Fig. 3: Characterization of chromosomal viscoelasticity.

a, Typical force (top) and distance (bottom) traces of an oscillatory measurement, where the data are shown in blue and the sine fit is shown in red. b, Box plot of the loss tangent in the absence and presence of polyamines (PA; P = 0.003, two-sided t-test for related samples, N = 6 chromosomes) or PEG (P = 0.0004, N = 10 chromosomes). The box plot marks the quartiles of the distribution, the whiskers show the whole distribution and the centre line marks the median. c, Box plot of the loss tangent before and after histone depletion in the presence of polyamines (P = 0.0003, two-sided t-test for related samples, N = 8 chromosomes) or PEG (P = 0.05, N = 4 chromosomes) and absence of either (P = 0.94, N = 3 chromosomes). The box plot follows the same definition as in b. d, Loss tangent as a function of the length normalized either to the length of the decondensed chromosome or to the length of the chromosome before histone depletion. N = 12 for PEG, N = 25 for polyamines, N = 8 for histone depletion with polyamines, N = 4 for histone depletion with PEG. e, Proposed model for energy dissipation. We model the chromosome as an elastic scaffold (blue line) in parallel with an effective solution of entangled chromatin loops (grey lines) formed by condensins (red rings). The solution dominates the dissipative response of the chromosome. f, The average normalized viscous and elastic stiffness as a function of the normalized length, both normalized to the values measured for each respective decondensed chromosome. The dashed lines illustrate scalings of ℓ(50 pN)⁻² and ℓ(50 pN)⁻⁵. N = 12 chromosomes for PEG and N = 25 chromosomes for polyamines. Chromosomes for these experiments were isolated from U2OS and HCT116 cells. In d and f, the error bars show the s.e.m.