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Alteration of the cortical actin cytoskeleton deregulates Ca2+ signaling, monospermic fertilization, and sperm entry.

Puppo A, Chun JT, Gragnaniello G, Garante E, Santella L - PLoS ONE (2008)

Bottom Line: We have measured changes in intracellular Ca2+ signals and F-actin structures during fertilization.Using heparin and other pharmacological agents that either hypo- or hyperpolymerize the cortical actin, we demonstrate that nearly all aspects of the fertilization process are profoundly affected by the dynamic restructuring of the egg cortical actin cytoskeleton.Our findings identify important roles for subplasmalemmal actin fibers in the process of sperm-egg interaction and in the subsequent events related to fertilization: the generation of Ca2+ signals, sperm penetration, cortical granule exocytosis, and the block to polyspermy.

View Article: PubMed Central - PubMed

Affiliation: Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli, Italy.

ABSTRACT

Background: When preparing for fertilization, oocytes undergo meiotic maturation during which structural changes occur in the endoplasmic reticulum (ER) that lead to a more efficient calcium response. During meiotic maturation and subsequent fertilization, the actin cytoskeleton also undergoes dramatic restructuring. We have recently observed that rearrangements of the actin cytoskeleton induced by actin-depolymerizing agents, or by actin-binding proteins, strongly modulate intracellular calcium (Ca2+) signals during the maturation process. However, the significance of the dynamic changes in F-actin within the fertilized egg has been largely unclear.

Methodology/principal findings: We have measured changes in intracellular Ca2+ signals and F-actin structures during fertilization. We also report the unexpected observation that the conventional antagonist of the InsP(3) receptor, heparin, hyperpolymerizes the cortical actin cytoskeleton in postmeiotic eggs. Using heparin and other pharmacological agents that either hypo- or hyperpolymerize the cortical actin, we demonstrate that nearly all aspects of the fertilization process are profoundly affected by the dynamic restructuring of the egg cortical actin cytoskeleton.

Conclusions/significance: Our findings identify important roles for subplasmalemmal actin fibers in the process of sperm-egg interaction and in the subsequent events related to fertilization: the generation of Ca2+ signals, sperm penetration, cortical granule exocytosis, and the block to polyspermy.

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Related in: MedlinePlus

Heparin partially inhibits cADPr-dependent Ca2+ release.(B) Activation of the caged cADPr pre-injected in A. aranciacus eggs results in intracellular release of Ca2+. The altitude of the Ca2+ peak was significantly reduced in heparin-treated eggs compared to the control (n = 7, in each case). (B) Transmission photomicrographs of control and heparin-treated eggs following cADPr uncaging (450 µM, pipette concentration) and subsequent Ca2+ release. The typical elevation of the vitelline layer seen in the control eggs (arrow) was absent in the eggs treated with heparin.
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pone-0003588-g004: Heparin partially inhibits cADPr-dependent Ca2+ release.(B) Activation of the caged cADPr pre-injected in A. aranciacus eggs results in intracellular release of Ca2+. The altitude of the Ca2+ peak was significantly reduced in heparin-treated eggs compared to the control (n = 7, in each case). (B) Transmission photomicrographs of control and heparin-treated eggs following cADPr uncaging (450 µM, pipette concentration) and subsequent Ca2+ release. The typical elevation of the vitelline layer seen in the control eggs (arrow) was absent in the eggs treated with heparin.

Mentions: As a specific inhibitor of InsP3 receptors, heparin should not interfere with Ca2+ release through the cADPr-gated ryanodine receptors. However, we found that Ca2+ release in starfish eggs by cADPr photoliberated from injected caged cADPr was substantially reduced by heparin. The peak values of 1.01±0.11 arbitrary units in the controls were reduced to 0.76±0.12 (Fig. 4A). Although cADPr uncaging inside the heparin-treated eggs still evoked a substantial Ca2+ release, the mobilization of Ca2+ failed to elevate the vitelline layer as seen in the control eggs (Fig. 4B, arrow). Taken together, these observations suggested that heparin may also influence cell elements other than InsP3 receptors, thereby interfering with the intracellular Ca2+ signaling in a more general way.


