Figure 11.

Model of aggregate size regulation in Dictyostelium by adenosine and caffeine. A) At the aggregation stage, adenosine may be decreasing extracellular cAMP accumulation, favouring cell growth and this might be due to enhanced TOR activity and increased cell movement and cell adhesion by increasing the cytosolic glucose concentration. Collectively all these parameters cause large aggregate formation in the presence of adenosine. B) Inactivation of TOR complex by caffeine leads to reduction in cell number and cell size. Caffeine increases countin expression acting on unknown upstream targets resulting in increased cell movement. Low levels of extracellar cAMP, faster cell movement and few cells available for aggregation are plausible reasons for small sized aggregate formation with caffeine. The compactness of the aggregate is maintained by expression of cell adhesion protein CsaA mainly.