Effects of calcium-BAPTA buffers and the calmodulin antagonist W-7 on mouse egg activation.
Results of numerous experiments indicate that the transient rise in intracellular Ca2+ following sperm-egg fusion is essential for the subsequent events that constitute egg activation. Some events of egg activation, e.g., cortical granule exocytosis, however, appear more sensitive to intracellular Ca2+ than other events, e.g., cell cycle resumption. To examine if specific events of egg activation have different thresholds for Ca2+, we manipulated buffered intracellular Ca2+ concentrations by microinjecting Ca2+-BAPTA buffers and then examined the effect on the cortical granule exocytosis, recruitment of maternal mRNAs, and cell cycle resumption. We find that whereas cortical granule exocytosis occurs over a narrow threshold range of injected free Ca2+ concentrations between 0.5 and 1.0 microM, recruitment of maternal mRNAs is only partially stimulated at injected free Ca2+ concentrations of 2.5 microM, and no evidence for cell cycle resumption was observed (up to 2.5 microM Ca2+). Although the Ca2+- and phospholipid-dependent protein kinase, protein kinase C, is implicated in aspects of egg activation, calmodulin is also a potential target for the transient increase in Ca2+ that occurs following fertilization. Whereas incubation of eggs in the presence of the calmodulin antagonist W-7 followed by insemination does not block cortical granule exocytosis, cell cycle resumption, as assessed by the metaphase-to-anaphase transition, a decrease in histone H1 kinase activity and the time course for the emission of the second polar body are significantly delayed/inhibited.
Xu
Z
Z
Center for Research on Reproduction and Women's Health, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6080, USA.
Lefevre
L
L
Ducibella
T
T
Schultz
R M
RM
Kopf
G S
GS
D000818:Animals; D002021:Buffers; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002453:Cell Cycle / Q000187:drug effects; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005260:Female; D005306:Fertilization; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D010063:Ovum / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D013084:Sperm-Ovum Interactions / Q000187:drug effects / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology*; D014158:Transcription, Genetic
D002021:Buffers; D002147:Calmodulin; D012333:RNA, Messenger; D013449:Sulfonamides; D000001:Calcimycin; D004533:Egtazic Acid; C017967:W 7; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium