Pregnancy success results from the interaction of multiple factors, among them are folliculogenesis and early embryonic development. Failure during these different processes can lead to difficulties in conception. Alternatives to overcome these problems are based on assisted reproductive techniques. Extracellular vesicles are cell-secreted vesicles present in different body fluids and contain bioactive materials, such as messenger RNA, microRNAs (miRNAs), and proteins. Thus, our hypothesis is that extracellular vesicles from follicular fluid from 3–6 mm ovarian follicles can modulate bovine embryo development in vitro. To test our hypothesis follicular fluid from bovine ovaries was aspirated and small-extracellular vesicles (<200 nm) were isolated for further analysis. Additionally, small-extracellular vesicles (EVs) were utilized for functional experiments investigating their role in modulating messenger RNA, microRNA as well as global DNA methylation and hydroxymethylation levels of bovine blastocysts. EVs from 3–6 mm follicles were used for RNA-seq and miRNA analysis. Functional annotation analysis of the EVs transcripts revealed messages related to chromatin remodeling and transcriptional regulation. EVs treatment during oocyte maturation and embryo development causes changes in blastocyst rates, as well as changes in the transcription levels of genes related to embryonic metabolism and development. Supplementation with EVs from 3–6 mm follicles during oocyte maturation and early embryo development (until the 4-cell stage) increased the levels of bta-miR-631 (enriched in EVs from 3–6 mm follicles) in embryos. Interestingly, the addition of EVs from 3–6 mm follicles induced changes in global DNA methylation and hydroxymethylation levels compared to embryos produced by the standard in vitro production system. Our results indicate that the supplementation of culture media with EVs isolated from the follicular fluid of 3–6 mm follicles during oocyte maturation and early embryo development can partially modify metabolic and developmental related genes as well as miRNA and global DNA methylation and hydroxymethylation, suggesting that EVs play an important role during oocyte maturation and early embryo development in vitro.

Oocytes that undergo in vitro maturation (IVM) are metabolically abnormal and accumulate excess lipid content. However, the mechanism of lipid accumulation and the role of cumulus cells in this process are unclear. Recently, it was shown that fatty acid binding proteins (FABPs) performed intra- and extracellular fatty acid transport. We postulated that FABP3 might be responsible for fatty acid transport from cumulus cells to the oocytes via transzonal projections (TZPs) during IVM. Transcript and protein levels of FABP3 were analyzed in both in vivo- and in vitro-matured cumulus-oocyte-complexes and were increased in IVM samples. Further analysis showed increased lipid content in oocytes and cumulus cells in IVM samples compared to in vivo-derived. We therefore speculated that altered traffic of fatty acids via FABP3 during IVM was the mechanism leading to the excess of lipids accumulated within IVM oocytes. Furthermore, we demonstrated an increase in FABP3 levels and lipid content during the first 9 h of IVM, further strengthening the possibility of fatty acid transport via FABP3 and TZPs. Additionally, disruptions of TZPs during IVM decreased lipid accumulation in oocytes. Our results shed light on a possible mechanism involving FABP3 and TZPs that causes excess lipid accumulation in oocytes during IVM.

The ovarian follicle encloses oocytes in a microenvironment throughout their growth and acquisition of competence. Evidence suggests a dynamic interplay among follicular cells and oocytes, since they are constantly exchanging “messages”. We dissected bovine ovarian follicles and recovered follicular cells (FCs—granulosa and cumulus cells) and cumulus-oocyte complexes (COCs) to investigate whether the PI3K-Akt signaling pathway impacted oocyte quality. Following follicle rupture, COCs were individually selected for in vitro cultures to track the follicular cells based on oocyte competence to reach the blastocyst stage after parthenogenetic activation. Levels of PI3K-Akt signaling pathway components in FCs correlated with oocyte competence. This pathway is upregulated in FCs from follicles with high-quality oocytes that are able to reach the blastocyst stage, as indicated by decreased levels of PTEN and increased levels of the PTEN regulators bta-miR-494 and bta-miR-20a. Using PI3K-Akt responsive genes, we showed decreased FOXO3a levels and BAX levels in lower quality groups, indicating changes in cell cycle progression, oxidative response and apoptosis. Based on these results, the measurement of levels of PI3K-Akt pathway components in FCs from ovarian follicles carrying oocytes with distinct developmental competences is a useful tool to identify putative molecular pathways involved in the acquisition of oocyte competence.