Padrão de metilação dos genes XIST e IGF2 em ovócitos de vacas nelore (Bos taurus indicus) em diferentes fases da ovogênese

Abstract

DNA methylation is one of the most studied epigenetic events and is responsible for epigenetic reprogramming which occurs during gametogenesis. Understanding how this reprogramming occurs in oogenesis is important to comprehend physiologic and genetic aspects involved in female gametogenesis in order to create parameters for oocyte competence and, consequently, to improve the in vitro embryo production, maximizing the use of gametes and improving production rates. The aim of this study was to evaluate the DNA methylation pattern in two DMRs involved in the control of XIST and IGF2 genes expression in oocytes from pre antral and antral follicles of Nellore cows. The extracted DNA from oocytes was treated with sodium bisulphite and amplified to XIST and IGF2 genes, which was cloned into DH5 cells, and then purified and sequenced. The methylation patterns found for oocytes of primordial, secondary, incompetent antral and competent antral follicles were 91.59 ± 6.4%, 85.70 ± 19.6%, 91.25 ± 7.2% and 92.58 ± ± 11.7%, respectively for XIST gene and 60.56 ± 29.1%, 59.68 ± 34.6%, 58.21 ± 33.0% and 67.47 ± 27.8%, respectively for IGF2 gene. XIST is more methylated than IGF2 gene (P<0,001). The hypermethylated pattern of XIST gene suggests that this event may be responsible for epigenetic reactivation of the X chromosome during oogenesis, which is observed in the final oocyte. The IGF2 gene was also hypermethylated, a different pattern found in matured oocytes. This suggests that the analyzed regions undergo differents epigenetic reprogramming processes during oogenenesis, which are only completed with oocyte maturation.