Miniproject-Proposal for the Complexity Science DTC
Till Bretschneider, Warwick Systems Biology Centre
T.Bretschneider@warwick.ac.uk
A model for cell motion based on active contours
Project outline:
Active contours are used in image processing to track deformable objects in time. We have developed a simple
mechanical model of an active contour in form of a visco-elastic contractile chain which is used to automatically
outline boundaries of migrating cells. This approach has been used to measure the spatio-temporal distribution of
fluorescently labeled proteins involved in cell motion, e.g. actin and myosin II.
The chain consists of a variable number of virtual nodes which are subject to three forces. (1) A central force pulls
all nodes inwards and is required for detecting concave structures. (2) A contraction force acting between adjacent
points confers elastic properties and ensures integrity of the chain. (3) An image force which is in the most simple
case proportional to the local contrast measured by each individual node in its local environment. This approach in
good approximation can be used to map positions along the cell outline between successive time points which has
been verified by more accurate level set methods.
The goal of the Miniproject is to relate and translate forces in the active contour model to a relevant physical
meaning in terms of quantities like membrane bending modulus, hydrostatic pressure and protrusive and retractive
forces. A simple mechanical model of the cell membrane will then be developed and ad hoc assumptions for local
forces acting on the membrane used to first simulate typical shape changes seen in moving cells. Existing spatiotemporal maps of actin and myosin distributions in the cortex of chemotaxing Dictyostelium cells will then be used
to guess the distributions of protrusion and retraction forces along the cell membrane, and tested whether the
model can reproduce the shape changes seen in the experiment.
Skills to be learnt: Modeling mechanics, programming in Matlab, image processing
References: Dormann et al. Simultaneous quantification of cell motility and protein-membrane-association
using active contours. Cell Motility & the Cytoskeleton, 52(4):221-230, 2002.
Machacek and Danuser Morphodynamic profiling of protrusion phenotypes. Biophys J., 90(4):1439-1452, 2006.
Svetina et al. A mechanism for the establishment of polar cell morphology based on the cytoskeleton-derived
forces exerted on the cell boundary. Eur Biophys J., 28:74–77, 1998.
Dalous et al. Reversal of cell polarity and actin-myosin cytoskeleton reorganization under mechanical and
chemical stimulation. Biophys. J., 94(3), in press, 2008.