MAPPING ELASTICITY OF REHYDRATED METAPHASE CHROMOSOMES BY SCANNING FORCE MICROSCOPY

Scanning force microscopy was used for mapping the viscoelastic proper ties of metaphase chromosomes. These properties were probed by scannin g with various imaging forces and subsequent calculation of the differ ence image. The procedure allows a mapping of the viscoelastic behavio r expressed as force-dependent indentation of the local surface featur e and results in an image with material contrast. The approach is demo nstrated on rehydrated metaphase chromosomes, which were spread and ai r-dried before rehydration in aqueous buffer. The rehydration resulted in a swelling of the chromosome structure and was accompanied by dras tic changes in the viscoelastic properties. For comparisons, force-dis tance curves on metaphase chromosomes were accumulated; these curves w ere also used for the calculation of the stiffness curve. The demonstr ated approach of mapping viscoelasticity by differential scanning forc e microscopy allows the detection of domains with varying mechanical p roperties in biomolecules such as chromosomes.