Alteration of the cortical actin cytoskeleton deregulates Ca2+ signaling, monospermic fertilization, and sperm entry.

Puppo A, Chun JT, Gragnaniello G, Garante E, Santella L - PLoS ONE (2008)

Heparin partially inhibits cADPr-dependent Ca2+ release.(B) Activation of the caged cADPr pre-injected in A. aranciacus eggs results in intracellular release of Ca2+. The altitude of the Ca2+ peak was significantly reduced in heparin-treated eggs compared to the control (n = 7, in each case). (B) Transmission photomicrographs of control and heparin-treated eggs following cADPr uncaging (450 µM, pipette concentration) and subsequent Ca2+ release. The typical elevation of the vitelline layer seen in the control eggs (arrow) was absent in the eggs treated with heparin.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2570615&req=5

pone-0003588-g004: Heparin partially inhibits cADPr-dependent Ca2+ release.(B) Activation of the caged cADPr pre-injected in A. aranciacus eggs results in intracellular release of Ca2+. The altitude of the Ca2+ peak was significantly reduced in heparin-treated eggs compared to the control (n = 7, in each case). (B) Transmission photomicrographs of control and heparin-treated eggs following cADPr uncaging (450 µM, pipette concentration) and subsequent Ca2+ release. The typical elevation of the vitelline layer seen in the control eggs (arrow) was absent in the eggs treated with heparin.
Mentions: As a specific inhibitor of InsP3 receptors, heparin should not interfere with Ca2+ release through the cADPr-gated ryanodine receptors. However, we found that Ca2+ release in starfish eggs by cADPr photoliberated from injected caged cADPr was substantially reduced by heparin. The peak values of 1.01±0.11 arbitrary units in the controls were reduced to 0.76±0.12 (Fig. 4A). Although cADPr uncaging inside the heparin-treated eggs still evoked a substantial Ca2+ release, the mobilization of Ca2+ failed to elevate the vitelline layer as seen in the control eggs (Fig. 4B, arrow). Taken together, these observations suggested that heparin may also influence cell elements other than InsP3 receptors, thereby interfering with the intracellular Ca2+ signaling in a more general way.

Bottom Line: We have measured changes in intracellular Ca2+ signals and F-actin structures during fertilization.Using heparin and other pharmacological agents that either hypo- or hyperpolymerize the cortical actin, we demonstrate that nearly all aspects of the fertilization process are profoundly affected by the dynamic restructuring of the egg cortical actin cytoskeleton.Our findings identify important roles for subplasmalemmal actin fibers in the process of sperm-egg interaction and in the subsequent events related to fertilization: the generation of Ca2+ signals, sperm penetration, cortical granule exocytosis, and the block to polyspermy.

View Article: PubMed Central - PubMed

Affiliation: Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli, Italy.

ABSTRACT

Background: When preparing for fertilization, oocytes undergo meiotic maturation during which structural changes occur in the endoplasmic reticulum (ER) that lead to a more efficient calcium response. During meiotic maturation and subsequent fertilization, the actin cytoskeleton also undergoes dramatic restructuring. We have recently observed that rearrangements of the actin cytoskeleton induced by actin-depolymerizing agents, or by actin-binding proteins, strongly modulate intracellular calcium (Ca2+) signals during the maturation process. However, the significance of the dynamic changes in F-actin within the fertilized egg has been largely unclear.

Methodology/principal findings: We have measured changes in intracellular Ca2+ signals and F-actin structures during fertilization. We also report the unexpected observation that the conventional antagonist of the InsP(3) receptor, heparin, hyperpolymerizes the cortical actin cytoskeleton in postmeiotic eggs. Using heparin and other pharmacological agents that either hypo- or hyperpolymerize the cortical actin, we demonstrate that nearly all aspects of the fertilization process are profoundly affected by the dynamic restructuring of the egg cortical actin cytoskeleton.

Conclusions/significance: Our findings identify important roles for subplasmalemmal actin fibers in the process of sperm-egg interaction and in the subsequent events related to fertilization: the generation of Ca2+ signals, sperm penetration, cortical granule exocytosis, and the block to polyspermy.

Show MeSH
Related in: MedlinePlus