Methylation status in the intragenic differentially methylated region of the IGF2 locus in Bos taurus indicus oocytes with different developmental competencies

Abstract

Oocyte quality is one of the most important aspects of in vitro embryo development. Extensive epigenetic programming must occur during oocyte growth and maturation. A specific DNA methylation pattern of the imprinted genes must be established on differentially methylated regions (DMR). The insulin-like growth factor 2 (IGF2) gene is an important growth factor, and it is imprinted in several mammalian species. The aim of this study was to evaluate the methylation pattern on the DMR of the last exon of IGF2 in immature and mature bovine oocytes with different developmental competencies. Mature oocytes from large follicles were less methylated (28.93%) than immature oocytes from large follicles (77.38% P = 0.002), and there was also a tendency towards lower methylation in mature oocytes from large follicles (28.93%) compared with mature oocytes from small follicles (52.58% P = 0.07). Immature oocytes from small and large follicles showed 53.85% (7/13) and 91.66% (11/12) hypermethylated sequences, respectively, whereas mature oocytes from small and large follicles showed 61.11% (11/18) and 40% (4/10), respectively. The hypomethylation pattern in mature oocytes from large follicles may be related to the higher competence of these oocytes. Our results suggest that the methylation pattern in this DMR may be a useful parameter to investigate as a molecular marker for oocyte competence in cattle and as a model for studies in other species.

DNA methylation and mRNA expression profiles in bovine oocytes derived from prepubertal and adult donors

“…The high preservation of methylation marks at the BTS sequences during early embryo development suggests efficient maintenance of methylation in bovine embryos (Kang et al 2005). Recently, it was shown that the methylation status of the oocyte correlates with follicle size, size of the oocyte, Epigenetic analysis of prepubertal bovine oocytes and oocyte developmental capacity (Fagundes et al 2011). While immature oocytes from follicles R8 mm showed significantly higher methylation than their matured counterparts from follicles of the same size category, oocytes from follicles 1-3 mm in diameter did not exhibit differences prior to and after maturation (Fagundes et al 2011).…”

“…Recently, it was shown that the methylation status of the oocyte correlates with follicle size, size of the oocyte, Epigenetic analysis of prepubertal bovine oocytes and oocyte developmental capacity (Fagundes et al 2011). While immature oocytes from follicles R8 mm showed significantly higher methylation than their matured counterparts from follicles of the same size category, oocytes from follicles 1-3 mm in diameter did not exhibit differences prior to and after maturation (Fagundes et al 2011). In the present study, we used oocytes from follicles O3 mm in size.…”

The methylation patterns of the IGF2 and IGF2R genes in bovine spermatozoa are not affected by flow‐cytometric sex sorting

“…X53553. In a study conducted in our laboratory, Fagundes et al (2011) evaluated the methylation patterns of immature and mature bovine oocytes, and identified the same difference in the number of CpGs in relation to the study of Gebert et al (2006). This difference may be due to the presence of a single nucleotide polymorphism.…”

Transcription Profile of Candidate Genes for the Acquisition of Competence During Oocyte Growth in Cattle

“…This hypothesis is supported by the results from our laboratory that showed that the methylation pattern of the intragenic DMR of the IGF2 gene in the bovine oocytes is only completed at the end of oogenesis, just before the initiation of oocyte maturation in oocytes obtained from ! 8.0 mm diameter follicles (Fagundes et al 2011).…”