title: Dynamic regulation of DNA methyltransferases in human oocytes and preimplantation embryos after assisted reproductive technologies.
abstract: DNA methylation is a key epigenetic modification which is essential for normal embryonic development. Major epigenetic reprogramming takes place during gametogenesis and in the early embryo; the complex DNA methylation patterns are established and maintained by DNA methyltransferases (DNMTs). However, the influence of assisted reproductive technologies (ART) on DNA methylation reprogramming enzymes has predominantly been studied in mice and less so in human oocytes and embryos. The expression and localization patterns of the four known DNMTs were analysed in human oocytes and IVF/ICSI embryos by immunocytochemistry and compared between a reference group of good quality fresh embryos and groups of abnormally developing embryos or embryo groups after cryopreservation. In humans, DNMT1o rather than DNMT1s seems to be the key player for maintaining methylation in early embryos. DNMT3b, rather than DNMT3a and DNMT3L, appears to ensure global DNA remethylation in the blastocysts before implantation. DNMT3L, an important regulator of maternal imprint methylation in mouse, was not detected in human oocytes (GV, MI and MII stage). Our study confirms the existence of species differences for mammalian DNA methylation enzymes. In poor quality fresh embryos, the switch towards nuclear DNMT3b expression was delayed and nuclear DNMT1, DNMT1s and DNMT3b expression was less common. Compared with the reference embryos, a smaller number of cryopreserved embryos showed nuclear DNMT1, while a delayed switch to nuclear DNMT3b and an extended DNMT1s temporal expression pattern were also observed. The spatial and temporal expression patterns of DNMTs seem to be disturbed in abnormally developing embryos and in embryos that have been cryopreserved. Further research must be performed in order to understand whether the potentially disturbed embryonic DNMT expression after cryopreservation has any long-term developmental consequences.
authors.affiliation: Department of Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, 1090 Brussels, Belgium laetitia.petrussa@vub.ac.be.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Petrussa
authors.affiliation: Department of Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, 1090 Brussels, Belgium Centre for Reproductive Medicine (CRM), Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, 1090 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, 1090 Brussels, Belgium Centre for Medical Genetics (CMG), Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, 1090 Brussels, Belgium.
authors.forename: Martine
authors.initials: M
authors.lastname: De Rycke
mesh_terms: D001755:Blastocyst / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D015925:Cryopreservation; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism*; D004477:Ectogenesis; D044127:Epigenesis, Genetic; D005260:Female; D005307:Fertilization in Vitro / Q000009:adverse effects; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007150:Immunohistochemistry; D007247:Infertility, Female / Q000378:metabolism / Q000473:pathology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects; D020554:Sperm Injections, Intracytoplasmic / Q000009:adverse effects; D000097584:DNA Methyltransferase 3B
chemical_list: D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D015254:DNA Modification Methylases; D007527:Isoenzymes; D012333:RNA, Messenger; D000097584:DNA Methyltransferase 3B; C000619380:DNMT1 protein, human; C000619381:Dnmt1 protein, mouse
keywords: DNA methylation; DNA methyltransferases; cryopreservation; epigenetics; human preimplantation embryo development