Practice question

Fertilization induces phosphoinositide signaling cascade generating crucial second messenger IP3. Phospholipase C isoforms, including sperm-contributed PLCζ and egg PLCγ activated by Src family tyrosine kinases downstream of sperm-receptor interaction, hydrolyze phosphatidylinositol 4,5-bisphosphate abundant in inner leaflet of plasma membrane. Cleavage yields membrane-retained diacylglycerol that activates protein kinase C and soluble inositol 1,4,5-trisphosphate that diffuses to endoplasmic reticulum. IP3 generation absolutely requires phospholipase C enzymatic catalysis; without PLC activity calcium wave fails. Protein kinase C, dynein ATPase and Na+/H+ exchanger act downstream modulating pH, cytoskeleton and motility but are not synthesizing IP3 upstream.