Figure 1. Dictyostelium discoideum, a simple eukaryotic amoeba. (a) Dictyostelium is found in leaf litter on forest floors. The mature fruiting body is around 1 mm tall, and composed of spore head, stalk and basal disc cells. Bar, 0.5 mm. Kindly provided by Owen Gilbert. (b) It can be cultured in the laboratory on a bacterial lawn whereby single cells form circular isogenic plaques as shown, or in liquid culture. (c) Dictyostelium single cells, here showing one cell expressing a green fluorescent-tagged cytosolic protein (prolyl oligopeptidase). Bar, 10 m. Reproduced from Williams (2005), by permission of Elsevier.

Figure 2. Dictyostelium can be used for analysis of drug-sensitive signalling pathways and drug targets. (a) Wild-type cells form fruiting bodies over a 24-h period. (b) The drug valproic acid, a short chain fatty acid used for bipolar disorder and epilepsy treatment, blocks cell aggregation at 1 mM – close to therapeutic concentrations. (c) Use of a clonal line of Dictyostelium containing a dominant active protein kinase A (PKA) enzyme overcomes this block, suggesting the signalling pathway containing this enzyme may be reduced by the drug. (d) Dictyostelium cells form immature fruiting bodies after 18 h of development, a process which is also blocked (e) in the presence of 0.5 mM VPA or (f) with novel drugs based around the structure of VPA. Bar, 0.5 mm. See also Boeckeler et al., (2006).