Salt-dependent chromosome viscoelasticity characterized by scanning force microscopy-based volume measurements.

Metaphase chromosomes prepared according to the standard spreading procedure exhibit viscoelastical behavior after rehydration. The salt-dependency of this elasticity was investigated using contact mode scanning force microscopy (SFM). Therefore, chromosomes were imaged in solutions of different ionic strength (0.3 x PBS and water). The elasticity was probed by stepwise increase of the loading force of the scanning tip, resulting in a set of images. The images were used for the determination of the height and the apparent volume of each chromosome, and these values were the base for a characterization of the viscoelastical response of the chromosomes under different salt conditions. Lower ionic strength resulted in a greater response of the chromosome structures to applied loading forces.