Cells and embryos expressing serine 88 to phenylalanine mutation undergo cell death. A) Homozygous embryos for the S88F mutation at day E3.5 appeared blebby and shrunken, indicative of cell death. An increased magnification of mutant cells undergoing apoptosis is shown. B) HT1080 cells transfected with GFP-Cdc25A-wt, GFP-Cdc25A-S88F, GFP-Cdc25-S88F/S82A or GFP-H2B control show that GFP-Cdc25A-S88F transfected cells round up and undergo cell death within 16 to 18 hours post transfection. C) Annexin V staining of HT1080 cells transfected with the same constructs as in B. The data from two independent experiments are shown.