Cell contact-induced inhibition of division in Dictyostelium

The developmental stage at which Dictyostelium discoideum strain v12/M2 cells was inhibited in resuming cell division was monitored by a Coulter counter. Neither vegetative nor pre-aggregating v12/M2 amoebae used as inocula in liquid growth cultures exhibited a delay in recommencing cell division. Inocula prepared from aggregates were delayed for 3 h before the onset of division. Although cyclic AMP had no effect upon vegetative or preaggregating stages the aggregating amoebae were inhibited for 9 h before resuming division. Following the onset of division by both controls and cyclic AMP-treated cells the normal growth rate of vegetative amoebae (3.2 h/generation) was attained. Aggregateless mutant vegetative amoebae and those of comparable ages to vas/M2 aggregates were not inhibited in the rate of cell division by cyclic AMP. Cyclic AMP sustains the delay in cell division only among amoebae derived from aggregates. Cyclic AMP induces structural components in the plasma membranes which may be necessary in cell adhesion and interactions. Consequently interactions between the membranes of apposing cells may transmit stimuli intracellularly to inhibit cell division.