Incompetence of Preovulatory Mouse Oocytes to Undergo Cortical Granule Exocytosis Following Induced Calcium Oscillations

Immature oocytes of many species are incompetent to undergo cortical granule (CG) exocytosis upon fertilization. In mouse eggs, CG exocytosis is dependent primarily on an inositol 1,4,5-trisphosphate (IP3)-mediated elevation of intracellular calcium ([Ca2+]i). While deficienciesupstreamof [Ca2+]irel...

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Bibliographic Details
Published in:Developmental biology 1999-03, Vol.207 (1), p.38-48
Main Authors: Abbott, Allison L., Fissore, Rafael A., Ducibella, Tom
Format: Article
Language:English
Subjects:
Animals
calcium
Calcium - metabolism
cortical granule exocytosis
Cytoplasmic Granules - metabolism
egg activation
Electroporation
Exocytosis - drug effects
Exocytosis - physiology
Female
Fluorescent Dyes - metabolism
Follicular Phase - physiology
Inositol 1,4,5-Trisphosphate - metabolism
Male
Mice
Microinjections
Microscopy, Fluorescence
mouse
Oocytes - cytology
Oocytes - metabolism
Spermatozoa - metabolism
Thimerosal - pharmacology
Zona Pellucida - drug effects
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Summary:Immature oocytes of many species are incompetent to undergo cortical granule (CG) exocytosis upon fertilization. In mouse eggs, CG exocytosis is dependent primarily on an inositol 1,4,5-trisphosphate (IP3)-mediated elevation of intracellular calcium ([Ca2+]i). While deficienciesupstreamof [Ca2+]irelease are known, this study examined whetherdownstreamdeficiencies also contribute to the incompetence of preovulatory mouse oocytes to release CGs. The experimental strategy was to bypass upstream deficiencies by inducing normal, fertilization-like [Ca2+]ioscillations in fully grown, germinal vesicle (GV) stage oocytes and determine if the extent of CG exocytosis was restored to levels observed in mature, metaphase II (MII)-stage eggs. Because IP3does not stimulate a normal Ca2+response in GV-stage oocytes, three alternate methods were used to induce oscillations: thimerosal treatment, electroporation, and sperm factor injection. Long-lasting oscillations from thimerosal treatment resulted in 64 and 10% mean CG release at the MII and GV stages, respectively (P< 0.001). Three electrical pulses induced mean [Ca2+]ielevations of approximately 730 and 650 nM in MII- and GV-stage oocytes, respectively, and 31% CG release in MII-stage eggs and 9% in GV-stage oocytes (P< 0.001). Sperm factor microinjection resulted in 86% CG release in MII-stage eggs, while similarly treated GV-stage oocytes exhibited < 1% CG release (P< 0.001). Taken together, these results demonstrate a deficiency downstream of [Ca2+]irelease which is developmentally regulated in the 12 h prior to ovulation.
ISSN:0012-1606
1095-564X
DOI:10.1006/dbio.1998.9159