Project Summary Recent discoveries of the phase-separation abilities of several chromatin regulators have led to novel models for chromatin organization. Directly testing the causal effects of phase-separation mechanisms requires an ability to quantitatively tune the phase-separation ability of an endogenous chromatin regulator and simultaneously test for gene expression and cell fate changes. For this goal, we will develop two tool kits: (1) a phase-dial to enhance or suppress the phase-separation potential of endogenous proteins in a quantitative and controlled manner, and (2) a robust and transferrable technological platform to correlate live imaging of phase condensates with the profiling of gene expression at the single cell level. Utilizing these tools, we will study the regulation and impact of heterochromatin formation and transcription activation during stem cell differentiation.