Most fertilizing mouse spermatozoa begin their acrosome reaction before contact with the zona pellucida during in vitro fertilization

To fuse with oocytes, spermatozoa of eutherian mammals must pass through extracellular coats, the cumulus cell layer, and the zona pellucida (ZP). It is generally believed that the acrosome reaction (AR) of spermatozoa, essential for zona penetration and fusion with oocytes, is triggered by sperm co...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2011-03, Vol.108 (12), p.4892-4896
Main Authors: Jin, Mayuko, Fujiwara, Eiji, Kakiuchi, Yasutaka, Okabe, Masaru, Satouh, Yuhkoh, Baba, Shoji A, Chiba, Kazuyoshi, Hirohashi, Noritaka
Format: Article
Language:English
Subjects:
Acrosome reaction
Acrosome Reaction - physiology
Acrosomes
Animals
Biological Sciences
Cells
Coculture Techniques
Cumulus Cells - cytology
Cumulus Cells - physiology
Cumulus oophorus
Female
Fertilization
Fertilization in Vitro
Fluorescence
fluorescence microscopy
Herpes zoster
Humans
In vitro fertilization
insemination
Male
Membranes
Mice
Mice, Knockout
Microscopy
Microscopy, Fluorescence
Oocytes
Oocytes - cytology
Oocytes - physiology
plasma membrane
Rodents
Spermatozoa
Spermatozoa - cytology
Spermatozoa - physiology
Studies
transgenic animals
Zona pellucida
Zona Pellucida - physiology
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Summary:To fuse with oocytes, spermatozoa of eutherian mammals must pass through extracellular coats, the cumulus cell layer, and the zona pellucida (ZP). It is generally believed that the acrosome reaction (AR) of spermatozoa, essential for zona penetration and fusion with oocytes, is triggered by sperm contact with the zona pellucida. Therefore, in most previous studies of sperm-oocyte interactions in the mouse, the cumulus has been removed before insemination to facilitate the examination of sperm-zona interactions. We used transgenic mouse spermatozoa, which enabled us to detect the onset of the acrosome reaction using fluorescence microscopy. We found that the spermatozoa that began the acrosome reaction before reaching the zona were able to penetrate the zona and fused with the oocyte's plasma membrane. In fact, most fertilizing spermatozoa underwent the acrosome reaction before reaching the zona pellucida of cumulus-enclosed oocytes, at least under the experimental conditions we used. The incidence of in vitro fertilization of cumulus-free oocytes was increased by coincubating oocytes with cumulus cells, suggesting an important role for cumulus cells and their matrix in natural fertilization.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1018202108