DNA methylation patterns in human tripronucleate zygotes

• Published in: Molecular human reproduction 2005-03, Vol.11 (3), p.167-171
• Main Authors: Xu, Yanwen, Zhang, John J., Grifo, James A., Krey, Lewis C.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cell Nucleus - genetics; Cell Nucleus - metabolism; Cell Nucleus - ultrastructure; Chromosomes, Human, X - chemistry; Chromosomes, Human, X - genetics; Chromosomes, Human, X - metabolism; Chromosomes, Human, Y - chemistry; Chromosomes, Human, Y - genetics; Chromosomes, Human, Y - metabolism; DNA - analysis; DNA - genetics; DNA - metabolism; DNA Methylation; DNA methylation immunostaining; Embryo, Mammalian - cytology; Embryo, Mammalian - metabolism; Embryology: invertebrates and vertebrates. Teratology; Female; Fertilization - genetics; FISH; Fundamental and applied biological sciences. Psychology; Humans; In Situ Hybridization, Fluorescence; Male; Mice; Mice, Inbred Strains; Sperm Injections, Intracytoplasmic; tripronucleate zygotes; Zygote - chemistry; Zygote - cytology; Zygote - metabolism
• ISSN: 1360-9947; 1460-2407
• DOI: 10.1093/molehr/gah145

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.