Digital image processing of optical density wave propagation in Dictyostelium discoideum and analysis of the effects of caffeine and ammonia

Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum were analyzed by digital image processing in a manner that immediately shows the following parameters: wave propagation velocity, period length, wave amplitude und wave shape. We have characterized the aggregation of AX-2 and the streamer F mutant NP 377 in terms of these parameters and investigated the influence of caffeine and ammonia. It was found that during normal aggregation oscillation frequency increases while at the same time wave propagation velocity decreases. Caffeine, a known inhibitor of cyclic AMP relay, reduces oscillation frequency and wave propagation velocity in a dose-dependent manner but most notably leads to the appearance of bimodal (harmonic) oscillations. These bimodal waves are also found in streamer F mutants without caffeine during early aggregation. The effect of caffeine is interpreted as an increase in the average chemotactic deadaptation time due to elevated cyclic GMP levels after a cyclic AMP stimulus. This increased deadaptation time results in some cells responding to every chemotactic signal, while others respond only to every second signal, leading to mixed population behavior and hence biphasic optical density waves. Ammonia has no significant influence on oscillation frequency and wave propagation velocity but shows a clear increase in the amplitude of the optical density waves. This may indicate a more vigorous chemotactic response by individual cells or a better synchronization of the responding cell populations due to shortened chemotactic deadaptation times

Analysis of optical density wave propagation and cell movement in the cellular slime mould Dictyostelium discoideum

We have studied optical density wave propagation during aggregation of the cellular slime mould Dictyostelium discoideum in a quantitative manner by digital image analysis. The waves are mostly single ended spiral waves starting from an aggregation center. We can measure a variety of parameters such as oscillation frequency, wave propagation velocity and wave shape. This allows the construction of dispersion curves under a variety of experimental conditions. During later development where the optical density waves are no longer visible we have started to measure movement of fluorescently labelled cells. Our main conclusions from these measurements are that the cells continue to move chemotactically to periodic signlas both in aggregates and in slugs. There is a dramatic difference in the movement pattern of prestalk and prespore cells: Prestalk cells move perpendicular to the long axis of the slug, they are most likely organized by a scroll wave. Prespore cells seem to move almost perpendicular to the prestalk cells, in the direction of the tip. This behaviour is explained on the basis of different relay properties of prespore and prestalk cells

Multiarmed Spirals in Excitable Media

Numerical studies of the properties of multiarmed spirals show that they can form spontaneously in low excitability media. The maximum number of arms in a multiarmed spiral is proportional to the ratio of the single spiral period to the refractoriness of the medium. Multiarmed spirals are formed due to attraction of single spirals if these spirals rotate in the same direction and their tips are less than one wavelength apart, i.e., a spiral broken not far from its tip can evolve into a 2-armed spiral. We propose this mechanism to be responsible for the formation of multiarmed spirals in mounds of the slime mold Dictyostelium discoideum

Coarsening Dynamics of Crystalline Thin Films

The formation of pyramid-like structures in thin-film growth on substrates with a quadratic symmetry, e.g., {001} surfaces, is shown to exhibit anisotropic scaling as there exist two length scales with different time dependences. Analytical and numerical results indicate that for most realizations coarsening of mounds is described by an exponent n=0.2357. However, depending on material parameters, n may lie between 0 (logarithmic coarsening) and 1/3. In contrast, growth on substrates with triangular symmetries ({111} surfaces) is dominated by a single length scale and an exponent n=1/3.Comment: RevTeX, 4 pages, 3 figure

A gradient method for the quantitative analysis of cell movement and tissue flow and its application to the analysis of multicellular Dictyostelium development

We describe the application of a novel image processing method, which allows quantitative analysis of cell and tissue movement in a series of digitized video images. The result is a vector velocity field showing average direction and velocity of movement for every pixel in the frame. We apply this method to the analysis of cell movement during different stages of the Dictyostelium developmental cycle. We analysed time-lapse video recordings of cell movement in single cells, mounds and slugs. The program can correctly assess the speed and direction of movement of either unlabelled or labelled cells in a time series of video images depending on the illumination conditions. Our analysis of cell movement during multicellular development shows that the entire morphogenesis of Dictyostelium is characterized by rotational cell movement. The analysis of cell and tissue movement by the velocity field method should be applicable to the analysis of morphogenetic processes in other systems such as gastrulation and neurulation in vertebrate embryos