Regulation of actin and myosin II during the cell cycle controls the mechanical properties of cells and triggers changes in cell shape. Current models for cell mechanics focus primarily on actomyosin in the cell cortex where F-actin and myosin II interact, and ignore possible contributions from the bulk cytoplasm in cell-cycle-regulated shape change. Therefore, Christine Field, Timothy Mitchison and co-workers (p. 2096) explore how bulk cytoplasmic actomyosin in Xenopus laevis egg extracts is regulated during the cell cycle. The authors report that gelation-contraction – a process in which bulk actin polymerises, gels into a filament network and contracts under the influence of myosin II – occurs extensively in periodic waves during the mitotic phase, but not during interphase, in a Cdk1-dependent manner. Furthermore, the authors report that actin nucleation, rather than actin disassembly and myosin II activity, is likely to be the most crucial factor for cell cycle regulation. The authors additionally demonstrate, by using live zebrafish embryos, that in vivo actin polymerisation around vesicles in the bulk cytoplasm is greatly enhanced during mitosis, which is consistent with enhanced nucleation. F-actin polymerisation in bulk cytoplasm appears, therefore, to be cell cycle regulated in early vertebrate embryos. Further studies should, the authors propose, elucidate additional details on the biophysics and regulation of actomyosin in the bulk cytoplasm.