Using light to study localized phase separation in living cells

Liquid-liquid phase separation driven by intrinsically disordered proteins has been shown to play a key role in the assembly of diverse intracellular compartments. However, the biophysical principles by which phase separation can be precisely localized within subregions of the cell are still largely unclear, particularly for low-abundance proteins. Our lab has developed several optogenetic platforms designed for spatiotemporally-controlling phase separation in living cells. We use this technology to demonstrate how localized phase separation can be induced under intracellular protein concentrations insufficient for global phase separation. The rapid responsiveness and quantitative tunability of these systems can further be used for mapping full intracellular phase diagrams of disordered proteins, including identifying various phase transition modes, thus making it a powerful tool for elucidating phase behavior in cells.