Oscillatory CaMKII activity in mouse egg activation.
Fertilization-induced intracellular calcium (Ca(2+)) oscillations stimulate the onset of mammalian development, and little is known about the biochemical mechanism by which these Ca(2+) signals are transduced into the events of egg activation. This study addresses the hypothesis that transient increases in Ca(2+) similar to those at fertilization stimulate oscillatory Ca(2+)/calmodulin-dependent kinase II (CaMKII) enzyme activity, incrementally driving the events of egg activation. Since groups of fertilized eggs normally oscillate asynchronously, synchronous oscillatory Ca(2+) signaling with a frequency similar to fertilization was experimentally induced in unfertilized mouse eggs by using ionomycin and manipulating extracellular calcium. Coanalysis of intracellular Ca(2+) levels and CaMKII activity in the same population of eggs demonstrated a rapid and transient enzyme response to each increase in Ca(2+). Enzyme activity increased 370% during the first Ca(2+) rise, representing about 60% of maximal activity, and had decreased to basal levels within 5 min from the time Ca(2+) reached its peak value. Single fertilized eggs monitored for Ca(2+) had a mean increase in CaMKII activity of 185%. One and two ionomycin-induced Ca(2+) transients resulted in 39 and 49% mean cortical granule (CG) loss, respectively, while CG exocytosis and resumption of meiosis were inhibited by a CaMKII antagonist. These studies demonstrate that changes in the level of Ca(2+) and in CaMKII activity can be studied in the same cell and that CaMKII activity is exquisitely sensitive to experimentally induced oscillations of Ca(2+) in vivo. The data support the hypothesis that CaMKII activity oscillates for a period of time after normal fertilization and temporally regulates many events of egg activation.
Markoulaki
Styliani
S
Sackler School of Biomedical Sciences, Program in Cell, Molecular and Developmental Biology, Tufts University School of Medicine, Boston, MA 02111, USA.
Matson
Sara
S
Abbott
Allison L
AL
Ducibella
Tom
T
D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005260:Female; D005306:Fertilization / Q000502:physiology; D005307:Fertilization in Vitro; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D010063:Ovum / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology
D004791:Enzyme Inhibitors; D015759:Ionomycin; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases