Cell cycle phase, cellular Ca²⁺ and development in Dictyostelium discoideum

Abstract

In Dictyostelium discoideum, the initial differentiation of cells is regulated by the phase of the cell cycle at starvation. Cells in S and early G2 (or with a low DNA content) have relatively high levels of cellular Ca²⁺ and display a prestalk tendency after starvation, whereas cells in mid to late G2 (or with a high DNA content) have relatively low levels of Ca²⁺ and display a prespore tendency. We found that there is a correlation between cytosolic Ca²⁺ and cell cycle phase, with high Ca²⁺ levels being restricted to cells in the S and early G2 phases. As expected on the basis of this correlation, cell cycle inhibitors influence the proportions of amoebae containing high or low Ca²⁺. However, it has been reported that in the rtoA mutant, which upon differentiation gives rise to many more stalk cells than spores (compared to the wild type), initial cell-type choice is independent of cell cycle phase at starvation. In contrast to the wild type, a disproportionately large fraction of rtoA amoebae fall into the high Ca²⁺ class, possibly due to an altered ability of this mutant to transport Ca²⁺.