Mol. Hum. Reprod. Advance Access first published online on February 4, 2005
This version published online on February 11, 2005
Molecular Human Reproduction, doi:10.1093/molehr/gah145
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1 Program for In Vitro Fertilization, Reproductive Surgery and Infertility, New York University School of Medicine, New York, NY10016, USA; Current address: Reproductive Medical Research Center, The 1st Affiliated Hospital of Sun Yat-sen University, Guangzhou, China 510080
* To whom correspondence should be addressed. In mammals, the dynamic reprogramming of DNA methylation begins during gametogenesis and continues through embryogenesis. Recently, immunofluorescence staining with an antibody against 5-methylcytosine (anti-5-MeC) has revealed active demethylation of the male pronucleus in zygotes beginning at 4-6 h after fertilization. In this study, we characterized the DNA methylation patterns in mouse zygotes and in human tripronucleate (3 PN) zygotes discarded after conventional fertilization or following ICSI. Pronuclei were subjected to fluorescence in-situ hybridization to identify the X and/or Y chromosomes and then stained with anti-5-MeC. In diandric 3 PN zygotes from conventional IVF, we consistently observed one strongly and two weakly stained pronuclei. In contrast, the majority of 3 PN ICSI zygotes, mainly digynic zygotes, displayed two strongly and one weakly stained pronuclei. Two zygotes from ICSI failed to show any staining difference among the three pronuclei. Our results indicate that the active demethylation of male pronuclei occurs in both mouse and human zygotes. It is possible that the abnormal methylation patterns resulting from a dysfunctional cytoplasm may occur in a small number of oocytes and may affect embryonic viability.
Received May 18, 2004
Accepted December 18, 2004
Article
DNA methylation patterns in human tripronucleate zygotes
2 Program for In Vitro Fertilization, Reproductive Surgery and Infertility, New York University School of Medicine, New York, NY10016, USA
Lewis C. Krey, E-mail: kreyivf{at}yahoo.com
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