Fig. 1: Chromosome mechanics are rate-dependent.

ai Examples of Bright-field and Fluorescence HILO images of Ki-67 over-expression (OE), wild-type (WT) and knock-down (KD) chromosomes in dumbbell configuration. Scale bar = 2 μm. aii Schematic of MCP load with Ki-67 expression. b Schematic of the force-extension experiments where one optical trap is displaced while the other is kept stationary, to apply stretching forces at a known speed. Fluorescence intensities of chromosomes were analysed to quantify MCP load. Individual examples of force-extension experiments at either 0.02 μm/s (bi) or 0.2 μm/s rate (bii) in WT chromosomes to illustrate the difference in response, showing linear and non-linear behaviour respectively. c Occurrence of linear and non-linear mechanical response with different force-loading rates in WT chromosomes. d Stretch modulus 'S' was acquired from chromosomes showing linear behaviour at force-extension of 0.02 μm/s (WT n = 20 chromosomes, KD n = 37 chromosomes and OE n = 24 chromosomes). e Stiffening exponent γ from chromosomes showing non-linear behaviour at force-extension of 0.2 μm/s (WT n = 36 chromosomes, KD n = 29 chromosomes and OE n = 43 chromosomes) compared to γ values for the worm-like chain (WLC) and hierarchical worm-like chain (HWLC) models. Comparisons to WT (Kruskal–Wallis test), p = 0.001. d, e Box plots; Centre: Median, Box bounds: 25th to 75th percentile, Whiskers: minimum and maximum data points (excluding outliers). Data are provided in a Source Data file.