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(b)
(a)
Figure 18.6.
Average Young's modulus of NIH3T3 cells measured over the nucleus
with (a) pyramidal tips and (b) 19
μ
m polystyrene sphere modiied tips. Drug
treatments clearly result in a mechanical softening of the cell. Although the absolute
modulus of the cell is dependent on the tip geometry, the relative change after
treatment with each drug is similar. The results demonstrate that the cells are
becoming softer locally and globally, which has a clear impact on the transmission of
force through the cytoarchitecture.
organelles, we can infer the transmission of force through the cytosol likely
via the cytoskeleton. However, we clearly observe mitochondria moving
both towards and away from the point of force on the nucleus. This implies
that force transmission is a complex process and that the cell is not behaving
as an isotropic and homogeneous material. In the next section, we will
demonstrate the direct visualization of cytoskeletal deformation in response
to applied loads from the AFM tip with simultaneous LSCM.
18.3.2 Force Transducon Through the Cytoskeleton
Utilizing simultaneous LSCM and AFM, we have demonstrated that it is
possible to directly correlate cytoskeletal viscous deformation in response
to applied mechanical loads.
19
Control of force dissipation was visualized
by generating cells transiently expressing GFP tagged to the actin and MT
cytoskeleton. In the previous section, we inferred that NIH3T3 cells transmit
force via the cytoskeleton, resulting in the movement of mitochondria.
NIH3T3 cells were transiently transfected with 1
μ
g of plasmid DNA encoding
for actin-GFP. Utilizing a simultaneous AFM and luorescence microscope (as
described in section 18.3.1), we were able to identify a cell expressing actin-
GFP and position the AFM tip above the nucleus. Images of the cell were
then acquired before and after indentation with the AFM tip at a maximum
force of 10 nN.
Figure 18.7
shows the deformations in the actin cytoskeleton
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