PLCζ1-independent oocyte activation causes abnormal fertilization. (a) The percentages of oocytes with each number of PN at 12 h after insemination. (b) Intracellular Ca2+ changes in oocytes after fertilization. Ratios of GEM-GECO fluorescence of oocytes with each genotype/number of pronuclei (representatives are shown). The numbers of PN formed (top left), and the mean numbers of Ca2+ spikes observed in oocytes (bottom right) are indicated. The numbers in parentheses indicate the numbers of oocytes observed. (c) Ca2+ spikes for oocytes fertilized by a single spermatozoon from Plcz1 KO males. Numbers of Ca2+ spikes for each number of pronuclei are indicated. Oocytes with one or two PN contained significantly more spikes than 0PN oocytes (*P < 0.005). (d) Ca2+ spikes for oocytes fertilized with differing numbers of Plcz1 KO sperm. Number of Ca2+ spikes for oocytes fertilized with 2 spermatozoa contained significantly more spikes than that fertilized with a single spermatozoon (*P < 0.005). (e) The percentages of oocytes that formed PN. Percentages are based on total numbers of oocytes fertilized with indicated number of Plcz1 KO sperm.