Ocean acidification increases polyspermy of a broadcast spawning bivalve species by hampering membrane depolarization and cortical granule exocytosis

We have investigated the consequences of having multiple fusion complexes on exocytotic granules, and have identified a new principle for interpreting the calcium dependence of calcium-triggered exocytosis. Strikingly different physiological responses to calcium are expected when active fusion complexes are distributed between granules in a deterministic or probabilistic manner. We have modeled these differences, and compared them with the calcium dependence of sea urchin egg cortical granule exocytosis. From the calcium dependence of cortical granule exocytosis, and from the exposure time and concentration dependence of N-ethylmaleimide inhibition, we determined that cortical granules do have spare active fusion complexes that are randomly distributed as a Poisson process among the population of granules. At high calcium concentrations, docking sites have on average nine active fusion complexes.

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Weak bases partially activate Xenopus eggs and permit changes in membrane conductance whilst inhibiting cortical granule exocytosis

Journal of Cell Science ◽

10.1242/jcs.87.2.205 ◽

1987 ◽

Vol 87 (2) ◽

pp. 205-220

Author(s):

M. Charbonneau ◽

D.J. Webb

Keyword(s):

Polar Body ◽

Membrane Conductance ◽

Transient Increase ◽

Cortical Granule ◽

Cortical Granules ◽

Weak Base ◽

Granule Exocytosis ◽

Weak Bases ◽

Prolonged Contact ◽

Cortical Granule Exocytosis

At extracellular pH values close to their pKa values the weak bases, ammonia and procaine, elicited a series of events in non-activated Xenopus eggs, some of which resembled those normally occurring at fertilization. These included: (1) a transient increase in membrane conductance; (2) modification of the microvilli; (3) thickening of the cortical cytoplasm and displacement of the cortical granules; (4) pigment accumulation; (5) contractions and shape changes. However, these eggs did not undergo the cortical reaction nor emit the second polar body. Cortical granule exocytosis of inseminated or artificially stimulated eggs was inhibited if the eggs had been previously treated for 15 min with the weak base and subsequently rinsed. Multiple sperm-entry sites were exhibited by the inseminated eggs, suggesting polyspermy. However, such eggs did not cleave and although sperm had fused with the egg membrane, they were not incorporated. Nevertheless, a transient increase in membrane conductance was evoked, which was longer in duration and had a slightly different form from that normally accompanying fertilization. In these eggs cortical granules were intact but displaced away from the plasma membrane. Prolonged contact with the weak base rendered eggs totally unresponsive to sperm or artificial stimuli but eggs recovered when rinsed sufficiently. These effects of weak bases on unfertilized Xenopus eggs or during fertilization were completely absent at pH 7.4. Although changes in intracellular pH or Ca2+ may be involved in these phenomena, direct action by the weak base itself cannot be ruled out.

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Induction of cortical granule exocytosis of pig oocytes by spermatozoa during meiotic maturation

Reproduction ◽

10.1530/jrf.0.1090247 ◽

1997 ◽

Vol 109 (2) ◽

pp. 247-255 ◽

Cited By ~ 36

Author(s):

W. H. Wang ◽

M. Hosoe ◽

Y. Shioya

Keyword(s):

Meiotic Maturation ◽

Cortical Granule ◽

Granule Exocytosis ◽

Cortical Granule Exocytosis

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Phosphoprotein inhibition of calcium-stimulated exocytosis in sea urchin eggs.

The Journal of Cell Biology ◽

10.1083/jcb.113.4.769 ◽

1991 ◽

Vol 113 (4) ◽

pp. 769-778 ◽

Cited By ~ 21

Author(s):

T Whalley ◽

I Crossley ◽

M Whitaker

Keyword(s):

Sea Urchin ◽

Okadaic Acid ◽

Cortical Granule ◽

Granule Exocytosis ◽

Sea Urchin Eggs ◽

Transduction Mechanisms ◽

Egg Signal ◽

Cortical Granule Exocytosis ◽

Gamma S

We have investigated the role of protein phosphorylation in the control of exocytosis in sea urchin eggs by treating eggs with a thio-analogue of ATP. ATP gamma S (adenosine 5'-O-3-thiotriphosphate) is a compound which can be used as a phosphoryl donor by protein kinases, leading to irreversible protein thiophosphorylation (Gratecos, D., and E.H. Fischer. 1974. Biochem. Biophys. Res. Commun. 58:960-967). Microinjection of ATP gamma S inhibits cortical granule exocytosis, but has no effect on the sperm-egg signal transduction mechanisms which normally cause exocytosis by generating an increase in [Ca2+]i. ATP gamma S requires cytosolic factors for its inhibition of cortical granule exocytosis: it does not affect exocytosis when applied directly to the isolated exocytotic apparatus. Our data suggest that ATP gamma S irreversibly inhibits exocytosis via thiophosphorylation of proteins associated with the egg cortex. We have identified two thiophosphorylated proteins (33 and 27 kD) that are associated with the isolated exocytotic apparatus. They may mediate the inhibition of exocytosis by ATP gamma S. In addition, we show that okadaic acid, an inhibitor of phosphoprotein phosphatases, prevents cortical granule exocytosis at fertilization without affecting calcium mobilization. Like ATP gamma S, okadaic acid has no effect on exocytosis in vitro. Our results suggest that an inhibitory phosphoprotein can obstruct calcium-stimulated exocytosis in sea urchin eggs; on the other hand, they do not readily support the idea that a protein phosphatase is an essential component of the mechanism controlling exocytosis.

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SNAP-25 is essential for cortical granule exocytosis in mouse eggs

AJP Cell Physiology ◽

10.1152/ajpcell.1998.274.6.c1496 ◽

1998 ◽

Vol 274 (6) ◽

pp. C1496-C1500 ◽

Cited By ~ 18

Author(s):

Yoshihide Ikebuchi ◽

Nobuyuki Masumoto ◽

Tetsu Matsuoka ◽

Takeshi Yokoi ◽

Masahiro Tahara ◽

...

Keyword(s):

Botulinum Neurotoxin ◽

Endocrine Cells ◽

Immunoblot Analysis ◽

Cortical Granule ◽

Rt Pcr ◽

Botulinum Neurotoxin A ◽

Granule Exocytosis ◽

Cortical Granule Exocytosis ◽

And Function ◽

Mouse Eggs

Synaptosome-associated protein of 25 kDa (SNAP-25) has been shown to play an important role in Ca2+-dependent exocytosis in neurons and endocrine cells. During fertilization, sperm-egg fusion induces cytosolic Ca2+mobilization and subsequently Ca2+-dependent cortical granule (CG) exocytosis in eggs. However, it is not yet clear whether SNAP-25 is involved in this process. In this study, we determined the expression and function of SNAP-25 in mouse eggs. mRNA and SNAP-25 were detected in metaphase II (MII) mouse eggs by RT-PCR and immunoblot analysis, respectively. Next, to determine the function of SNAP-25, we evaluated the change in CG exocytosis with a membrane dye, tetramethylammonium-1,6-diphenyl-1,3,5-hexatriene, after microinjection of a botulinum neurotoxin A (BoNT/A), which selectively cleaves SNAP-25 in MII eggs. Sperm-induced CG exocytosis was significantly inhibited in the BoNT/A-treated eggs. The inhibition was attenuated by coinjection of SNAP-25. These results suggest that SNAP-25 may be involved in Ca2+-dependent CG exocytosis during fertilization in mouse eggs.

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