Assistant Professor in Chemical and Biological Engineering
Princeton University

Measuring the Intracellular Dew Point: Phase Transitions in Cells

Increasing evidence suggests that phase transitions play an important role in the internal organization of living cells. We have shown that a number of membrane-less RNA and protein rich organelles, known as RNP bodies, represent condensed liquid phase droplets, which assemble by liquid-liquid phase separation. The nucleolus is a liquid-like nuclear body, which plays an important role in cell growth and size homeostasis. Using the reductive cell divisions of early C.elegans embryos, we show that a simple phase threshold model explains striking features of the intrinsic coupling of nucleolar assembly to cell size. We build on these findings to develop a Cahn-Hilliard model for nucleolar phase separation, which can quantitatively account for the dynamics of nucleolar assembly, for both an in vitro reconstituted system, and within living cells. We also provide evidence that internal structure within the nucleolus, and other RNP bodies, reflects multi-phase coexistence, with a particular structural organization defined by the different droplet surface tensions. These findings suggest that sequential RNA processing steps within membrane-less RNP bodies may be facilitated by phase separation and droplet coexistence within living cells.