IP3 Responsiveness Is Regulated in a Meiotic Cell Cycle Dependent Manner: Implications for Fertilization Induced Calcium Signalling

Fertilization of mammalian eggs is known to trigger a series of transient rises in cytosolic calcium, known as calcium oscillations, the initiation and duration of which are crucial for meiotic exit and subsequent entry into embryogenesis. It is not known how these calcium oscillations are terminated when the zygote exits meiosis; it is thought that responsiveness to inositol 1,4,5-trisphosphate (IP3) is involved, since the oscillations are known to be mediated by an IP3 dependent mechanism. Here we report that IP3 responsiveness is maintained throughout meiotic maturation and falls very rapidly after meiotic exit. We also show that inhibition of the major cell cycle kinase, CDK1, has no effect on responsiveness, but that prolonging CDK1 activity prevents the decline in responsiveness normally seen at meiotic exit. We conclude that CDK1 plays a role, but is not the only factor involved in controlling IP3 responsiveness during the meiotic cell cycle.