The cytosolic sperm factor that triggers Ca2+ oscillations and egg activation in mammals is a novel phospholipase C: PLCzeta.
When sperm activate eggs at fertilization the signal for activation involves increases in the intracellular free Ca2+ concentration. In mammals the Ca2+ changes at fertilization consist of intracellular Ca2+ oscillations that are driven by the generation of inositol 1,4,5-trisphosphate (InsP3). It is not established how sperm trigger the increases in InsP3 and Ca2+ at fertilization. One theory suggests that sperm initiate signals to activate the egg by introducing a specific factor into the egg cytoplasm after membrane fusion. This theory has been mainly based upon the observation that injecting a cytosolic sperm protein factor into eggs can trigger the same pattern of Ca2+ oscillations induced by the sperm. We have recently shown that this soluble sperm factor protein is a novel form of phospholipase C (PLC), and it is referred to as PLCzeta(zeta). We describe the evidence that led to the identification of PLCzeta and discuss the issues relating to its potential role in fertilization.
Swann
K
K
Department of Anatomy and Developmental Biology, University College London, London WC1E 6BT, UK. ucgakas@ucl.ac.uk
Larman
M G
MG
Saunders
C M
CM
Lai
F A
FA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D005260:Female; D005306:Fertilization / Q000502:physiology; D006801:Humans; D008297:Male; D008322:Mammals / Q000378:metabolism*; D051379:Mice; D010063:Ovum / Q000378:metabolism*; D051966:Phospholipase C gamma; D010738:Type C Phospholipases / Q000378:metabolism*
D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium