Dependence of cell shape on spatial confinement

Cell migration is one of the basic properties of almost all eukaryotic cells and is crucial in a large number of biological processes. The shape of migrating cells is primarily determined by the spatial and temporal dynamics of the intracellular actin cytoskeleton and associated proteins. However, the shape and migratory properties of cells in two-dimensional culture depend also on the specific interactions of cells with the underlying surface. It is known that amoebae Dictyostelium discoideum dynamically change their shape when migrating. In order to quantitatively classify cell shapes, one possible approach is to use descriptors based on invariant moments of mass distribution. For example, elongation (E) is equal to the ratio of the long and short radii of an ellipse that best fits the contour of a cell, and dispersion (D) describes how much mass is dispersed away from the centroid of the cell shape [1]. In order to quantify the dependence of the shape of D. discoideum cells on spatial confinement, we engineered patterned surfaces coated with anti-adhesive co-polymer PLL- g-PEG (polylysine grafted to polyethylene glycol), except for small patches of uncoated glass several square micrometers in size [2]. Contours of fluorescently labelled cells, which were deposited either onto the confined adhesive patches or onto the plain glass coverslips, were obtained by analysing the images obtained by confocal fluorescence microscopy. Comparison of the shape descriptors of confined vs. nonconfined cells showed that ranges of, and ratios between, cell elongation and dispersion values depended on the state of confinement. The methodology developed here will be useful in characterizing the role of proteins involved in the regulation of the cell- substratum adhesion and the cell shape dynamics by analysing the phenotypes of mutant cells devoid of these proteins.