Existence of Three Mechanisms for Blocking Polyspermy in Oocytes of the Mussel Mytilus edulis

We found the existence of a three-step mechanism to block polyspermy in the oocyte of the mussel Mytilus edulis. When the oocytes were inseminated within 30 min after spawning, they underwent monospermic fertilization over a wide range of sperm-oocyte ratios up to 5× 103. A transient depolarization...

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Bibliographic Details
Published in:The Biological bulletin (Lancaster) 1995-12, Vol.189 (3), p.330-339
Main Authors: Togo, Tatsuru, Osanai, Kenzi, Morisawa, Masaaki
Format: Article
Language:English
Subjects:
Animal reproduction
Blue mussel
Cell membranes
Development and Reproduction
Fertilization
Insemination
Marine biology
Membrane potential
Membranes
Mollusks
Mytilus edulis
Oocytes
Ova
Physiological aspects
Polyspermy
Reproduction
Reproduction (Biology)
Sea water
Sodium
Spermatozoa
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Summary:We found the existence of a three-step mechanism to block polyspermy in the oocyte of the mussel Mytilus edulis. When the oocytes were inseminated within 30 min after spawning, they underwent monospermic fertilization over a wide range of sperm-oocyte ratios up to 5× 103. A transient depolarization of the oocyte plasma membrane (fertilization potential) was observed immediately after insemination. Low-sodium seawater induced polyspermy and decreased the amplitude of the fertilization potential, suggesting the existence of a fast block to polyspermy that is dependent on depolarization of the plasma membrane. When the fertilized oocytes were inseminated again at a sperm-oocyte ratio that is great enough to give a high rate of polyspermy in initial insemination, many sperm could not undergo the acrosomal reaction and thus could not penetrate fertilized oocytes. The remaining sperm underwent an acrosomal reaction and the acrosomal process protruded through the vitelline coat, but it did not fuse with the oocyte plasma membrane. These findings suggest the existence of two strategies constituting a late polyspermy block: suppression of acrosomal reaction and block of contact or fusion between the plasma membranes of sperm and oocyte.
ISSN:0006-3185
1939-8697
DOI:10.2307/1542150