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J Assist Reprod Genet (2012) 29:951956 DOI 10.1007/s10815-012-9815-x
GAMETE BIOLOGY
Possible mechanism of polyspermy block in human oocytes observed by time-lapse cinematography
Yasuyuki Mio & Kyoko Iwata & Keitaro Yumoto &
Yoshiteru Kai & Haruka C. Sargant &
Chizuru Mizoguchi & Minako Ueda & Yuka Tsuchie &
Akifumi Imajo & Yumiko Iba & Kyoko Nishikori
Received: 23 March 2012 /Accepted: 28 May 2012 /Published online: 14 June 2012 # The Author(s) 2012. This article is published with open access at Springerlink.com
AbstractPurpose 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.
Keywords Polyspermy block . Time-lapse cinematography (TLC) . Human fertilization process . Zona pellucida . Embryonic development
Introduction
The development of assisted reproductive technology (ART) has recently enabled the direct observation of human oocytes, revealing various mysterious phenomena involving the beginning of life. However, it is undeniable that frequent microscopic examinations of human early embryos may have negative effects on them, making it difficult to obtain reliable detailed information of human embryonic development from still images. We therefore...