Elasticity mapping of living fibroblasts by AFM and immunofluorescence observation of the cytoskeleton

Using the force mapping mode of atomic force microscopy (AFM), we measured spatial distribution of elastic moduli of living mouse fibroblasts (NIH3T3) in a physiological condition. The nuclear portion of the cellular surface is about 10 times softer than the surroundings. Stiffer fibers are confirme d in the elastic images. In order to investigate origin of the softer nucle ar portion and the stiffer fibers, we fixed the identical cells imaged by t he AFM, and carried out immunofluorescence observation for three types of c ytoskeletal filaments - actin filaments, microtubules, and intermediate fil aments, using confocal laser scanning microscopy (CLSM). A comparison betwe en the AFM and the CLSM images revealed that the elasticity of the cells wa s concerned not only with the distribution of actin network, but also with intermediate filaments, whereas microtubules had no large effect on the mea sured elasticity. (C) 2000 Elsevier Science B.V. All rights reserved.