Abstract
To examine the effects of intra- and extranuclear mechanical environment on cell differentiation, we investigated the changes in the morphology and mechanical properties of the nucleus, and dynamics of intranuclear DNA in Saos-2 osteoblastic cells during their calcification process. In uncalcified control cells, their actin filaments distributed entirely in the cell body. In contrast, they rearranged their location and distributed at cell periphery in the calcified cells. The nuclear area, height, and volume were significantly decreased during the calcification. In the control cells, release of the intracellular force by the depolymerization of cytoskeletons induced an increase in the nuclear height, and it induced a decrease in the nuclear area in the calcified cells. An indentation test for nuclear surface using atomic force microscope demonstrated that the nuclei did not change their average elastic moduli in the calcification process, and they tended to be uniform in their mechanical properties. Fluorescence recovery after photobleaching of GFP-labeled histon 2B revealed that the intranuclear DNA was more stable in the calcified cells than in the control. These results may indicate that the changes in compressive force applied to the nucleus arising from the rearrangement of cytoskeletons affect the mechanical environment of the nucleus, and its change may affect gene expression and DNA replication in calcification process of Saos-2 cells.
