title: Characterization of the IGF2 Imprinted Gene Methylation Status in Bovine Oocytes during Folliculogenesis.
abstract: DNA methylation reprogramming occurs during mammalian gametogenesis and embryogenesis. Sex-specific DNA methylation patterns at specific CpG islands controlling imprinted genes are acquired during this window of development. Characterization of the DNA methylation dynamics of imprinted genes acquired by oocytes during folliculogenesis is essential for understanding the physiological and genetic aspects of female gametogenesis and to determine the parameters for oocyte competence. This knowledge can be used to improve in vitro embryo production (IVP), specifically because oocyte competence is one of the most important aspects determining the success of IVP. Imprinted genes, such as IGF2, play important roles in embryo development, placentation and fetal growth. The aim of this study was to characterize the DNA methylation profile of the CpG island located in IGF2 exon 10 in oocytes during bovine folliculogenesis. The methylation percentages in oocytes from primordial follicles, final secondary follicles, small antral follicles, large antral follicles, MII oocytes and spermatozoa were 73.74 ± 2.88%, 58.70 ± 7.46%, 56.00 ± 5.58%, 65.77 ± 5.10%, 56.35 ± 7.45% and 96.04 ± 0.78%, respectively. Oocytes from primordial follicles showed fewer hypomethylated alleles (15.5%) than MII oocytes (34.6%) (p = 0.039); spermatozoa showed only hypermethylated alleles. Moreover, MII oocytes were less methylated than spermatozoa (p<0.001). Our results showed that the methylation pattern of this region behaves differently between mature oocytes and spermatozoa. However, while this region has a classical imprinted pattern in spermatozoa that is fully methylated, it was variable in mature oocytes, showing hypermethylated and hypomethylated alleles. Furthermore, our results suggest that this CpG island may have received precocious reprogramming, considering that the hypermethylated pattern was already found in growing oocytes from primordial follicles. These results may contribute to our understanding of the reprogramming of imprinted genes during bovine oogenesis.
authors.affiliation: Laboratory of Animal Reproduction, Embrapa Genetic Resources and Biotechnology, Brasília, Distrito Federal, Brazil; Institute of Genetics and Biochemistry, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil.
authors.forename: Anelise dos Santos
authors.initials: Ados S
authors.lastname: Mendonça
authors.affiliation: Laboratory of Animal Reproduction, Embrapa Genetic Resources and Biotechnology, Brasília, Distrito Federal, Brazil; School of Agriculture and Veterinary Medicine, University of Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: Ana Luíza Silva
authors.initials: AL
authors.lastname: Guimarães
authors.affiliation: Embrapa Genetic Resources and Biotechnology, Brasília, Distrito Federal, Brazil.
authors.forename: Naiara Milagres Augusto
authors.initials: NM
authors.lastname: da Silva
authors.affiliation: Embrapa Genetic Resources and Biotechnology, Brasília, Distrito Federal, Brazil.
authors.forename: Alexandre Rodrigues
authors.initials: AR
authors.lastname: Caetano
authors.affiliation: Laboratory of Animal Reproduction, Embrapa Genetic Resources and Biotechnology, Brasília, Distrito Federal, Brazil; School of Agriculture and Veterinary Medicine, University of Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: Margot Alves Nunes
authors.initials: MA
authors.lastname: Dode
authors.affiliation: Laboratory of Animal Reproduction, Embrapa Genetic Resources and Biotechnology, Brasília, Distrito Federal, Brazil; Institute of Genetics and Biochemistry, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil; School of Veterinary Medicine, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil.
authors.forename: Maurício Machaim
authors.initials: MM
authors.lastname: Franco
mesh_terms: D000483:Alleles; D000818:Animals; D002417:Cattle / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018392:Genomic Imprinting; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008297:Male; D009865:Oocytes / Q000378:metabolism*; D006080:Ovarian Follicle / Q000254:growth & development* / Q000378:metabolism
chemical_list: D007335:Insulin-Like Growth Factor II