Correlations between prestalk-prespore tendencies and cAMP-related activities in Dictyostelium discoideum

Amoebae of the cellular slime mould Dictyostelium discoideum (strain Ax2) grown in axenic medium containing 86 mM glucose G(+) cells] or no glucose G(?) cells] were examined for the characteristics of aggregation, cAMP secretion rate, cAMP phosphodiesterase activity and cell surface cAMP-binding activity. (When G(+) and G(?) cells are mixed, G(+) cells preferentially differentiate into prespore cells and sort out to the posterior region of a slug.)Under the same conditions, G(?) cells aggregate later than G(+) cells and the formation of stable streams by G(?) cells was particularly delayed. The movements of G(?) cells during aggregation were less organized compared with the ordered behaviour of G(+) cells, yet G(?) cells seemed to be more sensitive to chemotactic signals. Furthermore, the cAMP-binding activity of G(?) cells was considerably higher than that of G(+) cells, a difference that is probably due to the difference in the number of the cAMP receptor sites. Also G(?) cells, compared to G(+) cells, secreted slightly more cAMP and showed higher activity of cell-bound phosphodiesterase activity at the aggregation stage, whereas the extracellular phosphodiesterase activity was lower, although these differences were minor.