Evidence that phospholipase C from the sperm is not responsible for initiating Ca(2+) release at fertilization in mouse eggs.
Release of Ca(2+) from intracellular stores at fertilization of mammalian eggs is mediated by inositol 1,4,5-trisphosphate (IP3), but the mechanism by which the sperm initiates IP3 production is not yet understood. We tested the hypothesis that phospholipase C (PLC) activity introduced into the mouse egg as a consequence of sperm-egg fusion is responsible for causing Ca(2+) release. We demonstrated that microinjecting purified, recombinant PLCgamma1 protein into mouse eggs caused Ca(2+) oscillations like those seen at fertilization. However, the PLC activity in the minimum amount of purified PLCgamma1 protein needed to elicit Ca(2+) release when injected into eggs was approximately 500-900 times the PLC activity contained in a single sperm. This indicates that a single mouse sperm does not contain enough PLC activity to be responsible for causing Ca(2+) release at fertilization. We also examined whether phosphatidylinositol 3-kinase (PI3K) could have a role in this process, and found that several inhibitors of PI3K-mediated signaling had no effect on Ca(2+) release at fertilization.
Mehlmann
L M
LM
Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032, USA. lmehlman@neuron.uchc.edu
Chattopadhyay
A
A
Carpenter
G
G
Jaffe
L A
LA
D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002457:Cell Extracts; D005260:Female; D005306:Fertilization / Q000502:physiology*; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D051379:Mice; D008845:Microinjections; D008954:Models, Biological; D010063:Ovum / Q000201:enzymology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051966:Phospholipase C gamma; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000502:physiology; D013094:Spermatozoa / Q000201:enzymology*; D010738:Type C Phospholipases / Q000378:metabolism*
D002118:Calcium; D002457:Cell Extracts; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051966:Phospholipase C gamma; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D010738:Type C Phospholipases