Cluster analysis of the cell migration in Dictyostelium

Research of eukaryotic cell motility had been based on the persistent random walk model before careful analysis of locomotion paths revealed additional features of the cell migration that lead to modifications and extensions of this standard model. The initial aim of our research was to characterize motility of cortexillin double-null cells of D. discoideum within the framework of a generalized Langevin model extended with a memory term. In the course of the analysis of wild-type and mutant cells, we noticed that cells belonging to a single strain are highly heterogeneous with respect to their mode of migration. This prompted us to perform unsupervised classification of all measured cell trajectories according to a set of attributes that quantitatively describe cell locomotion. The motile behavior of cells from two different strains, wild-type (AX2) and the strain lacking cortexillins I and II (CI-/CII-), was monitored by dark-field microscopy. For both strains, we measured the trajectories of randomly migrating vegetative and aggregation-competent cells. Migration of individual cells was characterized by a set of parameters derived from the speed distribution, the velocity autocorrelogram and the velocity periodogram. We determined that each of the four analyzed populations, i.e. AX2 and CI-/CII- cells in vegetative and aggregation-competent stages, can be divided into several homogenous subpopulations specified by the average speed and the low-frequency segment of the periodogram. CI-/CII- cells showed a larger dispersion of the average speed values relative to AX2 in both phases of their life cycle, whereas the aggregation-competent CI-/CII- cells displayed a loss of low-frequency oscillations. Finally, the motility data for each of the identified subpopulations were fitted to the generalized Langevin equation.