Effects of Calcium-BAPTA Buffers and the Calmodulin Antagonist W-7 on Mouse Egg Activation |
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Authors: | Zhe Xu Leah Lefevre Tom Ducibella Richard M. Schultz Gregory S. Kopf |
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Affiliation: | aCenter for Research on Reproduction and Women's Health, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6080;cDepartment of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6080;bDepartment of Obstetrics and Gynecology, Department of Anatomy and Cellular Biology, Tufts University School of Medicine, New England Medical Center Hospitals, Boston, Massachusetts, 02111 |
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Abstract: | 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 μM,recruitment of maternal mRNAs is only partially stimulated at injected free Ca2+concentrations of 2.5 μM,and no evidence for cell cycle resumption was observed (up to 2.5 μMCa2+). 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. |
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