Female Reproductive Fluids and Epigenetics

Physiological fertilization, and early embryo development, involves dramatic transcriptomic, epigenetic and morphological changes in a short temporal window. During this period gametes and early embryos are surrounded by reproductive fluids (oviductal and uterine), which contain nutrients, growth factors, hormones and extracellular vesicles acting as carriers of DNA, RNA, proteins and other factors with putative roles in intercellular communication. Under in vitro conditions, and in the absence of these fluids, embryos derived from Assisted Reproductive Technologies (ART) reveal transcriptional and epigenetic differences compared with in vivo embryos, which could result in long-term phenotypic consequences in adult life. Therefore, reproductive fluids supplementation in the culture medium offers an alternative to imitate physiological conditions and decrease these consequences. In vitro, oviductal fluid (OF) can modulate capacitation-associated events and sperm-zona pellucida interactions and contribute to the control of polyspermy in pigs. The use of in vitro fertilization media supplemented with reproductive fluids (Natur-IVF) improves embryo quality and blastocysts hatching ability. Moreover, Natur-IVF embryos show expression and methylation patterns closer to in vivo blastocysts. In cows, supplementation of culture media with reproductive fluids, or some isolated factors, improves blastocyst rate and survival after embryo transfer, and reverses the expression of some altered genes. However, considering the complexity of the oviductal and uterine fluids, it seems difficult that the use of just a few factors in isolation can reverse all undesired consequences of the IVP. On the other hand, sex-specific embryonic plasticity, as a consequence of the oviductal regulatory signals, have been proposed. Thus, we have analysed the sex-specific effect of supplementation with reproductive fluids in bovine embryos and data reveal sex-dependent impact in DNA methylation. All these results confirm that developmental programme can be modulated by reproductive fluids and it shows sex-specific effects. This strategy allows the possibility of minimizing undesired in vitro derived consequences.