Regulation of diacylglycerol production and protein kinase C stimulation during sperm- and PLCzeta-mediated mouse egg activation.
BACKGROUND
At fertilization in mammalian eggs, the sperm induces a series of Ca(2+) oscillations via the production of inositol 1,4,5-trisphosphate. Increased inositol 1,4,5-trisphosphate production appears to be triggered by a sperm-derived PLCzeta (phospholipase C-zeta) that enters the egg after gamete fusion. The specific phosphatidylinositol 4,5-bisphosphate hydrolytic activity of PLCzeta implies that DAG (diacylglycerol) production, and hence PKC (protein kinase C) stimulation, also occurs during mammalian egg fertilization. Fertilization-mediated increase in PKC activity has been demonstrated; however, its precise role is unclear.


RESULTS
We investigated PLCzeta- and fertilization-mediated generation of DAG in mouse eggs by monitoring plasma-membrane translocation of a fluorescent DAG-specific reporter. Consistent plasma-membrane DAG formation at fertilization, or after injection of physiological concentrations of PLCzeta, was barely detectable. However, when PLCzeta is overexpressed in eggs, significant plasma-membrane DAG production occurs in concert with a series of unexpected secondary high-frequency Ca(2+) oscillations. We show that these secondary Ca(2+) oscillations can be mimicked in a variety of situations by the stimulation of PKC and that they can be prevented by PKC inhibition. The way PKC leads to secondary Ca(2+) oscillations appears to involve Ca(2+) influx and the loading of thapsigargin-sensitive Ca(2+) stores.


CONCLUSIONS
Our results suggest that overproduction of DAG in PLCzeta-injected eggs can lead to PKC-mediated Ca(2+) influx and subsequent overloading of Ca(2+) stores. These results suggest that DAG generation in the plasma membrane of fertilizing mouse eggs is minimized since it can perturb egg Ca(2+) homoeostasis via excessive Ca(2+) influx.
Yu
Yuansong
Y
Department of Obstetrics and Gynaecology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, U.K.
Halet
Guillaume
G
Lai
F Anthony
FA
Swann
Karl
K
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D010063:Ovum / Q000201:enzymology / Q000378:metabolism*; D054801:Phosphoinositide Phospholipase C / Q000235:genetics / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000201:enzymology / Q000378:metabolism*
C011439:1,2-diacylglycerol; D004075:Diglycerides; D051745:Protein Kinase C-delta; D054801:Phosphoinositide Phospholipase C; C506061:Plch1 protein, mouse; D002118:Calcium