Biology Reference
In-Depth Information
18.4 CONCLUSIONS AND OUTLOOK
Three examples of recent work have been presented here in which the
application of AFM and simultaneous optical imaging has yielded signiicant
insights into our understanding of cellular nanomechanics. Moreover,
using these approaches we are able to begin elucidating the architectural
deformation and force transmission pathways through the cell in two and
even three dimensions at relatively high speed. What is immediately clear is
that localized nanomechanical forces are rapidly transmitted throughout the
cellular architecture and the regulation of force transmission can be quite
complex. Mitochondria found at cell edges (often greater than 30
μ
m away
from the point of force on the nucleus) were observed to be displaced both
towards and away from the contact point, indicating that they are somehow
connected to a complex network within the cell. Treatment with drugs
which result in the speciic disassembly of actin, MTs and focal adhesions
demonstrated that all three elements of the cytoarchitecture are required
for the displacement of mitochondria in response to applied loads. The
actin and MT cytoskeletons act as the tracks upon which mitochondria
travel and respond directly to the application of forces to the cell. Moreover,
both ilament systems are required for the transmission of force to occur
along with intact focal adhesions which enable the maintenance of cellular
tension in the cytoskeleton. Loss of any one of these systems results in the
impairment of force transduction and signiicant local and global decreases
in cellular Young's modulus.
Creating cells which transiently express GFP-tagged cytoskeletal ila-
ments (actin, tubulin and IFs) has allowed us to directly visualize the
deformation of the cytoskeleton in two and three dimensions. Similar
behaviours are observed here which agree with the results on mitochondrial
displacements. All elements of the cytoskeleton appear to deform
signiicantly and rapidly in response to applied loads. Furthermore, the
deformation of the cytoskeleton occurs throughout the cell rather than at
the local point where the cell has been mechanically stimulated. Moreover,
tubulin ilaments were observed to more both towards and away from the
point of contact, indicating that force transmission through the cytoskeleton
is highly complex. Finally, there appears to be a very important species type
dependence to the force transmission pathways which govern cytoskeletal
deformation which has not been taken into account in modern models of
cell mechanics.
Finally, applied forces to cells are clearly not isotropically and
homogenously transmitted through the cell and to the substrate. This was
veriied by measuring cellular traction forces in response to applied loads.
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