Figure 1. Model of the nucleus and the cell as “a vesicle within a vesicle”, osmotically challenged.

(A) Schematic of the model and parameters used in the mathematical model: membrane tension σ, non-osmotic volume b, number (N) of macromolecules that cannot freely cross either the cell or nuclear membranes, concentration of the buffer C^out. (B) Theoretical prediction of the effect of a change in the external concentration on the N/C ratio for various ratios of normalized cellular (ν_C) and nuclear (ν_N) non-osmotic volume values keeping the cell and nuclear membrane tensions (σ^C, σ^N) constant. (C) Predictions of osmotic shifts on the N/C ratio for various nuclear membrane tensions (σ^N), keeping a high cell tension (σ^C) constant. (D) Same as (C) keeping a low membrane tension. (E) Phase diagram of the N/C ratio sensitivity to osmotic shocks defined as [max(N/C ratio)-min(N/C ratio)] / (N/C ratio_isotonic) for various ratios of non-osmotic volumes and nuclear membrane tension.