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

In Dictyostelium discoideum, the initial differentiation of cells is regula ted 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 dis play a prespore tendency. We found that there is a correlation between cyto solic 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 correl ation, cell cycle inhibitors influence the proportions of amoebae containin g 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 cel l cycle phase at starvation. In contrast to the wild type, a disproportiona tely large fraction of rtoA amoebae fall into the high Ca2+ class, possibly due to an altered ability of this mutant to transport Ca2+.