Analysis of P granules in vivo and ex vivo

Corrected version -This version can be cited. RNA granules are dynamic sub-cellular compartments that lack enveloping membranes. RNA granules have been proposed to form by liquid-liquid phase separation, a thermodynamic process that partitions molecules between dilute and condensed liquid phases. P granules are archetypal RNA granules in C. elegans that display liquid-like behaviors. Here we describe in vivo and ex vivo approaches to analyze the material properties of P granules. We find that the liquid phase of P granules is stabilized by a molecularly-distinct, enveloping shell that is intrinsically non-dynamic. Consistent with a gel phase, the shell is resistant to dilution, high salt, and aliphatic alcohols, and dissolves in SDS. Solidification of RNA granules has been linked to neuronal degeneration. Our findings suggest that gel-like polymers are essential components of RNA granules that help stabilize liquid phases in the cellular environment.