Practice question

Post-fertilization transformation of quiescent metaphase II oocyte into activated zygote is initiated by repetitive calcium oscillations. Sperm-delivered PLC zeta generates IP3 causing IP3 receptor-mediated calcium release from endoplasmic reticulum stores. Each transient elevates cytosolic calcium activating CaMKII and downstream pathways leading to cyclin B degradation, exit from meiosis, cortical granule exocytosis, zona hardening and recruitment of maternal mRNAs for translation. Calcium signal also triggers zinc spark release. Therefore calcium serves as universal second messenger orchestrating egg activation events, meiotic resumption, developmental reprogramming essential for embryogenesis initiation and cleavage preparation.