title: Dynamic expression of DNA methyltransferases (DNMTs) in oocytes and early embryos.
abstract: Epigenetic mechanisms play critical roles in oogenesis and early embryo development in mammals. One of these epigenetic mechanisms, DNA methylation is accomplished through the activities of DNA methyltransferases (DNMTs), which are responsible for adding a methyl group to the fifth carbon atom of the cytosine residues within cytosine-phosphate-guanine (CpG) and non-CpG dinuclotide sites. Five DNMT enzymes have been identified in mammals including DNMT1, DNMT2, DNMT3A, DNMT3B, and DNMT3L. They function in two different methylation processes: maintenance and de novo. For maintenance methylation, DNMT1 preferentially transfers methyl groups to the hemi-methylated DNA strands following DNA replication. However, for de novo methylation activities both DNMT3A and DNMT3B function in the methylation of the unmodified cytosine residues. Although DNMT3L indirectly contributes to de novo methylation process, DNMT2 enables the methylation of the cytosine 38 in the anticodon loop of aspartic acid transfer RNA and does not methylate DNA. In this review article, we have evaluated and discussed the existing published studies to characterize the spatial and temporal expression patterns of the DNMTs in mouse, bovine and human oocytes and early embryos. We have also reviewed the effects of in vitro culture conditions (serum abundance and glucose concentration), aging, superovulation, vitrification, and somatic cell nuclear transfer technology on the dynamics of DNMTs.
authors.affiliation: Department of Histology and Embryology, Akdeniz University, School of Medicine, Antalya, Turkey.
authors.forename: Fatma
authors.initials: F
authors.lastname: Uysal
authors.affiliation: Department of Histology and Embryology, Akdeniz University, School of Medicine, Antalya, Turkey.
authors.forename: Gokhan
authors.initials: G
authors.lastname: Akkoyunlu
authors.affiliation: Department of Histology and Embryology, Akdeniz University, School of Medicine, Antalya, Turkey. Electronic address: sozturk@akdeniz.edu.tr.
authors.forename: Saffet
authors.initials: S
authors.lastname: Ozturk
mesh_terms: D000818:Animals; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D005260:Female; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D011247:Pregnancy; D000097584:DNA Methyltransferase 3B
chemical_list: D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D000097584:DNA Methyltransferase 3B; C000717967:DNMT3A protein, human; C000715535:Dnmt3a protein, mouse
keywords: DNA methylation; DNMT; Early embryo; Gene expression; Oocyte