Figure 2. NICD nuclear bodies form according to complex coacervation.

(A) Left: nuclear body intensity in HeLa cells expressing different levels of NICD. Each symbol represents an individual nuclear body. Dashed red line indicates average for 239 nuclear bodies from 30 cells. Right: histogram of nuclear body intensities. (B) NICD intensity in the surrounding nucleoplasm (non-nuclear body intensity) for 30 cells, each indicated by a single symbol. (C) NICD partition coefficient (nuclear body intensity / non-nuclear body intensity) from cells expressing different levels of NICD (239 nuclear bodies from 30 cells). (D) Histograms of the distances of closest approach between NICD molecules with and without the inclusion of Arg₆ peptides in atomistic Monte Carlo simulations. Purple bars indicate overlap between the two histograms. Inset: representative snapshot of the association of pairs of NICD molecules mediated by Arg₆ peptide (see also Figure S2B). (E) Complex coacervation model of NICD nuclear body formation. Species A (red) binds to a partner B (blue) with an affinity (K_D). The AB complex phase separates at concentrations greater than or equal to C_sat, to form droplets enriched in A and B. (F) Modeling complex coacervation of AB. When K_D = C_sat = [B]/2, phase separated AB appears sharply above a threshold concentration of A. At higher concentrations of A, the amount of phase separated AB plateaus. (G) Except at low concentrations of total A, the concentration of unbound A, which remains in the bulk phase, rises nearly linearly with total amount of A added. (H) When the droplet phase is of constant concentration (cf. Figure 2A), the partition coefficient of A (as AB complex) decreases with total A. See also Supplemental Figure S2.