Proclaiming fate in the early mouse embryo.

In the mouse embryo, the first differences between cells that result in distinct lineages have long been thought to arise only as a consequence of differential cell positioning at relatively late preimplantation stages. Differences in Oct4 transcription factor kinetics between cells at the 4-8-cell stage are now shown to be predictive of future lineages, providing further evidence for much earlier initiation of cell fate decisions.