DNA methylation, environmental exposures and early embryo development

The first crucial step in the developmental program occurs during pre-implantation, the time after the oocyte has been fertilized and before the embryo implants in the uterus. This period represents a vulnerable window as the epigenome undergoes dynamic changes in DNA methylation profiles. Alterations in the early embryonic reprogramming wave can impair DNA methylation patterns and induce permanent changes to the developmental program, leading to the onset of adverse health outcomes in offspring. Although there is an increasing body of evidence indicating that harmful exposures during preimplantation embryo development can trigger lasting epigenetic alterations in offspring, the mechanisms are still not fully understood. Since physiological or pathological changes in DNA methylation can occur as a response to environmental cues, proper environmental milieu plays a critical role in the success of embryonic development. In this review, we depict the mechanisms behind the embryonic epigenetic reprogramming of DNA methylation and highlight how maternal environmental stressors (e.g., alcohol, heat stress, nutrient availability) during pre-implantation and assisted reproductive technology procedures affect development and DNA methylation marks.

DNA methylation, environmental exposures and early embryo development

The first crucial step in the developmental program occurs during pre-implantation, the time after the oocyte has been fertilized and before the embryo implants in the uterus. This period represents a vulnerable window as the epigenome undergoes dynamic changes in DNA methylation profiles. Alterations in the early embryonic reprogramming wave can impair DNA methylation patterns and induce permanent changes to the developmental program, leading to the onset of adverse health outcomes in offspring. Although there is an increasing body of evidence indicating that harmful exposures during preimplantation embryo development can trigger lasting epigenetic alterations in offspring, the mechanisms are still not fully understood. Since physiological or pathological changes in DNA methylation can occur as a response to environmental cues, proper environmental milieu plays a critical role in the success of embryonic development. In this review, we depict the mechanisms behind the embryonic epigenetic reprogramming of DNA methylation and highlight how maternal environmental stressors (e.g., alcohol, heat stress, nutrient availability) during pre-implantation and assisted reproductive technology procedures affect development and DNA methylation marks.(AU)

Developmental programming in the preimplantation period: can it be exploited to enhance postnatal function in cattle?

The concept of developmental programming states that the function of an adult animal depends on environmental conditions to which it was exposed to before birth. Developmental programming can occur in the preimplantation period. Accordingly, certain environmental signals, acting either on the mother (for pregnancies established in vivo) or on the embryo directly (for cultured embryos), can program development of the preimplantation embryo to have effects on postnatal life. It is proposed that research on developmental programming in cattle could lead not only to elimination of adverse outcomes associated with in vitro production of embryos but also to discovery of approaches to produce a neonatal animal with superior prospects for achieving optimal production later in life.(AU)

Developmental programming in the preimplantation period: can it be exploited to enhance postnatal function in cattle?

The concept of developmental programming states that the function of an adult animal depends on environmental conditions to which it was exposed to before birth. Developmental programming can occur in the preimplantation period. Accordingly, certain environmental signals, acting either on the mother (for pregnancies established in vivo) or on the embryo directly (for cultured embryos), can program development of the preimplantation embryo to have effects on postnatal life. It is proposed that research on developmental programming in cattle could lead not only to elimination of adverse outcomes associated with in vitro production of embryos but also to discovery of approaches to produce a neonatal animal with superior prospects for achieving optimal production later in life.

How the maternal environment impacts fetal and placental development: implications for livestock production

Fetal survival is dependent upon proper placental growth and vascular ity early in pregnancy. The ability for the fetus to reach its genetic growth potential is dependent upon the continual plasticity of placental function throughout gestation. Inadequate maternal environment has b een documented to alter fetal organogenesis and growth, thus leading to improper postnatal growth and performance in many livestock species. The timing and duration of maternal nutritional restriction appears to influence the capillary vascularity, angiogenic profile, and vascular function of the placenta in cattle and sheep. In environments where fetal growth and/or fetal organogenesis are compromised, potential therapeutics may augment placental nutrient transport capacity and improve offspring performance. Supplementation of specific nutrients, including protein, as well as hormone supplements, such as indo lamines, during times of nutrient restriction may assist placental function. The use of Doppler ultrasonography has allowed for repeated measurements of uterine and umbilical blood flows including assessment of uteroplacental hemodynamics in cattle, sheep, and swine. Moreover, these variables can be monitored in conjugation with placental capacity and fetal growth at specific time points of gestation. Elucidating the consequences of inadequate maternal intake on the continual plasticity of placental function will allow us to determine the proper timing and duration for intervention.

How the maternal environment impacts fetal and placental development: implications for livestock production

Fetal survival is dependent upon proper placental growth and vascular ity early in pregnancy. The ability for the fetus to reach its genetic growth potential is dependent upon the continual plasticity of placental function throughout gestation. Inadequate maternal environment has b een documented to alter fetal organogenesis and growth, thus leading to improper postnatal growth and performance in many livestock species. The timing and duration of maternal nutritional restriction appears to influence the capillary vascularity, angiogenic profile, and vascular function of the placenta in cattle and sheep. In environments where fetal growth and/or fetal organogenesis are compromised, potential therapeutics may augment placental nutrient transport capacity and improve offspring performance. Supplementation of specific nutrients, including protein, as well as hormone supplements, such as indo lamines, during times of nutrient restriction may assist placental function. The use of Doppler ultrasonography has allowed for repeated measurements of uterine and umbilical blood flows including assessment of uteroplacental hemodynamics in cattle, sheep, and swine. Moreover, these variables can be monitored in conjugation with placental capacity and fetal growth at specific time points of gestation. Elucidating the consequences of inadequate maternal intake on the continual plasticity of placental function will allow us to determine the proper timing and duration for intervention.(AU)