Phase segregation of passive molecules in an active fluid: Implications for molecular segregation at the cell surface

There is growing evidence that the surface of living cells behaves as an active membrane composite1,2 whose composition is actively regulated by the mechanics of cotical actin and myosin. Consequently, molecules at the cell surface could be identified based on their interaction with cortical actin: passive molecules - which bind to actomyosin filaments and inert molecules - which do not. Based on this classification1, I will introduce a theoretical framework3 to show how cortical actomyosin, as an active fluid, could drive segregation of passive molecules from inert molecules at multiple scales. The theory makes many qualitative predictions, including the existence of a novel active phase segregated state, even at temperatures higher than the equilibrium critical segregation temperature. This active phase segregated state exhibits properties very distinct from the conventional equilibrium segregated state. In particular, it shows strong fluctuation dominated phase ordering, and intermittency, as in turbulence. I will also discuss how this theoretical framework could be extended to address features of large scale actomyosin-based segregation of different cell surface molecules, observed using fluorescence-based experiments.