During metazoan development, different cell lineages divide at different rates but how is the timing of cell division coupled with embryonic development? In C. elegans, lineage-specific cell-cycle duration is already apparent at the two-cell stage, when the anterior AB blastomere divides before the posterior P1 blastomere. The preferential activation of a DNA-replication checkpoint in P1 partly controls this asynchronous cell division. Now, Budirahardja and Gönczy (see p. 1303) report that the asymmetric distribution of the polo-like kinase PLK-1 (a positive mitotic regulator) also contributes to this asynchronous division. These researchers have discovered that anterior-posterior polarity cues cause PLK-1 to preferentially accumulate in AB. plk-1's mild inactivation by RNAi does not delay mitotic entry in AB but does so in P1, presumably because PLK-1's lower level in P1 makes this blastomere more sensitive to PLK-1 depletion. The researchers propose, therefore, that the PLK-1-dependent mitotic advancement in AB and the checkpoint-dependent mitotic delay in P1 together couple polarity cues and cell-cycle timing during worm development.