Quantitative studies on cell differentiation during morphogenesis of the cellular slime mold Dictyostelium discoideum

Taking advantage of the fact that differentiation of the prespore cell of Dictyostelium discoideum is characterized by synthesis of a prespore specific antigen, the process of its differentiation during the course of morphogenesis was quantitatively studied by determining the proportion of prespore cells and their cellular contents of the antigen, using the method of microfluorometry in combination with immunocytochemistry with antispore serum. The cells synthesizing the antigen became first detectable in the early aggregation center which was about to form a papilla. As the papilla elongated, the number of prespore cells rapidly increased up to the stationary level (70–80% of total cells) before completion of slug formation. During the process antigenic contents of prespore cells were gradually increased and leveled off in the early migration stage. When culmination was induced, antigenic contents were markedly increased to the maximum, which was followed by a sudden decrease immediately before spore formation. On the other hand, the proportions of prespore to total cells were kept constant at the stationary level all through the migration and culmination stages, in spite of a persistent decrease during culmination in the total number of cells due to continuous differentiation of the prestalk into the mature stalk cells. These results were discussed in relation to possible mechanisms of differentiation in this organism.