Feedback induced biphasic response in the chemotaxis pathway of Dictyostelium

Upon uniform stimulation by the chemoattractant cAMP, Dictyostelium cells exhibit a biphasic response. Initially, a rapid rise in the localized accumulation of PI(3,4,5)P₃ is accompanied by an increase in actin polymerization. This response peaks approximately 5-10 seconds after stimulation. It is then followed by a slower, smaller phase peaking approximately two minutes after the stimulus. Until recently, the nature of this biphasic response has been poorly understood. Moreover, the origin for the secondary phase is unknown. In this paper we conjecture the existence of a feedback path between the response and stimulus. Using a mathematical model of the chemoattractant-induced response in cells, and standard tools from control engineering, we show that positive feedback may elicit this second peak. Finally, we discuss some of the literature that suggests the possible existence of this loop.