Mutual relation between the cell-cycle progression and prespore differentiation in Dictyostelium development

In Dictyostelium discoideum Ax-2, the cell-cycle progression from the early aggregate to mound stage has been proposed to have some connection with prespore differentiation. Hereupon, we examined the role of cell-cycle progression during the development on cell differentiation, using two kinds of cell-cycle inhibitors. Nocodazole, an inhibitor of microtubule formation, was found to inhibit greatly cell division around the mound stage as well as during the vegetative growth phase, when applied to exponentially growing Ax-2 cells. Essentially the same inhibition was attained by treatment of starved Ax-2 cells with calyculin A, an inhibitor of serine/threonine protein phosphatases. It is noteworthy that the nocodazole-or calyculin A-treated cells exhibit abnormal morphogenesis to form a stick-like multicellular structure on non-nutrient agar, and also that prespore differentiation as exemplified by the prespore-specific Dp87 gene expression and prespore specific vacuole (PSV) formation was greatly suppressed. In contrast, the differentiation of prestalk (pstA) cells was scarcely affected by the drug treatments. Taken together these results seem to indicate that the cell-cycle progression around the mound stage is important for prespore differentiation.