title: Similar kinetics for 5-methylcytosine and 5-hydroxymethylcytosine during human preimplantation development in vitro.
abstract: After fertilization, the mammalian embryo undergoes epigenetic reprogramming with genome-wide DNA demethylation and subsequent remethylation. Oxidation of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC) was suggested to be an intermediate step in the DNA demethylation pathway. Other evidence, such as the stability of 5hmC in specific tissues, suggests that 5hmC constitutes a new epigenetic modification with its own biological function. Since few studies have been conducted on human material compared to animal models and species-specific epigenetic differences have been reported, we studied global DNA methylation and hydroxymethylation patterns in human in vitro preimplantation embryos using immunocytochemistry, comparing these patterns in good-quality and abnormally developing embryos. Our data showed that DNA methylation and hydroxymethylation modifications co-exist. 5mC and 5hmC signals were found in oocytes and in paternal and maternal pronuclei of zygotes, present in non-reciprocal patterns-which contrasts published data for the mouse. These two epigenetic modifications are present between Days 1 and 7 of in vitro development, with 5mC levels declining over cell divisions without noticeable remethylation during this period. A main decline in 5mC and 5hmC occurred as the embryo progressed from compaction to the blastocyst stage. No difference in (hydroxy)methylation was found between the inner cell mass and trophectoderm. When comparing normally and abnormally developing embryos, DNA (hydroxy)methylation reprogramming was abnormal in poor-quality embryos, especially during the first cleavages. Mol. Reprod. Dev. 83: 594-605, 2016 © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, Brussels, Belgium.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Petrussa
authors.affiliation: Department of Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, Brussels, Belgium.|Centre for Reproductive Medicine (CRM), Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, Brussels, Belgium.
authors.forename: Hilde
authors.initials: H
authors.lastname: Van de Velde
authors.affiliation: Department of Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, Brussels, Belgium.|Centre for Medical Genetics (CMG), Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, Brussels, Belgium.
authors.forename: Martine
authors.initials: M
authors.lastname: De Rycke
mesh_terms: D044503:5-Methylcytosine / Q000031:analogs & derivatives* / Q000378:metabolism*; D000818:Animals; D001755:Blastocyst / Q000166:cytology / Q000378:metabolism*; D019175:DNA Methylation / Q000502:physiology*; D047108:Embryonic Development / Q000502:physiology*; D006801:Humans; D051379:Mice
chemical_list: C011865:5-hydroxymethylcytosine; D044503:5-Methylcytosine