Bovine Oviduct Epithelial Cells Dedifferentiate Partly in Culture, While Maintaining their Ability to Improve Early Embryo Development Rate and Quality.

There are convincing arguments to suggest that the success of early reproductive events is reliant on a satisfactory dialogue between gametes-embryo and the oviduct epithelium. The aim of this study was to develop and characterize an in vitro model to study these interactions. Cattle zygotes produced in vitro were cultured in either SOF or TCM-199 in the presence or absence of bovine oviduct cell monolayers (BOEC), under 20% or 5% O2 . The embryonic development rate and its quality (cell numbers, cryosurvival) were evaluated, as were the BOEC contents in 11 candidate transcripts (real-time PCR) at different time points. A BOEC co-culture did indeed increase the rate of development in both media under 5% O2 (41 vs 27% and 28 vs 10% of Day 8 blastocysts in SOF and TCM-199, respectively; p < 0.05). The effect of BOEC on the developmental rate was more pronounced under 20% O2 (35 vs 6% and 27 vs 4% of Day 8 blastocysts in SOF and TCM-199, respectively; p < 0.05). BOEC significantly increased the embryonic cell count in TCM-199 (122.5 ± 11.1 vs 70.3 ± 9.6; p < 0.05) and embryonic cryosurvival in both media. The expression levels of SOD, FGF2 and TGF-β1 in BOEC remained steady during culture, although mRNA levels of OGP, C3, PGR and ESR2 were clearly reduced, suggesting a dedifferentiation of BOEC during culture. However, SSP1 and GPX4 transcripts were slightly increased during culture, this rise becoming significant by the end of the culture period. In conclusion, our co-culture system with bovine oviduct epithelial cells used for the development of bovine zygotes produced in vitro enhanced blastocyst formation and above all the quality of the resulting embryos, which was associated with specific transcriptomic changes.