Practice question

IP3 production begins locally where sperm fuses with egg membrane. Src kinase activated at fusion site phosphorylates PLC-gamma anchored near plasma membrane, triggering rapid hydrolysis of PIP2 precisely at entry cortex. Using fluorescent pleckstrin homology domain sensors, investigators observe PIP2 depletion at sperm entry point first. IP3 then diffuses inward toward ER rich in IP3 receptors, initiating calcium release first near entry and propagating as wave across egg via calcium-induced calcium release. Animal or vegetal pole initiation does not occur unless sperm fuses there. Nuclear production would be too distant for rapid wave initiation across large egg.