Cellular Sensing of Time and Space: Chemotactic Wave Paradox and Rectification of the Leading Edge Response

Abstract

Aggregation of Dictyostelium discoideum is mediated by chemotaxis towards propagating waves of chemoattractant cAMP. Because the direction of chemoattractant gradient reversed during the wave passage, how unidirectional migration is achieved remains unresolved. Analysis of cell trajectory and the leading edge response, to exogenously applied dynamic gradients indicated that chemotactic response is rectified; i.e. it is suppressed when the attractant concentration is decreasing over time. We suggest that the upper- and lower-bounds of wave speed that allows cells to move only in the front of the wave and not the back is dictated by the timescale of the underlying reaction-diffusion process.