Protein components of ribonucleoprotein granules from Drosophila germ cells oligomerize and show distinct spatial organization during germline development

Abstract

The assembly of large RNA-protein granules occurs in germ cells of many animals and these germ granules have provided a paradigm to study structure-functional aspects of similar structures in different cells. Germ granules in Drosophila oocyte’s posterior pole (polar granules) are composed of RNA, in the form of homotypic clusters, and proteins required for germline development. In the granules, Piwi protein Aubergine binds to a scaffold protein Tudor, which contains 11 Tudor domains. Using a super-resolution microscopy, we show that surprisingly, Aubergine and Tudor form distinct clusters within the same polar granules in early Drosophila embryos. These clusters partially overlap and, after germ cells form, they transition into spherical granules with the structural organization unexpected from these interacting proteins: Aubergine shell around the Tudor core. Consistent with the formation of distinct clusters, we show that Aubergine forms homo-oligomers and using all purified Tudor domains, we demonstrate that multiple domains, distributed along the entire Tudor structure, interact with Aubergine. Our data suggest that in polar granules, Aubergine and Tudor are assembled into distinct phases, partially mixed at their “interaction hubs”, and that association of distinct protein clusters may be an evolutionarily conserved mechanism for the assembly of germ granules.

Glial granules contain germline proteins in the Drosophila brain, which regulate brain transcriptome

“…Glial granules, described in this work, show distinct clusters of their protein components whose roles were mainly restricted to the development of germ cells where they assemble in membraneless RNA-protein granules (germ granules). Recently, it was shown that germ granules in Drosophila germ plasm are assembled from distinct partially overlapping protein and RNA homotypic clusters 5,7,8 . Similar to germ granules, glial granules show distinct protein clusters, which partially overlap, suggesting that the mechanisms of the assembly of glial granules is similar to germ granules.…”

“…ermline (germ) cells give rise to every cell type in the nextgeneration organism after the union of the egg and sperm 1,2 , and they express specific proteins and RNA that are assembled into large and dynamic membraneless granules referred to as germ granules [3][4][5][6][7][8][9] . Components of germ granules are required for germline fate 1,9,10 .…”

Patterning the Drosophila embryo: A paradigm for RNA‐based developmental genetic regulation

“…Polar granule targeting and assembly into homotypic clusters appears to involve different 3′ UTR elements, at least for pgc RNA (Eagle, Yeboah‐Kordieh, Niepielko, & Gavis, 2018). A more recent study indicates that two polar granule proteins, Aub and Tud, also form distinct clusters within the granules (Vo et al, 2019).…”

Modulation of Aub–TDRD interactions elucidates piRNA amplification and germplasm formation

“…Somatic development in the absence of Tud still takes place, but germ granule mRNPs do not assemble, and PGCs are not induced ( 31 ). Among TDRDs, Tud has the largest number of eTUD domains that interact with sDMAs of Aub ( 33 , 49 ). Along with Aub–piRNA binding of mRNAs ( 35 ), these multivalent interactions are critical for germ granule mRNP assembly.…”