Function of cAMP oscillations in Dictyostelium

Besides the role of periodic signals in the control of the chemotactic response during aggregation, there is another, no less important, function. Experiments indicate (Darmon, Brachet Pereira da Silva, 1975 Juliani Klein, 1978) that certain mutants of D. discoideum submitted to periodic stimulation at the frequency of one cAMP pulse every 5 min, aggregate normally, whereas they fail to do so in the absence of stimulation or when they are subjected to a constant cAMP signal in the course of time. 

Similar experiments carried out with the wild type (Gerisch et al, 1975) showed that periodic signals of cAMP, in contrast to constant stimuli, accelerate cell differentiation by inducing the precocious synthesis of proteins involved in the aggregation process. Initial experiments demonstrated the induction of proteins necessary for the establishment of intercellular contacts similar experiments (Klein Darmon, 1977 Juliani Klein, 1978 Chisholm, Hopkinson Lodish, 1987 Kimmel, 1987 Mann Firtel, 1987 Mann, Pinko Firtel, 1988) established that the periodic signals of cAMP induce a differentiation programme in which other proteins such as adenylate cyclase, the cAMP receptor, and phosphodiesterase are synthesized. These developmental responses depend on the periodic nature of the stimulation and do not occur when the cAMP stimulus remains constant. 

What is even more remarkable is that the effect of the periodic cAMP signals depends on their frequency. Thus, Wurster (1982) showed that the cAMP stimulation loses its efficacy when applied at the frequency of one pulse every 2 min it then becomes as ineffectual as constant signals or pulsatile signals applied in a random manner (Nanjundiah, 1988). 

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