Fig. 8. Mitotic Ca²⁺ transients cannot be detected during the second embryonic division. Two-cell embryos were co-injected with Fura-2/dextran and FITC-NLS-BSA to monitor [Ca²⁺]_i and the presence of nuclei, respectively, and transferred to the microscope stage shortly before the second mitotic division. Notice the disappearance of the nucleus at mitosis entry and the formation of two new nuclei following cytokinesis. No Ca²⁺ transients were seen during the second mitotic division (n=9). A significant increase in Fura-2 ratio occurred when blastomeres were subsequently challenged with ionomycin (5 µM). Images were acquired at 10-second intervals.