Fig. 1. Effect of U0126 and PD184352 on preimplantation development. (A) Schedule of mouse preimplantation development (top). At the time points indicated, embryos were treated with inhibitors (Drug, arrows) and observed (obs., arrowheads). The inhibitor was added at the late two-cell stage, and embryos were examined 1 day (2.5 dpc) and 2 days (3.5 dpc) later. The zona pellucida was removed before inhibitor treatment. (Below) Embryos treated with 20 µM U0126 or 5 µM PD184352 were compared with control embryos (control, DMSO and 20 µM U0124). Typical images of embryos are shown. The bottom row shows the results when U0126 treatment was allowed to continue for 24 hours but the drug was then washed out. Observation of these embryos took place at 2 and 3 days after initial treatment. (B) Reversibility of the inhibitor-induced developmental arrest. (Bottom right) Late two-cell-stage embryos shown in the bottom row were treated with 20 µM U0126 for 24 hours before the U0126 was washed out. The embryos were cultured in a drug-free medium and then observed until E4.5. The top two rows show control embryos, which were treated with DMSO (vehicle, top) or U0126 that was not washed out (middle). dpc, days post-coitum.