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1 Department of Obstetrics and
Gynecology, Queen Victoria Medical
Centre, Monash University,
Melbourne, Australia
Sperm penetration into the zona of 46 human eggs was
examined by electron microscopy. Preovulatory oocytes
were aspirated at laparoscopy and inseminated by
methods which produced normal pregnancies. These
were routinely fixed 3-72 hours after insemination and
examined for zona penetration. The mechanism of zona penetration was similar in
the non-activated oocytes, fertilized ova, and embryos
obtained, and resembled that which was reported in
most mammals. Sperm were tightly bound to the zona
by their plasma membranes. Both acrosome-reacted
and unreacted sperm were seen in the cumulus and entering the zona. The acrosome reaction involved multiple fusions and vesiculation of the plasma and outer
acrosome membranes. Fine and coarse vesiculation was
observed, and the sperm digested a clear pathway
through the zona. Sperm were rarely seen in the inner
zona and never seen in the perivitelline space of
monospermic ova, but freely penetrated these regions
in polyspermic ova. A block to polyspermy seemed to
operate at the level of the inner zona. Morphologic evidence for the involvement of the inner acrosome membrane in the acrosome reaction and a possible sequence
of events in zona penetration is presented. The findings
confirm most of late Professor Pierre Soupart’s work on
zona penetration.
Key words: ultrastructure, zona pellucida, human ova, acrosome reaction, monospermy, polyspermy, sperm penetration, in vitro fertilization
Accepted on June 24, 1982
This article has been cited by other articles:
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  J.M. Bedford Mammalian Fertilization Misread? Sperm Penetration of the Eutherian Zona Pellucida Is Unlikely to be a Lytic Event Biol Reprod, December 1, 1998; 59(6): 1275 - 1287. [Full Text]
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