Light affects cAMP signaling and cell movement activity in Dictyostelium discoideum

The multicellular, slug stage of the slime mould Dictyostelium discoideum lacks specific sensory cells and organs but can nevertheless respond in a very sensitive manner to external stimuli such as temperature and light. Within the migrating slug, the behavior of up to 100,000 individual amoebae is coordinated by cAMP mediated cell-cell signaling and chemotaxis. We report here the striking result that light directly modulates the cAMP cell-cell signaling system. Light-induced secretion of cAMP from the slug tips decreased the period length of optical density waves and speeded up cell movement. A local effect of light on cAMP release within the slug tip could modulate cell movement within the slug and thus control its phototactic turning and orientation toward a light source.