Adaptation of Chemoattractant Elicited Responses in Dictyostelium Discoideum

Abstract

During the developmental phase of the Dictyostelium life cycle, up to 10⁶ unicellular amoebae undergo aggregation to produce a multicellular structure. Aggregation is initiated by pulses of cAMP secreted by cells in the center of a territory. Surrounding cells respond by migrating up the concentration gradient toward the aggregation center and concomitantly synthesizing and secreting additional cAMP. Maximal synthesis of cAMP occurs within a few minutes of stimulation, then the rate rapidly declines due to desensitization. Extracellular phosphodiesterase degrades the secreted cAMP, and the cells subsequently resensitize, or regain the ability to be stimulated. In this way, waves of cAMP are propagated throughout the population, resulting in orderly chemotactic aggregation (Devreotes, 1982). The natural waves or oscillations are also essential for the expression of many developmentally regulated genes (Devreotes, 1982). Adaptation and subsequent resensitization of cAMP-induced processes are thus essential for multiple facets of development in this organism.