Inhibition of Differentiation in a Sporeless Mutant KS 17 of Dictyostelium discoideum

The cells of the cellular slime mold D. discoideum were harvested and suspended in salt solution and the supernatant of the cell suspension was then obtained. It was found that when the cells of the mutant strain KS17 were treated with the supernatant, differentiation into spores was inhibited, although fruits were normally formed, and that when they were treated with the highly concentrated supernatant, the differentiation into both the spores and stalks was repressed and the development ceased at the stage prior to fruiting. When the differentiation was inhibited, the cells remained in a completely undifferentiated stage. The inhibitory effect of the supernatant is due to the action of inhibiting substance secreted by the cells. The substance was secreted by the cells of all strains examined in D. discoideum. However, it only acted on KS17 cells to inhibit the differentiation.KS17 cells were treated with the supernatant at different stages of development. It was found that inhibitory effect varied remarkably with the stages. The effect was maximum at the aggregation stage and none at the migration stage. Some effect was also observed at the early culmination stage, but after this stage no effect was observed. The reason and significance of the different inhibitory effect at dif-ferent developmental stages were discussed.