Slime molds have such an unappealing name that it may seem hard to imagine why anyone would study them. But Dictyostelium discoideum is an unusual organism, one that straddles the boundary between the unicellular and the multicellular. Its life cycle includes individual amoeba-like cells, a multicellular migrating “slug,” and a spore-producing structure.
Dictyostelium discoideum is useful as a model because, like other model organisms, it is easy to grow in the laboratory and has a short generation time. In addition, its cells are readily accessible to microscopy and genetic studies. As a result, D. discoideum (affectionately called “Dicty” by its researchers) remains a fascinating organism. Researchers have made several discoveries in this species:
∙ Cell movement: A “Dicty” cell eats by producing extensions that engulf and absorb food particles by phagocytosis. Scientists have discovered that this movement is possible because proteins such as actin and myosin move rapidly within the cell. These same proteins produce muscle movement in animals. i muscle movement,
∙ Cytokinesis: Researchers observing cell division in D. discoideum have discovered that the protein myosin is also required for cytokinesis (the physical division of one cell into two). i cytokinesis,
∙ Chemotaxis: Starving Dicty cells move toward one another and form a multicellular “slug.” This movement toward a chemical stimulus, called chemotaxis, requires membrane proteins that not only detect the signals from other Dicty cells but also transmit the information to the inside of the cell. Similar signal transduction systems occur in many organisms. i cell
∙ Cell differentiation: When individual Dicty cells come together, chemical signals presumably determine which cells will become stalk cells (and die) and which will become spore cells (and survive). Such research may help answer questions about the origin of multicellularity. i multicellularity,