Biomedical Engineering Reference
In-Depth Information
atically elucidate these cell-cell interaction networks will enable the next step in
understanding biological regulation: marching up to a higher level of organiza-
tion in the vertical hierarchy of integration that characterizes complex living
organisms.
5.
CONCLUSION
Tensegrity is a principle that ensures structural stability within networks
comprised of multiple structural components, and hence governs their self-
assembly. Tensegrity is used at all size scales in the hierarchy of life, and it may
have played an important role in the mechanism by which hierarchical self-
assembly of inorganic components and small organic molecules led to formation
of living cells (38). Use of the tensegrity principle by cells also provides an en-
ergy-efficient way to build macroscopic hierarchical structures using tiers of
interconnected molecular networks (9).
On the other hand, the emergence of attractor landscapes within sparsely
connected information-processing biochemical networks provides a mechanism
for establishment of a limited number of stable network states that may have
enabled evolution to harness a wide variety of environmental signals, including
mechanical perturbation, for the regulation of cell fates. Thus, from the perspec-
tive of organismal biology, linking tensegrity-based structural networks and
physical constraints to cell fate regulation is a central requirement for the evolu-
tion of organisms of increasing size that cannot rely solely on chemical interac-
tions with their environment for control of their behavior. Living cells and
tissues must deal with macroscopic physical phenomena such as mechanical
forces, including tension, compression, shear, surface tension, and osmotic
stresses. These physical signals can regulate specific modes of cell behavior
controlled by molecular networks because of the link between structural net-
works and biochemical reactions (mechanochemistry on the cytoskeleton), and
because of the existence of information-processing networks that produce an
attractor landscape with stable states.
In both complex cellular structural networks and information networks,
simple properties emerge through the collective action of the parts that includes
mechanical and biochemical interactions. Hence the study of network properties
helps to bridge the gap between microscopic biochemistry and macroscopic
structure and behavior. Thus, elucidation of how simple, rule-governed behav-
iors (e.g., mechanical properties of cells and their behavioral control) emerge at
higher levels of organization may eventually lead to a fuller understanding of the
inner working of the living organism across many size scales. A key challenge
for a conceptual understanding of the fundamental principles of complex living
systems will be to learn when the myriad details can be abstracted away, and
when they matter. Although our work represents only a first step toward an un-
