Cell—Cell Interactions in the Development of Dictyostelium

Abstract

Dictyostelium discoideum is a cellular slime mold that, because of its intricate life cycle (Fig. 1), has attracted the attention of developmental biologists. With an adequate supply of food, amoebae of D. discoideum will grow and divide as individual cells. When the food supply is depleted (in the laboratory, this is accomplished by removing a nutrient broth or bacteria), the amoebae cease growing and enter into a developmental program. There is a period of protein synthesis and, if the amoebae are on a solid surface, this is followed by the cAMP-mediated aggregation of 10⁵–10⁶ amoebae into a single mound. This mound becomes encased in slime (hence the name slime mold) and sends up a fingerlike projection that eventually includes most of the amoebae. This projec tion falls over onto the agar surface and begins to crawl; this is the pseudoplasmodial or slug stage. During this migration, the amoebae differentiate into either prestalk or prespore cells. After a period of time determined by genetic and environmental factors, the prestalk cells that form the anterior section of the slug cease moving, while the prespore cells located in the posterior section of the slug continue migrating until another moundlike structure is formed. The prestalk cells then begin depositing cellulosic walls and push down through the prespore cells to the agar surface, forming a stalk. When the cells are in their proper position and differentiation is complete, the stalk cells die, leaving their walls to support a ball-like structure that contains the mature spores.