Ilka B. Bischofs, Franziska Klein, Dirk Lehnert, Martin Bastmeyer and Ulrich S. Schwarz

Filamentous Network Mechanics and Active Contractility Determine Cell and Tissue Shape

Biophys. J. 95: 3488-3496, 2008

For both cells and tissues, shape is closely correlated with function,
presumably via geometry-dependent distribution of tension. Here we
identify common shape determinants spanning cell and tissue
scales. For cells whose sites of adhesion are restricted to small
adhesive islands on a micro-patterned substrate, shape resembles a
sequence of inward-curved circular arcs. The same shape is observed
for fibroblast-populated collagen gels that are pinned to a flat
substrate. Quantitative image analysis reveals that in both cases, arc
radii increase with the spanning distance between the pinning
points. Although the Laplace law for interfaces under tension does
predict circular arcs, it cannot explain the observed dependence on
the spanning distance. Computer simulations and theoretical modelling
demonstrate that filamentous network mechanics and contractility give
rise to a modified Laplace law that quantitatively explains our
experimental findings on both cell and tissue scales. Our model in
conjunction with actomyosin inhibition experiments further suggests
that cell shape is regulated by two different control modes related to
motor contractility and structural changes in the actin cytoskeleton.