During early development, embryos secrete extracellular vesicles (EVs) that participate in embryo–maternal communication. Among other molecules, EVs carry microRNAs (miRNAs) that interfere with gene expression in target cells; miRNAs participate in embryo–maternal communication. Embryo selection based on secreted miRNAs may have an impact on bovine breeding programs. This research aimed to evaluate the size, concentration, and miRNA content of EVs secreted by bovine embryos with different developmental potential, during the compaction period (days 3.5–5). Individual culture media from in vitro–produced embryos were collected at day 5, while embryos were further cultured and classified at day 7, as G1 (conditioned-culture media by embryos arrested in the 8–16-cells stage) and G2 (conditioned-culture media by embryos that reached blastocyst stages at day 7). Collected nanoparticles from embryo conditioned culture media were cataloged as EVs by their morphology and the presence of classical molecular markers. Size and concentration of EVs from G1 were higher than EVs secreted by G2. We identified 95 miRNAs; bta-miR-103, bta-miR-502a, bta-miR-100, and bta-miR-1 were upregulated in G1, whereas bta-miR-92a, bta-miR-140, bta-miR-2285a, and bta-miR-222 were downregulated. The most significant upregulated pathways were fatty acid biosynthesis and metabolism, lysine degradation, gap junction, and signaling pathways regulating pluripotency of stem cells. The characteristics of EVs secreted by bovine embryos during the compaction period vary according to embryo competence. Embryos that reach the blastocyst stage secrete fewer and smaller vesicles. Furthermore, the loading of specific miRNAs into the EVs depends on embryo developmental competence.

As observed in other species during pregnancy, bovine placentomes are assumed to suppress classical MHC I antigens, whereas overexpress non-classical MHC I to be recognized but not rejected by maternal immune system. However, in cloned bovine classical antigens were overexpress early in the pregnancy instead of non-classical ones. Then, MHC I antigens were investigated by immunohistochemistry (N=23) and RT-qPCR (N=16) in control and cloned bovine placentomes in early gestation and near term. In controls, IL-A88 staining was present in all stages, majorly in maternal tissues, whereas Qa-2 reacted only near term. Clones had an opposite pattern. Trophoblast giant cells near the uterine epithelium were weakly stained. By PCR, especially the non-classical isoform BoLA-NC3 resulted in significant higher expression in early gestation and down-regulation near term in controls compared to clones, as stain produced by Qa-2 antibody. The presence of MHC I in the placentomes indicated that bovine epitheliochorial placentas followed similar principles than that known for other species. Controls and clones reacted differently to the applied antibodies and differ partly in gene expression, which may explain pregnancy problems.