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


RESULTS
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
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.
Puppo
A
A
Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli, Italy.
Chun
Jong T
JT
Gragnaniello
Giovanni
G
Garante
Ezio
E
Santella
Luigia
L
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D000199:Actins / Q000378:metabolism; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D047630:Depsipeptides / Q000494:pharmacology; D005260:Female; D005306:Fertilization / Q000187:drug effects / Q000502:physiology*; D006493:Heparin / Q000494:pharmacology; D008297:Male; D055503:Protein Multimerization / Q000187:drug effects; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology; D013215:Starfish / Q000502:physiology; D015053:Zygote / Q000378:metabolism / Q000502:physiology
D000199:Actins; D047630:Depsipeptides; C057531:jasplakinolide; D006493:Heparin