Propagating chemoattractant waves coordinate periodic cell movement in Dictyostelium slugs

Migration and behaviour of Dictyostelium slugs results from coordinated mov ement of its constituent cells. It has been proposed that cell movement is controlled by propagating waves of cAMP as during aggregation and in the mo und. We report the existence of optical density waves in slugs; they are in itiated in the tip and propagate backwards. The waves reflect periodic cell movement and are mediated by cAMP, as injection of cAMP or cAMP phosphodie sterase disrupts wave propagation and results in effects on cell movement a nd, therefore, slug migration. Inhibiting the function of the cAMP receptor cAR1 blocks wave propagation, showing that the signal is mediated by cAR1. Wave initiation is strictly dependent on the tip; in decapitated slugs no new waves are initiated and slug movement stops until a new tip regenerates . Isolated tips continue to migrate while producing waves. We conclude from these observations that the tip acts as a pacemaker for cAMP waves that co ordinate cell movement in slugs.