PT  - JOURNAL ARTICLE
AU  - Scott Takeo Aoki
AU  - Tina R Lynch
AU  - Sarah L Crittenden
AU  - Craig A Bingman
AU  - Marvin Wickens
AU  - Judith Kimble
TI  - Liquid droplet germ granules require assembly and localized regulators for mRNA repression
AID  - 10.1101/382838
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 382838
4099  - http://biorxiv.org/content/early/2019/07/05/382838.short
4100  - http://biorxiv.org/content/early/2019/07/05/382838.full
AB  - Cytoplasmic RNA-protein (RNP) granules have diverse biophysical properties, from liquid to solid, and play enigmatic roles in RNA metabolism. Nematode P-granules are paradigmatic liquid droplet granules and central to germ cell development. Here we analyze a key P-granule scaffolding protein, called PGL, to investigate the functional relationship between P-granule assembly and function. Using a protein-RNA tethering assay, we find that reporter mRNA expression is repressed when recruited to PGL granules. We determine the crystal structure of the PGL N-terminal region to 1.5 Å, discover its dimerization and identify key residues at the dimer interface. In vivo mutations of those interface residues prevent P-granule assembly, de-repress PGL-tethered mRNA and reduce fertility. Therefore, PGL dimerization lies at the heart of both P-granule assembly and function. Finally, we identify the P-granule-associated Argonaute WAGO-1 as crucial for repression of PGL-tethered mRNA. We conclude that P-granule function requires both assembly and localized regulators.