The disordered P granule protein LAF-1 drives phase separation into droplets with tunable viscosity and dynamics

TLDR

Phase transitions are key for intracellular organization, yet the molecular interactions and resulting condensed phases remain poorly understood. The study identifies LAF‑1’s role in the liquid phase separation of P granules, RNA/protein assemblies implicated in germ‑line maintenance. Microrheology techniques were adapted to measure the precise viscoelastic properties of LAF‑1 liquid droplets. Electrostatic interactions of disordered protein generate droplets with tunable material properties, and RNA fluidizes these droplets by lowering viscosity and increasing internal dynamics, illustrating how molecular interactions can produce adaptable liquid organelles.

Abstract

Significance Phase transitions have recently emerged as a key mechanism for intracellular organization. However, the underlying molecular interactions and nature of the resulting condensed phases are poorly understood. Here, we identify a role for LAF-1 in the liquid phase separation of P granules—RNA/protein assemblies implicated in germ-line maintenance. We adapt microrheology techniques to measure precise viscoelastic properties of LAF-1 liquid droplets. Our experiments reveal that electrostatic disordered protein interactions give rise to droplets with tunable material properties. RNA can fluidize protein droplets by decreasing the viscosity and increasing internal molecular dynamics. Our results provide insight into the mechanism by which molecular level interactions can give rise to liquid phase organelles with tunable material properties, potentially underlying biologically adaptable functions.