MZnanog mutant show proper cleavages during first 3 hours of development and abnormal epiboly. The movie starts when wild-type (right) and MZnanog (left) embryos are at 4-cell stage. For visualization, the embryos were injected with SYTOX Green at 1-cell stage. Following the cleavages from 4-cell to 1k-cell stage, there is no recognizable difference between wild-type and mutant embryos. Nanog mutants undergo the cleavages with the same timing and with the same number of cycles, which we confirmed by counting cell cycles (data not shown). The movie stops after 21 hours when the mutant embryo died through yolk lysis. The movie was recorded at room temperature.