Several factors have conspired against the imaging of the Dictyostelium cell cycle, not least the lack of markers to distinguish its different phases. But on , Muramoto and Chubb announce the creation of transgenic Dictyostelium that carry a live-cell fluorescent marker for the S phase. The role of the cell cycle during Dictyostelium development is controversial - whether differentiating cells replicate their DNA during development and the cell-cycle phase that the spores are in are matters of debate. Here, the authors report that after development is initiated, differentiating cells undergo a wave of DNA synthesis. Most spores, they reveal, are in G2, which begins after DNA synthesis and before mitosis starts. Furthermore, by inducing double-strand DNA breaks, they describe the first identified Dictyostelium checkpoint - at the G2-M transition. Since Dictyostelium has vertebrate DNA repair enzymes not present in yeast or invertebrates, these findings should illuminate future studies of the cell cycle's role in developmental processes in both Dictyostelium and other organisms.
