Effects of progesterone and EDTA on cyclic AMP and phosphodiesterase in Dictyostelium discoideum

Abstract

WHEN Dictyostelium discoideum amoebae are nutritionally deprived, they undergo a developmental programme which results in the formation of fruiting bodies composed of spore and stalk cells. Early events in this cycle are marked by the aggregation of previously individual amoebae. During this process they become elongated, and establish specific intercellular contacts, resulting in the formation of cell streams1. Orientation of cell movement during this period is thought to be directed by an external gradient of cyclic AMP (ref. 2). This compound elicits a chemotactic response from starved cells but not from growing cells3,4 and can induce a period of coordinated movement in nutritionally deprived cells5. A phosphodiesterase is also excreted by aggregating cells6,7 activity of which modulates the cyclic AMP gradient. Thus, a general model for communication between cells during aggregation is available. Little is known, however, about the regulation of metabolic events which result in the differentiation of growth phase cells into aggregation-competent, cyclic AMP-sensitive cells, and in particular, the influence of cyclic AMP on these processes. Since in other eukaryotes, changes in internal cyclic AMP are thought to mediate the actions of a variety of hormones, and regulate cell growth and development, we investigated the possible intracellular role of this nucleotide in D. discoideum.