Prestalk and prespore differentiation in Dictyostelium as detected by cell type-specific monoclonal antibodies.

Monoclonal antibodies specifically reactive against prestalk and prespore cells of the cellular slime mold Dictyostelium discoideum were obtained. By the use of these antibodies, we examined processes of differentiation of the two cell types during development. Cells stained with prespore-specific antibodies first appeared after 12-14 hr of starvation within cell aggregates with tips, coincidentally with the appearance of other prespore markers. The number of prespore cells then increased to a level of 70-80% of total cells at the slug stage. By contrast, cells stained with prestalk-specific antibodies began to appear after 3 hr of starvation and thereafter increased in number to a maximum of ca. 80% after 12 hr of starvation. Stained cells appeared at random in the aggregation field and were not morphologically distinguishable from unstained cells. Furthermore, cells showed a considerable heterogeneity in the amount of antigen they contain. Concomitantly with the increase in prespore cells, the number of cells stained by the prestalk antibodies decreased to a level of ca. 20% by the slug stage. From these experiments, we suggest that the prestalk antigen is synthesized in the majority of cells during the early period of aggregation. Within tight cell aggregates, some of these cells lose the antigen to become prespore cells and the normal proportion between the two cell types will eventually result within slugs.