Organizing principles shared between intracellular protein patterns and intracellular condensates

Intracellular protein pattern formation organizes many cell functions like cell division, cell polarity and bud-site selection. Key questions concern the nature of patterns formed, how they are oriented within the cell, and how the number and size of pattern domains are controlled. The main organizing principles are captured by (nearly) mass-conserving two-component reaction–diffusion systems. Although these reaction–diffusion dynamics operate far from equilibrium, it has much in common with the phenomenology of phase separation. In particular, their long-term dynamics can be understood as a coarsening process and its arrest. Since coarsening is a characteristic behavior of phase-separating systems, the questions of size control and number selection arise analogously for intracellular condensates formed by liquid-liquid phase separation. We show that similar concepts underlie both cellular self-organization processes and that these parallels allow us to use the same basic approaches to understand liquid-liquid phase separation and protein pattern formation.