Phase transitioned nuclear Oskar promotes cell division of Drosophila primordial germ cells

• Published in: eLife Vol. 7
• Main Authors: Kistler, Kathryn E, Trcek, Tatjana, Hurd, Thomas R, Chen, Ruoyu, Liang, Feng-Xia, Sall, Joseph, Kato, Masato, Lehmann, Ruth
• Format: Journal Article
• Language: English
• Published: England eLife Science Publications, Ltd 27.09.2018; eLife Sciences Publications Ltd; eLife Sciences Publications, Ltd
• Subjects: Animals; Biology; Cell adhesion & migration; Cell Biology; Cell cycle; Cell Differentiation - genetics; Cell division; Cell Division - genetics; Cell fate; Cell Nucleus - genetics; Clonal deletion; Cytoplasmic Granules - genetics; Displays (Marketing); Drosophila; Drosophila melanogaster - genetics; Drosophila melanogaster - growth & development; Drosophila Proteins - genetics; Eggs; Embryo; Embryonic development; Embryonic Development - genetics; Embryos; Gene Expression Regulation, Developmental; Gene regulation; Genes; Genetic regulation; Germ cells; Germ Cells - growth & development; Germ Cells - metabolism; germ granules; Granule cells; Hydrogels; Insects; Localization; mebraneless RNP granules; Microscopy; Oskar protein; phase transition; Phase transitions; Post-transcription; Proteins; Statistical analysis; Synergism; Transcription (Genetics); New York; United States > US; Oskar protein; cell biology; germ granules; mebraneless RNP granules; phase transition; D. melanogaster; germ cells
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.37949

Germ granules are non-membranous ribonucleoprotein granules deemed the hubs for post-transcriptional gene regulation and functionally linked to germ cell fate across species. Little is known about the physical properties of germ granules and how these relate to germ cell function. Here we study two types of germ granules in the Drosophila embryo: cytoplasmic germ granules that instruct primordial germ cells (PGCs) formation and nuclear germ granules within early PGCs with unknown function. We show that cytoplasmic and nuclear germ granules are phase transitioned condensates nucleated by Oskar protein that display liquid as well as hydrogel-like properties. Focusing on nuclear granules, we find that Oskar drives their formation in heterologous cell systems. Multiple, independent Oskar protein domains synergize to promote granule phase separation. Deletion of Oskar’s nuclear localization sequence specifically ablates nuclear granules in cell systems. In the embryo, nuclear germ granules promote germ cell divisions thereby increasing PGC number for the next generation.