The social amoeba Dictyostelium discoideum forages independently for bacteria in the soil. When the food is exhausted, the cells have several options - they can make resistant structures in the form of microcycts, macrocysts, or fruiting bodies. Macrocysts are reproductive structures, but have not yielded a system of genetic analysis. The PI suggests that standard strains are incompatible due to a form of parasitism, in which one mating type exploits the other. Using insertional mutagenesis and dominant drug resistance genes, he is attempting to silence the incompatibility mechanism and develop a system of reproductive genetic analysis. Insertional mutagenesis allows us to examine the nature of the genes that cause incompatibility. Fruiting bodies have an exceptionally complex development, leading to a stalk supporting a ball of viable spores. Because the stalk cells constitute 20% of the population and they die, there is competition to form a spore, rather than a stalk. The PI has used this evolutionary principle to design selection procedures which have produced mutants that form spores rather than stalk when they develop in chimeras with wild type cells. The mutated genes are being recovered and characterized. The affected genes should be central to the communication between developing cells. Dictyostelium discoideum and other social amoebae have an unusual evolutionary biology which can be applied to understanding their development.
