Possible mechanism of polyspermy block in human oocytes observed by time-lapse cinematography.
OBJECTIVE
To analyze the fertilization process related to polyspermy block in human oocytes using an in vitro culturing system for time-lapse cinematography.


METHODS
We had 122 oocytes donated for this study from couples that provided informed consent. We recorded human oocytes at 2,000 to 2,800 frames every 10 s during the fertilization process and thereafter every 2 min using a new in vitro culture system originally developed by the authors for time-lapse cinematography. We displayed 30 frames per second for analysis of the polyspermy block during fertilization.


RESULTS
Three oocytes showed the leading and following sperm within the zona pellucida in the same microscopic field. The dynamic images obtained during the fertilization process using this new system revealed that once a leading sperm penetrated the zona pellucida and attached to the oocyte membrane, a following sperm was arrested from further penetration into the zona pellucida within 10 s.


CONCLUSIONS
The present results strongly suggest the existence of a novel mechanism of polyspermy block that takes place at the zona pellucida immediately after fertilization. These findings are clearly different from previous mechanisms describing polyspermy block as the oocyte membrane block to sperm penetration and the zona reaction. The finding presented herein thus represents a novel discovery about the highly complicated polyspermy block mechanism occurring in human oocytes.
Reproductive Centre, Mio Fertility Clinic, 2-1-1 Kuzumo-Minami, Yonago, Japan. yasmio@mfc.or.jp
Yasuyuki
Y
Mio
Kyoko
K
Iwata
Keitaro
K
Yumoto
Yoshiteru
Y
Kai
Haruka C
HC
Sargant
Chizuru
C
Mizoguchi
Minako
M
Ueda
Yuka
Y
Tsuchie
Akifumi
A
Imajo
Yumiko
Y
Iba
Kyoko
K
Nishikori
D002462:Cell Membrane / Q000378:metabolism; D046149:Embryo Culture Techniques / Q000379:methods; D005260:Female; D005306:Fertilization; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D008297:Male; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D013081:Sperm Motility; D013094:Spermatozoa / Q000378:metabolism; D013997:Time Factors; D059008:Time-Lapse Imaging / Q000379:methods*; D015044:Zona Pellucida / Q000378:metabolism