DNA methylation dynamics during oocyte and embryo development and its associationwith environmental induced alterations

Abstract

Epigenetic mechanisms are fundamental to successful gametogenesis and development. The fertilized egg undergoes global DNA demethylation to facilitate remodelling from two differentiated gametespecific states to a pluripotent embryonic state. Maintenance of appropriate levels of DNA methylation during preimplantation development is essential to embryo viability. Recent advances in epigenetic research have highlighted the susceptibility of foetal epigenetic programming to maternal health and nutritional status, particularly, at the time of conception. There is much evidence that maternal stress impacts on ovarian function, leading to compromised oocytes presented for fertilization in a suboptimal environment. Similarly, declining fertility has become a substantive issue in western countries, where it is primarily associated with high mean ages at childbearing. Thus the use of assisted reproduction technologies (ART) interventions to overcome low fertility is increasing steadily across the globe. In addition, the use of prolonged in vitro culture following the removal and storage of oocytes and/or ovarian tissue in advance of cancer treatment, or to circumvent ovarian aging, is increasing rapidly. ART is associated with compromised pre and post -natal outcomes, including premature birth, low birth weight, congenital abnormalities and elevated risk of epigenetic disorders. There is extensive evidence from studies in cattle that embryos produced by conventional ART protocols are susceptible to errors in epigenetic programming. The present review discusses the impact of intrinsic physiological status and external environments on oocyte and embryo DNA methylation with regard to data available from mouse, human and bovine models.

An Interplay between Epigenetics and Translation in Oocyte Maturation and Embryo Development: Assisted Reproduction Perspective

“…Studies done on mice [ 272 ] and cattle [ 273 ] confirmed maternal diet effects on oocyte DNA methylation. Postpartum cows exposed to negative energy balance and metabolic stress had a number of maternally imprinted genes in their oocytes hypomethylated [ 274 ].…”

Application of multi-omics data integration and machine learning approaches to identify epigenetic and transcriptomic differences between in vitro and in vivo produced bovine embryos

“…However, several studies have shown that gene body methylation is also strongly involved in gene expression [28][29][30], with a bias for exonic regions [31]. Furthermore, epigenetic modifications can be induced by several external factors [32], affecting IVP and MOET embryos differentially. For example, known factors including the in vitro culture medium used [33], and paternal characteristics, such as bull age [34], have been shown to impact at the blastocyst stage.…”

Efeito da suplementação com ácido fólico durante a maturação oocitária na produção <i>in vitro</i> e expressão dos genes <i>IGF2</i> e <i>LIT1</i> em embriões bovinos

“…Assim como a BWS, a taxa de desenvolvimento da LOS aumenta significativamente quando os gametas ou embriões são submetidos à alguma técnica de reprodução assistida, seja ovulação da fêmea para coleta de oócitos ou PIVE (CHEN et al, 2013;HAJJ;HAAF, 2013;FAIR, 2016). O estudo desta região gênica utilizando bovinos como modelo animal, principalmente em relação aos genes que sofrem imprinting e demais alterações epigenéticas, podem ajudar a compreender a etiologia das síndromes de imprinting em humanos como a BWS (CHEN et al, 2013).…”