Manifestations of multicellularity: Dictyostelium reports in

The recent release of the Dictyostelium genome sequence is important because Dictyostelium has become a much-favoured model system for cell and developmental biologists. The sequence has revealed a remarkably high total number of approximately 12 500 genes, only a thousand fewer than are encoded by Drosophila. Previous protein-sequence comparisons suggested that Dictyostelium is evolutionarily closer to animals and fungi than to plants, and the global protein sequence comparison, now made possible by the genome sequence, confirms this. This review focuses on several classes of proteins that are shared by Dictyostelium and animals: a highly sophisticated array of microfilament components, a large family of G-protein-coupled receptors and a diverse set of SH2 domain-containing proteins. The presence of these proteins strengthens the case for a relatively close relationship with animals and extends the range of problems that can be addressed using Dictyostelium as a model organism.