Fertilization and the signaling of egg activation

After receiving the LH surge, a mature oocyte (egg) is collected in the oviduct of mammalian females. Following fusion of the gametes, the sperm elicits in the egg repeated calcium (Ca²⁺+) transients known as oscillations, which trigger egg activation. Completion of egg activation renders the meiotic and transcriptionally silent egg into a mitotically competent, transcriptionally active zygote that eventually undergoes cell differentiation and embryo development. Here, we discuss the major events of egg activation and the molecular players that underlie them. We describe the universal role of Ca²⁺+ on egg activation as well as the egg’s Ca²⁺+ toolkit. We explain how failure of egg activation results in infertility, and the value of ICSI and genetic models in identifying the molecular causes of this infertility. Finally, we point to areas where additional research is needed and how this knowledge will allow better control of fertility.