Biology Reference
In-Depth Information
purely circular deformation proile away from the point of force ( Fig. 18.9 ).
Rather individual ilaments were observed to move both towards and away
from the point of force. This is in contrast to the IF network which tends
to undergo a uniform outward deformation (data presented previously
)
around the nucleus and ilaments at the cell edge do not appear to be
signiicantly deformed.
Several important characteristics are revealed through these relatively
simple experimental approaches. First, forces are transduced rapidly
through the cellular architecture. Cytoskeletal deformation occurs within
seconds of a small point load and occurring many tens of microns away from
the contact point. This has important implications to our interpretation of
locally measured mechanical properties with AFM tips as the whole cell is
responding to such point loads especially during force curve measurements.
Secondly, there appears to be an important dependence of force transduction
pathways on the species type of the cell. F-actin in human ibroblasts
does not appear to deform signiicantly in response to point loads but
the opposite is true for mouse ibroblast cells. This difference in force
transduction pathway is likely due to the 3D arrangement in F-actin in these
two cell types. F-actin tends to align along the bottom of the cell (under the
nucleus) in human ibroblasts, but in mouse ibroblasts it is found around
and above the nucleus. Therefore, force delivered via the AFM tip is more
likely to be transmitted through the F-actin in mouse ibroblasts. This
species type dependence should make it clear that “generalized” models
of cell mechanics must somehow take into account cell type. Finally, in the
case of MT deformation, it was observed that tubulin ilaments deform
both towards and away from the contact point. This is clear evidence that
the cytoskeleton is a complex mesh that cannot be considered isotropic.
Moreover, this type of behaviour was only observed in the MT cytoskeleton
and not in the F-actin or IF cytoskeletal networks. These initial studies
clearly indicate that much more work is required (such as simultaneous
visualization of more than one ilament system, quantitative ilament
tracking and inally modelling) to fully understand how force is transduced
through the 3D cytoarchitecture.
19
18.3.3 Cellular Tracon Forces in Response to Mechanical
Loading
The development of traction force microscopy (TFM) approaches has
allowed the investigation of cellular traction mechanics on substrates
 
Search WWH ::




Custom Search