Genetic networks that regulate development in Dictyostelium cells

Genes and their RNA and protein products can be considered to be nodes in genetic networks when they are connected to two or more components by either regulatory or physical interactions. Some of the genes which have recently been shown to play essential roles in development of Dictyostelium discoideum are analyzed in terms of the networks within which they function. Development is divided into four partially overlapping stages: aggregation post-aggregation, cell type specialization, and terminal differentiation. The molecular consequences of mutations in one or mor e of these developmental genes, as well as the resulting morphological aberrations, shed light on the normal physiological processes by which the cells become mutually responsive, form mounds where prestalk and prespore cells diverge, regulate the proportions of the major cell types, and finally form fruiting bodies in which 80% of the cells are spores held up by the remaining cells within a stalk. Although only a small proportion of the total number of developmental genes in D. discoideum have been characterized to date their interactions allow us to make specific predictions concerning the network of cell type interactions. A working model is presented as a possible framework for positioning new developmental genes as they are discovered.