Fig. 2. Photorelease of cIns(1,4,5)P₃ triggers precocious mitosis entry. Fertilized one-cell embryos were microinjected with cIns(1,4,5)P₃ or water (vehicle) 32-34 hours after hCG, at which time approximately half of the embryos had undergone NEBD. Remaining interphase embryos were placed side-by-side on the microscope stage (cohorts of five to seven of each group) and exposed to UV light for 1 second. (A) An example of one such experiment in which six cIns(1,4,5)P₃-injected and six control (vehicle) embryos were simultaneously exposed to UV light. Notice the occurrence of Ca²⁺ transients in all cIns(1,4,5)P₃-injected embryos but not in controls. (B) Embryos were subsequently examined at 15 minute intervals to determine the timing of NEBD. The rate of mitosis entry was accelerated in cIns(1,4,5)P₃-injected embryos compared with controls (n=24 for both groups). Inset shows the 15 minute and 30 minute time points as bar charts. C, control; I, cIns(1,4,5)P₃. Data shown are from one of two similar replicates.