Abstract
PurposeTo analyze the fertilization process related to polyspermy block in human oocytes using an in vitro culturing system for time-lapse cinematography.MethodsWe 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.ResultsThree 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s10815-012-9815-x) contains supplementary material, which is available to authorized users.
Highlights
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
Capsule We found that the novel mechanism of polyspermy block which is definitely different from the membrane block or zona reaction in human fertilization process using time-lapse cinematography
Preliminary results of this study have been presented at the 65th annual meeting of American Society of Reproductive Medicine (ASRM) in 2009 and 3rd Congress of the Asia Pacific Initiative on Reproduction (ASPIRE) in 2010
Summary
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. We developed an in vitro culture system for time-lapse cinematography (TLC), based on Payne et al [13], to analyze the morphologically dynamic events occurring during early human embryonic development. This system enables non-invasive and continuous imaging of human oocyte fertilization and embryonic development. Our previous dynamic analyses of the fertilization process in human oocytes and of human embryonic development using the in vitro TLC system [12] confirmed for the first time the detailed time course of sequential events during embryonic development and revealed novel phenomena [fertilization cone, cytoplasmic strand, and splitting of the. We provide the results of this second detailed TLC analysis, which we believe confirms the existence of a novel mechanism for the prevention of polyspermy
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