of membraneless RNA-protein organelles (germ granules) in germ cells. Tudor domains are protein-protein interaction modules which bind to methylated polypeptides.DrosophilaTudor protein contains eleven Tudor domains, which is the highest number known in a single protein. The role of each of these domains in germ cell formation has not been systematically tested and it is not clear if some domains are functionally redundant. Using CRISPR methodology, we generated mutations in several uncharacterized Tudor domains and showed that they all caused defects in germ cell formation. Mutations in individual domains affected Tudor protein differently causing reduction in protein levels, defects in subcellular localization and in the assembly of germ granules. Our data suggest that multiple domains of Tudor protein are all needed for efficient germ cell formation highlighting the rational for keeping many Tudor domains in protein scaffolds of biomolecular condensates inDrosophilaand other organisms. 

Abstract Membraneless RNA-protein granules play important roles in many different cell types and organisms. In particular, granules found in germ cells have been used as a paradigm to study large and dynamic granules. These germ granules contain RNA and proteins required for germline development. Here, we unexpectedly identify large granules in specific subtypes of glial cells (“glial granules”) of the adult Drosophila brain which contain polypeptides with previously characterized roles in germ cells including scaffold Tudor, Vasa, Polar granule component and Piwi family proteins. Interestingly, our super-resolution microscopy analysis shows that in the glial granules, these proteins form distinct partially overlapping clusters. Furthermore, we show that glial granule scaffold protein Tudor functions in silencing of transposable elements and in small regulatory piRNA biogenesis. Remarkably, our data indicate that the adult brain contains a small population of cells, which express both neuroblast and germ cell proteins. These distinct cells are evolutionarily conserved and expand during aging suggesting the existence of age-dependent signaling. Our work uncovers previously unknown glial granules and indicates the involvement of their components in the regulation of brain transcriptome.