The role of the estradiol in the bovine oviduct: evidence in vivo and in vitro

The oviduct plays many roles in the embryo formation, as gametes final maturation and transport, fertilization process, embryo transport, and embryo early development. However, none of these steps need to occur in the oviduct mandatorily. The ability to develop embryos up to the blastocyst stage without any contact with the maternal reproductive tract hypothesized that the oviduct would be minor and inessential at the early stage of life. Today, however, it is widely known that the embryo-oviduct interaction, or interaction with oviductal cells’ products, can impact the embryo in different ways, especially regarding epigenetic characteristics, metabolism, and several quality markers. To reconnect the embryo in development to the oviductal cells (OC), many artificial approaches have been designed. In this thesis, we investigated the OC from two of these approaches: the ovarian superstimulation protocols (OVS) and the embryo-OC in vitro coculture. In the first study, cows were submitted to: i) OVS protocol only with follicle-stimulating hormone (FSH), ii) OVS protocol using FSH with equine chorionic gonadotrophin (eCG), or iii) single ovulation by hormone synchronization. The use of OVS protocols allows the development of multiples embryos inside the oviduct, making possible the interaction of the embryos with the OC. This first study demonstrated that OC from cows submitted to OVS using FSH+eCG has higher levels of estradiol, which also modulated gene expression of genes related to the fertilization process. Next, this hormone profile was applied in an in vitro culture system of OC. The OC can be cultured for application in a coculture system with embryos, which enable the in vitro produced embryo to interact with the OC. The culture of OC has still no gold standard protocol. Therefore, to analyze the effect of different hormone profiles obtained as a result of the first study, it was necessary to include another variation in the second study: different hormone profiles x OC collected in a different phase of the estrous cycle. When analyzing the data obtained from the RNAseq analysis, after in vitro culture, OC collected during the follicular phase presents a very different transcriptome profile than cells collected during the luteal phase, if no hormone treatment is applied. However, when high levels of estradiol are applied in the in vitro culture, the transcriptome profile of the OC become very similar to each other, independently of the estrous cycle when OC was collected. In conclusion, these two artificial approaches to enable the interaction of embryos with the oviduct modulate the OC depending on the hormone levels presented. Therefore, the hormone profile is an important factor to be considered in strategies to establish the interaction of embryos and oviductal cells. (AU)